/* * * packet.c * * Author: Tatu Ylonen * * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland * All rights reserved * * Created: Sat Mar 18 02:40:40 1995 ylo * * 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. * */ #include "includes.h" RCSID("$Id: packet.c,v 1.23 2000/03/28 20:31:27 markus Exp $"); #include "xmalloc.h" #include "buffer.h" #include "packet.h" #include "bufaux.h" #include "ssh.h" #include "crc32.h" #include "cipher.h" #include "getput.h" #include "compress.h" #include "deattack.h" #include "channels.h" /* * 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; /* * Cipher type. This value is only used to determine whether to pad the * packets with zeroes or random data. */ static int cipher_type = SSH_CIPHER_NONE; /* Protocol flags for the remote side. */ static unsigned 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. */ static Buffer input; /* Buffer for raw output data going to the socket. */ static 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; /* 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; /* * 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) { connection_in = fd_in; connection_out = fd_out; cipher_type = SSH_CIPHER_NONE; cipher_set_key(&send_context, SSH_CIPHER_NONE, (unsigned char *) "", 0, 1); cipher_set_key(&receive_context, SSH_CIPHER_NONE, (unsigned char *) "", 0, 0); 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() { 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; } /* returns 1 if connection is via ipv4 */ int packet_connection_is_ipv4() { 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 0; return 1; } /* Sets the connection into non-blocking mode. */ void packet_set_nonblocking() { /* 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() { return connection_in; } /* Returns the descriptor used for writing. */ int packet_get_connection_out() { return connection_out; } /* Closes the connection and clears and frees internal data structures. */ void packet_close() { 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 (packet_compression) { buffer_free(&compression_buffer); buffer_compress_uninit(); } } /* Sets remote side protocol flags. */ void packet_set_protocol_flags(unsigned int protocol_flags) { remote_protocol_flags = protocol_flags; channel_set_options((protocol_flags & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) != 0); } /* Returns the remote protocol flags set earlier by the above function. */ unsigned int packet_get_protocol_flags() { 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. */ void packet_start_compression(int level) { if (packet_compression) fatal("Compression already enabled."); packet_compression = 1; buffer_init(&compression_buffer); buffer_compress_init(level); } /* * Encrypts the given number of bytes, copying from src to dest. bytes is * known to be a multiple of 8. */ void packet_encrypt(CipherContext * cc, void *dest, void *src, unsigned int bytes) { cipher_encrypt(cc, dest, src, bytes); } /* * Decrypts the given number of bytes, copying from src to dest. bytes is * known to be a multiple of 8. */ void packet_decrypt(CipherContext * cc, void *dest, void *src, unsigned int bytes) { int i; if ((bytes % 8) != 0) fatal("packet_decrypt: bad ciphertext length %d", bytes); /* * Cryptographic attack detector for ssh - Modifications for packet.c * (C)1998 CORE-SDI, Buenos Aires Argentina Ariel Futoransky(futo@core-sdi.com) */ switch (cc->type) { case SSH_CIPHER_NONE: i = DEATTACK_OK; break; default: i = detect_attack(src, bytes, NULL); break; } if (i == DEATTACK_DETECTED) packet_disconnect("crc32 compensation attack: network attack detected"); cipher_decrypt(cc, dest, src, bytes); } /* * 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 unsigned char *key, unsigned int keylen, int cipher) { /* All other ciphers use the same key in both directions for now. */ cipher_set_key(&receive_context, cipher, key, keylen, 0); cipher_set_key(&send_context, cipher, key, keylen, 1); } /* Starts constructing a packet to send. */ void packet_start(int type) { char buf[9]; buffer_clear(&outgoing_packet); memset(buf, 0, 8); buf[8] = type; buffer_append(&outgoing_packet, buf, 9); } /* Appends a character to the packet data. */ void packet_put_char(int value) { char ch = value; buffer_append(&outgoing_packet, &ch, 1); } /* Appends an integer to the packet data. */ void packet_put_int(unsigned int value) { buffer_put_int(&outgoing_packet, value); } /* Appends a string to packet data. */ void packet_put_string(const char *buf, unsigned int len) { buffer_put_string(&outgoing_packet, buf, len); } /* Appends an arbitrary precision integer to packet data. */ void packet_put_bignum(BIGNUM * value) { buffer_put_bignum(&outgoing_packet, value); } /* * Finalizes and sends the packet. If the encryption key has been set, * encrypts the packet before sending. */ void packet_send() { char buf[8], *cp; int i, padding, len; unsigned 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. */ padding = 8 - len % 8; if (cipher_type != SSH_CIPHER_NONE) { 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 = crc32((unsigned char *) 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); buffer_append_space(&output, &cp, buffer_len(&outgoing_packet)); packet_encrypt(&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. */ } /* * 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(int *payload_len_ptr) { int type, len; fd_set set; char buf[8192]; /* 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(payload_len_ptr); if (type == SSH_SMSG_SUCCESS || type == SSH_SMSG_FAILURE || type == SSH_CMSG_EOF || type == SSH_CMSG_EXIT_CONFIRMATION) packet_integrity_check(*payload_len_ptr, 0, type); /* If we got a packet, return it. */ if (type != SSH_MSG_NONE) return type; /* * Otherwise, wait for some data to arrive, add it to the * buffer, and try again. */ FD_ZERO(&set); FD_SET(connection_in, &set); /* Wait for some data to arrive. */ select(connection_in + 1, &set, NULL, NULL, NULL); /* 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 */ } /* * 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 *payload_len_ptr, int expected_type) { int type; type = packet_read(payload_len_ptr); 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. * * The returned payload_len does include space consumed by: * Packet length * Padding * Packet type * Check bytes */ int packet_read_poll(int *payload_len_ptr) { unsigned int len, padded_len; unsigned char *ucp; char buf[8], *cp, *msg; unsigned int checksum, stored_checksum; restart: /* 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. */ ucp = (unsigned char *) buffer_ptr(&input); len = GET_32BIT(ucp); if (len < 1 + 2 + 2 || len > 256 * 1024) packet_disconnect("Bad packet length %d.", 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); /* Copy data to incoming_packet. */ buffer_clear(&incoming_packet); buffer_append_space(&incoming_packet, &cp, padded_len); packet_decrypt(&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 = crc32((unsigned char *) 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_poll: len %d != buffer_len %d.", len, buffer_len(&incoming_packet)); ucp = (unsigned char *) buffer_ptr(&incoming_packet) + len - 4; stored_checksum = GET_32BIT(ucp); if (checksum != stored_checksum) packet_disconnect("Corrupted check bytes on input."); buffer_consume_end(&incoming_packet, 4); /* If using packet compression, decompress the packet. */ 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)); } /* Get packet type. */ buffer_get(&incoming_packet, &buf[0], 1); /* Return length of payload (without type field). */ *payload_len_ptr = buffer_len(&incoming_packet); /* Handle disconnect message. */ if ((unsigned char) buf[0] == SSH_MSG_DISCONNECT) { msg = packet_get_string(NULL); log("Received disconnect: %.900s", msg); xfree(msg); fatal_cleanup(); } /* Ignore ignore messages. */ if ((unsigned char) buf[0] == SSH_MSG_IGNORE) goto restart; /* Send debug messages as debugging output. */ if ((unsigned char) buf[0] == SSH_MSG_DEBUG) { msg = packet_get_string(NULL); debug("Remote: %.900s", msg); xfree(msg); goto restart; } /* Return type. */ return (unsigned char) buf[0]; } /* * 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, 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. */ log("Disconnecting: %.100s", buf); fatal_cleanup(); } /* 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. */ if (!packet_connection_is_on_socket()) 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)); } /* * IPTOS_LOWDELAY, TCP_NODELAY and IPTOS_THROUGHPUT are IPv4 only */ if (!packet_connection_is_ipv4()) return; 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; } 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; } log("packet_set_maxsize: setting to %d", s); max_packet_size = s; return s; }