5 Author: Tatu Ylonen <ylo@cs.hut.fi>
7 Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
10 Created: Sat Mar 18 02:40:40 1995 ylo
12 This file contains code implementing the packet protocol and communication
13 with the other side. This same code is used both on client and server side.
32 /* This variable contains the file descriptors used for communicating with
33 the other side. connection_in is used for reading; connection_out
34 for writing. These can be the same descriptor, in which case it is
35 assumed to be a socket. */
36 static int connection_in = -1;
37 static int connection_out = -1;
39 /* Cipher type. This value is only used to determine whether to pad the
40 packets with zeroes or random data. */
41 static int cipher_type = SSH_CIPHER_NONE;
43 /* Protocol flags for the remote side. */
44 static unsigned int remote_protocol_flags = 0;
46 /* Encryption context for receiving data. This is only used for decryption. */
47 static CipherContext receive_context;
48 /* Encryption coontext for sending data. This is only used for encryption. */
49 static CipherContext send_context;
51 /* Buffer for raw input data from the socket. */
54 /* Buffer for raw output data going to the socket. */
57 /* Buffer for the partial outgoing packet being constructed. */
58 static Buffer outgoing_packet;
60 /* Buffer for the incoming packet currently being processed. */
61 static Buffer incoming_packet;
63 /* Scratch buffer for packet compression/decompression. */
64 static Buffer compression_buffer;
66 /* Flag indicating whether packet compression/decompression is enabled. */
67 static int packet_compression = 0;
69 /* Flag indicating whether this module has been initialized. */
70 static int initialized = 0;
72 /* Set to true if the connection is interactive. */
73 static int interactive_mode = 0;
75 /* Sets the descriptors used for communication. Disables encryption until
76 packet_set_encryption_key is called. */
79 packet_set_connection(int fd_in, int fd_out)
81 connection_in = fd_in;
82 connection_out = fd_out;
83 cipher_type = SSH_CIPHER_NONE;
84 cipher_set_key(&send_context, SSH_CIPHER_NONE, (unsigned char *)"", 0, 1);
85 cipher_set_key(&receive_context, SSH_CIPHER_NONE, (unsigned char *)"", 0, 0);
91 buffer_init(&outgoing_packet);
92 buffer_init(&incoming_packet);
95 /* Kludge: arrange the close function to be called from fatal(). */
96 fatal_add_cleanup((void (*)(void *))packet_close, NULL);
99 /* Sets the connection into non-blocking mode. */
102 packet_set_nonblocking()
104 /* Set the socket into non-blocking mode. */
105 if (fcntl(connection_in, F_SETFL, O_NONBLOCK) < 0)
106 error("fcntl O_NONBLOCK: %.100s", strerror(errno));
108 if (connection_out != connection_in)
110 if (fcntl(connection_out, F_SETFL, O_NONBLOCK) < 0)
111 error("fcntl O_NONBLOCK: %.100s", strerror(errno));
115 /* Returns the socket used for reading. */
118 packet_get_connection_in()
120 return connection_in;
123 /* Returns the descriptor used for writing. */
126 packet_get_connection_out()
128 return connection_out;
131 /* Closes the connection and clears and frees internal data structures. */
139 if (connection_in == connection_out)
141 shutdown(connection_out, SHUT_RDWR);
142 close(connection_out);
146 close(connection_in);
147 close(connection_out);
150 buffer_free(&output);
151 buffer_free(&outgoing_packet);
152 buffer_free(&incoming_packet);
153 if (packet_compression)
155 buffer_free(&compression_buffer);
156 buffer_compress_uninit();
160 /* Sets remote side protocol flags. */
163 packet_set_protocol_flags(unsigned int protocol_flags)
165 remote_protocol_flags = protocol_flags;
166 channel_set_options((protocol_flags & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) != 0);
169 /* Returns the remote protocol flags set earlier by the above function. */
172 packet_get_protocol_flags()
174 return remote_protocol_flags;
177 /* Starts packet compression from the next packet on in both directions.
178 Level is compression level 1 (fastest) - 9 (slow, best) as in gzip. */
181 packet_start_compression(int level)
183 if (packet_compression)
184 fatal("Compression already enabled.");
185 packet_compression = 1;
186 buffer_init(&compression_buffer);
187 buffer_compress_init(level);
190 /* Encrypts the given number of bytes, copying from src to dest.
191 bytes is known to be a multiple of 8. */
194 packet_encrypt(CipherContext *cc, void *dest, void *src,
197 assert((bytes % 8) == 0);
198 cipher_encrypt(cc, dest, src, bytes);
201 /* Decrypts the given number of bytes, copying from src to dest.
202 bytes is known to be a multiple of 8. */
205 packet_decrypt(CipherContext *cc, void *dest, void *src,
210 assert((bytes % 8) == 0);
213 Cryptographic attack detector for ssh - Modifications for packet.c
214 (C)1998 CORE-SDI, Buenos Aires Argentina
215 Ariel Futoransky(futo@core-sdi.com)
219 case SSH_CIPHER_NONE:
223 i = detect_attack(src, bytes, NULL);
227 if (i == DEATTACK_DETECTED)
228 packet_disconnect("crc32 compensation attack: network attack detected");
230 cipher_decrypt(cc, dest, src, bytes);
233 /* Causes any further packets to be encrypted using the given key. The same
234 key is used for both sending and reception. However, both directions
235 are encrypted independently of each other. */
238 packet_set_encryption_key(const unsigned char *key, unsigned int keylen,
239 int cipher, int is_client)
241 cipher_type = cipher;
242 if (cipher == SSH_CIPHER_RC4)
245 { /* In client: use first half for receiving, second for sending. */
246 cipher_set_key(&receive_context, cipher, key, keylen / 2, 0);
247 cipher_set_key(&send_context, cipher, key + keylen / 2,
251 { /* In server: use first half for sending, second for receiving. */
252 cipher_set_key(&receive_context, cipher, key + keylen / 2,
254 cipher_set_key(&send_context, cipher, key, keylen / 2, 1);
259 /* All other ciphers use the same key in both directions for now. */
260 cipher_set_key(&receive_context, cipher, key, keylen, 0);
261 cipher_set_key(&send_context, cipher, key, keylen, 1);
265 /* Starts constructing a packet to send. */
268 packet_start(int type)
272 buffer_clear(&outgoing_packet);
275 buffer_append(&outgoing_packet, buf, 9);
278 /* Appends a character to the packet data. */
281 packet_put_char(int value)
284 buffer_append(&outgoing_packet, &ch, 1);
287 /* Appends an integer to the packet data. */
290 packet_put_int(unsigned int value)
292 buffer_put_int(&outgoing_packet, value);
295 /* Appends a string to packet data. */
298 packet_put_string(const char *buf, unsigned int len)
300 buffer_put_string(&outgoing_packet, buf, len);
303 /* Appends an arbitrary precision integer to packet data. */
306 packet_put_bignum(BIGNUM *value)
308 buffer_put_bignum(&outgoing_packet, value);
311 /* Finalizes and sends the packet. If the encryption key has been set,
312 encrypts the packet before sending. */
319 unsigned int checksum;
322 /* If using packet compression, compress the payload of the outgoing
324 if (packet_compression)
326 buffer_clear(&compression_buffer);
327 buffer_consume(&outgoing_packet, 8); /* Skip padding. */
328 buffer_append(&compression_buffer, "\0\0\0\0\0\0\0\0", 8); /* padding */
329 buffer_compress(&outgoing_packet, &compression_buffer);
330 buffer_clear(&outgoing_packet);
331 buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
332 buffer_len(&compression_buffer));
335 /* Compute packet length without padding (add checksum, remove padding). */
336 len = buffer_len(&outgoing_packet) + 4 - 8;
338 /* Insert padding. */
339 padding = 8 - len % 8;
340 if (cipher_type != SSH_CIPHER_NONE)
342 cp = buffer_ptr(&outgoing_packet);
343 for (i = 0; i < padding; i++) {
346 cp[7 - i] = rand & 0xff;
350 buffer_consume(&outgoing_packet, 8 - padding);
352 /* Add check bytes. */
353 checksum = crc32((unsigned char *)buffer_ptr(&outgoing_packet),
354 buffer_len(&outgoing_packet));
355 PUT_32BIT(buf, checksum);
356 buffer_append(&outgoing_packet, buf, 4);
359 fprintf(stderr, "packet_send plain: ");
360 buffer_dump(&outgoing_packet);
363 /* Append to output. */
365 buffer_append(&output, buf, 4);
366 buffer_append_space(&output, &cp, buffer_len(&outgoing_packet));
367 packet_encrypt(&send_context, cp, buffer_ptr(&outgoing_packet),
368 buffer_len(&outgoing_packet));
371 fprintf(stderr, "encrypted: "); buffer_dump(&output);
374 buffer_clear(&outgoing_packet);
376 /* Note that the packet is now only buffered in output. It won\'t be
377 actually sent until packet_write_wait or packet_write_poll is called. */
380 /* Waits until a packet has been received, and returns its type. Note that
381 no other data is processed until this returns, so this function should
382 not be used during the interactive session. */
385 packet_read(int *payload_len_ptr)
391 /* Since we are blocking, ensure that all written packets have been sent. */
394 /* Stay in the loop until we have received a complete packet. */
397 /* Try to read a packet from the buffer. */
398 type = packet_read_poll(payload_len_ptr);
399 if (type == SSH_SMSG_SUCCESS
400 || type == SSH_SMSG_FAILURE
401 || type == SSH_CMSG_EOF
402 || type == SSH_CMSG_EXIT_CONFIRMATION)
403 packet_integrity_check(*payload_len_ptr, 0, type);
404 /* If we got a packet, return it. */
405 if (type != SSH_MSG_NONE)
407 /* Otherwise, wait for some data to arrive, add it to the buffer,
410 FD_SET(connection_in, &set);
411 /* Wait for some data to arrive. */
412 select(connection_in + 1, &set, NULL, NULL, NULL);
413 /* Read data from the socket. */
414 len = read(connection_in, buf, sizeof(buf));
416 fatal("Connection closed by remote host.");
418 fatal("Read from socket failed: %.100s", strerror(errno));
419 /* Append it to the buffer. */
420 packet_process_incoming(buf, len);
425 /* Waits until a packet has been received, verifies that its type matches
426 that given, and gives a fatal error and exits if there is a mismatch. */
429 packet_read_expect(int *payload_len_ptr, int expected_type)
433 type = packet_read(payload_len_ptr);
434 if (type != expected_type)
435 packet_disconnect("Protocol error: expected packet type %d, got %d",
436 expected_type, type);
439 /* Checks if a full packet is available in the data received so far via
440 packet_process_incoming. If so, reads the packet; otherwise returns
441 SSH_MSG_NONE. This does not wait for data from the connection.
443 SSH_MSG_DISCONNECT is handled specially here. Also,
444 SSH_MSG_IGNORE messages are skipped by this function and are never returned
447 The returned payload_len does include space consumed by:
457 packet_read_poll(int *payload_len_ptr)
459 unsigned int len, padded_len;
462 unsigned int checksum, stored_checksum;
466 /* Check if input size is less than minimum packet size. */
467 if (buffer_len(&input) < 4 + 8)
469 /* Get length of incoming packet. */
470 ucp = (unsigned char *)buffer_ptr(&input);
471 len = GET_32BIT(ucp);
472 if (len < 1 + 2 + 2 || len > 256*1024)
473 packet_disconnect("Bad packet length %d.", len);
474 padded_len = (len + 8) & ~7;
476 /* Check if the packet has been entirely received. */
477 if (buffer_len(&input) < 4 + padded_len)
480 /* The entire packet is in buffer. */
482 /* Consume packet length. */
483 buffer_consume(&input, 4);
485 /* Copy data to incoming_packet. */
486 buffer_clear(&incoming_packet);
487 buffer_append_space(&incoming_packet, &cp, padded_len);
488 packet_decrypt(&receive_context, cp, buffer_ptr(&input), padded_len);
489 buffer_consume(&input, padded_len);
492 fprintf(stderr, "read_poll plain: "); buffer_dump(&incoming_packet);
495 /* Compute packet checksum. */
496 checksum = crc32((unsigned char *)buffer_ptr(&incoming_packet),
497 buffer_len(&incoming_packet) - 4);
500 buffer_consume(&incoming_packet, 8 - len % 8);
502 /* Test check bytes. */
503 assert(len == buffer_len(&incoming_packet));
504 ucp = (unsigned char *)buffer_ptr(&incoming_packet) + len - 4;
505 stored_checksum = GET_32BIT(ucp);
506 if (checksum != stored_checksum)
507 packet_disconnect("Corrupted check bytes on input.");
508 buffer_consume_end(&incoming_packet, 4);
510 /* If using packet compression, decompress the packet. */
511 if (packet_compression)
513 buffer_clear(&compression_buffer);
514 buffer_uncompress(&incoming_packet, &compression_buffer);
515 buffer_clear(&incoming_packet);
516 buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
517 buffer_len(&compression_buffer));
520 /* Get packet type. */
521 buffer_get(&incoming_packet, &buf[0], 1);
523 /* Return length of payload (without type field). */
524 *payload_len_ptr = buffer_len(&incoming_packet);
526 /* Handle disconnect message. */
527 if ((unsigned char)buf[0] == SSH_MSG_DISCONNECT)
528 fatal("%.900s", packet_get_string(NULL));
530 /* Ignore ignore messages. */
531 if ((unsigned char)buf[0] == SSH_MSG_IGNORE)
534 /* Send debug messages as debugging output. */
535 if ((unsigned char)buf[0] == SSH_MSG_DEBUG)
537 debug("Remote: %.900s", packet_get_string(NULL));
542 return (unsigned char)buf[0];
545 /* Buffers the given amount of input characters. This is intended to be
546 used together with packet_read_poll. */
549 packet_process_incoming(const char *buf, unsigned int len)
551 buffer_append(&input, buf, len);
554 /* Returns a character from the packet. */
560 buffer_get(&incoming_packet, &ch, 1);
561 return (unsigned char)ch;
564 /* Returns an integer from the packet data. */
569 return buffer_get_int(&incoming_packet);
572 /* Returns an arbitrary precision integer from the packet data. The integer
573 must have been initialized before this call. */
576 packet_get_bignum(BIGNUM *value, int *length_ptr)
578 *length_ptr = buffer_get_bignum(&incoming_packet, value);
581 /* Returns a string from the packet data. The string is allocated using
582 xmalloc; it is the responsibility of the calling program to free it when
583 no longer needed. The length_ptr argument may be NULL, or point to an
584 integer into which the length of the string is stored. */
587 *packet_get_string(unsigned int *length_ptr)
589 return buffer_get_string(&incoming_packet, length_ptr);
592 /* Sends a diagnostic message from the server to the client. This message
593 can be sent at any time (but not while constructing another message).
594 The message is printed immediately, but only if the client is being
595 executed in verbose mode. These messages are primarily intended to
596 ease debugging authentication problems. The length of the formatted
597 message must not exceed 1024 bytes. This will automatically call
598 packet_write_wait. */
601 packet_send_debug(const char *fmt, ...)
607 vsnprintf(buf, sizeof(buf), fmt, args);
610 packet_start(SSH_MSG_DEBUG);
611 packet_put_string(buf, strlen(buf));
616 /* Logs the error plus constructs and sends a disconnect
617 packet, closes the connection, and exits. This function never returns.
618 The error message should not contain a newline. The length of the
619 formatted message must not exceed 1024 bytes. */
622 packet_disconnect(const char *fmt, ...)
626 static int disconnecting = 0;
627 if (disconnecting) /* Guard against recursive invocations. */
628 fatal("packet_disconnect called recursively.");
631 /* Format the message. Note that the caller must make sure the message
632 is of limited size. */
634 vsnprintf(buf, sizeof(buf), fmt, args);
637 /* Send the disconnect message to the other side, and wait for it to get
639 packet_start(SSH_MSG_DISCONNECT);
640 packet_put_string(buf, strlen(buf));
644 /* Stop listening for connections. */
645 channel_stop_listening();
647 /* Close the connection. */
650 /* Display the error locally and exit. */
651 fatal("Local: %.100s", buf);
654 /* Checks if there is any buffered output, and tries to write some of the
660 int len = buffer_len(&output);
663 len = write(connection_out, buffer_ptr(&output), len);
668 fatal("Write failed: %.100s", strerror(errno));
670 buffer_consume(&output, len);
674 /* Calls packet_write_poll repeatedly until all pending output data has
681 while (packet_have_data_to_write())
685 FD_SET(connection_out, &set);
686 select(connection_out + 1, NULL, &set, NULL, NULL);
691 /* Returns true if there is buffered data to write to the connection. */
694 packet_have_data_to_write()
696 return buffer_len(&output) != 0;
699 /* Returns true if there is not too much data to write to the connection. */
702 packet_not_very_much_data_to_write()
704 if (interactive_mode)
705 return buffer_len(&output) < 16384;
707 return buffer_len(&output) < 128*1024;
710 /* Informs that the current session is interactive. Sets IP flags for that. */
713 packet_set_interactive(int interactive, int keepalives)
717 /* Record that we are in interactive mode. */
718 interactive_mode = interactive;
720 /* Only set socket options if using a socket (as indicated by the descriptors
722 if (connection_in != connection_out)
727 /* Set keepalives if requested. */
728 if (setsockopt(connection_in, SOL_SOCKET, SO_KEEPALIVE, (void *)&on,
730 error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
735 /* Set IP options for an interactive connection. Use IPTOS_LOWDELAY
737 int lowdelay = IPTOS_LOWDELAY;
738 if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *)&lowdelay,
739 sizeof(lowdelay)) < 0)
740 error("setsockopt IPTOS_LOWDELAY: %.100s", strerror(errno));
741 if (setsockopt(connection_in, IPPROTO_TCP, TCP_NODELAY, (void *)&on,
743 error("setsockopt TCP_NODELAY: %.100s", strerror(errno));
747 /* Set IP options for a non-interactive connection. Use
749 int throughput = IPTOS_THROUGHPUT;
750 if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *)&throughput,
751 sizeof(throughput)) < 0)
752 error("setsockopt IPTOS_THROUGHPUT: %.100s", strerror(errno));
756 /* Returns true if the current connection is interactive. */
759 packet_is_interactive()
761 return interactive_mode;