packet.c
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packet.c
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	/*
	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	* All rights reserved
	* This file contains code implementing the packet protocol and communication
	* with the other side. This same code is used both on client and server side.
	*
	* As far as I am concerned, the code I have written for this software
	* can be used freely for any purpose. Any derived versions of this
	* software must be clearly marked as such, and if the derived work is
	* incompatible with the protocol description in the RFC file, it must be
	* called by a name other than "ssh" or "Secure Shell".
	*
	*
	* SSH2 packet format added by Markus Friedl.
	* Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "includes.h"
	RCSID("$OpenBSD: packet.c,v 1.104 2003/04/01 10:22:21 markus Exp $");

	#include "xmalloc.h"
	#include "buffer.h"
	#include "packet.h"
	#include "bufaux.h"
	#include "crc32.h"
	#include "getput.h"

	#include "compress.h"
	#include "deattack.h"
	#include "channels.h"

	#include "compat.h"
	#include "ssh1.h"
	#include "ssh2.h"

	#include "cipher.h"
	#include "kex.h"
	#include "mac.h"
	#include "log.h"
	#include "canohost.h"
	#include "misc.h"
	#include "ssh.h"

	#ifdef PACKET_DEBUG
	#define DBG(x) x
	#else
	#define DBG(x)
	#endif

	/*
	* This variable contains the file descriptors used for communicating with
	* the other side. connection_in is used for reading; connection_out for
	* writing. These can be the same descriptor, in which case it is assumed to
	* be a socket.
	*/
	static int connection_in = -1;
	static int connection_out = -1;

	/* Protocol flags for the remote side. */
	static u_int remote_protocol_flags = 0;

	/* Encryption context for receiving data. This is only used for decryption. */
	static CipherContext receive_context;

	/* Encryption context for sending data. This is only used for encryption. */
	static CipherContext send_context;

	/* Buffer for raw input data from the socket. */
	Buffer input;

	/* Buffer for raw output data going to the socket. */
	Buffer output;

	/* Buffer for the partial outgoing packet being constructed. */
	static Buffer outgoing_packet;

	/* Buffer for the incoming packet currently being processed. */
	static Buffer incoming_packet;

	/* Scratch buffer for packet compression/decompression. */
	static Buffer compression_buffer;
	static int compression_buffer_ready = 0;

	/* Flag indicating whether packet compression/decompression is enabled. */
	static int packet_compression = 0;

	/* default maximum packet size */
	int max_packet_size = 32768;

	/* Flag indicating whether this module has been initialized. */
	static int initialized = 0;

	/* Set to true if the connection is interactive. */
	static int interactive_mode = 0;

	/* Session key information for Encryption and MAC */
	Newkeys *newkeys[MODE_MAX];
	static u_int32_t read_seqnr = 0;
	static u_int32_t send_seqnr = 0;

	/* Session key for protocol v1 */
	static u_char ssh1_key[SSH_SESSION_KEY_LENGTH];
	static u_int ssh1_keylen;

	/* roundup current message to extra_pad bytes */
	static u_char extra_pad = 0;

	/*
	* Sets the descriptors used for communication. Disables encryption until
	* packet_set_encryption_key is called.
	*/
	void
	packet_set_connection(int fd_in, int fd_out)
	{
	Cipher *none = cipher_by_name("none");

	if (none == NULL)
	fatal("packet_set_connection: cannot load cipher 'none'");
	connection_in = fd_in;
	connection_out = fd_out;
	cipher_init(&send_context, none, "", 0, NULL, 0, CIPHER_ENCRYPT);
	cipher_init(&receive_context, none, "", 0, NULL, 0, CIPHER_DECRYPT);
	newkeys[MODE_IN] = newkeys[MODE_OUT] = NULL;
	if (!initialized) {
	initialized = 1;
	buffer_init(&input);
	buffer_init(&output);
	buffer_init(&outgoing_packet);
	buffer_init(&incoming_packet);
	}
	/* Kludge: arrange the close function to be called from fatal(). */
	fatal_add_cleanup((void () (void )) packet_close, NULL);
	}

	/* Returns 1 if remote host is connected via socket, 0 if not. */

	int
	packet_connection_is_on_socket(void)
	{
	struct sockaddr_storage from, to;
	socklen_t fromlen, tolen;

	/* filedescriptors in and out are the same, so it's a socket */
	if (connection_in == connection_out)
	return 1;
	fromlen = sizeof(from);
	memset(&from, 0, sizeof(from));
	if (getpeername(connection_in, (struct sockaddr *)&from, &fromlen) < 0)
	return 0;
	tolen = sizeof(to);
	memset(&to, 0, sizeof(to));
	if (getpeername(connection_out, (struct sockaddr *)&to, &tolen) < 0)
	return 0;
	if (fromlen != tolen \|\| memcmp(&from, &to, fromlen) != 0)
	return 0;
	if (from.ss_family != AF_INET && from.ss_family != AF_INET6)
	return 0;
	return 1;
	}

	/*
	* Exports an IV from the CipherContext required to export the key
	* state back from the unprivileged child to the privileged parent
	* process.
	*/

	void
	packet_get_keyiv(int mode, u_char *iv, u_int len)
	{
	CipherContext *cc;

	if (mode == MODE_OUT)
	cc = &send_context;
	else
	cc = &receive_context;

	cipher_get_keyiv(cc, iv, len);
	}

	int
	packet_get_keycontext(int mode, u_char *dat)
	{
	CipherContext *cc;

	if (mode == MODE_OUT)
	cc = &send_context;
	else
	cc = &receive_context;

	return (cipher_get_keycontext(cc, dat));
	}

	void
	packet_set_keycontext(int mode, u_char *dat)
	{
	CipherContext *cc;

	if (mode == MODE_OUT)
	cc = &send_context;
	else
	cc = &receive_context;

	cipher_set_keycontext(cc, dat);
	}

	int
	packet_get_keyiv_len(int mode)
	{
	CipherContext *cc;

	if (mode == MODE_OUT)
	cc = &send_context;
	else
	cc = &receive_context;

	return (cipher_get_keyiv_len(cc));
	}
	void
	packet_set_iv(int mode, u_char *dat)
	{
	CipherContext *cc;

	if (mode == MODE_OUT)
	cc = &send_context;
	else
	cc = &receive_context;

	cipher_set_keyiv(cc, dat);
	}
	int
	packet_get_ssh1_cipher()
	{
	return (cipher_get_number(receive_context.cipher));
	}


	u_int32_t
	packet_get_seqnr(int mode)
	{
	return (mode == MODE_IN ? read_seqnr : send_seqnr);
	}

	void
	packet_set_seqnr(int mode, u_int32_t seqnr)
	{
	if (mode == MODE_IN)
	read_seqnr = seqnr;
	else if (mode == MODE_OUT)
	send_seqnr = seqnr;
	else
	fatal("packet_set_seqnr: bad mode %d", mode);
	}

	/* returns 1 if connection is via ipv4 */

	int
	packet_connection_is_ipv4(void)
	{
	struct sockaddr_storage to;
	socklen_t tolen = sizeof(to);

	memset(&to, 0, sizeof(to));
	if (getsockname(connection_out, (struct sockaddr *)&to, &tolen) < 0)
	return 0;
	if (to.ss_family == AF_INET)
	return 1;
	#ifdef IPV4_IN_IPV6
	if (to.ss_family == AF_INET6 &&
	IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)&to)->sin6_addr))
	return 1;
	#endif
	return 0;
	}

	/* Sets the connection into non-blocking mode. */

	void
	packet_set_nonblocking(void)
	{
	/* Set the socket into non-blocking mode. */
	if (fcntl(connection_in, F_SETFL, O_NONBLOCK) < 0)
	error("fcntl O_NONBLOCK: %.100s", strerror(errno));

	if (connection_out != connection_in) {
	if (fcntl(connection_out, F_SETFL, O_NONBLOCK) < 0)
	error("fcntl O_NONBLOCK: %.100s", strerror(errno));
	}
	}

	/* Returns the socket used for reading. */

	int
	packet_get_connection_in(void)
	{
	return connection_in;
	}

	/* Returns the descriptor used for writing. */

	int
	packet_get_connection_out(void)
	{
	return connection_out;
	}

	/* Closes the connection and clears and frees internal data structures. */

	void
	packet_close(void)
	{
	if (!initialized)
	return;
	initialized = 0;
	if (connection_in == connection_out) {
	shutdown(connection_out, SHUT_RDWR);
	close(connection_out);
	} else {
	close(connection_in);
	close(connection_out);
	}
	buffer_free(&input);
	buffer_free(&output);
	buffer_free(&outgoing_packet);
	buffer_free(&incoming_packet);
	if (compression_buffer_ready) {
	buffer_free(&compression_buffer);
	buffer_compress_uninit();
	}
	cipher_cleanup(&send_context);
	cipher_cleanup(&receive_context);
	}

	/* Sets remote side protocol flags. */

	void
	packet_set_protocol_flags(u_int protocol_flags)
	{
	remote_protocol_flags = protocol_flags;
	}

	/* Returns the remote protocol flags set earlier by the above function. */

	u_int
	packet_get_protocol_flags(void)
	{
	return remote_protocol_flags;
	}

	/*
	* Starts packet compression from the next packet on in both directions.
	* Level is compression level 1 (fastest) - 9 (slow, best) as in gzip.
	*/

	static void
	packet_init_compression(void)
	{
	if (compression_buffer_ready == 1)
	return;
	compression_buffer_ready = 1;
	buffer_init(&compression_buffer);
	}

	void
	packet_start_compression(int level)
	{
	if (packet_compression && !compat20)
	fatal("Compression already enabled.");
	packet_compression = 1;
	packet_init_compression();
	buffer_compress_init_send(level);
	buffer_compress_init_recv();
	}

	/*
	* Causes any further packets to be encrypted using the given key. The same
	* key is used for both sending and reception. However, both directions are
	* encrypted independently of each other.
	*/

	void
	packet_set_encryption_key(const u_char *key, u_int keylen,
	int number)
	{
	Cipher *cipher = cipher_by_number(number);

	if (cipher == NULL)
	fatal("packet_set_encryption_key: unknown cipher number %d", number);
	if (keylen < 20)
	fatal("packet_set_encryption_key: keylen too small: %d", keylen);
	if (keylen > SSH_SESSION_KEY_LENGTH)
	fatal("packet_set_encryption_key: keylen too big: %d", keylen);
	memcpy(ssh1_key, key, keylen);
	ssh1_keylen = keylen;
	cipher_init(&send_context, cipher, key, keylen, NULL, 0, CIPHER_ENCRYPT);
	cipher_init(&receive_context, cipher, key, keylen, NULL, 0, CIPHER_DECRYPT);
	}

	u_int
	packet_get_encryption_key(u_char *key)
	{
	if (key == NULL)
	return (ssh1_keylen);
	memcpy(key, ssh1_key, ssh1_keylen);
	return (ssh1_keylen);
	}

	/* Start constructing a packet to send. */
	void
	packet_start(u_char type)
	{
	u_char buf[9];
	int len;

	DBG(debug("packet_start[%d]", type));
	len = compat20 ? 6 : 9;
	memset(buf, 0, len - 1);
	buf[len - 1] = type;
	buffer_clear(&outgoing_packet);
	buffer_append(&outgoing_packet, buf, len);
	}

	/* Append payload. */
	void
	packet_put_char(int value)
	{
	char ch = value;

	buffer_append(&outgoing_packet, &ch, 1);
	}
	void
	packet_put_int(u_int value)
	{
	buffer_put_int(&outgoing_packet, value);
	}
	void
	packet_put_string(const void *buf, u_int len)
	{
	buffer_put_string(&outgoing_packet, buf, len);
	}
	void
	packet_put_cstring(const char *str)
	{
	buffer_put_cstring(&outgoing_packet, str);
	}
	void
	packet_put_raw(const void *buf, u_int len)
	{
	buffer_append(&outgoing_packet, buf, len);
	}
	void
	packet_put_bignum(BIGNUM * value)
	{
	buffer_put_bignum(&outgoing_packet, value);
	}
	void
	packet_put_bignum2(BIGNUM * value)
	{
	buffer_put_bignum2(&outgoing_packet, value);
	}

	/*
	* Finalizes and sends the packet. If the encryption key has been set,
	* encrypts the packet before sending.
	*/

	static void
	packet_send1(void)
	{
	u_char buf[8], *cp;
	int i, padding, len;
	u_int checksum;
	u_int32_t rand = 0;

	/*
	* If using packet compression, compress the payload of the outgoing
	* packet.
	*/
	if (packet_compression) {
	buffer_clear(&compression_buffer);
	/* Skip padding. */
	buffer_consume(&outgoing_packet, 8);
	/* padding */
	buffer_append(&compression_buffer, "\0\0\0\0\0\0\0\0", 8);
	buffer_compress(&outgoing_packet, &compression_buffer);
	buffer_clear(&outgoing_packet);
	buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
	buffer_len(&compression_buffer));
	}
	/* Compute packet length without padding (add checksum, remove padding). */
	len = buffer_len(&outgoing_packet) + 4 - 8;

	/* Insert padding. Initialized to zero in packet_start1() */
	padding = 8 - len % 8;
	if (!send_context.plaintext) {
	cp = buffer_ptr(&outgoing_packet);
	for (i = 0; i < padding; i++) {
	if (i % 4 == 0)
	rand = arc4random();
	cp[7 - i] = rand & 0xff;
	rand >>= 8;
	}
	}
	buffer_consume(&outgoing_packet, 8 - padding);

	/* Add check bytes. */
	checksum = ssh_crc32(buffer_ptr(&outgoing_packet),
	buffer_len(&outgoing_packet));
	PUT_32BIT(buf, checksum);
	buffer_append(&outgoing_packet, buf, 4);

	#ifdef PACKET_DEBUG
	fprintf(stderr, "packet_send plain: ");
	buffer_dump(&outgoing_packet);
	#endif

	/* Append to output. */
	PUT_32BIT(buf, len);
	buffer_append(&output, buf, 4);
	cp = buffer_append_space(&output, buffer_len(&outgoing_packet));
	cipher_crypt(&send_context, cp, buffer_ptr(&outgoing_packet),
	buffer_len(&outgoing_packet));

	#ifdef PACKET_DEBUG
	fprintf(stderr, "encrypted: ");
	buffer_dump(&output);
	#endif

	buffer_clear(&outgoing_packet);

	/*
	* Note that the packet is now only buffered in output. It won\'t be
	* actually sent until packet_write_wait or packet_write_poll is
	* called.
	*/
	}

	void
	set_newkeys(int mode)
	{
	Enc *enc;
	Mac *mac;
	Comp *comp;
	CipherContext *cc;
	int encrypt;

	debug2("set_newkeys: mode %d", mode);

	if (mode == MODE_OUT) {
	cc = &send_context;
	encrypt = CIPHER_ENCRYPT;
	} else {
	cc = &receive_context;
	encrypt = CIPHER_DECRYPT;
	}
	if (newkeys[mode] != NULL) {
	debug("set_newkeys: rekeying");
	cipher_cleanup(cc);
	enc = &newkeys[mode]->enc;
	mac = &newkeys[mode]->mac;
	comp = &newkeys[mode]->comp;
	memset(mac->key, 0, mac->key_len);
	xfree(enc->name);
	xfree(enc->iv);
	xfree(enc->key);
	xfree(mac->name);
	xfree(mac->key);
	xfree(comp->name);
	xfree(newkeys[mode]);
	}
	newkeys[mode] = kex_get_newkeys(mode);
	if (newkeys[mode] == NULL)
	fatal("newkeys: no keys for mode %d", mode);
	enc = &newkeys[mode]->enc;
	mac = &newkeys[mode]->mac;
	comp = &newkeys[mode]->comp;
	if (mac->md != NULL)
	mac->enabled = 1;
	DBG(debug("cipher_init_context: %d", mode));
	cipher_init(cc, enc->cipher, enc->key, enc->key_len,
	enc->iv, enc->block_size, encrypt);
	/* Deleting the keys does not gain extra security */
	/* memset(enc->iv, 0, enc->block_size);
	memset(enc->key, 0, enc->key_len); */
	if (comp->type != 0 && comp->enabled == 0) {
	packet_init_compression();
	if (mode == MODE_OUT)
	buffer_compress_init_send(6);
	else
	buffer_compress_init_recv();
	comp->enabled = 1;
	}
	}

	/*
	* Finalize packet in SSH2 format (compress, mac, encrypt, enqueue)
	*/
	static void
	packet_send2(void)
	{
	u_char type, cp, macbuf = NULL;
	u_char padlen, pad;
	u_int packet_length = 0;
	u_int i, len;
	u_int32_t rand = 0;
	Enc *enc = NULL;
	Mac *mac = NULL;
	Comp *comp = NULL;
	int block_size;

	if (newkeys[MODE_OUT] != NULL) {
	enc = &newkeys[MODE_OUT]->enc;
	mac = &newkeys[MODE_OUT]->mac;
	comp = &newkeys[MODE_OUT]->comp;
	}
	block_size = enc ? enc->block_size : 8;

	cp = buffer_ptr(&outgoing_packet);
	type = cp[5];

	#ifdef PACKET_DEBUG
	fprintf(stderr, "plain: ");
	buffer_dump(&outgoing_packet);
	#endif

	if (comp && comp->enabled) {
	len = buffer_len(&outgoing_packet);
	/* skip header, compress only payload */
	buffer_consume(&outgoing_packet, 5);
	buffer_clear(&compression_buffer);
	buffer_compress(&outgoing_packet, &compression_buffer);
	buffer_clear(&outgoing_packet);
	buffer_append(&outgoing_packet, "\0\0\0\0\0", 5);
	buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
	buffer_len(&compression_buffer));
	DBG(debug("compression: raw %d compressed %d", len,
	buffer_len(&outgoing_packet)));
	}

	/* sizeof (packet_len + pad_len + payload) */
	len = buffer_len(&outgoing_packet);

	/*
	* calc size of padding, alloc space, get random data,
	* minimum padding is 4 bytes
	*/
	padlen = block_size - (len % block_size);
	if (padlen < 4)
	padlen += block_size;
	if (extra_pad) {
	/* will wrap if extra_pad+padlen > 255 */
	extra_pad = roundup(extra_pad, block_size);
	pad = extra_pad - ((len + padlen) % extra_pad);
	debug3("packet_send2: adding %d (len %d padlen %d extra_pad %d)",
	pad, len, padlen, extra_pad);
	padlen += pad;
	extra_pad = 0;
	}
	cp = buffer_append_space(&outgoing_packet, padlen);
	if (enc && !send_context.plaintext) {
	/* random padding */
	for (i = 0; i < padlen; i++) {
	if (i % 4 == 0)
	rand = arc4random();
	cp[i] = rand & 0xff;
	rand >>= 8;
	}
	} else {
	/* clear padding */
	memset(cp, 0, padlen);
	}
	/* packet_length includes payload, padding and padding length field */
	packet_length = buffer_len(&outgoing_packet) - 4;
	cp = buffer_ptr(&outgoing_packet);
	PUT_32BIT(cp, packet_length);
	cp[4] = padlen;
	DBG(debug("send: len %d (includes padlen %d)", packet_length+4, padlen));

	/* compute MAC over seqnr and packet(length fields, payload, padding) */
	if (mac && mac->enabled) {
	macbuf = mac_compute(mac, send_seqnr,
	buffer_ptr(&outgoing_packet),
	buffer_len(&outgoing_packet));
	DBG(debug("done calc MAC out #%d", send_seqnr));
	}
	/* encrypt packet and append to output buffer. */
	cp = buffer_append_space(&output, buffer_len(&outgoing_packet));
	cipher_crypt(&send_context, cp, buffer_ptr(&outgoing_packet),
	buffer_len(&outgoing_packet));
	/* append unencrypted MAC */
	if (mac && mac->enabled)
	buffer_append(&output, (char *)macbuf, mac->mac_len);
	#ifdef PACKET_DEBUG
	fprintf(stderr, "encrypted: ");
	buffer_dump(&output);
	#endif
	/* increment sequence number for outgoing packets */
	if (++send_seqnr == 0)
	log("outgoing seqnr wraps around");
	buffer_clear(&outgoing_packet);

	if (type == SSH2_MSG_NEWKEYS)
	set_newkeys(MODE_OUT);
	}

	void
	packet_send(void)
	{
	if (compat20)
	packet_send2();
	else
	packet_send1();
	DBG(debug("packet_send done"));
	}

	/*
	* Waits until a packet has been received, and returns its type. Note that
	* no other data is processed until this returns, so this function should not
	* be used during the interactive session.
	*/

	int
	packet_read_seqnr(u_int32_t *seqnr_p)
	{
	int type, len;
	fd_set *setp;
	char buf[8192];
	DBG(debug("packet_read()"));

	setp = (fd_set )xmalloc(howmany(connection_in+1, NFDBITS)
	sizeof(fd_mask));

	/* Since we are blocking, ensure that all written packets have been sent. */
	packet_write_wait();

	/* Stay in the loop until we have received a complete packet. */
	for (;;) {
	/* Try to read a packet from the buffer. */
	type = packet_read_poll_seqnr(seqnr_p);
	if (!compat20 && (
	type == SSH_SMSG_SUCCESS
	\|\| type == SSH_SMSG_FAILURE
	\|\| type == SSH_CMSG_EOF
	\|\| type == SSH_CMSG_EXIT_CONFIRMATION))
	packet_check_eom();
	/* If we got a packet, return it. */
	if (type != SSH_MSG_NONE) {
	xfree(setp);
	return type;
	}
	/*
	* Otherwise, wait for some data to arrive, add it to the
	* buffer, and try again.
	*/
	memset(setp, 0, howmany(connection_in + 1, NFDBITS) *
	sizeof(fd_mask));
	FD_SET(connection_in, setp);

	/* Wait for some data to arrive. */
	while (select(connection_in + 1, setp, NULL, NULL, NULL) == -1 &&
	(errno == EAGAIN \|\| errno == EINTR))
	;

	/* Read data from the socket. */
	len = read(connection_in, buf, sizeof(buf));
	if (len == 0) {
	log("Connection closed by %.200s", get_remote_ipaddr());
	fatal_cleanup();
	}
	if (len < 0)
	fatal("Read from socket failed: %.100s", strerror(errno));
	/* Append it to the buffer. */
	packet_process_incoming(buf, len);
	}
	/* NOTREACHED */
	}

	int
	packet_read(void)
	{
	return packet_read_seqnr(NULL);
	}

	/*
	* Waits until a packet has been received, verifies that its type matches
	* that given, and gives a fatal error and exits if there is a mismatch.
	*/

	void
	packet_read_expect(int expected_type)
	{
	int type;

	type = packet_read();
	if (type != expected_type)
	packet_disconnect("Protocol error: expected packet type %d, got %d",
	expected_type, type);
	}

	/* Checks if a full packet is available in the data received so far via
	* packet_process_incoming. If so, reads the packet; otherwise returns
	* SSH_MSG_NONE. This does not wait for data from the connection.
	*
	* SSH_MSG_DISCONNECT is handled specially here. Also,
	* SSH_MSG_IGNORE messages are skipped by this function and are never returned
	* to higher levels.
	*/

	static int
	packet_read_poll1(void)
	{
	u_int len, padded_len;
	u_char *cp, type;
	u_int checksum, stored_checksum;

	/* Check if input size is less than minimum packet size. */
	if (buffer_len(&input) < 4 + 8)
	return SSH_MSG_NONE;
	/* Get length of incoming packet. */
	cp = buffer_ptr(&input);
	len = GET_32BIT(cp);
	if (len < 1 + 2 + 2 \|\| len > 256 * 1024)
	packet_disconnect("Bad packet length %u.", len);
	padded_len = (len + 8) & ~7;

	/* Check if the packet has been entirely received. */
	if (buffer_len(&input) < 4 + padded_len)
	return SSH_MSG_NONE;

	/* The entire packet is in buffer. */

	/* Consume packet length. */
	buffer_consume(&input, 4);

	/*
	* Cryptographic attack detector for ssh
	* (C)1998 CORE-SDI, Buenos Aires Argentina
	* Ariel Futoransky(futo@core-sdi.com)
	*/
	if (!receive_context.plaintext &&
	detect_attack(buffer_ptr(&input), padded_len, NULL) == DEATTACK_DETECTED)
	packet_disconnect("crc32 compensation attack: network attack detected");

	/* Decrypt data to incoming_packet. */
	buffer_clear(&incoming_packet);
	cp = buffer_append_space(&incoming_packet, padded_len);
	cipher_crypt(&receive_context, cp, buffer_ptr(&input), padded_len);

	buffer_consume(&input, padded_len);

	#ifdef PACKET_DEBUG
	fprintf(stderr, "read_poll plain: ");
	buffer_dump(&incoming_packet);
	#endif

	/* Compute packet checksum. */
	checksum = ssh_crc32(buffer_ptr(&incoming_packet),
	buffer_len(&incoming_packet) - 4);

	/* Skip padding. */
	buffer_consume(&incoming_packet, 8 - len % 8);

	/* Test check bytes. */
	if (len != buffer_len(&incoming_packet))
	packet_disconnect("packet_read_poll1: len %d != buffer_len %d.",
	len, buffer_len(&incoming_packet));

	cp = (u_char *)buffer_ptr(&incoming_packet) + len - 4;
	stored_checksum = GET_32BIT(cp);
	if (checksum != stored_checksum)
	packet_disconnect("Corrupted check bytes on input.");
	buffer_consume_end(&incoming_packet, 4);

	if (packet_compression) {
	buffer_clear(&compression_buffer);
	buffer_uncompress(&incoming_packet, &compression_buffer);
	buffer_clear(&incoming_packet);
	buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
	buffer_len(&compression_buffer));
	}
	type = buffer_get_char(&incoming_packet);
	return type;
	}

	static int
	packet_read_poll2(u_int32_t *seqnr_p)
	{
	static u_int packet_length = 0;
	u_int padlen, need;
	u_char macbuf, cp, type;
	int maclen, block_size;
	Enc *enc = NULL;
	Mac *mac = NULL;
	Comp *comp = NULL;

	if (newkeys[MODE_IN] != NULL) {
	enc = &newkeys[MODE_IN]->enc;
	mac = &newkeys[MODE_IN]->mac;
	comp = &newkeys[MODE_IN]->comp;
	}
	maclen = mac && mac->enabled ? mac->mac_len : 0;
	block_size = enc ? enc->block_size : 8;

	if (packet_length == 0) {
	/*
	* check if input size is less than the cipher block size,
	* decrypt first block and extract length of incoming packet
	*/
	if (buffer_len(&input) < block_size)
	return SSH_MSG_NONE;
	buffer_clear(&incoming_packet);
	cp = buffer_append_space(&incoming_packet, block_size);
	cipher_crypt(&receive_context, cp, buffer_ptr(&input),
	block_size);
	cp = buffer_ptr(&incoming_packet);
	packet_length = GET_32BIT(cp);
	if (packet_length < 1 + 4 \|\| packet_length > 256 * 1024) {
	buffer_dump(&incoming_packet);
	packet_disconnect("Bad packet length %u.", packet_length);
	}
	DBG(debug("input: packet len %u", packet_length+4));
	buffer_consume(&input, block_size);
	}
	/* we have a partial packet of block_size bytes */
	need = 4 + packet_length - block_size;
	DBG(debug("partial packet %d, need %d, maclen %d", block_size,
	need, maclen));
	if (need % block_size != 0)
	fatal("padding error: need %d block %d mod %d",
	need, block_size, need % block_size);
	/*
	* check if the entire packet has been received and
	* decrypt into incoming_packet
	*/
	if (buffer_len(&input) < need + maclen)
	return SSH_MSG_NONE;
	#ifdef PACKET_DEBUG
	fprintf(stderr, "read_poll enc/full: ");
	buffer_dump(&input);
	#endif
	cp = buffer_append_space(&incoming_packet, need);
	cipher_crypt(&receive_context, cp, buffer_ptr(&input), need);
	buffer_consume(&input, need);
	/*
	* compute MAC over seqnr and packet,
	* increment sequence number for incoming packet
	*/
	if (mac && mac->enabled) {
	macbuf = mac_compute(mac, read_seqnr,
	buffer_ptr(&incoming_packet),
	buffer_len(&incoming_packet));
	if (memcmp(macbuf, buffer_ptr(&input), mac->mac_len) != 0)
	packet_disconnect("Corrupted MAC on input.");
	DBG(debug("MAC #%d ok", read_seqnr));
	buffer_consume(&input, mac->mac_len);
	}
	if (seqnr_p != NULL)
	*seqnr_p = read_seqnr;
	if (++read_seqnr == 0)
	log("incoming seqnr wraps around");

	/* get padlen */
	cp = buffer_ptr(&incoming_packet);
	padlen = cp[4];
	DBG(debug("input: padlen %d", padlen));
	if (padlen < 4)
	packet_disconnect("Corrupted padlen %d on input.", padlen);

	/* skip packet size + padlen, discard padding */
	buffer_consume(&incoming_packet, 4 + 1);
	buffer_consume_end(&incoming_packet, padlen);

	DBG(debug("input: len before de-compress %d", buffer_len(&incoming_packet)));
	if (comp && comp->enabled) {
	buffer_clear(&compression_buffer);
	buffer_uncompress(&incoming_packet, &compression_buffer);
	buffer_clear(&incoming_packet);
	buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
	buffer_len(&compression_buffer));
	DBG(debug("input: len after de-compress %d",
	buffer_len(&incoming_packet)));
	}
	/*
	* get packet type, implies consume.
	* return length of payload (without type field)
	*/
	type = buffer_get_char(&incoming_packet);
	if (type == SSH2_MSG_NEWKEYS)
	set_newkeys(MODE_IN);
	#ifdef PACKET_DEBUG
	fprintf(stderr, "read/plain[%d]:\r\n", type);
	buffer_dump(&incoming_packet);
	#endif
	/* reset for next packet */
	packet_length = 0;
	return type;
	}

	int
	packet_read_poll_seqnr(u_int32_t *seqnr_p)
	{
	u_int reason, seqnr;
	u_char type;
	char *msg;

	for (;;) {
	if (compat20) {
	type = packet_read_poll2(seqnr_p);
	if (type)
	DBG(debug("received packet type %d", type));
	switch (type) {
	case SSH2_MSG_IGNORE:
	break;
	case SSH2_MSG_DEBUG:
	packet_get_char();
	msg = packet_get_string(NULL);
	debug("Remote: %.900s", msg);
	xfree(msg);
	msg = packet_get_string(NULL);
	xfree(msg);
	break;
	case SSH2_MSG_DISCONNECT:
	reason = packet_get_int();
	msg = packet_get_string(NULL);
	log("Received disconnect from %s: %u: %.400s",
	get_remote_ipaddr(), reason, msg);
	xfree(msg);
	fatal_cleanup();
	break;
	case SSH2_MSG_UNIMPLEMENTED:
	seqnr = packet_get_int();
	debug("Received SSH2_MSG_UNIMPLEMENTED for %u",
	seqnr);
	break;
	default:
	return type;
	break;
	}
	} else {
	type = packet_read_poll1();
	switch (type) {
	case SSH_MSG_IGNORE:
	break;
	case SSH_MSG_DEBUG:
	msg = packet_get_string(NULL);
	debug("Remote: %.900s", msg);
	xfree(msg);
	break;
	case SSH_MSG_DISCONNECT:
	msg = packet_get_string(NULL);
	log("Received disconnect from %s: %.400s",
	get_remote_ipaddr(), msg);
	fatal_cleanup();
	xfree(msg);
	break;
	default:
	if (type)
	DBG(debug("received packet type %d", type));
	return type;
	break;
	}
	}
	}
	}

	int
	packet_read_poll(void)
	{
	return packet_read_poll_seqnr(NULL);
	}

	/*
	* Buffers the given amount of input characters. This is intended to be used
	* together with packet_read_poll.
	*/

	void
	packet_process_incoming(const char *buf, u_int len)
	{
	buffer_append(&input, buf, len);
	}

	/* Returns a character from the packet. */

	u_int
	packet_get_char(void)
	{
	char ch;

	buffer_get(&incoming_packet, &ch, 1);
	return (u_char) ch;
	}

	/* Returns an integer from the packet data. */

	u_int
	packet_get_int(void)
	{
	return buffer_get_int(&incoming_packet);
	}

	/*
	* Returns an arbitrary precision integer from the packet data. The integer
	* must have been initialized before this call.
	*/

	void
	packet_get_bignum(BIGNUM * value)
	{
	buffer_get_bignum(&incoming_packet, value);
	}

	void
	packet_get_bignum2(BIGNUM * value)
	{
	buffer_get_bignum2(&incoming_packet, value);
	}

	void *
	packet_get_raw(int *length_ptr)
	{
	int bytes = buffer_len(&incoming_packet);

	if (length_ptr != NULL)
	*length_ptr = bytes;
	return buffer_ptr(&incoming_packet);
	}

	int
	packet_remaining(void)
	{
	return buffer_len(&incoming_packet);
	}

	/*
	* Returns a string from the packet data. The string is allocated using
	* xmalloc; it is the responsibility of the calling program to free it when
	* no longer needed. The length_ptr argument may be NULL, or point to an
	* integer into which the length of the string is stored.
	*/

	void *
	packet_get_string(u_int *length_ptr)
	{
	return buffer_get_string(&incoming_packet, length_ptr);
	}

	/*
	* Sends a diagnostic message from the server to the client. This message
	* can be sent at any time (but not while constructing another message). The
	* message is printed immediately, but only if the client is being executed
	* in verbose mode. These messages are primarily intended to ease debugging
	* authentication problems. The length of the formatted message must not
	* exceed 1024 bytes. This will automatically call packet_write_wait.
	*/

	void
	packet_send_debug(const char *fmt,...)
	{
	char buf[1024];
	va_list args;

	if (compat20 && (datafellows & SSH_BUG_DEBUG))
	return;

	va_start(args, fmt);
	vsnprintf(buf, sizeof(buf), fmt, args);
	va_end(args);

	if (compat20) {
	packet_start(SSH2_MSG_DEBUG);
	packet_put_char(0); /* bool: always display */
	packet_put_cstring(buf);
	packet_put_cstring("");
	} else {
	packet_start(SSH_MSG_DEBUG);
	packet_put_cstring(buf);
	}
	packet_send();
	packet_write_wait();
	}

	/*
	* Logs the error plus constructs and sends a disconnect packet, closes the
	* connection, and exits. This function never returns. The error message
	* should not contain a newline. The length of the formatted message must
	* not exceed 1024 bytes.
	*/

	void
	packet_disconnect(const char *fmt,...)
	{
	char buf[1024];
	va_list args;
	static int disconnecting = 0;

	if (disconnecting) /* Guard against recursive invocations. */
	fatal("packet_disconnect called recursively.");
	disconnecting = 1;

	/*
	* Format the message. Note that the caller must make sure the
	* message is of limited size.
	*/
	va_start(args, fmt);
	vsnprintf(buf, sizeof(buf), fmt, args);
	va_end(args);

	/* Display the error locally */
	log("Disconnecting: %.100s", buf);

	/* Send the disconnect message to the other side, and wait for it to get sent. */
	if (compat20) {
	packet_start(SSH2_MSG_DISCONNECT);
	packet_put_int(SSH2_DISCONNECT_PROTOCOL_ERROR);
	packet_put_cstring(buf);
	packet_put_cstring("");
	} else {
	packet_start(SSH_MSG_DISCONNECT);
	packet_put_cstring(buf);
	}
	packet_send();
	packet_write_wait();

	/* Stop listening for connections. */
	channel_close_all();

	/* Close the connection. */
	packet_close();

	fatal_cleanup();
	}

	/* Checks if there is any buffered output, and tries to write some of the output. */

	void
	packet_write_poll(void)
	{
	int len = buffer_len(&output);

	if (len > 0) {
	len = write(connection_out, buffer_ptr(&output), len);
	if (len <= 0) {
	if (errno == EAGAIN)
	return;
	else
	fatal("Write failed: %.100s", strerror(errno));
	}
	buffer_consume(&output, len);
	}
	}

	/*
	* Calls packet_write_poll repeatedly until all pending output data has been
	* written.
	*/

	void
	packet_write_wait(void)
	{
	fd_set *setp;

	setp = (fd_set )xmalloc(howmany(connection_out + 1, NFDBITS)
	sizeof(fd_mask));
	packet_write_poll();
	while (packet_have_data_to_write()) {
	memset(setp, 0, howmany(connection_out + 1, NFDBITS) *
	sizeof(fd_mask));
	FD_SET(connection_out, setp);
	while (select(connection_out + 1, NULL, setp, NULL, NULL) == -1 &&
	(errno == EAGAIN \|\| errno == EINTR))
	;
	packet_write_poll();
	}
	xfree(setp);
	}

	/* Returns true if there is buffered data to write to the connection. */

	int
	packet_have_data_to_write(void)
	{
	return buffer_len(&output) != 0;
	}

	/* Returns true if there is not too much data to write to the connection. */

	int
	packet_not_very_much_data_to_write(void)
	{
	if (interactive_mode)
	return buffer_len(&output) < 16384;
	else
	return buffer_len(&output) < 128 * 1024;
	}

	static void
	packet_set_tos(int interactive)
	{
	int tos = interactive ? IPTOS_LOWDELAY : IPTOS_THROUGHPUT;

	if (!packet_connection_is_on_socket() \|\|
	!packet_connection_is_ipv4())
	return;
	if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, &tos,
	sizeof(tos)) < 0)
	error("setsockopt IP_TOS %d: %.100s:",
	tos, strerror(errno));
	}

	/* Informs that the current session is interactive. Sets IP flags for that. */

	void
	packet_set_interactive(int interactive)
	{
	static int called = 0;

	if (called)
	return;
	called = 1;

	/* Record that we are in interactive mode. */
	interactive_mode = interactive;

	/* Only set socket options if using a socket. */
	if (!packet_connection_is_on_socket())
	if (interactive)
	set_nodelay(connection_in);
	#if defined(IP_TOS) && !defined(IP_TOS_IS_BROKEN)
	packet_set_tos(interactive);
	#endif

	}

	/* Returns true if the current connection is interactive. */

	int
	packet_is_interactive(void)
	{
	return interactive_mode;
	}

	int
	packet_set_maxsize(int s)
	{
	static int called = 0;

	if (called) {
	log("packet_set_maxsize: called twice: old %d new %d",
	max_packet_size, s);
	return -1;
	}
	if (s < 4 * 1024 \|\| s > 1024 * 1024) {
	log("packet_set_maxsize: bad size %d", s);
	return -1;
	}
	called = 1;
	debug("packet_set_maxsize: setting to %d", s);
	max_packet_size = s;
	return s;
	}

	/* roundup current message to pad bytes */
	void
	packet_add_padding(u_char pad)
	{
	extra_pad = pad;
	}

	/*
	* 9.2. Ignored Data Message
	*
	* byte SSH_MSG_IGNORE
	* string data
	*
	* All implementations MUST understand (and ignore) this message at any
	* time (after receiving the protocol version). No implementation is
	* required to send them. This message can be used as an additional
	* protection measure against advanced traffic analysis techniques.
	*/
	void
	packet_send_ignore(int nbytes)
	{
	u_int32_t rand = 0;
	int i;

	packet_start(compat20 ? SSH2_MSG_IGNORE : SSH_MSG_IGNORE);
	packet_put_int(nbytes);
	for (i = 0; i < nbytes; i++) {
	if (i % 4 == 0)
	rand = arc4random();
	packet_put_char(rand & 0xff);
	rand >>= 8;
	}
	}

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