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767 lines
20 KiB
C
767 lines
20 KiB
C
/*
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packet.c
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Author: Tatu Ylonen <ylo@cs.hut.fi>
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Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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All rights reserved
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Created: Sat Mar 18 02:40:40 1995 ylo
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This file contains code implementing the packet protocol and communication
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with the other side. This same code is used both on client and server side.
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*/
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#include "includes.h"
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RCSID("$Id: packet.c,v 1.2 1999/11/08 05:15:55 damien Exp $");
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#include "xmalloc.h"
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#include "buffer.h"
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#include "packet.h"
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#include "bufaux.h"
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#include "ssh.h"
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#include "crc32.h"
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#include "cipher.h"
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#include "getput.h"
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#include "compress.h"
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#include "deattack.h"
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/* This variable contains the file descriptors used for communicating with
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the other side. connection_in is used for reading; connection_out
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for writing. These can be the same descriptor, in which case it is
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assumed to be a socket. */
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static int connection_in = -1;
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static int connection_out = -1;
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/* Cipher type. This value is only used to determine whether to pad the
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packets with zeroes or random data. */
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static int cipher_type = SSH_CIPHER_NONE;
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/* Protocol flags for the remote side. */
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static unsigned int remote_protocol_flags = 0;
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/* Encryption context for receiving data. This is only used for decryption. */
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static CipherContext receive_context;
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/* Encryption coontext for sending data. This is only used for encryption. */
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static CipherContext send_context;
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/* Buffer for raw input data from the socket. */
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static Buffer input;
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/* Buffer for raw output data going to the socket. */
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static Buffer output;
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/* Buffer for the partial outgoing packet being constructed. */
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static Buffer outgoing_packet;
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/* Buffer for the incoming packet currently being processed. */
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static Buffer incoming_packet;
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/* Scratch buffer for packet compression/decompression. */
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static Buffer compression_buffer;
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/* Flag indicating whether packet compression/decompression is enabled. */
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static int packet_compression = 0;
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/* Flag indicating whether this module has been initialized. */
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static int initialized = 0;
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/* Set to true if the connection is interactive. */
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static int interactive_mode = 0;
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/* Sets the descriptors used for communication. Disables encryption until
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packet_set_encryption_key is called. */
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void
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packet_set_connection(int fd_in, int fd_out)
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{
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connection_in = fd_in;
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connection_out = fd_out;
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cipher_type = SSH_CIPHER_NONE;
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cipher_set_key(&send_context, SSH_CIPHER_NONE, (unsigned char *)"", 0, 1);
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cipher_set_key(&receive_context, SSH_CIPHER_NONE, (unsigned char *)"", 0, 0);
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if (!initialized)
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{
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initialized = 1;
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buffer_init(&input);
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buffer_init(&output);
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buffer_init(&outgoing_packet);
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buffer_init(&incoming_packet);
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}
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/* Kludge: arrange the close function to be called from fatal(). */
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fatal_add_cleanup((void (*)(void *))packet_close, NULL);
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}
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/* Sets the connection into non-blocking mode. */
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void
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packet_set_nonblocking()
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{
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/* Set the socket into non-blocking mode. */
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if (fcntl(connection_in, F_SETFL, O_NONBLOCK) < 0)
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error("fcntl O_NONBLOCK: %.100s", strerror(errno));
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if (connection_out != connection_in)
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{
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if (fcntl(connection_out, F_SETFL, O_NONBLOCK) < 0)
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error("fcntl O_NONBLOCK: %.100s", strerror(errno));
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}
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}
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/* Returns the socket used for reading. */
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int
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packet_get_connection_in()
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{
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return connection_in;
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}
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/* Returns the descriptor used for writing. */
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int
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packet_get_connection_out()
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{
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return connection_out;
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}
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/* Closes the connection and clears and frees internal data structures. */
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void
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packet_close()
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{
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if (!initialized)
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return;
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initialized = 0;
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if (connection_in == connection_out)
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{
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shutdown(connection_out, SHUT_RDWR);
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close(connection_out);
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}
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else
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{
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close(connection_in);
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close(connection_out);
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}
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buffer_free(&input);
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buffer_free(&output);
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buffer_free(&outgoing_packet);
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buffer_free(&incoming_packet);
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if (packet_compression)
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{
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buffer_free(&compression_buffer);
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buffer_compress_uninit();
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}
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}
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/* Sets remote side protocol flags. */
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void
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packet_set_protocol_flags(unsigned int protocol_flags)
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{
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remote_protocol_flags = protocol_flags;
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channel_set_options((protocol_flags & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) != 0);
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}
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/* Returns the remote protocol flags set earlier by the above function. */
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unsigned int
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packet_get_protocol_flags()
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{
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return remote_protocol_flags;
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}
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/* Starts packet compression from the next packet on in both directions.
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Level is compression level 1 (fastest) - 9 (slow, best) as in gzip. */
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void
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packet_start_compression(int level)
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{
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if (packet_compression)
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fatal("Compression already enabled.");
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packet_compression = 1;
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buffer_init(&compression_buffer);
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buffer_compress_init(level);
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}
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/* Encrypts the given number of bytes, copying from src to dest.
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bytes is known to be a multiple of 8. */
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void
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packet_encrypt(CipherContext *cc, void *dest, void *src,
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unsigned int bytes)
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{
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cipher_encrypt(cc, dest, src, bytes);
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}
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/* Decrypts the given number of bytes, copying from src to dest.
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bytes is known to be a multiple of 8. */
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void
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packet_decrypt(CipherContext *cc, void *dest, void *src,
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unsigned int bytes)
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{
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int i;
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if ((bytes % 8) != 0)
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fatal("packet_decrypt: bad ciphertext length %d", bytes);
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/*
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Cryptographic attack detector for ssh - Modifications for packet.c
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(C)1998 CORE-SDI, Buenos Aires Argentina
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Ariel Futoransky(futo@core-sdi.com)
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*/
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switch (cc->type)
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{
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case SSH_CIPHER_NONE:
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i = DEATTACK_OK;
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break;
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default:
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i = detect_attack(src, bytes, NULL);
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break;
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}
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if (i == DEATTACK_DETECTED)
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packet_disconnect("crc32 compensation attack: network attack detected");
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cipher_decrypt(cc, dest, src, bytes);
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}
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/* Causes any further packets to be encrypted using the given key. The same
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key is used for both sending and reception. However, both directions
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are encrypted independently of each other. */
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void
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packet_set_encryption_key(const unsigned char *key, unsigned int keylen,
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int cipher, int is_client)
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{
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cipher_type = cipher;
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if (cipher == SSH_CIPHER_RC4)
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{
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if (is_client)
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{ /* In client: use first half for receiving, second for sending. */
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cipher_set_key(&receive_context, cipher, key, keylen / 2, 0);
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cipher_set_key(&send_context, cipher, key + keylen / 2,
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keylen / 2, 1);
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}
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else
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{ /* In server: use first half for sending, second for receiving. */
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cipher_set_key(&receive_context, cipher, key + keylen / 2,
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keylen / 2, 0);
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cipher_set_key(&send_context, cipher, key, keylen / 2, 1);
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}
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}
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else
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{
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/* All other ciphers use the same key in both directions for now. */
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cipher_set_key(&receive_context, cipher, key, keylen, 0);
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cipher_set_key(&send_context, cipher, key, keylen, 1);
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}
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}
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/* Starts constructing a packet to send. */
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void
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packet_start(int type)
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{
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char buf[9];
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buffer_clear(&outgoing_packet);
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memset(buf, 0, 8);
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buf[8] = type;
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buffer_append(&outgoing_packet, buf, 9);
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}
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/* Appends a character to the packet data. */
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void
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packet_put_char(int value)
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{
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char ch = value;
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buffer_append(&outgoing_packet, &ch, 1);
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}
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/* Appends an integer to the packet data. */
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void
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packet_put_int(unsigned int value)
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{
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buffer_put_int(&outgoing_packet, value);
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}
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/* Appends a string to packet data. */
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void
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packet_put_string(const char *buf, unsigned int len)
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{
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buffer_put_string(&outgoing_packet, buf, len);
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}
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/* Appends an arbitrary precision integer to packet data. */
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void
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packet_put_bignum(BIGNUM *value)
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{
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buffer_put_bignum(&outgoing_packet, value);
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}
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/* Finalizes and sends the packet. If the encryption key has been set,
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encrypts the packet before sending. */
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void
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packet_send()
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{
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char buf[8], *cp;
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int i, padding, len;
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unsigned int checksum;
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u_int32_t rand = 0;
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/* If using packet compression, compress the payload of the outgoing
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packet. */
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if (packet_compression)
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{
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buffer_clear(&compression_buffer);
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buffer_consume(&outgoing_packet, 8); /* Skip padding. */
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buffer_append(&compression_buffer, "\0\0\0\0\0\0\0\0", 8); /* padding */
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buffer_compress(&outgoing_packet, &compression_buffer);
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buffer_clear(&outgoing_packet);
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buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
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buffer_len(&compression_buffer));
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}
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/* Compute packet length without padding (add checksum, remove padding). */
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len = buffer_len(&outgoing_packet) + 4 - 8;
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/* Insert padding. */
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padding = 8 - len % 8;
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if (cipher_type != SSH_CIPHER_NONE)
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{
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cp = buffer_ptr(&outgoing_packet);
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for (i = 0; i < padding; i++) {
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if (i % 4 == 0)
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rand = arc4random();
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cp[7 - i] = rand & 0xff;
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rand >>= 8;
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}
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}
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buffer_consume(&outgoing_packet, 8 - padding);
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/* Add check bytes. */
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checksum = crc32((unsigned char *)buffer_ptr(&outgoing_packet),
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buffer_len(&outgoing_packet));
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PUT_32BIT(buf, checksum);
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buffer_append(&outgoing_packet, buf, 4);
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#ifdef PACKET_DEBUG
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fprintf(stderr, "packet_send plain: ");
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buffer_dump(&outgoing_packet);
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#endif
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/* Append to output. */
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PUT_32BIT(buf, len);
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buffer_append(&output, buf, 4);
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buffer_append_space(&output, &cp, buffer_len(&outgoing_packet));
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packet_encrypt(&send_context, cp, buffer_ptr(&outgoing_packet),
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buffer_len(&outgoing_packet));
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#ifdef PACKET_DEBUG
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fprintf(stderr, "encrypted: "); buffer_dump(&output);
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#endif
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buffer_clear(&outgoing_packet);
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/* Note that the packet is now only buffered in output. It won\'t be
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actually sent until packet_write_wait or packet_write_poll is called. */
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}
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/* Waits until a packet has been received, and returns its type. Note that
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no other data is processed until this returns, so this function should
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not be used during the interactive session. */
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int
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packet_read(int *payload_len_ptr)
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{
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int type, len;
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fd_set set;
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char buf[8192];
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/* Since we are blocking, ensure that all written packets have been sent. */
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packet_write_wait();
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/* Stay in the loop until we have received a complete packet. */
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for (;;)
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{
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/* Try to read a packet from the buffer. */
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type = packet_read_poll(payload_len_ptr);
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if (type == SSH_SMSG_SUCCESS
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|| type == SSH_SMSG_FAILURE
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|| type == SSH_CMSG_EOF
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|| type == SSH_CMSG_EXIT_CONFIRMATION)
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packet_integrity_check(*payload_len_ptr, 0, type);
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/* If we got a packet, return it. */
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if (type != SSH_MSG_NONE)
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return type;
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/* Otherwise, wait for some data to arrive, add it to the buffer,
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and try again. */
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FD_ZERO(&set);
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FD_SET(connection_in, &set);
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/* Wait for some data to arrive. */
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select(connection_in + 1, &set, NULL, NULL, NULL);
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/* Read data from the socket. */
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len = read(connection_in, buf, sizeof(buf));
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if (len == 0)
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fatal("Connection closed by remote host.");
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if (len < 0)
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fatal("Read from socket failed: %.100s", strerror(errno));
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/* Append it to the buffer. */
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packet_process_incoming(buf, len);
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}
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/*NOTREACHED*/
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}
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/* Waits until a packet has been received, verifies that its type matches
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that given, and gives a fatal error and exits if there is a mismatch. */
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void
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packet_read_expect(int *payload_len_ptr, int expected_type)
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{
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int type;
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type = packet_read(payload_len_ptr);
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if (type != expected_type)
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packet_disconnect("Protocol error: expected packet type %d, got %d",
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expected_type, type);
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}
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/* Checks if a full packet is available in the data received so far via
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packet_process_incoming. If so, reads the packet; otherwise returns
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SSH_MSG_NONE. This does not wait for data from the connection.
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SSH_MSG_DISCONNECT is handled specially here. Also,
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SSH_MSG_IGNORE messages are skipped by this function and are never returned
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to higher levels.
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The returned payload_len does include space consumed by:
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Packet length
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Padding
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Packet type
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Check bytes
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*/
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int
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packet_read_poll(int *payload_len_ptr)
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{
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unsigned int len, padded_len;
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unsigned char *ucp;
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char buf[8], *cp;
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unsigned int checksum, stored_checksum;
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restart:
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/* Check if input size is less than minimum packet size. */
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if (buffer_len(&input) < 4 + 8)
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return SSH_MSG_NONE;
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/* Get length of incoming packet. */
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ucp = (unsigned char *)buffer_ptr(&input);
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len = GET_32BIT(ucp);
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if (len < 1 + 2 + 2 || len > 256*1024)
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packet_disconnect("Bad packet length %d.", len);
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padded_len = (len + 8) & ~7;
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/* Check if the packet has been entirely received. */
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if (buffer_len(&input) < 4 + padded_len)
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return SSH_MSG_NONE;
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/* The entire packet is in buffer. */
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/* Consume packet length. */
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buffer_consume(&input, 4);
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/* Copy data to incoming_packet. */
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buffer_clear(&incoming_packet);
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buffer_append_space(&incoming_packet, &cp, padded_len);
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packet_decrypt(&receive_context, cp, buffer_ptr(&input), padded_len);
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buffer_consume(&input, padded_len);
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#ifdef PACKET_DEBUG
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fprintf(stderr, "read_poll plain: "); buffer_dump(&incoming_packet);
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#endif
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/* Compute packet checksum. */
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checksum = crc32((unsigned char *)buffer_ptr(&incoming_packet),
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buffer_len(&incoming_packet) - 4);
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/* Skip padding. */
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buffer_consume(&incoming_packet, 8 - len % 8);
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/* Test check bytes. */
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if (len != buffer_len(&incoming_packet))
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packet_disconnect("packet_read_poll: len %d != buffer_len %d.",
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len, buffer_len(&incoming_packet));
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ucp = (unsigned char *)buffer_ptr(&incoming_packet) + len - 4;
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stored_checksum = GET_32BIT(ucp);
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if (checksum != stored_checksum)
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packet_disconnect("Corrupted check bytes on input.");
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buffer_consume_end(&incoming_packet, 4);
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/* If using packet compression, decompress the packet. */
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if (packet_compression)
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{
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buffer_clear(&compression_buffer);
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buffer_uncompress(&incoming_packet, &compression_buffer);
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buffer_clear(&incoming_packet);
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buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
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buffer_len(&compression_buffer));
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}
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/* Get packet type. */
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buffer_get(&incoming_packet, &buf[0], 1);
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/* Return length of payload (without type field). */
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*payload_len_ptr = buffer_len(&incoming_packet);
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/* Handle disconnect message. */
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if ((unsigned char)buf[0] == SSH_MSG_DISCONNECT)
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fatal("%.900s", packet_get_string(NULL));
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/* Ignore ignore messages. */
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if ((unsigned char)buf[0] == SSH_MSG_IGNORE)
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goto restart;
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/* Send debug messages as debugging output. */
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if ((unsigned char)buf[0] == SSH_MSG_DEBUG)
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{
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debug("Remote: %.900s", packet_get_string(NULL));
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goto restart;
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}
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/* Return type. */
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return (unsigned char)buf[0];
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}
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/* Buffers the given amount of input characters. This is intended to be
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used together with packet_read_poll. */
|
|
|
|
void
|
|
packet_process_incoming(const char *buf, unsigned int len)
|
|
{
|
|
buffer_append(&input, buf, len);
|
|
}
|
|
|
|
/* Returns a character from the packet. */
|
|
|
|
unsigned int
|
|
packet_get_char()
|
|
{
|
|
char ch;
|
|
buffer_get(&incoming_packet, &ch, 1);
|
|
return (unsigned char)ch;
|
|
}
|
|
|
|
/* Returns an integer from the packet data. */
|
|
|
|
unsigned int
|
|
packet_get_int()
|
|
{
|
|
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, int *length_ptr)
|
|
{
|
|
*length_ptr = buffer_get_bignum(&incoming_packet, value);
|
|
}
|
|
|
|
/* 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. */
|
|
|
|
char
|
|
*packet_get_string(unsigned 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;
|
|
|
|
va_start(args, fmt);
|
|
vsnprintf(buf, sizeof(buf), fmt, args);
|
|
va_end(args);
|
|
|
|
packet_start(SSH_MSG_DEBUG);
|
|
packet_put_string(buf, strlen(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);
|
|
|
|
/* Send the disconnect message to the other side, and wait for it to get
|
|
sent. */
|
|
packet_start(SSH_MSG_DISCONNECT);
|
|
packet_put_string(buf, strlen(buf));
|
|
packet_send();
|
|
packet_write_wait();
|
|
|
|
/* Stop listening for connections. */
|
|
channel_stop_listening();
|
|
|
|
/* Close the connection. */
|
|
packet_close();
|
|
|
|
/* Display the error locally and exit. */
|
|
fatal("Local: %.100s", buf);
|
|
}
|
|
|
|
/* Checks if there is any buffered output, and tries to write some of the
|
|
output. */
|
|
|
|
void
|
|
packet_write_poll()
|
|
{
|
|
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()
|
|
{
|
|
packet_write_poll();
|
|
while (packet_have_data_to_write())
|
|
{
|
|
fd_set set;
|
|
FD_ZERO(&set);
|
|
FD_SET(connection_out, &set);
|
|
select(connection_out + 1, NULL, &set, NULL, NULL);
|
|
packet_write_poll();
|
|
}
|
|
}
|
|
|
|
/* Returns true if there is buffered data to write to the connection. */
|
|
|
|
int
|
|
packet_have_data_to_write()
|
|
{
|
|
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()
|
|
{
|
|
if (interactive_mode)
|
|
return buffer_len(&output) < 16384;
|
|
else
|
|
return buffer_len(&output) < 128*1024;
|
|
}
|
|
|
|
/* Informs that the current session is interactive. Sets IP flags for that. */
|
|
|
|
void
|
|
packet_set_interactive(int interactive, int keepalives)
|
|
{
|
|
int on = 1;
|
|
|
|
/* Record that we are in interactive mode. */
|
|
interactive_mode = interactive;
|
|
|
|
/* Only set socket options if using a socket (as indicated by the descriptors
|
|
being the same). */
|
|
if (connection_in != connection_out)
|
|
return;
|
|
|
|
if (keepalives)
|
|
{
|
|
/* Set keepalives if requested. */
|
|
if (setsockopt(connection_in, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
|
|
sizeof(on)) < 0)
|
|
error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
|
|
}
|
|
|
|
if (interactive)
|
|
{
|
|
/* Set IP options for an interactive connection. Use IPTOS_LOWDELAY
|
|
and TCP_NODELAY. */
|
|
int lowdelay = IPTOS_LOWDELAY;
|
|
if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *)&lowdelay,
|
|
sizeof(lowdelay)) < 0)
|
|
error("setsockopt IPTOS_LOWDELAY: %.100s", strerror(errno));
|
|
if (setsockopt(connection_in, IPPROTO_TCP, TCP_NODELAY, (void *)&on,
|
|
sizeof(on)) < 0)
|
|
error("setsockopt TCP_NODELAY: %.100s", strerror(errno));
|
|
}
|
|
else
|
|
{
|
|
/* Set IP options for a non-interactive connection. Use
|
|
IPTOS_THROUGHPUT. */
|
|
int throughput = IPTOS_THROUGHPUT;
|
|
if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *)&throughput,
|
|
sizeof(throughput)) < 0)
|
|
error("setsockopt IPTOS_THROUGHPUT: %.100s", strerror(errno));
|
|
}
|
|
}
|
|
|
|
/* Returns true if the current connection is interactive. */
|
|
|
|
int
|
|
packet_is_interactive()
|
|
{
|
|
return interactive_mode;
|
|
}
|