diff --git a/en_US.ISO8859-1/books/handbook/basics/chapter.sgml b/en_US.ISO8859-1/books/handbook/basics/chapter.sgml index d78284a74e..0f81646e7e 100644 --- a/en_US.ISO8859-1/books/handbook/basics/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/basics/chapter.sgml @@ -1,2515 +1,2569 @@ Chris Shumway Rewritten by UNIX Basics Synopsis The following chapter will cover the basic commands and functionality of the FreeBSD operating system. Much of this material is relevant for any &unix; like operating system. Feel free to skim over this chapter if you are familiar with the material. If you are new to FreeBSD, then you will definitely want to read through this chapter carefully. After reading this chapter, you will know: How to use the virtual consoles of FreeBSD. - How &unix; file permissions work. + How &unix; file permissions work along with + understanding file flags in &os;. The default &os; file system layout. The &os; disk organization. How to mount and unmount file systems. What processes, daemons, and signals are. What a shell is, and how to change your default login environment. How to use basic text editors. What devices and device nodes are. What binary format is used under &os;. How to read manual pages for more information. Virtual Consoles and Terminals virtual consoles terminals FreeBSD can be used in various ways. One of them is typing commands to a text terminal. A lot of the flexibility and power of a &unix; operating system is readily available at your hands when using FreeBSD this way. This section describes what terminals and consoles are, and how you can use them in FreeBSD. The Console console If you have not configured FreeBSD to automatically start a graphical environment during startup, the system will present you with a login prompt after it boots, right after the startup scripts finish running. You will see something similar to: Additional ABI support:. Local package initialization:. Additional TCP options:. Fri Sep 20 13:01:06 EEST 2002 FreeBSD/i386 (pc3.example.org) (ttyv0) login: The messages might be a bit different on your system, but you will see something similar. The last two lines are what we are interested in right now. The second last line reads: FreeBSD/i386 (pc3.example.org) (ttyv0) This line contains some bits of information about the system you have just booted. You are looking at a FreeBSD console, running on an Intel or compatible processor of the x86 architecture This is what i386 means. Note that even if you are not running FreeBSD on an Intel 386 CPU, this is going to be i386. It is not the type of your processor, but the processor architecture that is shown here. . The name of this machine (every &unix; machine has a name) is pc3.example.org, and you are now looking at its system console—the ttyv0 terminal. Finally, the last line is always: login: This is the part where you are supposed to type in your username to log into FreeBSD. The next section describes how you can do this. Logging into FreeBSD FreeBSD is a multiuser, multiprocessing system. This is the formal description that is usually given to a system that can be used by many different people, who simultaneously run a lot of programs on a single machine. Every multiuser system needs some way to distinguish one user from the rest. In FreeBSD (and all the &unix; like operating systems), this is accomplished by requiring that every user must log into the system before being able to run programs. Every user has a unique name (the username) and a personal, secret key (the password). FreeBSD will ask for these two before allowing a user to run any programs. startup scripts Right after FreeBSD boots and finishes running its startup scripts Startup scripts are programs that are run automatically by FreeBSD when booting. Their main function is to set things up for everything else to run, and start any services that you have configured to run in the background doing useful things. , it will present you with a prompt and ask for a valid username: login: For the sake of this example, let us assume that your username is john. Type john at this prompt and press Enter. You should then be presented with a prompt to enter a password: login: john Password: Type in john's password now, and press Enter. The password is not echoed! You need not worry about this right now. Suffice it to say that it is done for security reasons. If you have typed your password correctly, you should by now be logged into FreeBSD and ready to try out all the available commands. You should see the MOTD or message of the day followed by a command prompt (a #, $, or % character). This indicates you have successfully logged into FreeBSD. Multiple Consoles Running &unix; commands in one console is fine, but FreeBSD can run many programs at once. Having one console where commands can be typed would be a bit of a waste when an operating system like FreeBSD can run dozens of programs at the same time. This is where virtual consoles can be very helpful. FreeBSD can be configured to present you with many different virtual consoles. You can switch from one of them to any other virtual console by pressing a couple of keys on your keyboard. Each console has its own different output channel, and FreeBSD takes care of properly redirecting keyboard input and monitor output as you switch from one virtual console to the next. Special key combinations have been reserved by FreeBSD for switching consoles A fairly technical and accurate description of all the details of the FreeBSD console and keyboard drivers can be found in the manual pages of &man.syscons.4;, &man.atkbd.4;, &man.vidcontrol.1; and &man.kbdcontrol.1;. We will not expand on the details here, but the interested reader can always consult the manual pages for a more detailed and thorough explanation of how things work. . You can use AltF1, AltF2, through AltF8 to switch to a different virtual console in FreeBSD. As you are switching from one console to the next, FreeBSD takes care of saving and restoring the screen output. The result is an illusion of having multiple virtual screens and keyboards that you can use to type commands for FreeBSD to run. The programs that you launch on one virtual console do not stop running when that console is not visible. They continue running when you have switched to a different virtual console. The <filename>/etc/ttys</filename> File The default configuration of FreeBSD will start up with eight virtual consoles. This is not a hardwired setting though, and you can easily customize your installation to boot with more or fewer virtual consoles. The number and settings of the virtual consoles are configured in the /etc/ttys file. You can use the /etc/ttys file to configure the virtual consoles of FreeBSD. Each uncommented line in this file (lines that do not start with a # character) contains settings for a single terminal or virtual console. The default version of this file that ships with FreeBSD configures nine virtual consoles, and enables eight of them. They are the lines that start with ttyv: # name getty type status comments # ttyv0 "/usr/libexec/getty Pc" cons25 on secure # Virtual terminals ttyv1 "/usr/libexec/getty Pc" cons25 on secure ttyv2 "/usr/libexec/getty Pc" cons25 on secure ttyv3 "/usr/libexec/getty Pc" cons25 on secure ttyv4 "/usr/libexec/getty Pc" cons25 on secure ttyv5 "/usr/libexec/getty Pc" cons25 on secure ttyv6 "/usr/libexec/getty Pc" cons25 on secure ttyv7 "/usr/libexec/getty Pc" cons25 on secure ttyv8 "/usr/X11R6/bin/xdm -nodaemon" xterm off secure For a detailed description of every column in this file and all the options you can use to set things up for the virtual consoles, consult the &man.ttys.5; manual page. Single User Mode Console A detailed description of what single user mode is can be found in . It is worth noting that there is only one console when you are running FreeBSD in single user mode. There are no virtual consoles available. The settings of the single user mode console can also be found in the /etc/ttys file. Look for the line that starts with console: # name getty type status comments # # If console is marked "insecure", then init will ask for the root password # when going to single-user mode. console none unknown off secure As the comments above the console line indicate, you can edit this line and change secure to insecure. If you do that, when FreeBSD boots into single user mode, it will still ask for the root password. Be careful when changing this to insecure. If you ever forget the root password, booting into single user mode is a bit involved. It is still possible, but it might be a bit hard for someone who is not very comfortable with the FreeBSD booting process and the programs involved. Permissions UNIX FreeBSD, being a direct descendant of BSD &unix;, is based on several key &unix; concepts. The first and most pronounced is that FreeBSD is a multi-user operating system. The system can handle several users all working simultaneously on completely unrelated tasks. The system is responsible for properly sharing and managing requests for hardware devices, peripherals, memory, and CPU time fairly to each user. Because the system is capable of supporting multiple users, everything the system manages has a set of permissions governing who can read, write, and execute the resource. These permissions are stored as three octets broken into three pieces, one for the owner of the file, one for the group that the file belongs to, and one for everyone else. This numerical representation works like this: permissions file permissions Value Permission Directory Listing 0 No read, no write, no execute --- 1 No read, no write, execute --x 2 No read, write, no execute -w- 3 No read, write, execute -wx 4 Read, no write, no execute r-- 5 Read, no write, execute r-x 6 Read, write, no execute rw- 7 Read, write, execute rwx ls directories You can use the command line argument to &man.ls.1; to view a long directory listing that includes a column with information about a file's permissions for the owner, group, and everyone else. For example, a ls -l in an arbitrary directory may show: &prompt.user; ls -l total 530 -rw-r--r-- 1 root wheel 512 Sep 5 12:31 myfile -rw-r--r-- 1 root wheel 512 Sep 5 12:31 otherfile -rw-r--r-- 1 root wheel 7680 Sep 5 12:31 email.txt ... Here is how the first column of ls -l is broken up: -rw-r--r-- The first (leftmost) character tells if this file is a regular file, a directory, a special character device, a socket, or any other special pseudo-file device. In this case, the - indicates a regular file. The next three characters, rw- in this example, give the permissions for the owner of the file. The next three characters, r--, give the permissions for the group that the file belongs to. The final three characters, r--, give the permissions for the rest of the world. A dash means that the permission is turned off. In the case of this file, the permissions are set so the owner can read and write to the file, the group can read the file, and the rest of the world can only read the file. According to the table above, the permissions for this file would be 644, where each digit represents the three parts of the file's permission. This is all well and good, but how does the system control permissions on devices? FreeBSD actually treats most hardware devices as a file that programs can open, read, and write data to just like any other file. These special device files are stored on the /dev directory. Directories are also treated as files. They have read, write, and execute permissions. The executable bit for a directory has a slightly different meaning than that of files. When a directory is marked executable, it means it can be traversed into, that is, it is possible to cd (change directory) into it. This also means that within the directory it is possible to access files whose names are known (subject, of course, to the permissions on the files themselves). In particular, in order to perform a directory listing, read permission must be set on the directory, whilst to delete a file that one knows the name of, it is necessary to have write and execute permissions to the directory containing the file. There are more permission bits, but they are primarily used in special circumstances such as setuid binaries and sticky directories. If you want more information on file permissions and how to set them, be sure to look at the &man.chmod.1; manual page. Tom Rhodes Contributed by Symbolic Permissions permissionssymbolic Symbolic permissions, sometimes referred to as symbolic expressions, use characters in place of octal values to assign permissions to files or directories. Symbolic expressions use the syntax of (who) (action) (permissions), where the following values are available: Option Letter Represents (who) u User (who) g Group owner (who) o Other (who) a All (world) (action) + Adding permissions (action) - Removing permissions (action) = Explicitly set permissions (permissions) r Read (permissions) w Write (permissions) x Execute (permissions) t Sticky bit (permissions) s Set UID or GID These values are used with the &man.chmod.1; command just like before, but with letters. For an example, you could use the following command to block other users from accessing FILE: &prompt.user; chmod go= FILE A comma separated list can be provided when more than one set of changes to a file must be made. For example the following command will remove the groups and world write permission on FILE, then it adds the execute permissions for everyone: &prompt.user; chmod go-w,a+x FILE + + + + + + Tom + Rhodes + Contributed by + + + + + &os; File Flags + + In addition to file permissions discussed previously, &os; + supports the use of file flags. These flags + add an additional level of security and control over files, but + not directories. + + These file flags add an additional level of control over + files, helping to ensure that in some cases not even the + root can remove or files. + + File flags are altered by using the &man.chflags.1; utility, + using a simple interface. For example, to enable the system + undeletable flag on the file file1, + issue the following command: + + &prompt.root; chflags sunlink + file1 + + And to disable the system undeletable flag, simply + issue the previous command with no in + front of the . Observe: + + &prompt.root; chflags nosunlink + file1 + + To view the flags of this file, use the &man.ls.1; + with the flags: + + &prompt.root; ls -lo file1 + + + The output should look like the following: + + -rw-r--r-- 1 trhodes trhodes sunlnk 0 Mar 1 05:54 file1 + + Several flags may only added or removed to files by the + root user. In other cases, the file owner + may set these flags. It is recommended an administrator read + over the &man.chflags.1; and &man.chflags.2; manual pages for + more information. + Directory Structure directory hierarchy The FreeBSD directory hierarchy is fundamental to obtaining an overall understanding of the system. The most important concept to grasp is that of the root directory, /. This directory is the first one mounted at boot time and it contains the base system necessary to prepare the operating system for multi-user operation. The root directory also contains mount points for every other file system that you may want to mount. A mount point is a directory where additional file systems can be grafted onto the root file system. Standard mount points include /usr, /var, /tmp, /mnt, and /cdrom. These directories are usually referenced to entries in the file /etc/fstab. /etc/fstab is a table of various file systems and mount points for reference by the system. Most of the file systems in /etc/fstab are mounted automatically at boot time from the script &man.rc.8; unless they contain the option. Details can be found in . A complete description of the file system hierarchy is available in &man.hier.7;. For now, a brief overview of the most common directories will suffice. Directory Description / Root directory of the file system. /bin/ User utilities fundamental to both single-user and multi-user environments. /boot/ Programs and configuration files used during operating system bootstrap. /boot/defaults/ Default bootstrapping configuration files; see &man.loader.conf.5;. /dev/ Device nodes; see &man.intro.4;. /etc/ System configuration files and scripts. /etc/defaults/ Default system configuration files; see &man.rc.8;. /etc/mail/ Configuration files for mail transport agents such as &man.sendmail.8;. /etc/namedb/ named configuration files; see &man.named.8;. /etc/periodic/ Scripts that are run daily, weekly, and monthly, via &man.cron.8;; see &man.periodic.8;. /etc/ppp/ ppp configuration files; see &man.ppp.8;. /mnt/ Empty directory commonly used by system administrators as a temporary mount point. /proc/ Process file system; see &man.procfs.5;, &man.mount.procfs.8;. /rescue/ Statically linked programs for emergency recovery; see &man.rescue.8;. /root/ Home directory for the root account. /sbin/ System programs and administration utilities fundamental to both single-user and multi-user environments. /stand/ Programs used in a standalone environment. /tmp/ Temporary files, usually a &man.mfs.8; memory-based file system (the contents of /tmp are usually NOT preserved across a system reboot). /usr/ The majority of user utilities and applications. /usr/bin/ Common utilities, programming tools, and applications. /usr/include/ Standard C include files. /usr/lib/ Archive libraries. /usr/libdata/ Miscellaneous utility data files. /usr/libexec/ System daemons & system utilities (executed by other programs). /usr/local/ Local executables, libraries, etc. Also used as the default destination for the FreeBSD ports framework. Within /usr/local, the general layout sketched out by &man.hier.7; for /usr should be used. Exceptions are the man directory, which is directly under /usr/local rather than under /usr/local/share, and the ports documentation is in share/doc/port. /usr/obj/ Architecture-specific target tree produced by building the /usr/src tree. /usr/ports The FreeBSD Ports Collection (optional). /usr/sbin/ System daemons & system utilities (executed by users). /usr/share/ Architecture-independent files. /usr/src/ BSD and/or local source files. /usr/X11R6/ X11R6 distribution executables, libraries, etc (optional). /var/ Multi-purpose log, temporary, transient, and spool files. /var/log/ Miscellaneous system log files. /var/mail/ User mailbox files. /var/spool/ Miscellaneous printer and mail system spooling directories. /var/tmp/ Temporary files that are kept between system reboots. /var/yp NIS maps. Disk Organization The smallest unit of organization that FreeBSD uses to find files is the filename. Filenames are case-sensitive, which means that readme.txt and README.TXT are two separate files. FreeBSD does not use the extension (.txt) of a file to determine whether the file is a program, or a document, or some other form of data. Files are stored in directories. A directory may contain no files, or it may contain many hundreds of files. A directory can also contain other directories, allowing you to build up a hierarchy of directories within one another. This makes it much easier to organize your data. Files and directories are referenced by giving the file or directory name, followed by a forward slash, /, followed by any other directory names that are necessary. If you have directory foo, which contains directory bar, which contains the file readme.txt, then the full name, or path to the file is foo/bar/readme.txt. Directories and files are stored in a filesystem. Each filesystem contains exactly one directory at the very top level, called the root directory for that filesystem. This root directory can then contain other directories. So far this is probably similar to any other operating system you may have used. There are a few differences; for example, &ms-dos; uses \ to separate file and directory names, while &macos; uses :. FreeBSD does not use drive letters, or other drive names in the path. You would not write c:/foo/bar/readme.txt on FreeBSD. Instead, one filesystem is designated the root filesystem. The root filesystem's root directory is referred to as /. Every other filesystem is then mounted under the root filesystem. No matter how many disks you have on your FreeBSD system, every directory appears to be part of the same disk. Suppose you have three filesystems, called A, B, and C. Each filesystem has one root directory, which contains two other directories, called A1, A2 (and likewise B1, B2 and C1, C2). Call A the root filesystem. If you used the ls command to view the contents of this directory you would see two subdirectories, A1 and A2. The directory tree looks like this: / | +--- A1 | `--- A2 A filesystem must be mounted on to a directory in another filesystem. So now suppose that you mount filesystem B on to the directory A1. The root directory of B replaces A1, and the directories in B appear accordingly: / | +--- A1 | | | +--- B1 | | | `--- B2 | `--- A2 Any files that are in the B1 or B2 directories can be reached with the path /A1/B1 or /A1/B2 as necessary. Any files that were in /A1 have been temporarily hidden. They will reappear if B is unmounted from A. If B had been mounted on A2 then the diagram would look like this: / | +--- A1 | `--- A2 | +--- B1 | `--- B2 and the paths would be /A2/B1 and /A2/B2 respectively. Filesystems can be mounted on top of one another. Continuing the last example, the C filesystem could be mounted on top of the B1 directory in the B filesystem, leading to this arrangement: / | +--- A1 | `--- A2 | +--- B1 | | | +--- C1 | | | `--- C2 | `--- B2 Or C could be mounted directly on to the A filesystem, under the A1 directory: / | +--- A1 | | | +--- C1 | | | `--- C2 | `--- A2 | +--- B1 | `--- B2 If you are familiar with &ms-dos;, this is similar, although not identical, to the join command. This is not normally something you need to concern yourself with. Typically you create filesystems when installing FreeBSD and decide where to mount them, and then never change them unless you add a new disk. It is entirely possible to have one large root filesystem, and not need to create any others. There are some drawbacks to this approach, and one advantage. Benefits of Multiple Filesystems Different filesystems can have different mount options. For example, with careful planning, the root filesystem can be mounted read-only, making it impossible for you to inadvertently delete or edit a critical file. Separating user-writable filesystems, such as /home, from other filesystems also allows them to be mounted nosuid; this option prevents the suid/guid bits on executables stored on the filesystem from taking effect, possibly improving security. FreeBSD automatically optimizes the layout of files on a filesystem, depending on how the filesystem is being used. So a filesystem that contains many small files that are written frequently will have a different optimization to one that contains fewer, larger files. By having one big filesystem this optimization breaks down. FreeBSD's filesystems are very robust should you lose power. However, a power loss at a critical point could still damage the structure of the filesystem. By splitting your data over multiple filesystems it is more likely that the system will still come up, making it easier for you to restore from backup as necessary. Benefit of a Single Filesystem Filesystems are a fixed size. If you create a filesystem when you install FreeBSD and give it a specific size, you may later discover that you need to make the partition bigger. This is not easily accomplished without backing up, recreating the filesystem with the new size, and then restoring the backed up data. FreeBSD 4.4 and later versions feature the &man.growfs.8; command, which makes it possible to increase the size of filesystem on the fly, removing this limitation. Filesystems are contained in partitions. This does not have the same meaning as the common usage of the term partition (for example, &ms-dos; partition), because of &os;'s &unix; heritage. Each partition is identified by a letter from a through to h. Each partition can contain only one filesystem, which means that filesystems are often described by either their typical mount point in the filesystem hierarchy, or the letter of the partition they are contained in. FreeBSD also uses disk space for swap space. Swap space provides FreeBSD with virtual memory. This allows your computer to behave as though it has much more memory than it actually does. When FreeBSD runs out of memory it moves some of the data that is not currently being used to the swap space, and moves it back in (moving something else out) when it needs it. Some partitions have certain conventions associated with them. Partition Convention a Normally contains the root filesystem b Normally contains swap space c Normally the same size as the enclosing slice. This allows utilities that need to work on the entire slice (for example, a bad block scanner) to work on the c partition. You would not normally create a filesystem on this partition. d Partition d used to have a special meaning associated with it, although that is now gone. To this day, some tools may operate oddly if told to work on partition d, so sysinstall will not normally create partition d. Each partition-that-contains-a-filesystem is stored in what FreeBSD calls a slice. Slice is FreeBSD's term for what the common call partitions, and again, this is because of FreeBSD's &unix; background. Slices are numbered, starting at 1, through to 4. slices partitions dangerously dedicated Slice numbers follow the device name, prefixed with an s, starting at 1. So da0s1 is the first slice on the first SCSI drive. There can only be four physical slices on a disk, but you can have logical slices inside physical slices of the appropriate type. These extended slices are numbered starting at 5, so ad0s5 is the first extended slice on the first IDE disk. These devices are used by file systems that expect to occupy a slice. Slices, dangerously dedicated physical drives, and other drives contain partitions, which are represented as letters from a to h. This letter is appended to the device name, so da0a is the a partition on the first da drive, which is dangerously dedicated. ad1s3e is the fifth partition in the third slice of the second IDE disk drive. Finally, each disk on the system is identified. A disk name starts with a code that indicates the type of disk, and then a number, indicating which disk it is. Unlike slices, disk numbering starts at 0. Common codes that you will see are listed in . When referring to a partition FreeBSD requires that you also name the slice and disk that contains the partition, and when referring to a slice you should also refer to the disk name. Do this by listing the disk name, s, the slice number, and then the partition letter. Examples are shown in . shows a conceptual model of the disk layout that should help make things clearer. In order to install FreeBSD you must first configure the disk slices, then create partitions within the slice you will use for FreeBSD, and then create a filesystem (or swap space) in each partition, and decide where that filesystem will be mounted. Disk Device Codes Code Meaning ad ATAPI (IDE) disk da SCSI direct access disk acd ATAPI (IDE) CDROM cd SCSI CDROM fd Floppy disk
Sample Disk, Slice, and Partition Names Name Meaning ad0s1a The first partition (a) on the first slice (s1) on the first IDE disk (ad0). da1s2e The fifth partition (e) on the second slice (s2) on the second SCSI disk (da1). Conceptual Model of a Disk This diagram shows FreeBSD's view of the first IDE disk attached to the system. Assume that the disk is 4 GB in size, and contains two 2 GB slices (&ms-dos; partitions). The first slice contains a &ms-dos; disk, C:, and the second slice contains a FreeBSD installation. This example FreeBSD installation has three partitions, and a swap partition. The three partitions will each hold a filesystem. Partition a will be used for the root filesystem, e for the /var directory hierarchy, and f for the /usr directory hierarchy. .-----------------. --. | | | | DOS / Windows | | : : > First slice, ad0s1 : : | | | | :=================: ==: --. | | | Partition a, mounted as / | | | > referred to as ad0s2a | | | | | :-----------------: ==: | | | | Partition b, used as swap | | | > referred to as ad0s2b | | | | | :-----------------: ==: | Partition c, no | | | Partition e, used as /var > filesystem, all | | > referred to as ad0s2e | of FreeBSD slice, | | | | ad0s2c :-----------------: ==: | | | | | : : | Partition f, used as /usr | : : > referred to as ad0s2f | : : | | | | | | | | --' | `-----------------' --' Mounting and Unmounting File Systems The file system is best visualized as a tree, rooted, as it were, at /. /dev, /usr, and the other directories in the root directory are branches, which may have their own branches, such as /usr/local, and so on. root file system There are various reasons to house some of these directories on separate file systems. /var contains the directories log/, spool/, and various types of temporary files, and as such, may get filled up. Filling up the root file system is not a good idea, so splitting /var from / is often favorable. Another common reason to contain certain directory trees on other file systems is if they are to be housed on separate physical disks, or are separate virtual disks, such as Network File System mounts, or CDROM drives. The <filename>fstab</filename> File file systems mounted with fstab During the boot process, file systems listed in /etc/fstab are automatically mounted (unless they are listed with the option). The /etc/fstab file contains a list of lines of the following format: device /mount-point fstype options dumpfreq passno device A device name (which should exist), as explained in . mount-point A directory (which should exist), on which to mount the file system. fstype The file system type to pass to &man.mount.8;. The default FreeBSD file system is ufs. options Either for read-write file systems, or for read-only file systems, followed by any other options that may be needed. A common option is for file systems not normally mounted during the boot sequence. Other options are listed in the &man.mount.8; manual page. dumpfreq This is used by &man.dump.8; to determine which file systems require dumping. If the field is missing, a value of zero is assumed. passno This determines the order in which file systems should be checked. File systems that should be skipped should have their passno set to zero. The root file system (which needs to be checked before everything else) should have its passno set to one, and other file systems' passno should be set to values greater than one. If more than one file systems have the same passno then &man.fsck.8; will attempt to check file systems in parallel if possible. Consult the &man.fstab.5; manual page for more information on the format of the /etc/fstab file and the options it contains. The <command>mount</command> Command file systems mounting The &man.mount.8; command is what is ultimately used to mount file systems. In its most basic form, you use: &prompt.root; mount device mountpoint There are plenty of options, as mentioned in the &man.mount.8; manual page, but the most common are: Mount Options Mount all the file systems listed in /etc/fstab. Except those marked as noauto, excluded by the flag, or those that are already mounted. Do everything except for the actual mount system call. This option is useful in conjunction with the flag to determine what &man.mount.8; is actually trying to do. Force the mount of an unclean file system (dangerous), or forces the revocation of write access when downgrading a file system's mount status from read-write to read-only. Mount the file system read-only. This is identical to using the ( for &os; versions older than 5.2) argument to the option. fstype Mount the given file system as the given file system type, or mount only file systems of the given type, if given the option. ufs is the default file system type. Update mount options on the file system. Be verbose. Mount the file system read-write. The option takes a comma-separated list of the options, including the following: nodev Do not interpret special devices on the file system. This is a useful security option. noexec Do not allow execution of binaries on this file system. This is also a useful security option. nosuid Do not interpret setuid or setgid flags on the file system. This is also a useful security option. The <command>umount</command> Command file systems unmounting The &man.umount.8; command takes, as a parameter, one of a mountpoint, a device name, or the or option. All forms take to force unmounting, and for verbosity. Be warned that is not generally a good idea. Forcibly unmounting file systems might crash the computer or damage data on the file system. and are used to unmount all mounted file systems, possibly modified by the file system types listed after . , however, does not attempt to unmount the root file system. Processes FreeBSD is a multi-tasking operating system. This means that it seems as though more than one program is running at once. Each program running at any one time is called a process. Every command you run will start at least one new process, and there are a number of system processes that run all the time, keeping the system functional. Each process is uniquely identified by a number called a process ID, or PID, and, like files, each process also has one owner and group. The owner and group information is used to determine what files and devices the process can open, using the file permissions discussed earlier. Most processes also have a parent process. The parent process is the process that started them. For example, if you are typing commands to the shell then the shell is a process, and any commands you run are also processes. Each process you run in this way will have your shell as its parent process. The exception to this is a special process called &man.init.8;. init is always the first process, so its PID is always 1. init is started automatically by the kernel when FreeBSD starts. Two commands are particularly useful to see the processes on the system, &man.ps.1; and &man.top.1;. The ps command is used to show a static list of the currently running processes, and can show their PID, how much memory they are using, the command line they were started with, and so on. The top command displays all the running processes, and updates the display every few seconds, so that you can interactively see what your computer is doing. By default, ps only shows you the commands that are running and are owned by you. For example: &prompt.user; ps PID TT STAT TIME COMMAND 298 p0 Ss 0:01.10 tcsh 7078 p0 S 2:40.88 xemacs mdoc.xsl (xemacs-21.1.14) 37393 p0 I 0:03.11 xemacs freebsd.dsl (xemacs-21.1.14) 48630 p0 S 2:50.89 /usr/local/lib/netscape-linux/navigator-linux-4.77.bi 48730 p0 IW 0:00.00 (dns helper) (navigator-linux-) 72210 p0 R+ 0:00.00 ps 390 p1 Is 0:01.14 tcsh 7059 p2 Is+ 1:36.18 /usr/local/bin/mutt -y 6688 p3 IWs 0:00.00 tcsh 10735 p4 IWs 0:00.00 tcsh 20256 p5 IWs 0:00.00 tcsh 262 v0 IWs 0:00.00 -tcsh (tcsh) 270 v0 IW+ 0:00.00 /bin/sh /usr/X11R6/bin/startx -- -bpp 16 280 v0 IW+ 0:00.00 xinit /home/nik/.xinitrc -- -bpp 16 284 v0 IW 0:00.00 /bin/sh /home/nik/.xinitrc 285 v0 S 0:38.45 /usr/X11R6/bin/sawfish As you can see in this example, the output from &man.ps.1; is organized into a number of columns. PID is the process ID discussed earlier. PIDs are assigned starting from 1, go up to 99999, and wrap around back to the beginning when you run out. The TT column shows the tty the program is running on, and can safely be ignored for the moment. STAT shows the program's state, and again, can be safely ignored. TIME is the amount of time the program has been running on the CPU—this is usually not the elapsed time since you started the program, as most programs spend a lot of time waiting for things to happen before they need to spend time on the CPU. Finally, COMMAND is the command line that was used to run the program. &man.ps.1; supports a number of different options to change the information that is displayed. One of the most useful sets is auxww. displays information about all the running processes, not just your own. displays the username of the process' owner, as well as memory usage. displays information about daemon processes, and causes &man.ps.1; to display the full command line, rather than truncating it once it gets too long to fit on the screen. The output from &man.top.1; is similar. A sample session looks like this: &prompt.user; top last pid: 72257; load averages: 0.13, 0.09, 0.03 up 0+13:38:33 22:39:10 47 processes: 1 running, 46 sleeping CPU states: 12.6% user, 0.0% nice, 7.8% system, 0.0% interrupt, 79.7% idle Mem: 36M Active, 5256K Inact, 13M Wired, 6312K Cache, 15M Buf, 408K Free Swap: 256M Total, 38M Used, 217M Free, 15% Inuse PID USERNAME PRI NICE SIZE RES STATE TIME WCPU CPU COMMAND 72257 nik 28 0 1960K 1044K RUN 0:00 14.86% 1.42% top 7078 nik 2 0 15280K 10960K select 2:54 0.88% 0.88% xemacs-21.1.14 281 nik 2 0 18636K 7112K select 5:36 0.73% 0.73% XF86_SVGA 296 nik 2 0 3240K 1644K select 0:12 0.05% 0.05% xterm 48630 nik 2 0 29816K 9148K select 3:18 0.00% 0.00% navigator-linu 175 root 2 0 924K 252K select 1:41 0.00% 0.00% syslogd 7059 nik 2 0 7260K 4644K poll 1:38 0.00% 0.00% mutt ... The output is split into two sections. The header (the first five lines) shows the PID of the last process to run, the system load averages (which are a measure of how busy the system is), the system uptime (time since the last reboot) and the current time. The other figures in the header relate to how many processes are running (47 in this case), how much memory and swap space has been taken up, and how much time the system is spending in different CPU states. Below that are a series of columns containing similar information to the output from &man.ps.1;. As before you can see the PID, the username, the amount of CPU time taken, and the command that was run. &man.top.1; also defaults to showing you the amount of memory space taken by the process. This is split into two columns, one for total size, and one for resident size—total size is how much memory the application has needed, and the resident size is how much it is actually using at the moment. In this example you can see that &netscape; has required almost 30 MB of RAM, but is currently only using 9 MB. &man.top.1; automatically updates this display every two seconds; this can be changed with the option. Daemons, Signals, and Killing Processes When you run an editor it is easy to control the editor, tell it to load files, and so on. You can do this because the editor provides facilities to do so, and because the editor is attached to a terminal. Some programs are not designed to be run with continuous user input, and so they disconnect from the terminal at the first opportunity. For example, a web server spends all day responding to web requests, it normally does not need any input from you. Programs that transport email from site to site are another example of this class of application. We call these programs daemons. Daemons were characters in Greek mythology; neither good or evil, they were little attendant spirits that, by and large, did useful things for mankind. Much like the web servers and mail servers of today do useful things. This is why the BSD mascot has, for a long time, been the cheerful looking daemon with sneakers and a pitchfork. There is a convention to name programs that normally run as daemons with a trailing d. BIND is the Berkeley Internet Name Daemon (and the actual program that executes is called named), the Apache web server program is called httpd, the line printer spooling daemon is lpd and so on. This is a convention, not a hard and fast rule; for example, the main mail daemon for the Sendmail application is called sendmail, and not maild, as you might imagine. Sometimes you will need to communicate with a daemon process. These communications are called signals, and you can communicate with a daemon (or with any other running process) by sending it a signal. There are a number of different signals that you can send—some of them have a specific meaning, others are interpreted by the application, and the application's documentation will tell you how that application interprets signals. You can only send a signal to a process that you own. If you send a signal to someone else's process with &man.kill.1; or &man.kill.2; permission will be denied. The exception to this is the root user, who can send signals to everyone's processes. FreeBSD will also send applications signals in some cases. If an application is badly written, and tries to access memory that it is not supposed to, FreeBSD sends the process the Segmentation Violation signal (SIGSEGV). If an application has used the &man.alarm.3; system call to be alerted after a period of time has elapsed then it will be sent the Alarm signal (SIGALRM), and so on. Two signals can be used to stop a process, SIGTERM and SIGKILL. SIGTERM is the polite way to kill a process; the process can catch the signal, realize that you want it to shut down, close any log files it may have open, and generally finish whatever it is doing at the time before shutting down. In some cases a process may even ignore SIGTERM if it is in the middle of some task that can not be interrupted. SIGKILL can not be ignored by a process. This is the I do not care what you are doing, stop right now signal. If you send SIGKILL to a process then FreeBSD will stop that process there and then Not quite true—there are a few things that can not be interrupted. For example, if the process is trying to read from a file that is on another computer on the network, and the other computer has gone away for some reason (been turned off, or the network has a fault), then the process is said to be uninterruptible. Eventually the process will time out, typically after two minutes. As soon as this time out occurs the process will be killed. . The other signals you might want to use are SIGHUP, SIGUSR1, and SIGUSR2. These are general purpose signals, and different applications will do different things when they are sent. Suppose that you have changed your web server's configuration file—you would like to tell the web server to re-read its configuration. You could stop and restart httpd, but this would result in a brief outage period on your web server, which may be undesirable. Most daemons are written to respond to the SIGHUP signal by re-reading their configuration file. So instead of killing and restarting httpd you would send it the SIGHUP signal. Because there is no standard way to respond to these signals, different daemons will have different behavior, so be sure and read the documentation for the daemon in question. Signals are sent using the &man.kill.1; command, as this example shows. Sending a Signal to a Process This example shows how to send a signal to &man.inetd.8;. The inetd configuration file is /etc/inetd.conf, and inetd will re-read this configuration file when it is sent SIGHUP. Find the process ID of the process you want to send the signal to. Do this using &man.ps.1; and &man.grep.1;. The &man.grep.1; command is used to search through output, looking for the string you specify. This command is run as a normal user, and &man.inetd.8; is run as root, so the options must be given to &man.ps.1;. &prompt.user; ps -ax | grep inetd 198 ?? IWs 0:00.00 inetd -wW So the &man.inetd.8; PID is 198. In some cases the grep inetd command might also occur in this output. This is because of the way &man.ps.1; has to find the list of running processes. Use &man.kill.1; to send the signal. Because &man.inetd.8; is being run by root you must use &man.su.1; to become root first. &prompt.user; su Password: &prompt.root; /bin/kill -s HUP 198 In common with most &unix; commands, &man.kill.1; will not print any output if it is successful. If you send a signal to a process that you do not own then you will see kill: PID: Operation not permitted. If you mistype the PID you will either send the signal to the wrong process, which could be bad, or, if you are lucky, you will have sent the signal to a PID that is not currently in use, and you will see kill: PID: No such process. Why Use <command>/bin/kill</command>? Many shells provide the kill command as a built in command; that is, the shell will send the signal directly, rather than running /bin/kill. This can be very useful, but different shells have a different syntax for specifying the name of the signal to send. Rather than try to learn all of them, it can be simpler just to use the /bin/kill ... command directly. Sending other signals is very similar, just substitute TERM or KILL in the command line as necessary. Killing random process on the system can be a bad idea. In particular, &man.init.8;, process ID 1, is very special. Running /bin/kill -s KILL 1 is a quick way to shutdown your system. Always double check the arguments you run &man.kill.1; with before you press Return. Shells shells command line In FreeBSD, a lot of everyday work is done in a command line interface called a shell. A shell's main job is to take commands from the input channel and execute them. A lot of shells also have built in functions to help everyday tasks such as file management, file globbing, command line editing, command macros, and environment variables. FreeBSD comes with a set of shells, such as sh, the Bourne Shell, and tcsh, the improved C-shell. Many other shells are available from the FreeBSD Ports Collection, such as zsh and bash. Which shell do you use? It is really a matter of taste. If you are a C programmer you might feel more comfortable with a C-like shell such as tcsh. If you have come from Linux or are new to a &unix; command line interface you might try bash. The point is that each shell has unique properties that may or may not work with your preferred working environment, and that you have a choice of what shell to use. One common feature in a shell is filename completion. Given the typing of the first few letters of a command or filename, you can usually have the shell automatically complete the rest of the command or filename by hitting the Tab key on the keyboard. Here is an example. Suppose you have two files called foobar and foo.bar. You want to delete foo.bar. So what you would type on the keyboard is: rm fo[Tab].[Tab]. The shell would print out rm foo[BEEP].bar. The [BEEP] is the console bell, which is the shell telling me it was unable to totally complete the filename because there is more than one match. Both foobar and foo.bar start with fo, but it was able to complete to foo. If you type in ., then hit Tab again, the shell would be able to fill in the rest of the filename for you. environment variables Another feature of the shell is the use of environment variables. Environment variables are a variable key pair stored in the shell's environment space. This space can be read by any program invoked by the shell, and thus contains a lot of program configuration. Here is a list of common environment variables and what they mean: environment variables Variable Description USER Current logged in user's name. PATH Colon separated list of directories to search for binaries. DISPLAY Network name of the X11 display to connect to, if available. SHELL The current shell. TERM The name of the user's terminal. Used to determine the capabilities of the terminal. TERMCAP Database entry of the terminal escape codes to perform various terminal functions. OSTYPE Type of operating system. e.g., FreeBSD. MACHTYPE The CPU architecture that the system is running on. EDITOR The user's preferred text editor. PAGER The user's preferred text pager. MANPATH Colon separated list of directories to search for manual pages. Bourne shells Setting an environment variable differs somewhat from shell to shell. For example, in the C-Style shells such as tcsh and csh, you would use setenv to set environment variables. Under Bourne shells such as sh and bash, you would use export to set your current environment variables. For example, to set or modify the EDITOR environment variable, under csh or tcsh a command like this would set EDITOR to /usr/local/bin/emacs: &prompt.user; setenv EDITOR /usr/local/bin/emacs Under Bourne shells: &prompt.user; export EDITOR="/usr/local/bin/emacs" You can also make most shells expand the environment variable by placing a $ character in front of it on the command line. For example, echo $TERM would print out whatever $TERM is set to, because the shell expands $TERM and passes it on to echo. Shells treat a lot of special characters, called meta-characters as special representations of data. The most common one is the * character, which represents any number of characters in a filename. These special meta-characters can be used to do filename globbing. For example, typing in echo * is almost the same as typing in ls because the shell takes all the files that match * and puts them on the command line for echo to see. To prevent the shell from interpreting these special characters, they can be escaped from the shell by putting a backslash (\) character in front of them. echo $TERM prints whatever your terminal is set to. echo \$TERM prints $TERM as is. Changing Your Shell The easiest way to change your shell is to use the chsh command. Running chsh will place you into the editor that is in your EDITOR environment variable; if it is not set, you will be placed in vi. Change the Shell: line accordingly. You can also give chsh the option; this will set your shell for you, without requiring you to enter an editor. For example, if you wanted to change your shell to bash, the following should do the trick: &prompt.user; chsh -s /usr/local/bin/bash Running chsh with no parameters and editing the shell from there would work also. The shell that you wish to use must be present in the /etc/shells file. If you have installed a shell from the ports collection, then this should have been done for you already. If you installed the shell by hand, you must do this. For example, if you installed bash by hand and placed it into /usr/local/bin, you would want to: &prompt.root; echo "/usr/local/bin/bash" >> /etc/shells Then rerun chsh. Text Editors text editors editors A lot of configuration in FreeBSD is done by editing text files. Because of this, it would be a good idea to become familiar with a text editor. FreeBSD comes with a few as part of the base system, and many more are available in the Ports Collection. ee editors ee The easiest and simplest editor to learn is an editor called ee, which stands for easy editor. To start ee, one would type at the command line ee filename where filename is the name of the file to be edited. For example, to edit /etc/rc.conf, type in ee /etc/rc.conf. Once inside of ee, all of the commands for manipulating the editor's functions are listed at the top of the display. The caret ^ character represents the Ctrl key on the keyboard, so ^e expands to the key combination Ctrle. To leave ee, hit the Esc key, then choose leave editor. The editor will prompt you to save any changes if the file has been modified. vi editors vi emacs editors emacs FreeBSD also comes with more powerful text editors such as vi as part of the base system, while other editors, like Emacs and vim, are part of the FreeBSD Ports Collection (editors/emacs and editors/vim). These editors offer much more functionality and power at the expense of being a little more complicated to learn. However if you plan on doing a lot of text editing, learning a more powerful editor such as vim or Emacs will save you much more time in the long run. Devices and Device Nodes A device is a term used mostly for hardware-related activities in a system, including disks, printers, graphics cards, and keyboards. When FreeBSD boots, the majority of what FreeBSD displays are devices being detected. You can look through the boot messages again by viewing /var/run/dmesg.boot. For example, acd0 is the first IDE CDROM drive, while kbd0 represents the keyboard. Most of these devices in a &unix; operating system must be accessed through special files called device nodes, which are located in the /dev directory. Creating Device Nodes When adding a new device to your system, or compiling in support for additional devices, you may need to create one or more device nodes for the new devices. MAKEDEV Script On systems without DEVFS (this concerns all FreeBSD versions before 5.0), device nodes are created using the &man.MAKEDEV.8; script as shown below: &prompt.root; cd /dev &prompt.root; sh MAKEDEV ad1 This example would make the proper device nodes for the second IDE drive when installed. <literal>DEVFS</literal> (DEVice File System) The device file system, or DEVFS, provides access to kernel's device namespace in the global file system namespace. Instead of having to create and modify device nodes, DEVFS maintains this particular file system for you. See the &man.devfs.5; manual page for more information. DEVFS is used by default in FreeBSD 5.0 and above. Binary Formats To understand why &os; uses the &man.elf.5; format, you must first know a little about the three currently dominant executable formats for &unix;: &man.a.out.5; The oldest and classic &unix; object format. It uses a short and compact header with a magic number at the beginning that is often used to characterize the format (see &man.a.out.5; for more details). It contains three loaded segments: .text, .data, and .bss plus a symbol table and a string table. COFF The SVR3 object format. The header now comprises a section table, so you can have more than just .text, .data, and .bss sections. &man.elf.5; The successor to COFF, featuring multiple sections and 32-bit or 64-bit possible values. One major drawback: ELF was also designed with the assumption that there would be only one ABI per system architecture. That assumption is actually quite incorrect, and not even in the commercial SYSV world (which has at least three ABIs: SVR4, Solaris, SCO) does it hold true. FreeBSD tries to work around this problem somewhat by providing a utility for branding a known ELF executable with information about the ABI it is compliant with. See the manual page for &man.brandelf.1; for more information. FreeBSD comes from the classic camp and used the &man.a.out.5; format, a technology tried and proven through many generations of BSD releases, until the beginning of the 3.X branch. Though it was possible to build and run native ELF binaries (and kernels) on a FreeBSD system for some time before that, FreeBSD initially resisted the push to switch to ELF as the default format. Why? Well, when the Linux camp made their painful transition to ELF, it was not so much to flee the a.out executable format as it was their inflexible jump-table based shared library mechanism, which made the construction of shared libraries very difficult for vendors and developers alike. Since the ELF tools available offered a solution to the shared library problem and were generally seen as the way forward anyway, the migration cost was accepted as necessary and the transition made. FreeBSD's shared library mechanism is based more closely on Sun's &sunos; style shared library mechanism and, as such, is very easy to use. So, why are there so many different formats? Back in the dim, dark past, there was simple hardware. This simple hardware supported a simple, small system. a.out was completely adequate for the job of representing binaries on this simple system (a PDP-11). As people ported &unix; from this simple system, they retained the a.out format because it was sufficient for the early ports of &unix; to architectures like the Motorola 68k, VAXen, etc. Then some bright hardware engineer decided that if he could force software to do some sleazy tricks, then he would be able to shave a few gates off the design and allow his CPU core to run faster. While it was made to work with this new kind of hardware (known these days as RISC), a.out was ill-suited for this hardware, so many formats were developed to get to a better performance from this hardware than the limited, simple a.out format could offer. Things like COFF, ECOFF, and a few obscure others were invented and their limitations explored before things seemed to settle on ELF. In addition, program sizes were getting huge and disks (and physical memory) were still relatively small so the concept of a shared library was born. The VM system also became more sophisticated. While each one of these advancements was done using the a.out format, its usefulness was stretched more and more with each new feature. In addition, people wanted to dynamically load things at run time, or to junk parts of their program after the init code had run to save in core memory and swap space. Languages became more sophisticated and people wanted code called before main automatically. Lots of hacks were done to the a.out format to allow all of these things to happen, and they basically worked for a time. In time, a.out was not up to handling all these problems without an ever increasing overhead in code and complexity. While ELF solved many of these problems, it would be painful to switch from the system that basically worked. So ELF had to wait until it was more painful to remain with a.out than it was to migrate to ELF. However, as time passed, the build tools that FreeBSD derived their build tools from (the assembler and loader especially) evolved in two parallel trees. The FreeBSD tree added shared libraries and fixed some bugs. The GNU folks that originally wrote these programs rewrote them and added simpler support for building cross compilers, plugging in different formats at will, and so on. Since many people wanted to build cross compilers targeting FreeBSD, they were out of luck since the older sources that FreeBSD had for as and ld were not up to the task. The new GNU tools chain (binutils) does support cross compiling, ELF, shared libraries, C++ extensions, etc. In addition, many vendors are releasing ELF binaries, and it is a good thing for FreeBSD to run them. ELF is more expressive than a.out and allows more extensibility in the base system. The ELF tools are better maintained, and offer cross compilation support, which is important to many people. ELF may be a little slower than a.out, but trying to measure it can be difficult. There are also numerous details that are different between the two in how they map pages, handle init code, etc. None of these are very important, but they are differences. In time support for a.out will be moved out of the GENERIC kernel, and eventually removed from the kernel once the need to run legacy a.out programs is past. For More Information Manual Pages manual pages The most comprehensive documentation on FreeBSD is in the form of manual pages. Nearly every program on the system comes with a short reference manual explaining the basic operation and various arguments. These manuals can be viewed with the man command. Use of the man command is simple: &prompt.user; man command command is the name of the command you wish to learn about. For example, to learn more about ls command type: &prompt.user; man ls The online manual is divided up into numbered sections: User commands. System calls and error numbers. Functions in the C libraries. Device drivers. File formats. Games and other diversions. Miscellaneous information. System maintenance and operation commands. Kernel developers. In some cases, the same topic may appear in more than one section of the online manual. For example, there is a chmod user command and a chmod() system call. In this case, you can tell the man command which one you want by specifying the section: &prompt.user; man 1 chmod This will display the manual page for the user command chmod. References to a particular section of the online manual are traditionally placed in parenthesis in written documentation, so &man.chmod.1; refers to the chmod user command and &man.chmod.2; refers to the system call. This is fine if you know the name of the command and simply wish to know how to use it, but what if you cannot recall the command name? You can use man to search for keywords in the command descriptions by using the switch: &prompt.user; man -k mail With this command you will be presented with a list of commands that have the keyword mail in their descriptions. This is actually functionally equivalent to using the apropos command. So, you are looking at all those fancy commands in /usr/bin but do not have the faintest idea what most of them actually do? Simply do: &prompt.user; cd /usr/bin &prompt.user; man -f * or &prompt.user; cd /usr/bin &prompt.user; whatis * which does the same thing. GNU Info Files Free Software Foundation FreeBSD includes many applications and utilities produced by the Free Software Foundation (FSF). In addition to manual pages, these programs come with more extensive hypertext documents called info files which can be viewed with the info command or, if you installed emacs, the info mode of emacs. To use the &man.info.1; command, simply type: &prompt.user; info For a brief introduction, type h. For a quick command reference, type ?. - diff --git a/en_US.ISO8859-1/books/handbook/security/chapter.sgml b/en_US.ISO8859-1/books/handbook/security/chapter.sgml index 9a422a7ce6..9cda20c8c1 100644 --- a/en_US.ISO8859-1/books/handbook/security/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/security/chapter.sgml @@ -1,4890 +1,5054 @@ Matthew Dillon Much of this chapter has been taken from the security(7) manual page by Security security Synopsis This chapter will provide a basic introduction to system security concepts, some general good rules of thumb, and some advanced topics under &os;. A lot of the topics covered here can be applied to system and Internet security in general as well. The Internet is no longer a friendly place in which everyone wants to be your kind neighbor. Securing your system is imperative to protect your data, intellectual property, time, and much more from the hands of hackers and the like. &os; provides an array of utilities and mechanisms to ensure the integrity and security of your system and network. After reading this chapter, you will know: Basic system security concepts, in respect to &os;. About the various crypt mechanisms available in &os;, such as DES and MD5. How to set up one-time password authentication. How to configure TCP Wrappers for use with inetd. How to set up KerberosIV on &os; releases prior to 5.0. How to set up Kerberos5 on post &os; 5.0 releases. How to configure IPsec and create a VPN between &os;/&windows; machines. How to configure and use OpenSSH, &os;'s SSH implementation. What file system ACLs are and how to use them. + + How to use the Portaudit + utility to audit third party software packages installed + from the Ports Collection. + + How to utilize the &os; security advisories publications. + + Have an idea of what Process Accounting is and how to + enable it on &os;. + Before reading this chapter, you should: Understand basic &os; and Internet concepts. Additional security topics are covered throughout this book. For example, Mandatory Access Control is discussed in and Internet Firewalls are discussed in . Introduction Security is a function that begins and ends with the system administrator. While all BSD &unix; multi-user systems have some inherent security, the job of building and maintaining additional security mechanisms to keep those users honest is probably one of the single largest undertakings of the sysadmin. Machines are only as secure as you make them, and security concerns are ever competing with the human necessity for convenience. &unix; systems, in general, are capable of running a huge number of simultaneous processes and many of these processes operate as servers — meaning that external entities can connect and talk to them. As yesterday's mini-computers and mainframes become today's desktops, and as computers become networked and internetwork, security becomes an even bigger issue. Security is best implemented through a layered onion approach. In a nutshell, what you want to do is to create as many layers of security as are convenient and then carefully monitor the system for intrusions. You do not want to overbuild your security or you will interfere with the detection side, and detection is one of the single most important aspects of any security mechanism. For example, it makes little sense to set the schg flag (see &man.chflags.1;) on every system binary because while this may temporarily protect the binaries, it prevents an attacker who has broken in from making an easily detectable change that may result in your security mechanisms not detecting the attacker at all. System security also pertains to dealing with various forms of attack, including attacks that attempt to crash, or otherwise make a system unusable, but do not attempt to compromise the root account (break root). Security concerns can be split up into several categories: Denial of service attacks. User account compromises. Root compromise through accessible servers. Root compromise via user accounts. Backdoor creation. DoS attacks Denial of Service (DoS) security DoS attacks Denial of Service (DoS) Denial of Service (DoS) A denial of service attack is an action that deprives the machine of needed resources. Typically, DoS attacks are brute-force mechanisms that attempt to crash or otherwise make a machine unusable by overwhelming its servers or network stack. Some DoS attacks try to take advantage of bugs in the networking stack to crash a machine with a single packet. The latter can only be fixed by applying a bug fix to the kernel. Attacks on servers can often be fixed by properly specifying options to limit the load the servers incur on the system under adverse conditions. Brute-force network attacks are harder to deal with. A spoofed-packet attack, for example, is nearly impossible to stop, short of cutting your system off from the Internet. It may not be able to take your machine down, but it can saturate your Internet connection. security account compromises A user account compromise is even more common than a DoS attack. Many sysadmins still run standard telnetd, rlogind, rshd, and ftpd servers on their machines. These servers, by default, do not operate over encrypted connections. The result is that if you have any moderate-sized user base, one or more of your users logging into your system from a remote location (which is the most common and convenient way to login to a system) will have his or her password sniffed. The attentive system admin will analyze his remote access logs looking for suspicious source addresses even for successful logins. One must always assume that once an attacker has access to a user account, the attacker can break root. However, the reality is that in a well secured and maintained system, access to a user account does not necessarily give the attacker access to root. The distinction is important because without access to root the attacker cannot generally hide his tracks and may, at best, be able to do nothing more than mess with the user's files, or crash the machine. User account compromises are very common because users tend not to take the precautions that sysadmins take. security backdoors System administrators must keep in mind that there are potentially many ways to break root on a machine. The attacker may know the root password, the attacker may find a bug in a root-run server and be able to break root over a network connection to that server, or the attacker may know of a bug in a suid-root program that allows the attacker to break root once he has broken into a user's account. If an attacker has found a way to break root on a machine, the attacker may not have a need to install a backdoor. Many of the root holes found and closed to date involve a considerable amount of work by the attacker to cleanup after himself, so most attackers install backdoors. A backdoor provides the attacker with a way to easily regain root access to the system, but it also gives the smart system administrator a convenient way to detect the intrusion. Making it impossible for an attacker to install a backdoor may actually be detrimental to your security, because it will not close off the hole the attacker found to break in the first place. Security remedies should always be implemented with a multi-layered onion peel approach and can be categorized as follows: Securing root and staff accounts. Securing root–run servers and suid/sgid binaries. Securing user accounts. Securing the password file. Securing the kernel core, raw devices, and file systems. Quick detection of inappropriate changes made to the system. Paranoia. The next section of this chapter will cover the above bullet items in greater depth. Securing &os; security securing &os; Command vs. Protocol Throughout this document, we will use bold text to refer to an application, and a monospaced font to refer to specific commands. Protocols will use a normal font. This typographical distinction is useful for instances such as ssh, since it is a protocol as well as command. The sections that follow will cover the methods of securing your &os; system that were mentioned in the last section of this chapter. Securing the <username>root</username> Account and Staff Accounts su First off, do not bother securing staff accounts if you have not secured the root account. Most systems have a password assigned to the root account. The first thing you do is assume that the password is always compromised. This does not mean that you should remove the password. The password is almost always necessary for console access to the machine. What it does mean is that you should not make it possible to use the password outside of the console or possibly even with the &man.su.1; command. For example, make sure that your ptys are specified as being insecure in the /etc/ttys file so that direct root logins via telnet or rlogin are disallowed. If using other login services such as sshd, make sure that direct root logins are disabled there as well. You can do this by editing your /etc/ssh/sshd_config file, and making sure that PermitRootLogin is set to NO. Consider every access method — services such as FTP often fall through the cracks. Direct root logins should only be allowed via the system console. wheel Of course, as a sysadmin you have to be able to get to root, so we open up a few holes. But we make sure these holes require additional password verification to operate. One way to make root accessible is to add appropriate staff accounts to the wheel group (in /etc/group). The staff members placed in the wheel group are allowed to su to root. You should never give staff members native wheel access by putting them in the wheel group in their password entry. Staff accounts should be placed in a staff group, and then added to the wheel group via the /etc/group file. Only those staff members who actually need to have root access should be placed in the wheel group. It is also possible, when using an authentication method such as Kerberos, to use Kerberos' .k5login file in the root account to allow a &man.ksu.1; to root without having to place anyone at all in the wheel group. This may be the better solution since the wheel mechanism still allows an intruder to break root if the intruder has gotten hold of your password file and can break into a staff account. While having the wheel mechanism is better than having nothing at all, it is not necessarily the safest option. An indirect way to secure staff accounts, and ultimately root access is to use an alternative login access method and do what is known as starring out the encrypted password for the staff accounts. Using the &man.vipw.8; command, one can replace each instance of an encrypted password with a single * character. This command will update the /etc/master.passwd file and user/password database to disable password-authenticated logins. A staff account entry such as: foobar:R9DT/Fa1/LV9U:1000:1000::0:0:Foo Bar:/home/foobar:/usr/local/bin/tcsh Should be changed to this: foobar:*:1000:1000::0:0:Foo Bar:/home/foobar:/usr/local/bin/tcsh This change will prevent normal logins from occurring, since the encrypted password will never match *. With this done, staff members must use another mechanism to authenticate themselves such as &man.kerberos.1; or &man.ssh.1; using a public/private key pair. When using something like Kerberos, one generally must secure the machines which run the Kerberos servers and your desktop workstation. When using a public/private key pair with ssh, one must generally secure the machine used to login from (typically one's workstation). An additional layer of protection can be added to the key pair by password protecting the key pair when creating it with &man.ssh-keygen.1;. Being able to star out the passwords for staff accounts also guarantees that staff members can only login through secure access methods that you have set up. This forces all staff members to use secure, encrypted connections for all of their sessions, which closes an important hole used by many intruders: sniffing the network from an unrelated, less secure machine. The more indirect security mechanisms also assume that you are logging in from a more restrictive server to a less restrictive server. For example, if your main box is running all sorts of servers, your workstation should not be running any. In order for your workstation to be reasonably secure you should run as few servers as possible, up to and including no servers at all, and you should run a password-protected screen blanker. Of course, given physical access to a workstation an attacker can break any sort of security you put on it. This is definitely a problem that you should consider, but you should also consider the fact that the vast majority of break-ins occur remotely, over a network, from people who do not have physical access to your workstation or servers. KerberosIV Using something like Kerberos also gives you the ability to disable or change the password for a staff account in one place, and have it immediately affect all the machines on which the staff member may have an account. If a staff member's account gets compromised, the ability to instantly change his password on all machines should not be underrated. With discrete passwords, changing a password on N machines can be a mess. You can also impose re-passwording restrictions with Kerberos: not only can a Kerberos ticket be made to timeout after a while, but the Kerberos system can require that the user choose a new password after a certain period of time (say, once a month). Securing Root-run Servers and SUID/SGID Binaries ntalk comsat finger sandboxes sshd telnetd rshd rlogind The prudent sysadmin only runs the servers he needs to, no more, no less. Be aware that third party servers are often the most bug-prone. For example, running an old version of imapd or popper is like giving a universal root ticket out to the entire world. Never run a server that you have not checked out carefully. Many servers do not need to be run as root. For example, the ntalk, comsat, and finger daemons can be run in special user sandboxes. A sandbox is not perfect, unless you go through a large amount of trouble, but the onion approach to security still stands: If someone is able to break in through a server running in a sandbox, they still have to break out of the sandbox. The more layers the attacker must break through, the lower the likelihood of his success. Root holes have historically been found in virtually every server ever run as root, including basic system servers. If you are running a machine through which people only login via sshd and never login via telnetd or rshd or rlogind, then turn off those services! &os; now defaults to running ntalkd, comsat, and finger in a sandbox. Another program which may be a candidate for running in a sandbox is &man.named.8;. /etc/defaults/rc.conf includes the arguments necessary to run named in a sandbox in a commented-out form. Depending on whether you are installing a new system or upgrading an existing system, the special user accounts used by these sandboxes may not be installed. The prudent sysadmin would research and implement sandboxes for servers whenever possible. sendmail There are a number of other servers that typically do not run in sandboxes: sendmail, popper, imapd, ftpd, and others. There are alternatives to some of these, but installing them may require more work than you are willing to perform (the convenience factor strikes again). You may have to run these servers as root and rely on other mechanisms to detect break-ins that might occur through them. The other big potential root holes in a system are the suid-root and sgid binaries installed on the system. Most of these binaries, such as rlogin, reside in /bin, /sbin, /usr/bin, or /usr/sbin. While nothing is 100% safe, the system-default suid and sgid binaries can be considered reasonably safe. Still, root holes are occasionally found in these binaries. A root hole was found in Xlib in 1998 that made xterm (which is typically suid) vulnerable. It is better to be safe than sorry and the prudent sysadmin will restrict suid binaries, that only staff should run, to a special group that only staff can access, and get rid of (chmod 000) any suid binaries that nobody uses. A server with no display generally does not need an xterm binary. Sgid binaries can be almost as dangerous. If an intruder can break an sgid-kmem binary, the intruder might be able to read /dev/kmem and thus read the encrypted password file, potentially compromising any passworded account. Alternatively an intruder who breaks group kmem can monitor keystrokes sent through ptys, including ptys used by users who login through secure methods. An intruder that breaks the tty group can write to almost any user's tty. If a user is running a terminal program or emulator with a keyboard-simulation feature, the intruder can potentially generate a data stream that causes the user's terminal to echo a command, which is then run as that user. Securing User Accounts User accounts are usually the most difficult to secure. While you can impose Draconian access restrictions on your staff and star out their passwords, you may not be able to do so with any general user accounts you might have. If you do have sufficient control, then you may win out and be able to secure the user accounts properly. If not, you simply have to be more vigilant in your monitoring of those accounts. Use of ssh and Kerberos for user accounts is more problematic, due to the extra administration and technical support required, but still a very good solution compared to a crypted password file. Securing the Password File The only sure fire way is to * out as many passwords as you can and use ssh or Kerberos for access to those accounts. Even though the encrypted password file (/etc/spwd.db) can only be read by root, it may be possible for an intruder to obtain read access to that file even if the attacker cannot obtain root-write access. Your security scripts should always check for and report changes to the password file (see the Checking file integrity section below). Securing the Kernel Core, Raw Devices, and File systems If an attacker breaks root he can do just about anything, but there are certain conveniences. For example, most modern kernels have a packet sniffing device driver built in. Under &os; it is called the bpf device. An intruder will commonly attempt to run a packet sniffer on a compromised machine. You do not need to give the intruder the capability and most systems do not have the need for the bpf device compiled in. sysctl But even if you turn off the bpf device, you still have /dev/mem and /dev/kmem to worry about. For that matter, the intruder can still write to raw disk devices. Also, there is another kernel feature called the module loader, &man.kldload.8;. An enterprising intruder can use a KLD module to install his own bpf device, or other sniffing device, on a running kernel. To avoid these problems you have to run the kernel at a higher secure level, at least securelevel 1. The securelevel can be set with a sysctl on the kern.securelevel variable. Once you have set the securelevel to 1, write access to raw devices will be denied and special chflags flags, such as schg, will be enforced. You must also ensure that the schg flag is set on critical startup binaries, directories, and script files — everything that gets run up to the point where the securelevel is set. This might be overdoing it, and upgrading the system is much more difficult when you operate at a higher secure level. You may compromise and run the system at a higher secure level but not set the schg flag for every system file and directory under the sun. Another possibility is to simply mount / and /usr read-only. It should be noted that being too Draconian in what you attempt to protect may prevent the all-important detection of an intrusion. Checking File Integrity: Binaries, Configuration Files, Etc. When it comes right down to it, you can only protect your core system configuration and control files so much before the convenience factor rears its ugly head. For example, using chflags to set the schg bit on most of the files in / and /usr is probably counterproductive, because while it may protect the files, it also closes a detection window. The last layer of your security onion is perhaps the most important — detection. The rest of your security is pretty much useless (or, worse, presents you with a false sense of safety) if you cannot detect potential incursions. Half the job of the onion is to slow down the attacker, rather than stop him, in order to give the detection side of the equation a chance to catch him in the act. The best way to detect an incursion is to look for modified, missing, or unexpected files. The best way to look for modified files is from another (often centralized) limited-access system. Writing your security scripts on the extra-secure limited-access system makes them mostly invisible to potential attackers, and this is important. In order to take maximum advantage you generally have to give the limited-access box significant access to the other machines in the business, usually either by doing a read-only NFS export of the other machines to the limited-access box, or by setting up ssh key-pairs to allow the limited-access box to ssh to the other machines. Except for its network traffic, NFS is the least visible method — allowing you to monitor the file systems on each client box virtually undetected. If your limited-access server is connected to the client boxes through a switch, the NFS method is often the better choice. If your limited-access server is connected to the client boxes through a hub, or through several layers of routing, the NFS method may be too insecure (network-wise) and using ssh may be the better choice even with the audit-trail tracks that ssh lays. Once you give a limited-access box, at least read access to the client systems it is supposed to monitor, you must write scripts to do the actual monitoring. Given an NFS mount, you can write scripts out of simple system utilities such as &man.find.1; and &man.md5.1;. It is best to physically md5 the client-box files at least once a day, and to test control files such as those found in /etc and /usr/local/etc even more often. When mismatches are found, relative to the base md5 information the limited-access machine knows is valid, it should scream at a sysadmin to go check it out. A good security script will also check for inappropriate suid binaries and for new or deleted files on system partitions such as / and /usr. When using ssh rather than NFS, writing the security script is much more difficult. You essentially have to scp the scripts to the client box in order to run them, making them visible, and for safety you also need to scp the binaries (such as find) that those scripts use. The ssh client on the client box may already be compromised. All in all, using ssh may be necessary when running over insecure links, but it is also a lot harder to deal with. A good security script will also check for changes to user and staff members access configuration files: .rhosts, .shosts, .ssh/authorized_keys and so forth… files that might fall outside the purview of the MD5 check. If you have a huge amount of user disk space, it may take too long to run through every file on those partitions. In this case, setting mount flags to disallow suid binaries and devices on those partitions is a good idea. The nodev and nosuid options (see &man.mount.8;) are what you want to look into. You should probably scan them anyway, at least once a week, since the object of this layer is to detect a break-in whether or not the break-in is effective. Process accounting (see &man.accton.8;) is a relatively low-overhead feature of the operating system which might help as a post-break-in evaluation mechanism. It is especially useful in tracking down how an intruder has actually broken into a system, assuming the file is still intact after the break-in occurs. Finally, security scripts should process the log files, and the logs themselves should be generated in as secure a manner as possible — remote syslog can be very useful. An intruder tries to cover his tracks, and log files are critical to the sysadmin trying to track down the time and method of the initial break-in. One way to keep a permanent record of the log files is to run the system console to a serial port and collect the information on a continuing basis through a secure machine monitoring the consoles. Paranoia A little paranoia never hurts. As a rule, a sysadmin can add any number of security features, as long as they do not affect convenience, and can add security features that do affect convenience with some added thought. Even more importantly, a security administrator should mix it up a bit — if you use recommendations such as those given by this document verbatim, you give away your methodologies to the prospective attacker who also has access to this document. Denial of Service Attacks Denial of Service (DoS) This section covers Denial of Service attacks. A DoS attack is typically a packet attack. While there is not much you can do about modern spoofed packet attacks that saturate your network, you can generally limit the damage by ensuring that the attacks cannot take down your servers. Limiting server forks. Limiting springboard attacks (ICMP response attacks, ping broadcast, etc.). Kernel Route Cache. A common DoS attack is against a forking server that attempts to cause the server to eat processes, file descriptors, and memory, until the machine dies. inetd (see &man.inetd.8;) has several options to limit this sort of attack. It should be noted that while it is possible to prevent a machine from going down, it is not generally possible to prevent a service from being disrupted by the attack. Read the inetd manual page carefully and pay specific attention to the , , and options. Note that spoofed-IP attacks will circumvent the option to inetd, so typically a combination of options must be used. Some standalone servers have self-fork-limitation parameters. Sendmail has its option, which tends to work much better than trying to use sendmail's load limiting options due to the load lag. You should specify a MaxDaemonChildren parameter, when you start sendmail, high enough to handle your expected load, but not so high that the computer cannot handle that number of sendmails without falling on its face. It is also prudent to run sendmail in queued mode () and to run the daemon (sendmail -bd) separate from the queue-runs (sendmail -q15m). If you still want real-time delivery you can run the queue at a much lower interval, such as , but be sure to specify a reasonable MaxDaemonChildren option for that sendmail to prevent cascade failures. Syslogd can be attacked directly and it is strongly recommended that you use the option whenever possible, and the option otherwise. You should also be fairly careful with connect-back services such as TCP Wrapper's reverse-identd, which can be attacked directly. You generally do not want to use the reverse-ident feature of TCP Wrapper for this reason. It is a very good idea to protect internal services from external access by firewalling them off at your border routers. The idea here is to prevent saturation attacks from outside your LAN, not so much to protect internal services from network-based root compromise. Always configure an exclusive firewall, i.e., firewall everything except ports A, B, C, D, and M-Z. This way you can firewall off all of your low ports except for certain specific services such as named (if you are primary for a zone), ntalkd, sendmail, and other Internet-accessible services. If you try to configure the firewall the other way — as an inclusive or permissive firewall, there is a good chance that you will forget to close a couple of services, or that you will add a new internal service and forget to update the firewall. You can still open up the high-numbered port range on the firewall, to allow permissive-like operation, without compromising your low ports. Also take note that &os; allows you to control the range of port numbers used for dynamic binding, via the various net.inet.ip.portrange sysctl's (sysctl -a | fgrep portrange), which can also ease the complexity of your firewall's configuration. For example, you might use a normal first/last range of 4000 to 5000, and a hiport range of 49152 to 65535, then block off everything under 4000 in your firewall (except for certain specific Internet-accessible ports, of course). ICMP_BANDLIM Another common DoS attack is called a springboard attack — to attack a server in a manner that causes the server to generate responses which overloads the server, the local network, or some other machine. The most common attack of this nature is the ICMP ping broadcast attack. The attacker spoofs ping packets sent to your LAN's broadcast address with the source IP address set to the actual machine they wish to attack. If your border routers are not configured to stomp on ping's to broadcast addresses, your LAN winds up generating sufficient responses to the spoofed source address to saturate the victim, especially when the attacker uses the same trick on several dozen broadcast addresses over several dozen different networks at once. Broadcast attacks of over a hundred and twenty megabits have been measured. A second common springboard attack is against the ICMP error reporting system. By constructing packets that generate ICMP error responses, an attacker can saturate a server's incoming network and cause the server to saturate its outgoing network with ICMP responses. This type of attack can also crash the server by running it out of mbuf's, especially if the server cannot drain the ICMP responses it generates fast enough. The &os; kernel has a new kernel compile option called which limits the effectiveness of these sorts of attacks. The last major class of springboard attacks is related to certain internal inetd services such as the udp echo service. An attacker simply spoofs a UDP packet with the source address being server A's echo port, and the destination address being server B's echo port, where server A and B are both on your LAN. The two servers then bounce this one packet back and forth between each other. The attacker can overload both servers and their LANs simply by injecting a few packets in this manner. Similar problems exist with the internal chargen port. A competent sysadmin will turn off all of these inetd-internal test services. Spoofed packet attacks may also be used to overload the kernel route cache. Refer to the net.inet.ip.rtexpire, rtminexpire, and rtmaxcache sysctl parameters. A spoofed packet attack that uses a random source IP will cause the kernel to generate a temporary cached route in the route table, viewable with netstat -rna | fgrep W3. These routes typically timeout in 1600 seconds or so. If the kernel detects that the cached route table has gotten too big it will dynamically reduce the rtexpire but will never decrease it to less than rtminexpire. There are two problems: The kernel does not react quickly enough when a lightly loaded server is suddenly attacked. The rtminexpire is not low enough for the kernel to survive a sustained attack. If your servers are connected to the Internet via a T3 or better, it may be prudent to manually override both rtexpire and rtminexpire via &man.sysctl.8;. Never set either parameter to zero (unless you want to crash the machine). Setting both parameters to 2 seconds should be sufficient to protect the route table from attack. Access Issues with Kerberos and SSH ssh KerberosIV There are a few issues with both Kerberos and ssh that need to be addressed if you intend to use them. Kerberos V is an excellent authentication protocol, but there are bugs in the kerberized telnet and rlogin applications that make them unsuitable for dealing with binary streams. Also, by default Kerberos does not encrypt a session unless you use the option. ssh encrypts everything by default. ssh works quite well in every respect except that it forwards encryption keys by default. What this means is that if you have a secure workstation holding keys that give you access to the rest of the system, and you ssh to an insecure machine, your keys are usable. The actual keys themselves are not exposed, but ssh installs a forwarding port for the duration of your login, and if an attacker has broken root on the insecure machine he can utilize that port to use your keys to gain access to any other machine that your keys unlock. We recommend that you use ssh in combination with Kerberos whenever possible for staff logins. ssh can be compiled with Kerberos support. This reduces your reliance on potentially exposed ssh keys while at the same time protecting passwords via Kerberos. ssh keys should only be used for automated tasks from secure machines (something that Kerberos is unsuited to do). We also recommend that you either turn off key-forwarding in the ssh configuration, or that you make use of the from=IP/DOMAIN option that ssh allows in its authorized_keys file to make the key only usable to entities logging in from specific machines. Bill Swingle Parts rewritten and updated by DES, MD5, and Crypt security crypt crypt DES MD5 Every user on a &unix; system has a password associated with their account. It seems obvious that these passwords need to be known only to the user and the actual operating system. In order to keep these passwords secret, they are encrypted with what is known as a one-way hash, that is, they can only be easily encrypted but not decrypted. In other words, what we told you a moment ago was obvious is not even true: the operating system itself does not really know the password. It only knows the encrypted form of the password. The only way to get the plain-text password is by a brute force search of the space of possible passwords. Unfortunately the only secure way to encrypt passwords when &unix; came into being was based on DES, the Data Encryption Standard. This was not such a problem for users resident in the US, but since the source code for DES could not be exported outside the US, &os; had to find a way to both comply with US law and retain compatibility with all the other &unix; variants that still used DES. The solution was to divide up the encryption libraries so that US users could install the DES libraries and use DES but international users still had an encryption method that could be exported abroad. This is how &os; came to use MD5 as its default encryption method. MD5 is believed to be more secure than DES, so installing DES is offered primarily for compatibility reasons. Recognizing Your Crypt Mechanism Before &os; 4.4 libcrypt.a was a symbolic link pointing to the library which was used for encryption. &os; 4.4 changed libcrypt.a to provide a configurable password authentication hash library. Currently the library supports DES, MD5 and Blowfish hash functions. By default &os; uses MD5 to encrypt passwords. It is pretty easy to identify which encryption method &os; is set up to use. Examining the encrypted passwords in the /etc/master.passwd file is one way. Passwords encrypted with the MD5 hash are longer than those encrypted with the DES hash and also begin with the characters $1$. Passwords starting with $2a$ are encrypted with the Blowfish hash function. DES password strings do not have any particular identifying characteristics, but they are shorter than MD5 passwords, and are coded in a 64-character alphabet which does not include the $ character, so a relatively short string which does not begin with a dollar sign is very likely a DES password. The password format used for new passwords is controlled by the passwd_format login capability in /etc/login.conf, which takes values of des, md5 or blf. See the &man.login.conf.5; manual page for more information about login capabilities. One-time Passwords one-time passwords security one-time passwords S/Key is a one-time password scheme based on a one-way hash function. &os; uses the MD4 hash for compatibility but other systems have used MD5 and DES-MAC. S/Key has been part of the &os; base system since version 1.1.5 and is also used on a growing number of other operating systems. S/Key is a registered trademark of Bell Communications Research, Inc. From version 5.0 of &os;, S/Key has been replaced with the functionally equivalent OPIE (One-time Passwords In Everything). OPIE uses the MD5 hash by default. There are three different sorts of passwords which we will discuss below. The first is your usual &unix; style or Kerberos password; we will call this a &unix; password. The second sort is the one-time password which is generated by the S/Key key program or the OPIE &man.opiekey.1; program and accepted by the keyinit or &man.opiepasswd.1; programs and the login prompt; we will call this a one-time password. The final sort of password is the secret password which you give to the key/opiekey programs (and sometimes the keyinit/opiepasswd programs) which it uses to generate one-time passwords; we will call it a secret password or just unqualified password. The secret password does not have anything to do with your &unix; password; they can be the same but this is not recommended. S/Key and OPIE secret passwords are not limited to 8 characters like old &unix; passwordsUnder &os; the standard login password may be up to 128 characters in length., they can be as long as you like. Passwords of six or seven word long phrases are fairly common. For the most part, the S/Key or OPIE system operates completely independently of the &unix; password system. Besides the password, there are two other pieces of data that are important to S/Key and OPIE. One is what is known as the seed or key, consisting of two letters and five digits. The other is what is called the iteration count, a number between 1 and 100. S/Key creates the one-time password by concatenating the seed and the secret password, then applying the MD4/MD5 hash as many times as specified by the iteration count and turning the result into six short English words. These six English words are your one-time password. The authentication system (primarily PAM) keeps track of the last one-time password used, and the user is authenticated if the hash of the user-provided password is equal to the previous password. Because a one-way hash is used it is impossible to generate future one-time passwords if a successfully used password is captured; the iteration count is decremented after each successful login to keep the user and the login program in sync. When the iteration count gets down to 1, S/Key and OPIE must be reinitialized. There are three programs involved in each system which we will discuss below. The key and opiekey programs accept an iteration count, a seed, and a secret password, and generate a one-time password or a consecutive list of one-time passwords. The keyinit and opiepasswd programs are used to initialize S/Key and OPIE respectively, and to change passwords, iteration counts, or seeds; they take either a secret passphrase, or an iteration count, seed, and one-time password. The keyinfo and opieinfo programs examine the relevant credentials files (/etc/skeykeys or /etc/opiekeys) and print out the invoking user's current iteration count and seed. There are four different sorts of operations we will cover. The first is using keyinit or opiepasswd over a secure connection to set up one-time-passwords for the first time, or to change your password or seed. The second operation is using keyinit or opiepasswd over an insecure connection, in conjunction with key or opiekey over a secure connection, to do the same. The third is using key/opiekey to log in over an insecure connection. The fourth is using key or opiekey to generate a number of keys which can be written down or printed out to carry with you when going to some location without secure connections to anywhere. Secure Connection Initialization To initialize S/Key for the first time, change your password, or change your seed while logged in over a secure connection (e.g. on the console of a machine or via ssh), use the keyinit command without any parameters while logged in as yourself: &prompt.user; keyinit Adding unfurl: Reminder - Only use this method if you are directly connected. If you are using telnet or rlogin exit with no password and use keyinit -s. Enter secret password: Again secret password: ID unfurl s/key is 99 to17757 DEFY CLUB PRO NASH LACE SOFT For OPIE, opiepasswd is used instead: &prompt.user; opiepasswd -c [grimreaper] ~ $ opiepasswd -f -c Adding unfurl: Only use this method from the console; NEVER from remote. If you are using telnet, xterm, or a dial-in, type ^C now or exit with no password. Then run opiepasswd without the -c parameter. Using MD5 to compute responses. Enter new secret pass phrase: Again new secret pass phrase: ID unfurl OTP key is 499 to4268 MOS MALL GOAT ARM AVID COED At the Enter new secret pass phrase: or Enter secret password: prompts, you should enter a password or phrase. Remember, this is not the password that you will use to login with, this is used to generate your one-time login keys. The ID line gives the parameters of your particular instance: your login name, the iteration count, and seed. When logging in the system will remember these parameters and present them back to you so you do not have to remember them. The last line gives the particular one-time password which corresponds to those parameters and your secret password; if you were to re-login immediately, this one-time password is the one you would use. Insecure Connection Initialization To initialize or change your secret password over an insecure connection, you will need to already have a secure connection to some place where you can run key or opiekey; this might be in the form of a desk accessory on a &macintosh;, or a shell prompt on a machine you trust. You will also need to make up an iteration count (100 is probably a good value), and you may make up your own seed or use a randomly-generated one. Over on the insecure connection (to the machine you are initializing), use the keyinit -s command: &prompt.user; keyinit -s Updating unfurl: Old key: to17758 Reminder you need the 6 English words from the key command. Enter sequence count from 1 to 9999: 100 Enter new key [default to17759]: s/key 100 to 17759 s/key access password: s/key access password:CURE MIKE BANE HIM RACY GORE For OPIE, you need to use opiepasswd: &prompt.user; opiepasswd Updating unfurl: You need the response from an OTP generator. Old secret pass phrase: otp-md5 498 to4268 ext Response: GAME GAG WELT OUT DOWN CHAT New secret pass phrase: otp-md5 499 to4269 Response: LINE PAP MILK NELL BUOY TROY ID mark OTP key is 499 gr4269 LINE PAP MILK NELL BUOY TROY To accept the default seed (which the keyinit program confusingly calls a key), press Return. Then before entering an access password, move over to your secure connection or S/Key desk accessory, and give it the same parameters: &prompt.user; key 100 to17759 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: <secret password> CURE MIKE BANE HIM RACY GORE Or for OPIE: &prompt.user; opiekey 498 to4268 Using the MD5 algorithm to compute response. Reminder: Don't use opiekey from telnet or dial-in sessions. Enter secret pass phrase: GAME GAG WELT OUT DOWN CHAT Now switch back over to the insecure connection, and copy the one-time password generated over to the relevant program. Generating a Single One-time Password Once you have initialized S/Key or OPIE, when you login you will be presented with a prompt like this: &prompt.user; telnet example.com Trying 10.0.0.1... Connected to example.com Escape character is '^]'. FreeBSD/i386 (example.com) (ttypa) login: <username> s/key 97 fw13894 Password: Or for OPIE: &prompt.user; telnet example.com Trying 10.0.0.1... Connected to example.com Escape character is '^]'. FreeBSD/i386 (example.com) (ttypa) login: <username> otp-md5 498 gr4269 ext Password: As a side note, the S/Key and OPIE prompts have a useful feature (not shown here): if you press Return at the password prompt, the prompter will turn echo on, so you can see what you are typing. This can be extremely useful if you are attempting to type in a password by hand, such as from a printout. MS-DOS Windows MacOS At this point you need to generate your one-time password to answer this login prompt. This must be done on a trusted system that you can run key or opiekey on. (There are versions of these for DOS, &windows; and &macos; as well.) They need both the iteration count and the seed as command line options. You can cut-and-paste these right from the login prompt on the machine that you are logging in to. On the trusted system: &prompt.user; key 97 fw13894 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: WELD LIP ACTS ENDS ME HAAG For OPIE: &prompt.user; opiekey 498 to4268 Using the MD5 algorithm to compute response. Reminder: Don't use opiekey from telnet or dial-in sessions. Enter secret pass phrase: GAME GAG WELT OUT DOWN CHAT Now that you have your one-time password you can continue logging in: login: <username> s/key 97 fw13894 Password: <return to enable echo> s/key 97 fw13894 Password [echo on]: WELD LIP ACTS ENDS ME HAAG Last login: Tue Mar 21 11:56:41 from 10.0.0.2 ... Generating Multiple One-time Passwords Sometimes you have to go places where you do not have access to a trusted machine or secure connection. In this case, it is possible to use the key and opiekey commands to generate a number of one-time passwords beforehand to be printed out and taken with you. For example: &prompt.user; key -n 5 30 zz99999 Reminder - Do not use this program while logged in via telnet or rlogin. Enter secret password: <secret password> 26: SODA RUDE LEA LIND BUDD SILT 27: JILT SPY DUTY GLOW COWL ROT 28: THEM OW COLA RUNT BONG SCOT 29: COT MASH BARR BRIM NAN FLAG 30: CAN KNEE CAST NAME FOLK BILK Or for OPIE: &prompt.user; opiekey -n 5 30 zz99999 Using the MD5 algorithm to compute response. Reminder: Don't use opiekey from telnet or dial-in sessions. Enter secret pass phrase: <secret password> 26: JOAN BORE FOSS DES NAY QUIT 27: LATE BIAS SLAY FOLK MUCH TRIG 28: SALT TIN ANTI LOON NEAL USE 29: RIO ODIN GO BYE FURY TIC 30: GREW JIVE SAN GIRD BOIL PHI The requests five keys in sequence, the specifies what the last iteration number should be. Note that these are printed out in reverse order of eventual use. If you are really paranoid, you might want to write the results down by hand; otherwise you can cut-and-paste into lpr. Note that each line shows both the iteration count and the one-time password; you may still find it handy to scratch off passwords as you use them. Restricting Use of &unix; Passwords S/Key can place restrictions on the use of &unix; passwords based on the host name, user name, terminal port, or IP address of a login session. These restrictions can be found in the configuration file /etc/skey.access. The &man.skey.access.5; manual page has more information on the complete format of the file and also details some security cautions to be aware of before depending on this file for security. If there is no /etc/skey.access file (this is the default on &os; 4.X systems), then all users will be allowed to use &unix; passwords. If the file exists, however, then all users will be required to use S/Key unless explicitly permitted to do otherwise by configuration statements in the skey.access file. In all cases, &unix; passwords are permitted on the console. Here is a sample skey.access configuration file which illustrates the three most common sorts of configuration statements: permit internet 192.168.0.0 255.255.0.0 permit user fnord permit port ttyd0 The first line (permit internet) allows users whose IP source address (which is vulnerable to spoofing) matches the specified value and mask, to use &unix; passwords. This should not be considered a security mechanism, but rather, a means to remind authorized users that they are using an insecure network and need to use S/Key for authentication. The second line (permit user) allows the specified username, in this case fnord, to use &unix; passwords at any time. Generally speaking, this should only be used for people who are either unable to use the key program, like those with dumb terminals, or those who are ineducable. The third line (permit port) allows all users logging in on the specified terminal line to use &unix; passwords; this would be used for dial-ups. OPIE can restrict the use of &unix; passwords based on the IP address of a login session just like S/Key does. The relevant file is /etc/opieaccess, which is present by default on &os; 5.0 and newer systems. Please check &man.opieaccess.5; for more information on this file and which security considerations you should be aware of when using it. Here is a sample opieaccess file: permit 192.168.0.0 255.255.0.0 This line allows users whose IP source address (which is vulnerable to spoofing) matches the specified value and mask, to use &unix; passwords at any time. If no rules in opieaccess are matched, the default is to deny non-OPIE logins. Tom Rhodes Written by: TCP Wrappers TCP Wrappers Anyone familiar with &man.inetd.8; has probably heard of TCP Wrappers at some point. But few individuals seem to fully comprehend its usefulness in a network environment. It seems that everyone wants to install a firewall to handle network connections. While a firewall has a wide variety of uses, there are some things that a firewall not handle such as sending text back to the connection originator. The TCP software does this and much more. In the next few sections many of the TCP Wrappers features will be discussed, and, when applicable, example configuration lines will be provided. The TCP Wrappers software extends the abilities of inetd to provide support for every server daemon under its control. Using this method it is possible to provide logging support, return messages to connections, permit a daemon to only accept internal connections, etc. While some of these features can be provided by implementing a firewall, this will add not only an extra layer of protection but go beyond the amount of control a firewall can provide. The added functionality of TCP Wrappers should not be considered a replacement for a good firewall. TCP Wrappers can be used in conjunction with a firewall or other security enhancements though and it can serve nicely as an extra layer of protection for the system. Since this is an extension to the configuration of inetd, the reader is expected have read the inetd configuration section. While programs run by &man.inetd.8; are not exactly daemons, they have traditionally been called daemons. This is the term we will use in this section too. Initial Configuration The only requirement of using TCP Wrappers in &os; is to ensure the inetd server is started from rc.conf with the option; this is the default setting. Of course, proper configuration of /etc/hosts.allow is also expected, but &man.syslogd.8; will throw messages in the system logs in these cases. Unlike other implementations of TCP Wrappers, the use of hosts.deny has been deprecated. All configuration options should be placed in /etc/hosts.allow. In the simplest configuration, daemon connection policies are set to either be permitted or blocked depending on the options in /etc/hosts.allow. The default configuration in &os; is to allow a connection to every daemon started with inetd. Changing this will be discussed only after the basic configuration is covered. Basic configuration usually takes the form of daemon : address : action. Where daemon is the daemon name which inetd started. The address can be a valid hostname, an IP address or an IPv6 address enclosed in brackets ([ ]). The action field can be either allow or deny to grant or deny access appropriately. Keep in mind that configuration works off a first rule match semantic, meaning that the configuration file is scanned in ascending order for a matching rule. When a match is found the rule is applied and the search process will halt. Several other options exist but they will be explained in a later section. A simple configuration line may easily be constructed from that information alone. For example, to allow POP3 connections via the mail/qpopper daemon, the following lines should be appended to hosts.allow: # This line is required for POP3 connections: qpopper : ALL : allow After adding this line, inetd will need restarted. This can be accomplished by use of the &man.kill.1; command, or with the restart parameter with /etc/rc.d/inetd. Advanced Configuration TCP Wrappers has advanced options too; they will allow for more control over the way connections are handled. In some cases it may be a good idea to return a comment to certain hosts or daemon connections. In other cases, perhaps a log file should be recorded or an email sent to the administrator. Other situations may require the use of a service for local connections only. This is all possible through the use of configuration options known as wildcards, expansion characters and external command execution. The next two sections are written to cover these situations. External Commands Suppose that a situation occurs where a connection should be denied yet a reason should be sent to the individual who attempted to establish that connection. How could it be done? That action can be made possible by using the option. When a connection attempt is made, will be called to execute a shell command or script. An example already exists in the hosts.allow file: # The rest of the daemons are protected. ALL : ALL \ : severity auth.info \ : twist /bin/echo "You are not welcome to use %d from %h." This example shows that the message, You are not allowed to use daemon from hostname. will be returned for any daemon not previously configured in the access file. This is extremely useful for sending a reply back to the connection initiator right after the established connection is dropped. Note that any message returned must be wrapped in quote " characters; there are no exceptions to this rule. It may be possible to launch a denial of service attack on the server if an attacker, or group of attackers could flood these daemons with connection requests. Another possibility is to use the option in these cases. Like , the implicitly denies the connection and may be used to run external shell commands or scripts. Unlike , will not send a reply back to the individual who established the connection. For an example, consider the following configuration line: # We do not allow connections from example.com: ALL : .example.com \ : spawn (/bin/echo %a from %h attempted to access %d >> \ /var/log/connections.log) \ : deny This will deny all connection attempts from the *.example.com domain; simultaneously logging the hostname, IP address and the daemon which they attempted to access in the /var/log/connections.log file. Aside from the already explained substitution characters above, e.g. %a, a few others exist. See the &man.hosts.access.5; manual page for the complete list. Wildcard Options Thus far the ALL example has been used continuously throughout the examples. Other options exist which could extend the functionality a bit further. For instance, ALL may be used to match every instance of either a daemon, domain or an IP address. Another wildcard available is PARANOID which may be used to match any host which provides an IP address that may be forged. In other words, paranoid may be used to define an action to be taken whenever a connection is made from an IP address that differs from its hostname. The following example may shed some more light on this discussion: # Block possibly spoofed requests to sendmail: sendmail : PARANOID : deny In that example all connection requests to sendmail which have an IP address that varies from its hostname will be denied. Using the PARANOID may severely cripple servers if the client or server has a broken DNS setup. Administrator discretion is advised. To learn more about wildcards and their associated functionality, see the &man.hosts.access.5; manual page. Before any of the specific configuration lines above will work, the first configuration line should be commented out in hosts.allow. This was noted at the beginning of this section. Mark Murray Contributed by Mark Dapoz Based on a contribution by <application>KerberosIV</application> Kerberos is a network add-on system/protocol that allows users to authenticate themselves through the services of a secure server. Services such as remote login, remote copy, secure inter-system file copying and other high-risk tasks are made considerably safer and more controllable. The following instructions can be used as a guide on how to set up Kerberos as distributed for &os;. However, you should refer to the relevant manual pages for a complete description. Installing <application>KerberosIV</application> MIT KerberosIV installing Kerberos is an optional component of &os;. The easiest way to install this software is by selecting the krb4 or krb5 distribution in sysinstall during the initial installation of &os;. This will install the eBones (KerberosIV) or Heimdal (Kerberos5) implementation of Kerberos. These implementations are included because they are developed outside the USA/Canada and were thus available to system owners outside those countries during the era of restrictive export controls on cryptographic code from the USA. Alternatively, the MIT implementation of Kerberos is available from the Ports Collection as security/krb5. Creating the Initial Database This is done on the Kerberos server only. First make sure that you do not have any old Kerberos databases around. You should change to the directory /etc/kerberosIV and check that only the following files are present: &prompt.root; cd /etc/kerberosIV &prompt.root; ls README krb.conf krb.realms If any additional files (such as principal.* or master_key) exist, then use the kdb_destroy command to destroy the old Kerberos database, or if Kerberos is not running, simply delete the extra files. You should now edit the krb.conf and krb.realms files to define your Kerberos realm. In this case the realm will be EXAMPLE.COM and the server is grunt.example.com. We edit or create the krb.conf file: &prompt.root; cat krb.conf EXAMPLE.COM EXAMPLE.COM grunt.example.com admin server CS.BERKELEY.EDU okeeffe.berkeley.edu ATHENA.MIT.EDU kerberos.mit.edu ATHENA.MIT.EDU kerberos-1.mit.edu ATHENA.MIT.EDU kerberos-2.mit.edu ATHENA.MIT.EDU kerberos-3.mit.edu LCS.MIT.EDU kerberos.lcs.mit.edu TELECOM.MIT.EDU bitsy.mit.edu ARC.NASA.GOV trident.arc.nasa.gov In this case, the other realms do not need to be there. They are here as an example of how a machine may be made aware of multiple realms. You may wish to not include them for simplicity. The first line names the realm in which this system works. The other lines contain realm/host entries. The first item on a line is a realm, and the second is a host in that realm that is acting as a key distribution center. The words admin server following a host's name means that host also provides an administrative database server. For further explanation of these terms, please consult the Kerberos manual pages. Now we have to add grunt.example.com to the EXAMPLE.COM realm and also add an entry to put all hosts in the .example.com domain in the EXAMPLE.COM realm. The krb.realms file would be updated as follows: &prompt.root; cat krb.realms grunt.example.com EXAMPLE.COM .example.com EXAMPLE.COM .berkeley.edu CS.BERKELEY.EDU .MIT.EDU ATHENA.MIT.EDU .mit.edu ATHENA.MIT.EDU Again, the other realms do not need to be there. They are here as an example of how a machine may be made aware of multiple realms. You may wish to remove them to simplify things. The first line puts the specific system into the named realm. The rest of the lines show how to default systems of a particular subdomain to a named realm. Now we are ready to create the database. This only needs to run on the Kerberos server (or Key Distribution Center). Issue the kdb_init command to do this: &prompt.root; kdb_init Realm name [default ATHENA.MIT.EDU ]: EXAMPLE.COM You will be prompted for the database Master Password. It is important that you NOT FORGET this password. Enter Kerberos master key: Now we have to save the key so that servers on the local machine can pick it up. Use the kstash command to do this: &prompt.root; kstash Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! This saves the encrypted master password in /etc/kerberosIV/master_key. Making It All Run KerberosIV initial startup Two principals need to be added to the database for each system that will be secured with Kerberos. Their names are kpasswd and rcmd. These two principals are made for each system, with the instance being the name of the individual system. These daemons, kpasswd and rcmd allow other systems to change Kerberos passwords and run commands like &man.rcp.1;, &man.rlogin.1; and &man.rsh.1;. Now let us add these entries: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: passwd Instance: grunt <Not found>, Create [y] ? y Principal: passwd, Instance: grunt, kdc_key_ver: 1 New Password: <---- enter RANDOM here Verifying password New Password: <---- enter RANDOM here Random password [y] ? y Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: rcmd Instance: grunt <Not found>, Create [y] ? Principal: rcmd, Instance: grunt, kdc_key_ver: 1 New Password: <---- enter RANDOM here Verifying password New Password: <---- enter RANDOM here Random password [y] ? Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Creating the Server File We now have to extract all the instances which define the services on each machine. For this we use the ext_srvtab command. This will create a file which must be copied or moved by secure means to each Kerberos client's /etc/kerberosIV directory. This file must be present on each server and client, and is crucial to the operation of Kerberos. &prompt.root; ext_srvtab grunt Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Generating 'grunt-new-srvtab'.... Now, this command only generates a temporary file which must be renamed to srvtab so that all the servers can pick it up. Use the &man.mv.1; command to move it into place on the original system: &prompt.root; mv grunt-new-srvtab srvtab If the file is for a client system, and the network is not deemed safe, then copy the client-new-srvtab to removable media and transport it by secure physical means. Be sure to rename it to srvtab in the client's /etc/kerberosIV directory, and make sure it is mode 600: &prompt.root; mv grumble-new-srvtab srvtab &prompt.root; chmod 600 srvtab Populating the Database We now have to add some user entries into the database. First let us create an entry for the user jane. Use the kdb_edit command to do this: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: jane Instance: <Not found>, Create [y] ? y Principal: jane, Instance: , kdc_key_ver: 1 New Password: <---- enter a secure password here Verifying password New Password: <---- re-enter the password here Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Testing It All Out First we have to start the Kerberos daemons. Note that if you have correctly edited your /etc/rc.conf then this will happen automatically when you reboot. This is only necessary on the Kerberos server. Kerberos clients will automatically get what they need from the /etc/kerberosIV directory. &prompt.root; kerberos & Kerberos server starting Sleep forever on error Log file is /var/log/kerberos.log Current Kerberos master key version is 1. Master key entered. BEWARE! Current Kerberos master key version is 1 Local realm: EXAMPLE.COM &prompt.root; kadmind -n & KADM Server KADM0.0A initializing Please do not use 'kill -9' to kill this job, use a regular kill instead Current Kerberos master key version is 1. Master key entered. BEWARE! Now we can try using the kinit command to get a ticket for the ID jane that we created above: &prompt.user; kinit jane MIT Project Athena (grunt.example.com) Kerberos Initialization for "jane" Password: Try listing the tokens using klist to see if we really have them: &prompt.user; klist Ticket file: /tmp/tkt245 Principal: jane@EXAMPLE.COM Issued Expires Principal Apr 30 11:23:22 Apr 30 19:23:22 krbtgt.EXAMPLE.COM@EXAMPLE.COM Now try changing the password using &man.passwd.1; to check if the kpasswd daemon can get authorization to the Kerberos database: &prompt.user; passwd realm EXAMPLE.COM Old password for jane: New Password for jane: Verifying password New Password for jane: Password changed. Adding <command>su</command> Privileges Kerberos allows us to give each user who needs root privileges their own separate &man.su.1; password. We could now add an ID which is authorized to &man.su.1; to root. This is controlled by having an instance of root associated with a principal. Using kdb_edit we can create the entry jane.root in the Kerberos database: &prompt.root; kdb_edit Opening database... Enter Kerberos master key: Current Kerberos master key version is 1. Master key entered. BEWARE! Previous or default values are in [brackets] , enter return to leave the same, or new value. Principal name: jane Instance: root <Not found>, Create [y] ? y Principal: jane, Instance: root, kdc_key_ver: 1 New Password: <---- enter a SECURE password here Verifying password New Password: <---- re-enter the password here Principal's new key version = 1 Expiration date (enter yyyy-mm-dd) [ 2000-01-01 ] ? Max ticket lifetime (*5 minutes) [ 255 ] ? 12 <--- Keep this short! Attributes [ 0 ] ? Edit O.K. Principal name: <---- null entry here will cause an exit Now try getting tokens for it to make sure it works: &prompt.root; kinit jane.root MIT Project Athena (grunt.example.com) Kerberos Initialization for "jane.root" Password: Now we need to add the user to root's .klogin file: &prompt.root; cat /root/.klogin jane.root@EXAMPLE.COM Now try doing the &man.su.1;: &prompt.user; su Password: and take a look at what tokens we have: &prompt.root; klist Ticket file: /tmp/tkt_root_245 Principal: jane.root@EXAMPLE.COM Issued Expires Principal May 2 20:43:12 May 3 04:43:12 krbtgt.EXAMPLE.COM@EXAMPLE.COM Using Other Commands In an earlier example, we created a principal called jane with an instance root. This was based on a user with the same name as the principal, and this is a Kerberos default; that a <principal>.<instance> of the form <username>.root will allow that <username> to &man.su.1; to root if the necessary entries are in the .klogin file in root's home directory: &prompt.root; cat /root/.klogin jane.root@EXAMPLE.COM Likewise, if a user has in their own home directory lines of the form: &prompt.user; cat ~/.klogin jane@EXAMPLE.COM jack@EXAMPLE.COM This allows anyone in the EXAMPLE.COM realm who has authenticated themselves as jane or jack (via kinit, see above) to access to jane's account or files on this system (grunt) via &man.rlogin.1;, &man.rsh.1; or &man.rcp.1;. For example, jane now logs into another system using Kerberos: &prompt.user; kinit MIT Project Athena (grunt.example.com) Password: &prompt.user; rlogin grunt Last login: Mon May 1 21:14:47 from grumble Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995 Or jack logs into jane's account on the same machine (jane having set up the .klogin file as above, and the person in charge of Kerberos having set up principal jack with a null instance): &prompt.user; kinit &prompt.user; rlogin grunt -l jane MIT Project Athena (grunt.example.com) Password: Last login: Mon May 1 21:16:55 from grumble Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD BUILT-19950429 (GR386) #0: Sat Apr 29 17:50:09 SAT 1995 Tillman Hodgson Contributed by Mark Murray Based on a contribution by <application>Kerberos5</application> Every &os; release beyond &os;-5.1 includes support only for Kerberos5. Hence Kerberos5 is the only version included, and its configuration is similar in many aspects to that of KerberosIV. The following information only applies to Kerberos5 in post &os;-5.0 releases. Users who wish to use the KerberosIV package may install the security/krb4 port. Kerberos is a network add-on system/protocol that allows users to authenticate themselves through the services of a secure server. Services such as remote login, remote copy, secure inter-system file copying and other high-risk tasks are made considerably safer and more controllable. Kerberos can be described as an identity-verifying proxy system. It can also be described as a trusted third-party authentication system. Kerberos provides only one function — the secure authentication of users on the network. It does not provide authorization functions (what users are allowed to do) or auditing functions (what those users did). After a client and server have used Kerberos to prove their identity, they can also encrypt all of their communications to assure privacy and data integrity as they go about their business. Therefore it is highly recommended that Kerberos be used with other security methods which provide authorization and audit services. The following instructions can be used as a guide on how to set up Kerberos as distributed for &os;. However, you should refer to the relevant manual pages for a complete description. For purposes of demonstrating a Kerberos installation, the various name spaces will be handled as follows: The DNS domain (zone) will be example.org. The Kerberos realm will be EXAMPLE.ORG. Please use real domain names when setting up Kerberos even if you intend to run it internally. This avoids DNS problems and assures inter-operation with other Kerberos realms. History Kerberos5 history Kerberos was created by MIT as a solution to network security problems. The Kerberos protocol uses strong cryptography so that a client can prove its identity to a server (and vice versa) across an insecure network connection. Kerberos is both the name of a network authentication protocol and an adjective to describe programs that implement the program (Kerberos telnet, for example). The current version of the protocol is version 5, described in RFC 1510. Several free implementations of this protocol are available, covering a wide range of operating systems. The Massachusetts Institute of Technology (MIT), where Kerberos was originally developed, continues to develop their Kerberos package. It is commonly used in the US as a cryptography product, as such it has historically been affected by US export regulations. The MIT Kerberos is available as a port (security/krb5). Heimdal Kerberos is another version 5 implementation, and was explicitly developed outside of the US to avoid export regulations (and is thus often included in non-commercial &unix; variants). The Heimdal Kerberos distribution is available as a port (security/heimdal), and a minimal installation of it is included in the base &os; install. In order to reach the widest audience, these instructions assume the use of the Heimdal distribution included in &os;. Setting up a Heimdal <acronym>KDC</acronym> Kerberos5 Key Distribution Center The Key Distribution Center (KDC) is the centralized authentication service that Kerberos provides — it is the computer that issues Kerberos tickets. The KDC is considered trusted by all other computers in the Kerberos realm, and thus has heightened security concerns. Note that while running the Kerberos server requires very few computing resources, a dedicated machine acting only as a KDC is recommended for security reasons. To begin setting up a KDC, ensure that your /etc/rc.conf file contains the correct settings to act as a KDC (you may need to adjust paths to reflect your own system): kerberos5_server_enable="YES" kadmind5_server_enable="YES" kerberos_stash="YES" The is only available in &os; 4.X. Next we will set up your Kerberos config file, /etc/krb5.conf: [libdefaults] default_realm = EXAMPLE.ORG [realms] EXAMPLE.ORG = { kdc = kerberos.example.org admin_server = kerberos.example.org } [domain_realm] .example.org = EXAMPLE.ORG Note that this /etc/krb5.conf file implies that your KDC will have the fully-qualified hostname of kerberos.example.org. You will need to add a CNAME (alias) entry to your zone file to accomplish this if your KDC has a different hostname. For large networks with a properly configured BIND DNS server, the above example could be trimmed to: [libdefaults] default_realm = EXAMPLE.ORG With the following lines being appended to the example.org zonefile: _kerberos._udp IN SRV 01 00 88 kerberos.example.org. _kerberos._tcp IN SRV 01 00 88 kerberos.example.org. _kpasswd._udp IN SRV 01 00 464 kerberos.example.org. _kerberos-adm._tcp IN SRV 01 00 749 kerberos.example.org. _kerberos IN TXT EXAMPLE.ORG. For clients to be able to find the Kerberos services, you must have either a fully configured /etc/krb5.conf or a miminally configured /etc/krb5.conf and a properly configured DNS server. Next we will create the Kerberos database. This database contains the keys of all principals encrypted with a master password. You are not required to remember this password, it will be stored in a file (/var/heimdal/m-key). To create the master key, run kstash and enter a password. Once the master key has been created, you can initialize the database using the kadmin program with the -l option (standing for local). This option instructs kadmin to modify the database files directly rather than going through the kadmind network service. This handles the chicken-and-egg problem of trying to connect to the database before it is created. Once you have the kadmin prompt, use the init command to create your realms initial database. Lastly, while still in kadmin, create your first principal using the add command. Stick to the defaults options for the principal for now, you can always change them later with the modify command. Note that you can use the ? command at any prompt to see the available options. A sample database creation session is shown below: &prompt.root; kstash Master key: xxxxxxxx Verifying password - Master key: xxxxxxxx &prompt.root; kadmin -l kadmin> init EXAMPLE.ORG Realm max ticket life [unlimited]: kadmin> add tillman Max ticket life [unlimited]: Max renewable life [unlimited]: Attributes []: Password: xxxxxxxx Verifying password - Password: xxxxxxxx Now it is time to start up the KDC services. Run /etc/rc.d/kerberos start and /etc/rc.d/kadmind start to bring up the services. Note that you will not have any kerberized daemons running at this point but you should be able to confirm the that the KDC is functioning by obtaining and listing a ticket for the principal (user) that you just created from the command-line of the KDC itself: &prompt.user; k5init tillman tillman@EXAMPLE.ORG's Password: &prompt.user; k5list Credentials cache: FILE:/tmp/krb5cc_500 Principal: tillman@EXAMPLE.ORG Issued Expires Principal Aug 27 15:37:58 Aug 28 01:37:58 krbtgt/EXAMPLE.ORG@EXAMPLE.ORG <application>Kerberos</application> enabling a server with Heimdal services Kerberos5 enabling services First, we need a copy of the Kerberos configuration file, /etc/krb5.conf. To do so, simply copy it over to the client computer from the KDC in a secure fashion (using network utilities, such as &man.scp.1;, or physically via a floppy disk). Next you need a /etc/krb5.keytab file. This is the major difference between a server providing Kerberos enabled daemons and a workstation — the server must have a keytab file. This file contains the servers host key, which allows it and the KDC to verify each others identity. It must be transmitted to the server in a secure fashion, as the security of the server can be broken if the key is made public. This explicitly means that transferring it via a clear text channel, such as FTP, is a very bad idea. Typically, you transfer to the keytab to the server using the kadmin program. This is handy because you also need to create the host principal (the KDC end of the krb5.keytab) using kadmin. Note that you must have already obtained a ticket and that this ticket must be allowed to use the kadmin interface in the kadmind.acl. See the section titled Remote administration in the Heimdal info pages (info heimdal) for details on designing access control lists. If you do not want to enable remote kadmin access, you can simply securely connect to the KDC (via local console, &man.ssh.1; or Kerberos &man.telnet.1;) and perform administration locally using kadmin -l. After installing the /etc/krb5.conf file, you can use kadmin from the Kerberos server. The add --random-key command will let you add the servers host principal, and the ext command will allow you to extract the servers host principal to its own keytab. For example: &prompt.root; kadmin kadmin> add --random-key host/myserver.example.org Max ticket life [unlimited]: Max renewable life [unlimited]: Attributes []: kadmin> ext host/myserver.example.org kadmin> exit Note that the ext command (short for extract) stores the extracted key in /etc/krb5.keytab by default. If you do not have kadmind running on the KDC (possibly for security reasons) and thus do not have access to kadmin remotely, you can add the host principal (host/myserver.EXAMPLE.ORG) directly on the KDC and then extract it to a temporary file (to avoid over-writing the /etc/krb5.keytab on the KDC) using something like this: &prompt.root; kadmin kadmin> ext --keytab=/tmp/example.keytab host/myserver.example.org kadmin> exit You can then securely copy the keytab to the server computer (using scp or a floppy, for example). Be sure to specify a non-default keytab name to avoid over-writing the keytab on the KDC. At this point your server can communicate with the KDC (due to its krb5.conf file) and it can prove its own identity (due to the krb5.keytab file). It is now ready for you to enable some Kerberos services. For this example we will enable the telnet service by putting a line like this into your /etc/inetd.conf and then restarting the &man.inetd.8; service with /etc/rc.d/inetd restart: telnet stream tcp nowait root /usr/libexec/telnetd telnetd -a user The critical bit is that the -a (for authentication) type is set to user. Consult the &man.telnetd.8; manual page for more details. <application>Kerberos</application> enabling a client with Heimdal Kerberos5 configure clients Setting up a client computer is almost trivially easy. As far as Kerberos configuration goes, you only need the Kerberos configuration file, located at /etc/krb5.conf. Simply securely copy it over to the client computer from the KDC. Test your client computer by attempting to use kinit, klist, and kdestroy from the client to obtain, show, and then delete a ticket for the principal you created above. You should also be able to use Kerberos applications to connect to Kerberos enabled servers, though if that does not work and obtaining a ticket does the problem is likely with the server and not with the client or the KDC. When testing an application like telnet, try using a packet sniffer (such as &man.tcpdump.1;) to confirm that your password is not sent in the clear. Try using telnet with the -x option, which encrypts the entire data stream (similar to ssh). The core Kerberos client applications (traditionally named kinit, klist, kdestroy, and kpasswd) are installed in the base &os; install. Note that &os; versions prior to 5.0 renamed them to k5init, k5list, k5destroy, k5passwd, and k5stash (though it is typically only used once). Various non-core Kerberos client applications are also installed by default. This is where the minimal nature of the base Heimdal installation is felt: telnet is the only Kerberos enabled service. The Heimdal port adds some of the missing client applications: Kerberos enabled versions of ftp, rsh, rcp, rlogin, and a few other less common programs. The MIT port also contains a full suite of Kerberos client applications. User configuration files: <filename>.k5login</filename> and <filename>.k5users</filename> .k5login .k5users Users within a realm typically have their Kerberos principal (such as tillman@EXAMPLE.ORG) mapped to a local user account (such as a local account named tillman). Client applications such as telnet usually do not require a user name or a principal. Occasionally, however, you want to grant access to a local user account to someone who does not have a matching Kerberos principal. For example, tillman@EXAMPLE.ORG may need access to the local user account webdevelopers. Other principals may also need access to that local account. The .k5login and .k5users files, placed in a users home directory, can be used similar to a powerful combination of .hosts and .rhosts, solving this problem. For example, if a .k5login with the following contents: tillman@example.org jdoe@example.org Were to be placed into the home directory of the local user webdevelopers then both principals listed would have access to that account without requiring a shared password. Reading the manual pages for these commands is recommended. Note that the ksu manual page covers .k5users. <application>Kerberos</application> Tips, Tricks, and Troubleshooting Kerberos5 troubleshooting When using either the Heimdal or MIT Kerberos ports ensure that your PATH environment variable lists the Kerberos versions of the client applications before the system versions. Do all the computers in your realm have synchronized time settings? If not, authentication may fail. describes how to synchronize clocks using NTP. MIT and Heimdal inter-operate nicely. Except for kadmin, the protocol for which is not standardized. If you change your hostname, you also need to change your host/ principal and update your keytab. This also applies to special keytab entries like the www/ principal used for Apache's www/mod_auth_kerb. All hosts in your realm must be resolvable (both forwards and reverse) in DNS (or /etc/hosts as a minimum). CNAMEs will work, but the A and PTR records must be correct and in place. The error message is not very intuitive: Kerberos5 refuses authentication because Read req failed: Key table entry not found. Some operating systems that may being acting as clients to your KDC do not set the permissions for ksu to be setuid root. This means that ksu does not work, which is a good security idea but annoying. This is not a KDC error. With MIT Kerberos, if you want to allow a principal to have a ticket life longer than the default ten hours, you must use modify_principal in kadmin to change the maxlife of both the principal in question and the krbtgt principal. Then the principal can use the -l option with kinit to request a ticket with a longer lifetime. If you run a packet sniffer on your KDC to add in troubleshooting and then run kinit from a workstation, you will notice that your TGT is sent immediately upon running kinit — even before you type your password! The explanation is that the Kerberos server freely transmits a TGT (Ticket Granting Ticket) to any unauthorized request; however, every TGT is encrypted in a key derived from the user's password. Therefore, when a user types their password it is not being sent to the KDC, it is being used to decrypt the TGT that kinit already obtained. If the decryption process results in a valid ticket with a valid time stamp, the user has valid Kerberos credentials. These credentials include a session key for establishing secure communications with the Kerberos server in the future, as well as the actual ticket-granting ticket, which is actually encrypted with the Kerberos server's own key. This second layer of encryption is unknown to the user, but it is what allows the Kerberos server to verify the authenticity of each TGT. If you want to use long ticket lifetimes (a week, for example) and you are using OpenSSH to connect to the machine where your ticket is stored, make sure that Kerberos is set to no in your sshd_config or else your tickets will be deleted when you log out. Remember that host principals can have a longer ticket lifetime as well. If your user principal has a lifetime of a week but the host you are connecting to has a lifetime of nine hours, you will have an expired host principal in your cache and the ticket cache will not work as expected. When setting up a krb5.dict file to prevent specific bad passwords from being used (the manual page for kadmind covers this briefly), remember that it only applies to principals that have a password policy assigned to them. The krb5.dict files format is simple: one string per line. Creating a symbolic link to /usr/share/dict/words might be useful. Differences with the <acronym>MIT</acronym> port The major difference between the MIT and Heimdal installs relates to the kadmin program which has a different (but equivalent) set of commands and uses a different protocol. This has a large implications if your KDC is MIT as you will not be able to use the Heimdal kadmin program to administer your KDC remotely (or vice versa, for that matter). The client applications may also take slightly different command line options to accomplish the same tasks. Following the instructions on the MIT Kerberos web site () is recommended. Be careful of path issues: the MIT port installs into /usr/local/ by default, and the normal system applications may be run instead of MIT if your PATH environment variable lists the system directories first. With the MIT security/krb5 port that is provided by &os;, be sure to read the /usr/local/share/doc/krb5/README.FreeBSD file installed by the port if you want to understand why logins via telnetd and klogind behave somewhat oddly. Most importantly, correcting the incorrect permissions on cache file behavior requires that the login.krb5 binary be used for authentication so that it can properly change ownership for the forwarded credentials. Mitigating limitations found in <application>Kerberos</application> Kerberos5 limitations and shortcomings <application>Kerberos</application> is an all-or-nothing approach Every service enabled on the network must be modified to work with Kerberos (or be otherwise secured against network attacks) or else the users credentials could be stolen and re-used. An example of this would be Kerberos enabling all remote shells (via rsh and telnet, for example) but not converting the POP3 mail server which sends passwords in plain text. <application>Kerberos</application> is intended for single-user workstations In a multi-user environment, Kerberos is less secure. This is because it stores the tickets in the /tmp directory, which is readable by all users. If a user is sharing a computer with several other people simultaneously (i.e. multi-user), it is possible that the user's tickets can be stolen (copied) by another user. This can be overcome with the -c filename command-line option or (preferably) the KRB5CCNAME environment variable, but this is rarely done. In principal, storing the ticket in the users home directory and using simple file permissions can mitigate this problem. The KDC is a single point of failure By design, the KDC must be as secure as the master password database is contained on it. The KDC should have absolutely no other services running on it and should be physically secured. The danger is high because Kerberos stores all passwords encrypted with the same key (the master key), which in turn is stored as a file on the KDC. As a side note, a compromised master key is not quite as bad as one might normally fear. The master key is only used to encrypt the Kerberos database and as a seed for the random number generator. As long as access to your KDC is secure, an attacker cannot do much with the master key. Additionally, if the KDC is unavailable (perhaps due to a denial of service attack or network problems) the network services are unusable as authentication can not be performed, a recipe for a denial-of-service attack. This can alleviated with multiple KDCs (a single master and one or more slaves) and with careful implementation of secondary or fall-back authentication (PAM is excellent for this). <application>Kerberos</application> Shortcomings Kerberos allows users, hosts and services to authenticate between themselves. It does not have a mechanism to authenticate the KDC to the users, hosts or services. This means that a trojanned kinit (for example) could record all user names and passwords. Something like security/tripwire or other file system integrity checking tools can alleviate this. Resources and further information Kerberos5 external resources The Kerberos FAQ Designing an Authentication System: a Dialog in Four Scenes RFC 1510, The Kerberos Network Authentication Service (V5) MIT Kerberos home page Heimdal Kerberos home page Tom Rhodes Written by: OpenSSL security OpenSSL One feature that many users overlook is the OpenSSL toolkit included in &os;. OpenSSL provides an encryption transport layer on top of the normal communications layer; thus allowing it to be intertwined with many network applications and services. Some uses of OpenSSL may include encrypted authentication of mail clients, web based transactions such as credit card payments and more. Many ports such as www/apache13-ssl, and mail/sylpheed-claws will offer compilation support for building with OpenSSL. In most cases the Ports Collection will attempt to build the security/openssl port unless the WITH_OPENSSL_BASE make variable is explicitly set to yes. The version of OpenSSL included in &os; supports Secure Sockets Layer v2/v3 (SSLv2/SSLv3), Transport Layer Security v1 (TLSv1) network security protocols and can be used as a general cryptographic library. While OpenSSL supports the IDEA algorithm, it is disabled by default due to United States patents. To use it, the license should be reviewed and, if the restrictions are acceptable, the MAKE_IDEA variable must be set in make.conf. One of the most common uses of OpenSSL is to provide certificates for use with software applications. These certificates ensure that the credentials of the company or individual are valid and not fraudulent. If the certificate in question has not been verified by one of the several Certificate Authorities, or CAs, a warning is usually produced. A Certificate Authority is a company, such as VeriSign, which will sign certificates in order to validate credentials of individuals or companies. This process has a cost associated with it and is definitely not a requirement for using certificates; however, it can put some of the more paranoid users at ease. Generating Certificates OpenSSL certificate generation To generate a certificate, the following command is available: &prompt.root; openssl req -new -nodes -out req.pem -keyout cert.pem Generating a 1024 bit RSA private key ................++++++ .......................................++++++ writing new private key to 'cert.pem' ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [AU]:US State or Province Name (full name) [Some-State]:PA Locality Name (eg, city) []:Pittsburgh Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Company Organizational Unit Name (eg, section) []:Systems Administrator Common Name (eg, YOUR name) []:localhost.example.org Email Address []:trhodes@FreeBSD.org Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []:SOME PASSWORD An optional company name []:Another Name Notice the response directly after the Common Name prompt shows a domain name. This prompt requires a server name to be entered for verification purposes; placing anything but a domain name would yield a useless certificate. Other options, for instance expire time, alternate encryption algorithms, etc. are available. A complete list may be obtained by viewing the &man.openssl.1; manual page. A cert.pem file should now exist in the directory which the aforementioned command was issued. This is the certificate which may be sent to any CA for signing. In cases where a signature from a CA is not required, a self signed certificate can be created. First, generate the RSA key: &prompt.root; openssl dsaparam -rand -genkey -out myRSA.key 1024 Next, generate the CA key: &prompt.root; openssl gendsa -des3 -out \ myca.key myRSA.key Use this key to create the certificate: &prompt.root; openssl req -new -x509 -days 365 -key \ myca.key -out new.crt Two new files should appear in the directory: a certificate authority signature file, myca.key and the certificate itself, new.crt. These should be placed in a directory, preferably under /etc, which is readable only by root. Permissions of 0700 should be fine for this and they can be set with the chmod utility. Using Certificates, an Example So what can these files do? A good use would be to encrypt connections to the Sendmail MTA. This would dissolve the use of clear text authentication for users who send mail via the local MTA. This is not the best use in the world as some MUAs will present the user with an error if they have not installed the certificate locally. Refer to the documentation included with the software for more information on certificate installation. The following lines should be placed inside the local .mc file: dnl SSL Options define(`confCACERT_PATH',`/etc/certs')dnl define(`confCACERT',`/etc/certs/new.crt')dnl define(`confSERVER_CERT',`/etc/certs/new.crt')dnl define(`confSERVER_KEY',`/etc/certs/myca.key')dnl define(`confTLS_SRV_OPTIONS', `V')dnl Where /etc/certs/ is the directory to be used for storing the certificate and key files locally. The last few requirements are a rebuild of the local .cf file. This is easily achieved by typing make install within the /etc/mail directory. Follow that up with make restart which should start the Sendmail daemon. If all went well there will be no error messages in the /var/log/maillog file and Sendmail will show up in the process list. For a simple test, simply connect to the mail server using the &man.telnet.1; utility: &prompt.root; telnet example.com 25 Trying 192.0.34.166... Connected to example.com. Escape character is '^]'. 220 example.com ESMTP Sendmail 8.12.10/8.12.10; Tue, 31 Aug 2004 03:41:22 -0400 (EDT) ehlo example.com 250-example.com Hello example.com [192.0.34.166], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 250-DSN 250-ETRN 250-AUTH LOGIN PLAIN 250-STARTTLS 250-DELIVERBY 250 HELP quit 221 2.0.0 example.com closing connection Connection closed by foreign host. If the STARTTLS line appears in the output then everything is working correctly. Nik Clayton
nik@FreeBSD.org
 Written by IPsec VPN over IPsec Creating a VPN between two networks, separated by the Internet, using FreeBSD gateways. Hiten M. Pandya
hmp@FreeBSD.org
 Written by Understanding IPsec This section will guide you through the process of setting up IPsec, and to use it in an environment which consists of FreeBSD and µsoft.windows; 2000/XP machines, to make them communicate securely. In order to set up IPsec, it is necessary that you are familiar with the concepts of building a custom kernel (see ). IPsec is a protocol which sits on top of the Internet Protocol (IP) layer. It allows two or more hosts to communicate in a secure manner (hence the name). The FreeBSD IPsec network stack is based on the KAME implementation, which has support for both protocol families, IPv4 and IPv6. FreeBSD 5.X contains a hardware accelerated IPsec stack, known as Fast IPsec, that was obtained from OpenBSD. It employs cryptographic hardware (whenever possible) via the &man.crypto.4; subsystem to optimize the performance of IPsec. This subsystem is new, and does not support all the features that are available in the KAME version of IPsec. However, in order to enable hardware-accelerated IPsec, the following kernel option has to be added to your kernel configuration file: kernel options FAST_IPSEC options FAST_IPSEC # new IPsec (cannot define w/ IPSEC) Note, that it is not currently possible to use the Fast IPsec subsystem in lue with the KAME implementation of IPsec. Consult the &man.fast.ipsec.4; manual page for more information. IPsec ESP IPsec AH IPsec consists of two sub-protocols: Encapsulated Security Payload (ESP), protects the IP packet data from third party interference, by encrypting the contents using symmetric cryptography algorithms (like Blowfish, 3DES). Authentication Header (AH), protects the IP packet header from third party interference and spoofing, by computing a cryptographic checksum and hashing the IP packet header fields with a secure hashing function. This is then followed by an additional header that contains the hash, to allow the information in the packet to be authenticated. ESP and AH can either be used together or separately, depending on the environment. VPN virtual private network VPN IPsec can either be used to directly encrypt the traffic between two hosts (known as Transport Mode); or to build virtual tunnels between two subnets, which could be used for secure communication between two corporate networks (known as Tunnel Mode). The latter is more commonly known as a Virtual Private Network (VPN). The &man.ipsec.4; manual page should be consulted for detailed information on the IPsec subsystem in FreeBSD. To add IPsec support to your kernel, add the following options to your kernel configuration file: kernel options IPSEC kernel options IPSEC_ESP options IPSEC #IP security options IPSEC_ESP #IP security (crypto; define w/ IPSEC) kernel options IPSEC_DEBUG If IPsec debugging support is desired, the following kernel option should also be added: options IPSEC_DEBUG #debug for IP security The Problem There is no standard for what constitutes a VPN. VPNs can be implemented using a number of different technologies, each of which have their own strengths and weaknesses. This section presents a scenario, and the strategies used for implementing a VPN for this scenario. The Scenario: Two networks, connected to the Internet, to behave as one VPN creating The premise is as follows: You have at least two sites Both sites are using IP internally Both sites are connected to the Internet, through a gateway that is running FreeBSD. The gateway on each network has at least one public IP address. The internal addresses of the two networks can be public or private IP addresses, it does not matter. You can be running NAT on the gateway machine if necessary. The internal IP addresses of the two networks do not collide. While I expect it is theoretically possible to use a combination of VPN technology and NAT to get this to work, I expect it to be a configuration nightmare. If you find that you are trying to connect two networks, both of which, internally, use the same private IP address range (e.g. both of them use 192.168.1.x), then one of the networks will have to be renumbered. The network topology might look something like this: Network #1 [ Internal Hosts ] Private Net, 192.168.1.2-254 [ Win9x/NT/2K ] [ UNIX ] | | .---[fxp1]---. Private IP, 192.168.1.1 | FreeBSD | `---[fxp0]---' Public IP, A.B.C.D | | -=-=- Internet -=-=- | | .---[fxp0]---. Public IP, W.X.Y.Z | FreeBSD | `---[fxp1]---' Private IP, 192.168.2.1 | | Network #2 [ Internal Hosts ] [ Win9x/NT/2K ] Private Net, 192.168.2.2-254 [ UNIX ] Notice the two public IP addresses. I will use the letters to refer to them in the rest of this article. Anywhere you see those letters in this article, replace them with your own public IP addresses. Note also that internally, the two gateway machines have .1 IP addresses, and that the two networks have different private IP addresses (192.168.1.x and 192.168.2.x respectively). All the machines on the private networks have been configured to use the .1 machine as their default gateway. The intention is that, from a network point of view, each network should view the machines on the other network as though they were directly attached the same router -- albeit a slightly slow router with an occasional tendency to drop packets. This means that (for example), machine 192.168.1.20 should be able to run ping 192.168.2.34 and have it work, transparently. &windows; machines should be able to see the machines on the other network, browse file shares, and so on, in exactly the same way that they can browse machines on the local network. And the whole thing has to be secure. This means that traffic between the two networks has to be encrypted. Creating a VPN between these two networks is a multi-step process. The stages are as follows: Create a virtual network link between the two networks, across the Internet. Test it, using tools like &man.ping.8;, to make sure it works. Apply security policies to ensure that traffic between the two networks is transparently encrypted and decrypted as necessary. Test this, using tools like &man.tcpdump.1;, to ensure that traffic is encrypted. Configure additional software on the FreeBSD gateways, to allow &windows; machines to see one another across the VPN. Step 1: Creating and testing a <quote>virtual</quote> network link Suppose that you were logged in to the gateway machine on network #1 (with public IP address A.B.C.D, private IP address 192.168.1.1), and you ran ping 192.168.2.1, which is the private address of the machine with IP address W.X.Y.Z. What needs to happen in order for this to work? The gateway machine needs to know how to reach 192.168.2.1. In other words, it needs to have a route to 192.168.2.1. Private IP addresses, such as those in the 192.168.x range are not supposed to appear on the Internet at large. Instead, each packet you send to 192.168.2.1 will need to be wrapped up inside another packet. This packet will need to appear to be from A.B.C.D, and it will have to be sent to W.X.Y.Z. This process is called encapsulation. Once this packet arrives at W.X.Y.Z it will need to unencapsulated, and delivered to 192.168.2.1. You can think of this as requiring a tunnel between the two networks. The two tunnel mouths are the IP addresses A.B.C.D and W.X.Y.Z, and the tunnel must be told the addresses of the private IP addresses that will be allowed to pass through it. The tunnel is used to transfer traffic with private IP addresses across the public Internet. This tunnel is created by using the generic interface, or gif devices on FreeBSD. As you can imagine, the gif interface on each gateway host must be configured with four IP addresses; two for the public IP addresses, and two for the private IP addresses. Support for the gif device must be compiled in to the &os; kernel on both machines. You can do this by adding the line: pseudo-device gif to the kernel configuration files on both machines, and then compile, install, and reboot as normal. Configuring the tunnel is a two step process. First the tunnel must be told what the outside (or public) IP addresses are, using &man.gifconfig.8;. Then the private IP addresses must be configured using &man.ifconfig.8;. In &os; 5.X, the functionality provided by the &man.gifconfig.8; utility has been merged into &man.ifconfig.8;. On the gateway machine on network #1 you would run the following two commands to configure the tunnel. gifconfig gif0 A.B.C.D W.X.Y.Z ifconfig gif0 inet 192.168.1.1 192.168.2.1 netmask 0xffffffff On the other gateway machine you run the same commands, but with the order of the IP addresses reversed. gifconfig gif0 W.X.Y.Z A.B.C.D ifconfig gif0 inet 192.168.2.1 192.168.1.1 netmask 0xffffffff You can then run: gifconfig gif0 to see the configuration. For example, on the network #1 gateway, you would see this: &prompt.root; gifconfig gif0 gif0: flags=8011<UP,POINTTOPOINT,MULTICAST> mtu 1280 inet 192.168.1.1 --> 192.168.2.1 netmask 0xffffffff physical address inet A.B.C.D --> W.X.Y.Z As you can see, a tunnel has been created between the physical addresses A.B.C.D and W.X.Y.Z, and the traffic allowed through the tunnel is that between 192.168.1.1 and 192.168.2.1. This will also have added an entry to the routing table on both machines, which you can examine with the command netstat -rn. This output is from the gateway host on network #1. &prompt.root; netstat -rn Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire ... 192.168.2.1 192.168.1.1 UH 0 0 gif0 ... As the Flags value indicates, this is a host route, which means that each gateway knows how to reach the other gateway, but they do not know how to reach the rest of their respective networks. That problem will be fixed shortly. It is likely that you are running a firewall on both machines. This will need to be circumvented for your VPN traffic. You might want to allow all traffic between both networks, or you might want to include firewall rules that protect both ends of the VPN from one another. It greatly simplifies testing if you configure the firewall to allow all traffic through the VPN. You can always tighten things up later. If you are using &man.ipfw.8; on the gateway machines then a command like ipfw add 1 allow ip from any to any via gif0 will allow all traffic between the two end points of the VPN, without affecting your other firewall rules. Obviously you will need to run this command on both gateway hosts. This is sufficient to allow each gateway machine to ping the other. On 192.168.1.1, you should be able to run ping 192.168.2.1 and get a response, and you should be able to do the same thing on the other gateway machine. However, you will not be able to reach internal machines on either network yet. This is because of the routing -- although the gateway machines know how to reach one another, they do not know how to reach the network behind each one. To solve this problem you must add a static route on each gateway machine. The command to do this on the first gateway would be: route add 192.168.2.0 192.168.2.1 netmask 0xffffff00 This says In order to reach the hosts on the network 192.168.2.0, send the packets to the host 192.168.2.1. You will need to run a similar command on the other gateway, but with the 192.168.1.x addresses instead. IP traffic from hosts on one network will now be able to reach hosts on the other network. That has now created two thirds of a VPN between the two networks, in as much as it is virtual and it is a network. It is not private yet. You can test this using &man.ping.8; and &man.tcpdump.1;. Log in to the gateway host and run tcpdump dst host 192.168.2.1 In another log in session on the same host run ping 192.168.2.1 You will see output that looks something like this: 16:10:24.018080 192.168.1.1 > 192.168.2.1: icmp: echo request 16:10:24.018109 192.168.1.1 > 192.168.2.1: icmp: echo reply 16:10:25.018814 192.168.1.1 > 192.168.2.1: icmp: echo request 16:10:25.018847 192.168.1.1 > 192.168.2.1: icmp: echo reply 16:10:26.028896 192.168.1.1 > 192.168.2.1: icmp: echo request 16:10:26.029112 192.168.1.1 > 192.168.2.1: icmp: echo reply As you can see, the ICMP messages are going back and forth unencrypted. If you had used the parameter to &man.tcpdump.1; to grab more bytes of data from the packets you would see more information. Obviously this is unacceptable. The next section will discuss securing the link between the two networks so that it all traffic is automatically encrypted. Summary: Configure both kernels with pseudo-device gif. Edit /etc/rc.conf on gateway host #1 and add the following lines (replacing IP addresses as necessary). gifconfig_gif0="A.B.C.D W.X.Y.Z" ifconfig_gif0="inet 192.168.1.1 192.168.2.1 netmask 0xffffffff" static_routes="vpn" route_vpn="192.168.2.0 192.168.2.1 netmask 0xffffff00" Edit your firewall script (/etc/rc.firewall, or similar) on both hosts, and add ipfw add 1 allow ip from any to any via gif0 Make similar changes to /etc/rc.conf on gateway host #2, reversing the order of IP addresses. Step 2: Securing the link To secure the link we will be using IPsec. IPsec provides a mechanism for two hosts to agree on an encryption key, and to then use this key in order to encrypt data between the two hosts. The are two areas of configuration to be considered here. There must be a mechanism for two hosts to agree on the encryption mechanism to use. Once two hosts have agreed on this mechanism there is said to be a security association between them. There must be a mechanism for specifying which traffic should be encrypted. Obviously, you do not want to encrypt all your outgoing traffic -- you only want to encrypt the traffic that is part of the VPN. The rules that you put in place to determine what traffic will be encrypted are called security policies. Security associations and security policies are both maintained by the kernel, and can be modified by userland programs. However, before you can do this you must configure the kernel to support IPsec and the Encapsulated Security Payload (ESP) protocol. This is done by configuring a kernel with: kernel options IPSEC options IPSEC options IPSEC_ESP and recompiling, reinstalling, and rebooting. As before you will need to do this to the kernels on both of the gateway hosts. IKE You have two choices when it comes to setting up security associations. You can configure them by hand between two hosts, which entails choosing the encryption algorithm, encryption keys, and so forth, or you can use daemons that implement the Internet Key Exchange protocol (IKE) to do this for you. I recommend the latter. Apart from anything else, it is easier to set up. IPsec security policies setkey Editing and displaying security policies is carried out using &man.setkey.8;. By analogy, setkey is to the kernel's security policy tables as &man.route.8; is to the kernel's routing tables. setkey can also display the current security associations, and to continue the analogy further, is akin to netstat -r in that respect. There are a number of choices for daemons to manage security associations with FreeBSD. This article will describe how to use one of these, racoon. racoon is in the FreeBSD ports collection, in the security/ category, and is installed in the usual way. racoon racoon must be run on both gateway hosts. On each host it is configured with the IP address of the other end of the VPN, and a secret key (which you choose, and must be the same on both gateways). The two daemons then contact one another, confirm that they are who they say they are (by using the secret key that you configured). The daemons then generate a new secret key, and use this to encrypt the traffic over the VPN. They periodically change this secret, so that even if an attacker were to crack one of the keys (which is as theoretically close to unfeasible as it gets) it will not do them much good -- by the time they have cracked the key the two daemons have chosen another one. racoon's configuration is stored in ${PREFIX}/etc/racoon. You should find a configuration file there, which should not need to be changed too much. The other component of racoon's configuration, which you will need to change, is the pre-shared key. The default racoon configuration expects to find this in the file ${PREFIX}/etc/racoon/psk.txt. It is important to note that the pre-shared key is not the key that will be used to encrypt your traffic across the VPN link, it is simply a token that allows the key management daemons to trust one another. psk.txt contains a line for each remote site you are dealing with. In this example, where there are two sites, each psk.txt file will contain one line (because each end of the VPN is only dealing with one other end). On gateway host #1 this line should look like this: W.X.Y.Z secret That is, the public IP address of the remote end, whitespace, and a text string that provides the secret. Obviously, you should not use secret as your key -- the normal rules for choosing a password apply. On gateway host #2 the line would look like this A.B.C.D secret That is, the public IP address of the remote end, and the same secret key. psk.txt must be mode 0600 (i.e., only read/write to root) before racoon will run. You must run racoon on both gateway machines. You will also need to add some firewall rules to allow the IKE traffic, which is carried over UDP to the ISAKMP (Internet Security Association Key Management Protocol) port. Again, this should be fairly early in your firewall ruleset. ipfw add 1 allow udp from A.B.C.D to W.X.Y.Z isakmp ipfw add 1 allow udp from W.X.Y.Z to A.B.C.D isakmp Once racoon is running you can try pinging one gateway host from the other. The connection is still not encrypted, but racoon will then set up the security associations between the two hosts -- this might take a moment, and you may see this as a short delay before the ping commands start responding. Once the security association has been set up you can view it using &man.setkey.8;. Run setkey -D on either host to view the security association information. That's one half of the problem. They other half is setting your security policies. To create a sensible security policy, let's review what's been set up so far. This discussions hold for both ends of the link. Each IP packet that you send out has a header that contains data about the packet. The header includes the IP addresses of both the source and destination. As we already know, private IP addresses, such as the 192.168.x.y range are not supposed to appear on the public Internet. Instead, they must first be encapsulated inside another packet. This packet must have the public source and destination IP addresses substituted for the private addresses. So if your outgoing packet started looking like this: .----------------------. | Src: 192.168.1.1 | | Dst: 192.168.2.1 | | <other header info> | +----------------------+ | <packet data> | `----------------------' Then it will be encapsulated inside another packet, looking something like this: .--------------------------. | Src: A.B.C.D | | Dst: W.X.Y.Z | | <other header info> | +--------------------------+ | .----------------------. | | | Src: 192.168.1.1 | | | | Dst: 192.168.2.1 | | | | <other header info> | | | +----------------------+ | | | <packet data> | | | `----------------------' | `--------------------------' This encapsulation is carried out by the gif device. As you can see, the packet now has real IP addresses on the outside, and our original packet has been wrapped up as data inside the packet that will be put out on the Internet. Obviously, we want all traffic between the VPNs to be encrypted. You might try putting this in to words, as: If a packet leaves from A.B.C.D, and it is destined for W.X.Y.Z, then encrypt it, using the necessary security associations. If a packet arrives from W.X.Y.Z, and it is destined for A.B.C.D, then decrypt it, using the necessary security associations. That's close, but not quite right. If you did this, all traffic to and from W.X.Y.Z, even traffic that was not part of the VPN, would be encrypted. That's not quite what you want. The correct policy is as follows If a packet leaves from A.B.C.D, and that packet is encapsulating another packet, and it is destined for W.X.Y.Z, then encrypt it, using the necessary security associations. If a packet arrives from W.X.Y.Z, and that packet is encapsulating another packet, and it is destined for A.B.C.D, then decrypt it, using the necessary security associations. A subtle change, but a necessary one. Security policies are also set using &man.setkey.8;. &man.setkey.8; features a configuration language for defining the policy. You can either enter configuration instructions via stdin, or you can use the option to specify a filename that contains configuration instructions. The configuration on gateway host #1 (which has the public IP address A.B.C.D) to force all outbound traffic to W.X.Y.Z to be encrypted is: spdadd A.B.C.D/32 W.X.Y.Z/32 ipencap -P out ipsec esp/tunnel/A.B.C.D-W.X.Y.Z/require; Put these commands in a file (e.g. /etc/ipsec.conf) and then run &prompt.root; setkey -f /etc/ipsec.conf tells &man.setkey.8; that we want to add a rule to the secure policy database. The rest of this line specifies which packets will match this policy. A.B.C.D/32 and W.X.Y.Z/32 are the IP addresses and netmasks that identify the network or hosts that this policy will apply to. In this case, we want it to apply to traffic between these two hosts. tells the kernel that this policy should only apply to packets that encapsulate other packets. says that this policy applies to outgoing packets, and says that the packet will be secured. The second line specifies how this packet will be encrypted. is the protocol that will be used, while indicates that the packet will be further encapsulated in an IPsec packet. The repeated use of A.B.C.D and W.X.Y.Z is used to select the security association to use, and the final mandates that packets must be encrypted if they match this rule. This rule only matches outgoing packets. You will need a similar rule to match incoming packets. spdadd W.X.Y.Z/32 A.B.C.D/32 ipencap -P in ipsec esp/tunnel/W.X.Y.Z-A.B.C.D/require; Note the instead of in this case, and the necessary reversal of the IP addresses. The other gateway host (which has the public IP address W.X.Y.Z) will need similar rules. spdadd W.X.Y.Z/32 A.B.C.D/32 ipencap -P out ipsec esp/tunnel/W.X.Y.Z-A.B.C.D/require; spdadd A.B.C.D/32 W.X.Y.Z/32 ipencap -P in ipsec esp/tunnel/A.B.C.D-W.X.Y.Z/require; Finally, you need to add firewall rules to allow ESP and IPENCAP packets back and forth. These rules will need to be added to both hosts. ipfw add 1 allow esp from A.B.C.D to W.X.Y.Z ipfw add 1 allow esp from W.X.Y.Z to A.B.C.D ipfw add 1 allow ipencap from A.B.C.D to W.X.Y.Z ipfw add 1 allow ipencap from W.X.Y.Z to A.B.C.D Because the rules are symmetric you can use the same rules on each gateway host. Outgoing packets will now look something like this: .------------------------------. --------------------------. | Src: A.B.C.D | | | Dst: W.X.Y.Z | | | <other header info> | | Encrypted +------------------------------+ | packet. | .--------------------------. | -------------. | contents | | Src: A.B.C.D | | | | are | | Dst: W.X.Y.Z | | | | completely | | <other header info> | | | |- secure | +--------------------------+ | | Encap'd | from third | | .----------------------. | | -. | packet | party | | | Src: 192.168.1.1 | | | | Original |- with real | snooping | | | Dst: 192.168.2.1 | | | | packet, | IP addr | | | | <other header info> | | | |- private | | | | +----------------------+ | | | IP addr | | | | | <packet data> | | | | | | | | `----------------------' | | -' | | | `--------------------------' | -------------' | `------------------------------' --------------------------' When they are received by the far end of the VPN they will first be decrypted (using the security associations that have been negotiated by racoon). Then they will enter the gif interface, which will unwrap the second layer, until you are left with the innermost packet, which can then travel in to the inner network. You can check the security using the same &man.ping.8; test from earlier. First, log in to the A.B.C.D gateway machine, and run: tcpdump dst host 192.168.2.1 In another log in session on the same host run ping 192.168.2.1 This time you should see output like the following: XXX tcpdump output Now, as you can see, &man.tcpdump.1; shows the ESP packets. If you try to examine them with the option you will see (apparently) gibberish, because of the encryption. Congratulations. You have just set up a VPN between two remote sites. Summary Configure both kernels with: options IPSEC options IPSEC_ESP Install security/racoon. Edit ${PREFIX}/etc/racoon/psk.txt on both gateway hosts, adding an entry for the remote host's IP address and a secret key that they both know. Make sure this file is mode 0600. Add the following lines to /etc/rc.conf on each host: ipsec_enable="YES" ipsec_file="/etc/ipsec.conf" Create an /etc/ipsec.conf on each host that contains the necessary spdadd lines. On gateway host #1 this would be: spdadd A.B.C.D/32 W.X.Y.Z/32 ipencap -P out ipsec esp/tunnel/A.B.C.D-W.X.Y.Z/require; spdadd W.X.Y.Z/32 A.B.C.D/32 ipencap -P in ipsec esp/tunnel/W.X.Y.Z-A.B.C.D/require; On gateway host #2 this would be: spdadd W.X.Y.Z/32 A.B.C.D/32 ipencap -P out ipsec esp/tunnel/W.X.Y.Z-A.B.C.D/require; spdadd A.B.C.D/32 W.X.Y.Z/32 ipencap -P in ipsec esp/tunnel/A.B.C.D-W.X.Y.Z/require; Add firewall rules to allow IKE, ESP, and IPENCAP traffic to both hosts: ipfw add 1 allow udp from A.B.C.D to W.X.Y.Z isakmp ipfw add 1 allow udp from W.X.Y.Z to A.B.C.D isakmp ipfw add 1 allow esp from A.B.C.D to W.X.Y.Z ipfw add 1 allow esp from W.X.Y.Z to A.B.C.D ipfw add 1 allow ipencap from A.B.C.D to W.X.Y.Z ipfw add 1 allow ipencap from W.X.Y.Z to A.B.C.D The previous two steps should suffice to get the VPN up and running. Machines on each network will be able to refer to one another using IP addresses, and all traffic across the link will be automatically and securely encrypted. Chern Lee Contributed by OpenSSH OpenSSH security OpenSSH OpenSSH is a set of network connectivity tools used to access remote machines securely. It can be used as a direct replacement for rlogin, rsh, rcp, and telnet. Additionally, any other TCP/IP connections can be tunneled/forwarded securely through SSH. OpenSSH encrypts all traffic to effectively eliminate eavesdropping, connection hijacking, and other network-level attacks. OpenSSH is maintained by the OpenBSD project, and is based upon SSH v1.2.12 with all the recent bug fixes and updates. It is compatible with both SSH protocols 1 and 2. OpenSSH has been in the base system since FreeBSD 4.0. Advantages of Using OpenSSH Normally, when using &man.telnet.1; or &man.rlogin.1;, data is sent over the network in an clear, un-encrypted form. Network sniffers anywhere in between the client and server can steal your user/password information or data transferred in your session. OpenSSH offers a variety of authentication and encryption methods to prevent this from happening. Enabling sshd OpenSSH enabling Be sure to make the following addition to your rc.conf file: sshd_enable="YES" This will load &man.sshd.8;, the daemon program for OpenSSH, the next time your system initializes. Alternatively, you can simply run directly the sshd daemon by typing sshd on the command line. SSH Client OpenSSH client The &man.ssh.1; utility works similarly to &man.rlogin.1;. &prompt.root; ssh user@example.com Host key not found from the list of known hosts. Are you sure you want to continue connecting (yes/no)? yes Host 'example.com' added to the list of known hosts. user@example.com's password: ******* The login will continue just as it would have if a session was created using rlogin or telnet. SSH utilizes a key fingerprint system for verifying the authenticity of the server when the client connects. The user is prompted to enter yes only when connecting for the first time. Future attempts to login are all verified against the saved fingerprint key. The SSH client will alert you if the saved fingerprint differs from the received fingerprint on future login attempts. The fingerprints are saved in ~/.ssh/known_hosts, or ~/.ssh/known_hosts2 for SSH v2 fingerprints. By default, OpenSSH servers are configured to only accept SSH v2 connections. The client, however, can choose between version 1 and 2. Version 2 is known to be more robust and secure than its predecessor. The &man.ssh.1; command can be forced to use either protocol by passing it the or argument for v1 and v2, respectively. Secure Copy OpenSSH secure copy scp The &man.scp.1; command works similarly to &man.rcp.1;; it copies a file to or from a remote machine, except in a secure fashion. &prompt.root; scp user@example.com:/COPYRIGHT COPYRIGHT user@example.com's password: ******* COPYRIGHT 100% |*****************************| 4735 00:00 &prompt.root; Since the fingerprint was already saved for this host in the previous example, it is verified when using &man.scp.1; here. The arguments passed to &man.scp.1; are similar to &man.cp.1;, with the file or files in the first argument, and the destination in the second. Since the file is fetched over the network, through SSH, one or more of the file arguments takes on the form . Configuration OpenSSH configuration The system-wide configuration files for both the OpenSSH daemon and client reside within the /etc/ssh directory. ssh_config configures the client settings, while sshd_config configures the daemon. Additionally, the (/usr/sbin/sshd by default), and rc.conf options can provide more levels of configuration. ssh-keygen Instead of using passwords, &man.ssh-keygen.1; can be used to generate RSA keys to authenticate a user: &prompt.user; ssh-keygen -t rsa1 Initializing random number generator... Generating p: .++ (distance 66) Generating q: ..............................++ (distance 498) Computing the keys... Key generation complete. Enter file in which to save the key (/home/user/.ssh/identity): Enter passphrase: Enter the same passphrase again: Your identification has been saved in /home/user/.ssh/identity. ... &man.ssh-keygen.1; will create a public and private key pair for use in authentication. The private key is stored in ~/.ssh/identity, whereas the public key is stored in ~/.ssh/identity.pub. The public key must be placed in ~/.ssh/authorized_keys of the remote machine in order for the setup to work. This will allow connection to the remote machine based upon RSA authentication instead of passwords. The option will create RSA keys for use by SSH protocol version 1. If you want to use RSA keys with the SSH protocol version 2, you have to use the command ssh-keygen -t rsa. If a passphrase is used in &man.ssh-keygen.1;, the user will be prompted for a password each time in order to use the private key. A SSH protocol version 2 DSA key can be created for the same purpose by using the ssh-keygen -t dsa command. This will create a public/private DSA key for use in SSH protocol version 2 sessions only. The public key is stored in ~/.ssh/id_dsa.pub, while the private key is in ~/.ssh/id_dsa. DSA public keys are also placed in ~/.ssh/authorized_keys on the remote machine. &man.ssh-agent.1; and &man.ssh-add.1; are utilities used in managing multiple passworded private keys. The various options and files can be different according to the OpenSSH version you have on your system, to avoid problems you should consult the &man.ssh-keygen.1; manual page. SSH Tunneling OpenSSH tunneling OpenSSH has the ability to create a tunnel to encapsulate another protocol in an encrypted session. The following command tells &man.ssh.1; to create a tunnel for telnet: &prompt.user; ssh -2 -N -f -L 5023:localhost:23 user@foo.example.com &prompt.user; The ssh command is used with the following options: Forces ssh to use version 2 of the protocol. (Do not use if you are working with older SSH servers) Indicates no command, or tunnel only. If omitted, ssh would initiate a normal session. Forces ssh to run in the background. Indicates a local tunnel in localport:remotehost:remoteport fashion. The remote SSH server. An SSH tunnel works by creating a listen socket on localhost on the specified port. It then forwards any connection received on the local host/port via the SSH connection to the specified remote host and port. In the example, port 5023 on localhost is being forwarded to port 23 on localhost of the remote machine. Since 23 is telnet, this would create a secure telnet session through an SSH tunnel. This can be used to wrap any number of insecure TCP protocols such as SMTP, POP3, FTP, etc. Using SSH to Create a Secure Tunnel for SMTP &prompt.user; ssh -2 -N -f -L 5025:localhost:25 user@mailserver.example.com user@mailserver.example.com's password: ***** &prompt.user; telnet localhost 5025 Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. 220 mailserver.example.com ESMTP This can be used in conjunction with an &man.ssh-keygen.1; and additional user accounts to create a more seamless/hassle-free SSH tunneling environment. Keys can be used in place of typing a password, and the tunnels can be run as a separate user. Practical SSH Tunneling Examples Secure Access of a POP3 Server At work, there is an SSH server that accepts connections from the outside. On the same office network resides a mail server running a POP3 server. The network, or network path between your home and office may or may not be completely trustable. Because of this, you need to check your e-mail in a secure manner. The solution is to create an SSH connection to your office's SSH server, and tunnel through to the mail server. &prompt.user; ssh -2 -N -f -L 2110:mail.example.com:110 user@ssh-server.example.com user@ssh-server.example.com's password: ****** When the tunnel is up and running, you can point your mail client to send POP3 requests to localhost port 2110. A connection here will be forwarded securely across the tunnel to mail.example.com. Bypassing a Draconian Firewall Some network administrators impose extremely draconian firewall rules, filtering not only incoming connections, but outgoing connections. You may be only given access to contact remote machines on ports 22 and 80 for SSH and web surfing. You may wish to access another (perhaps non-work related) service, such as an Ogg Vorbis server to stream music. If this Ogg Vorbis server is streaming on some other port than 22 or 80, you will not be able to access it. The solution is to create an SSH connection to a machine outside of your network's firewall, and use it to tunnel to the Ogg Vorbis server. &prompt.user; ssh -2 -N -f -L 8888:music.example.com:8000 user@unfirewalled-system.example.org user@unfirewalled-system.example.org's password: ******* Your streaming client can now be pointed to localhost port 8888, which will be forwarded over to music.example.com port 8000, successfully evading the firewall. Further Reading OpenSSH &man.ssh.1; &man.scp.1; &man.ssh-keygen.1; &man.ssh-agent.1; &man.ssh-add.1; &man.sshd.8; &man.sftp-server.8; Tom Rhodes Contributed by ACL File System Access Control Lists In conjunction with file system enhancements like snapshots, FreeBSD 5.0 and later offers the security of File System Access Control Lists (ACLs). Access Control Lists extend the standard &unix; permission model in a highly compatible (&posix;.1e) way. This feature permits an administrator to make use of and take advantage of a more sophisticated security model. To enable ACL support for UFS file systems, the following: options UFS_ACL must be compiled into the kernel. If this option has not been compiled in, a warning message will be displayed when attempting to mount a file system supporting ACLs. This option is included in the GENERIC kernel. ACLs rely on extended attributes being enabled on the file system. Extended attributes are natively supported in the next generation &unix; file system, UFS2. A higher level of administrative overhead is required to configure extended attributes on UFS1 than on UFS2. The performance of extended attributes on UFS2 is also substantially higher. As a result, UFS2 is generally recommended in preference to UFS1 for use with access control lists. ACLs are enabled by the mount-time administrative flag, , which may be added to /etc/fstab. The mount-time flag can also be automatically set in a persistent manner using &man.tunefs.8; to modify a superblock ACLs flag in the file system header. In general, it is preferred to use the superblock flag for several reasons: The mount-time ACLs flag cannot be changed by a remount (&man.mount.8; ), only by means of a complete &man.umount.8; and fresh &man.mount.8;. This means that ACLs cannot be enabled on the root file system after boot. It also means that you cannot change the disposition of a file system once it is in use. Setting the superblock flag will cause the file system to always be mounted with ACLs enabled even if there is not an fstab entry or if the devices re-order. This prevents accidental mounting of the file system without ACLs enabled, which can result in ACLs being improperly enforced, and hence security problems. We may change the ACLs behavior to allow the flag to be enabled without a complete fresh &man.mount.8;, but we consider it desirable to discourage accidental mounting without ACLs enabled, because you can shoot your feet quite nastily if you enable ACLs, then disable them, then re-enable them without flushing the extended attributes. In general, once you have enabled ACLs on a file system, they should not be disabled, as the resulting file protections may not be compatible with those intended by the users of the system, and re-enabling ACLs may re-attach the previous ACLs to files that have since had their permissions changed, resulting in other unpredictable behavior. File systems with ACLs enabled will show a + (plus) sign in their permission settings when viewed. For example: drwx------ 2 robert robert 512 Dec 27 11:54 private drwxrwx---+ 2 robert robert 512 Dec 23 10:57 directory1 drwxrwx---+ 2 robert robert 512 Dec 22 10:20 directory2 drwxrwx---+ 2 robert robert 512 Dec 27 11:57 directory3 drwxr-xr-x 2 robert robert 512 Nov 10 11:54 public_html Here we see that the directory1, directory2, and directory3 directories are all taking advantage of ACLs. The public_html directory is not. Making Use of <acronym>ACL</acronym>s The file system ACLs can be viewed by the &man.getfacl.1; utility. For instance, to view the ACL settings on the test file, one would use the command: &prompt.user; getfacl test #file:test #owner:1001 #group:1001 user::rw- group::r-- other::r-- To change the ACL settings on this file, invoke the &man.setfacl.1; utility. Observe: &prompt.user; setfacl -k test The flag will remove all of the currently defined ACLs from a file or file system. The more preferable method would be to use as it leaves the basic fields required for ACLs to work. &prompt.user; setfacl -m u:trhodes:rwx,group:web:r--,o::--- test In the aforementioned command, the option was used to modify the default ACL entries. Since there were no pre-defined entries, as they were removed by the previous command, this will restore the default options and assign the options listed. Take care to notice that if you add a user or group which does not exist on the system, an Invalid argument error will be printed to stdout. + + + + + Tom + Rhodes + Contributed by + + + + + + Portaudit + + Monitoring Third Party Security Issues + + In recent years, the security world has made many improvements + to how vulnerability assessment is handled. The threat of system + intrusion increases as third party utilities are installed and + configured for virtually any operating system available + today. + + Vulnerability assessment is a key factor in security, and + while &os; releases advisories for the base system, doing so + for every third party utility is beyond the &os; Project's + capability. There is a way to mitigate third party + vulnerabilities and warn administrators of known security + issues. A &os; add on utility known as + Portaudit exists solely for this + purpose. + + The security/portaudit port + polls a database, updated and maintained by the &os; Security + Team and ports developers, for known security issues. + + To begin using Portaudit, one + must install it from the Ports Collection: + + &prompt.root; cd /usr/ports/security/portaudit && + make install clean + + During the install process, the configuration files for + &man.periodic.8; will be updated, permitting + Portaudit output in the daily security + runs. No more configuration will be required here. + + After installation, an administrator must update the database + stored locally in + /var/db/portaudit by + invoking the following command: + + &prompt.root; portaudit -F + + + The database will automatically be updated during the + &man.periodic.8; run; thus, the previous command is completely + optional. It is only required for the following + examples. + + + To audit the third party utilities installed as part of + the Ports Collection, an administrator need only run the + following command: + + &prompt.root; portaudit -a + + An example of output is provided: + + Affected package: cups-base-1.1.22.0_1 +Type of problem: cups-base -- HPGL buffer overflow vulnerability. +Reference: <http://www.FreeBSD.org/ports/portaudit/40a3bca2-6809-11d9-a9e7-0001020eed82.html> + +1 problem(s) in your installed packages found. + +You are advised to update or deinstall the affected package(s) immediately. + + By pointing a web browser to the URL shown, + an administrator may obtain more information about the + vulnerability in question. This will include versions affected, + by &os; Port version, along with other web sites which may contain + security advisories. + + In short, Portaudit is a power + utility and extremely useful when coupled with the + Portupgrade port. + + Tom Rhodes Contributed by FreeBSD Security Advisories &os; Security Advisories Like many production quality operating systems, &os; publishes Security Advisories. These advisories are usually mailed to the security lists and noted in the Errata only after the appropriate releases have been patched. This section will work to explain what an advisory is, how to understand it, and what measures to take in order to patch a system. What does an advisory look like? The &os; security advisories look similar to the one below, taken from the &a.security-notifications.name; mailing list. ============================================================================= &os;-SA-XX:XX.UTIL Security Advisory The &os; Project Topic: denial of service due to some problem Category: core Module: sys Announced: 2003-09-23 Credits: Person@EMAIL-ADDRESS Affects: All releases of &os; &os; 4-STABLE prior to the correction date Corrected: 2003-09-23 16:42:59 UTC (RELENG_4, 4.9-PRERELEASE) 2003-09-23 20:08:42 UTC (RELENG_5_1, 5.1-RELEASE-p6) 2003-09-23 20:07:06 UTC (RELENG_5_0, 5.0-RELEASE-p15) 2003-09-23 16:44:58 UTC (RELENG_4_8, 4.8-RELEASE-p8) 2003-09-23 16:47:34 UTC (RELENG_4_7, 4.7-RELEASE-p18) 2003-09-23 16:49:46 UTC (RELENG_4_6, 4.6-RELEASE-p21) 2003-09-23 16:51:24 UTC (RELENG_4_5, 4.5-RELEASE-p33) 2003-09-23 16:52:45 UTC (RELENG_4_4, 4.4-RELEASE-p43) 2003-09-23 16:54:39 UTC (RELENG_4_3, 4.3-RELEASE-p39) &os; only: NO For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit http://www.FreeBSD.org/security/. I. Background II. Problem Description III. Impact IV. Workaround V. Solution VI. Correction details VII. References The Topic field indicates exactly what the problem is. It is basically an introduction to the current security advisory and notes the utility with the vulnerability. The Category refers to the affected part of the system which may be one of core, contrib, or ports. The core category means that the vulnerability affects a core component of the &os; operating system. The contrib category means that the vulnerability affects software contributed to the &os; Project, such as sendmail. Finally the ports category indicates that the vulnerability affects add on software available as part of the Ports Collection. The Module field refers to the component location, for instance sys. In this example, we see that the module, sys, is affected; therefore, this vulnerability affects a component used within the kernel. The Announced field reflects the date said security advisory was published, or announced to the world. This means that the security team has verified that the problem does exist and that a patch has been committed to the &os; source code repository. The Credits field gives credit to the individual or organization who noticed the vulnerability and reported it. The Affects field explains which releases of &os; are affected by this vulnerability. For the kernel, a quick look over the output from ident on the affected files will help in determining the revision. For ports, the version number is listed after the port name in /var/db/pkg. If the system does not sync with the &os; CVS repository and rebuild daily, chances are that it is affected. The Corrected field indicates the date, time, time offset, and release that was corrected. The &os; only field indicates whether this vulnerability affects just &os;, or if it affects other operating systems as well. The Background field gives information on exactly what the affected utility is. Most of the time this is why the utility exists in &os;, what it is used for, and a bit of information on how the utility came to be. The Problem Description field explains the security hole in depth. This can include information on flawed code, or even how the utility could be maliciously used to open a security hole. The Impact field describes what type of impact the problem could have on a system. For example, this could be anything from a denial of service attack, to extra privileges available to users, or even giving the attacker superuser access. The Workaround field offers a feasible workaround to system administrators who may be incapable of upgrading the system. This may be due to time constraints, network availability, or a slew of other reasons. Regardless, security should not be taken lightly, and an affected system should either be patched or the security hole workaround should be implemented. The Solution field offers instructions on patching the affected system. This is a step by step tested and verified method for getting a system patched and working securely. The Correction Details field displays the CVS branch or release name with the periods changed to underscore characters. It also shows the revision number of the affected files within each branch. The References field usually offers sources of other information. This can included web URLs, books, mailing lists, and newsgroups. + + + + + + Tom + Rhodes + Contributed by + + + + + Process Accounting + + Process Accounting + + Process accounting is a security method in which an + administrator may keep track of system resources used, + their allocation among users, provide for system monitoring, + and minimally track a user's commands. + + This indeed has its own positive and negative points. One of + the positives is that an intrusion may be narrowed down + to the point of entry. A negative is the amount of logs + generated by process accounting, and the disk space they may + require. This section will walk an administrator through + the basics of process accounting. + + + Enable and Utilizing Process Accounting + Before making use of process accounting, an administrator + must be enabled. To do this, execute the following + commands: + + &prompt.root; touch + /var/account/acct + + &prompt.root; accton + /var/account/acct + + &prompt.root; echo 'accounting_enable="YES"' + >> /etc/rc.conf + + Once enabled, accounting will begin to track + CPU stats, commands, etc. All accounting + logs are in a non-human readable format and may be viewed + using the &man.sa.8; utility. If issued without any options, + sa will print information relating to the + number of per user calls, the total elapsed time in minutes, + total CPU and user time in minutes, average + number of I/O operations, etc. + + To view information about commands being issued, one + would use the &man.lastcomm.1; utility. The + lastcomm may be used to print out commands + issued by users on specific &man.ttys.5;, for example: + + &prompt.root; lastcomm ls + trhodes ttyp1 + + Would print out all known usage of the ls + by trhodes on the ttyp1 terminal. + + Many other useful options exist and are explained in the + &man.lastcomm.1;, &man.acct.5; and &man.sa.8; manual + pages. + + -