packet.c

OpenSSH 是 SSH （Secure SHell） 协议的免费开源实现。它用安全、加密的网络连接工具代替了 telnet、ftp、 rlogin、rsh 和 rcp 工具。OpenSSH 支持

/*
 * Author: Tatu Ylonen <[e-mail]>
 * Copyright (c) 1995 Tatu Ylonen <[e-mail]>, 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 1.116 2004/10/20 11:48:53 markus Exp $");

#include "openbsd-compat/sys-queue.h"

#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 */
u_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 struct packet_state {
	u_int32_t seqnr;
	u_int32_t packets;
	u_int64_t blocks;
} p_read, p_send;

static u_int64_t max_blocks_in, max_blocks_out;
static u_int32_t rekey_limit;

/* 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;

struct packet {
	TAILQ_ENTRY(packet) next;
	u_char type;
	Buffer payload;
};
TAILQ_HEAD(, packet) outgoing;

/*
 * 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, (const u_char *)"",
	    0, NULL, 0, CIPHER_ENCRYPT);
	cipher_init(&receive_context, none, (const u_char *)"",
	    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);
		TAILQ_INIT(&outgoing);
	}
}

/* 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(void)
{
	return (cipher_get_number(receive_context.cipher));
}

void
packet_get_state(int mode, u_int32_t *seqnr, u_int64_t *blocks, u_int32_t *packets)
{
	struct packet_state *state;

	state = (mode == MODE_IN) ? &p_read : &p_send;
	*seqnr = state->seqnr;
	*blocks = state->blocks;
	*packets = state->packets;
}

void
packet_set_state(int mode, u_int32_t seqnr, u_int64_t blocks, u_int32_t packets)
{
	struct packet_state *state;

	state = (mode == MODE_IN) ? &p_read : &p_send;
	state->seqnr = seqnr;
	state->blocks = blocks;
	state->packets = packets;
}

/* 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. */
	set_nonblock(connection_in);

	if (connection_out != connection_in)
		set_nonblock(connection_out);
}

/* 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;