openssh-portable/packet.c

799 lines
20 KiB
C

/*
*
* packet.c
*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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 1.8 1999/12/16 02:18:04 damien 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"
/*
* 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);
}
/* 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;
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) {
log("Received disconnect: %.900s", packet_get_string(NULL));
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) {
debug("Remote: %.900s", packet_get_string(NULL));
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 (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;
}
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;
}