packet.c

   1 /*
   2  *
   3  * packet.c
   4  *
   5  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   6  *
   7  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   8  *                    All rights reserved
   9  *
  10  * Created: Sat Mar 18 02:40:40 1995 ylo
  11  *
  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.
  14  *
  15  * SSH2 packet format added by Markus Friedl.
  16  *
  17  */
  18
  19 #include "includes.h"
  20 RCSID("$OpenBSD: packet.c,v 1.33 2000/06/20 01:39:43 markus Exp $");
  21
  22 #include "xmalloc.h"
  23 #include "buffer.h"
  24 #include "packet.h"
  25 #include "bufaux.h"
  26 #include "ssh.h"
  27 #include "crc32.h"
  28 #include "cipher.h"
  29 #include "getput.h"
  30
  31 #include "compress.h"
  32 #include "deattack.h"
  33 #include "channels.h"
  34
  35 #include "compat.h"
  36 #include "ssh2.h"
  37
  38 #include <openssl/bn.h>
  39 #include <openssl/dh.h>
  40 #include <openssl/hmac.h>
  41 #include "buffer.h"
  42 #include "kex.h"
  43 #include "hmac.h"
  44
  45 #ifdef PACKET_DEBUG
  46 #define DBG(x) x
  47 #else
  48 #define DBG(x)
  49 #endif
  50
  51 /*
  52  * This variable contains the file descriptors used for communicating with
  53  * the other side.  connection_in is used for reading; connection_out for
  54  * writing.  These can be the same descriptor, in which case it is assumed to
  55  * be a socket.
  56  */
  57 static int connection_in = -1;
  58 static int connection_out = -1;
  59
  60 /*
  61  * Cipher type.  This value is only used to determine whether to pad the
  62  * packets with zeroes or random data.
  63  */
  64 static int cipher_type = SSH_CIPHER_NONE;
  65
  66 /* Protocol flags for the remote side. */
  67 static unsigned int remote_protocol_flags = 0;
  68
  69 /* Encryption context for receiving data.  This is only used for decryption. */
  70 static CipherContext receive_context;
  71
  72 /* Encryption context for sending data.  This is only used for encryption. */
  73 static CipherContext send_context;
  74
  75 /* Buffer for raw input data from the socket. */
  76 static Buffer input;
  77
  78 /* Buffer for raw output data going to the socket. */
  79 static Buffer output;
  80
  81 /* Buffer for the partial outgoing packet being constructed. */
  82 static Buffer outgoing_packet;
  83
  84 /* Buffer for the incoming packet currently being processed. */
  85 static Buffer incoming_packet;
  86
  87 /* Scratch buffer for packet compression/decompression. */
  88 static Buffer compression_buffer;
  89
  90 /* Flag indicating whether packet compression/decompression is enabled. */
  91 static int packet_compression = 0;
  92
  93 /* default maximum packet size */
  94 int max_packet_size = 32768;
  95
  96 /* Flag indicating whether this module has been initialized. */
  97 static int initialized = 0;
  98
  99 /* Set to true if the connection is interactive. */
 100 static int interactive_mode = 0;
 101
 102 /* True if SSH2 packet format is used */
 103 int use_ssh2_packet_format = 0;
 104
 105 /* Session key information for Encryption and MAC */
 106 Kex     *kex = NULL;
 107
 108 void
 109 packet_set_kex(Kex *k)
 110 {
 111         if( k->mac[MODE_IN ].key == NULL ||
 112             k->enc[MODE_IN ].key == NULL ||
 113             k->enc[MODE_IN ].iv  == NULL ||
 114             k->mac[MODE_OUT].key == NULL ||
 115             k->enc[MODE_OUT].key == NULL ||
 116             k->enc[MODE_OUT].iv  == NULL)
 117                 fatal("bad KEX");
 118         kex = k;
 119 }
 120 void
 121 clear_enc_keys(Enc *enc, int len)
 122 {
 123         memset(enc->iv,  0, len);
 124         memset(enc->key, 0, len);
 125         xfree(enc->iv);
 126         xfree(enc->key);
 127         enc->iv = NULL;
 128         enc->key = NULL;
 129 }
 130 void
 131 packet_set_ssh2_format(void)
 132 {
 133         DBG(debug("use_ssh2_packet_format"));
 134         use_ssh2_packet_format = 1;
 135 }
 136
 137 /*
 138  * Sets the descriptors used for communication.  Disables encryption until
 139  * packet_set_encryption_key is called.
 140  */
 141 void
 142 packet_set_connection(int fd_in, int fd_out)
 143 {
 144         connection_in = fd_in;
 145         connection_out = fd_out;
 146         cipher_type = SSH_CIPHER_NONE;
 147         cipher_set_key(&send_context, SSH_CIPHER_NONE, (unsigned char *) "", 0);
 148         cipher_set_key(&receive_context, SSH_CIPHER_NONE, (unsigned char *) "", 0);
 149         if (!initialized) {
 150                 initialized = 1;
 151                 buffer_init(&input);
 152                 buffer_init(&output);
 153                 buffer_init(&outgoing_packet);
 154                 buffer_init(&incoming_packet);
 155         }
 156         /* Kludge: arrange the close function to be called from fatal(). */
 157         fatal_add_cleanup((void (*) (void *)) packet_close, NULL);
 158 }
 159
 160 /* Returns 1 if remote host is connected via socket, 0 if not. */
 161
 162 int
 163 packet_connection_is_on_socket()
 164 {
 165         struct sockaddr_storage from, to;
 166         socklen_t fromlen, tolen;
 167
 168         /* filedescriptors in and out are the same, so it's a socket */
 169         if (connection_in == connection_out)
 170                 return 1;
 171         fromlen = sizeof(from);
 172         memset(&from, 0, sizeof(from));
 173         if (getpeername(connection_in, (struct sockaddr *)&from, &fromlen) < 0)
 174                 return 0;
 175         tolen = sizeof(to);
 176         memset(&to, 0, sizeof(to));
 177         if (getpeername(connection_out, (struct sockaddr *)&to, &tolen) < 0)
 178                 return 0;
 179         if (fromlen != tolen || memcmp(&from, &to, fromlen) != 0)
 180                 return 0;
 181         if (from.ss_family != AF_INET && from.ss_family != AF_INET6)
 182                 return 0;
 183         return 1;
 184 }
 185
 186 /* returns 1 if connection is via ipv4 */
 187
 188 int
 189 packet_connection_is_ipv4()
 190 {
 191         struct sockaddr_storage to;
 192         socklen_t tolen = sizeof(to);
 193
 194         memset(&to, 0, sizeof(to));
 195         if (getsockname(connection_out, (struct sockaddr *)&to, &tolen) < 0)
 196                 return 0;
 197         if (to.ss_family != AF_INET)
 198                 return 0;
 199         return 1;
 200 }
 201
 202 /* Sets the connection into non-blocking mode. */
 203
 204 void
 205 packet_set_nonblocking()
 206 {
 207         /* Set the socket into non-blocking mode. */
 208         if (fcntl(connection_in, F_SETFL, O_NONBLOCK) < 0)
 209                 error("fcntl O_NONBLOCK: %.100s", strerror(errno));
 210
 211         if (connection_out != connection_in) {
 212                 if (fcntl(connection_out, F_SETFL, O_NONBLOCK) < 0)
 213                         error("fcntl O_NONBLOCK: %.100s", strerror(errno));
 214         }
 215 }
 216
 217 /* Returns the socket used for reading. */
 218
 219 int
 220 packet_get_connection_in()
 221 {
 222         return connection_in;
 223 }
 224
 225 /* Returns the descriptor used for writing. */
 226
 227 int
 228 packet_get_connection_out()
 229 {
 230         return connection_out;
 231 }
 232
 233 /* Closes the connection and clears and frees internal data structures. */
 234
 235 void
 236 packet_close()
 237 {
 238         if (!initialized)
 239                 return;
 240         initialized = 0;
 241         if (connection_in == connection_out) {
 242                 shutdown(connection_out, SHUT_RDWR);
 243                 close(connection_out);
 244         } else {
 245                 close(connection_in);
 246                 close(connection_out);
 247         }
 248         buffer_free(&input);
 249         buffer_free(&output);
 250         buffer_free(&outgoing_packet);
 251         buffer_free(&incoming_packet);
 252         if (packet_compression) {
 253                 buffer_free(&compression_buffer);
 254                 buffer_compress_uninit();
 255         }
 256 }
 257
 258 /* Sets remote side protocol flags. */
 259
 260 void
 261 packet_set_protocol_flags(unsigned int protocol_flags)
 262 {
 263         remote_protocol_flags = protocol_flags;
 264         channel_set_options((protocol_flags & SSH_PROTOFLAG_HOST_IN_FWD_OPEN) != 0);
 265 }
 266
 267 /* Returns the remote protocol flags set earlier by the above function. */
 268
 269 unsigned int
 270 packet_get_protocol_flags()
 271 {
 272         return remote_protocol_flags;
 273 }
 274
 275 /*
 276  * Starts packet compression from the next packet on in both directions.
 277  * Level is compression level 1 (fastest) - 9 (slow, best) as in gzip.
 278  */
 279
 280 /*** XXXXX todo: kex means re-init */
 281 void
 282 packet_start_compression(int level)
 283 {
 284         if (packet_compression)
 285                 fatal("Compression already enabled.");
 286         packet_compression = 1;
 287         buffer_init(&compression_buffer);
 288         buffer_compress_init(level);
 289 }
 290
 291 /*
 292  * Encrypts the given number of bytes, copying from src to dest. bytes is
 293  * known to be a multiple of 8.
 294  */
 295
 296 void
 297 packet_encrypt(CipherContext * cc, void *dest, void *src,
 298     unsigned int bytes)
 299 {
 300         cipher_encrypt(cc, dest, src, bytes);
 301 }
 302
 303 /*
 304  * Decrypts the given number of bytes, copying from src to dest. bytes is
 305  * known to be a multiple of 8.
 306  */
 307
 308 void
 309 packet_decrypt(CipherContext * cc, void *dest, void *src,
 310     unsigned int bytes)
 311 {
 312         int i;
 313
 314         if ((bytes % 8) != 0)
 315                 fatal("packet_decrypt: bad ciphertext length %d", bytes);
 316
 317         /*
 318          * Cryptographic attack detector for ssh - Modifications for packet.c
 319          * (C)1998 CORE-SDI, Buenos Aires Argentina Ariel Futoransky(futo@core-sdi.com)
 320          */
 321
 322         if (cc->type == SSH_CIPHER_NONE || compat20) {
 323                 i = DEATTACK_OK;
 324         } else {
 325                 i = detect_attack(src, bytes, NULL);
 326         }
 327         if (i == DEATTACK_DETECTED)
 328                 packet_disconnect("crc32 compensation attack: network attack detected");
 329
 330         cipher_decrypt(cc, dest, src, bytes);
 331 }
 332
 333 /*
 334  * Causes any further packets to be encrypted using the given key.  The same
 335  * key is used for both sending and reception.  However, both directions are
 336  * encrypted independently of each other.
 337  */
 338
 339 void
 340 packet_set_encryption_key(const unsigned char *key, unsigned int keylen,
 341     int cipher)
 342 {
 343         if (keylen < 20)
 344                 fatal("keylen too small: %d", keylen);
 345
 346         /* All other ciphers use the same key in both directions for now. */
 347         cipher_set_key(&receive_context, cipher, key, keylen);
 348         cipher_set_key(&send_context, cipher, key, keylen);
 349 }
 350
 351 /* Starts constructing a packet to send. */
 352
 353 void
 354 packet_start1(int type)
 355 {
 356         char buf[9];
 357
 358         buffer_clear(&outgoing_packet);
 359         memset(buf, 0, 8);
 360         buf[8] = type;
 361         buffer_append(&outgoing_packet, buf, 9);
 362 }
 363
 364 void
 365 packet_start2(int type)
 366 {
 367         char buf[4+1+1];
 368
 369         buffer_clear(&outgoing_packet);
 370         memset(buf, 0, sizeof buf);
 371         /* buf[0..3] = payload_len; */
 372         /* buf[4] =    pad_len; */
 373         buf[5] = type & 0xff;
 374         buffer_append(&outgoing_packet, buf, sizeof buf);
 375 }
 376
 377 void
 378 packet_start(int type)
 379 {
 380         DBG(debug("packet_start[%d]",type));
 381         if (use_ssh2_packet_format)
 382                 packet_start2(type);
 383         else
 384                 packet_start1(type);
 385 }
 386
 387 /* Appends a character to the packet data. */
 388
 389 void
 390 packet_put_char(int value)
 391 {
 392         char ch = value;
 393         buffer_append(&outgoing_packet, &ch, 1);
 394 }
 395
 396 /* Appends an integer to the packet data. */
 397
 398 void
 399 packet_put_int(unsigned int value)
 400 {
 401         buffer_put_int(&outgoing_packet, value);
 402 }
 403
 404 /* Appends a string to packet data. */
 405
 406 void
 407 packet_put_string(const char *buf, unsigned int len)
 408 {
 409         buffer_put_string(&outgoing_packet, buf, len);
 410 }
 411 void
 412 packet_put_cstring(const char *str)
 413 {
 414         buffer_put_string(&outgoing_packet, str, strlen(str));
 415 }
 416
 417 void
 418 packet_put_raw(const char *buf, unsigned int len)
 419 {
 420         buffer_append(&outgoing_packet, buf, len);
 421 }
 422
 423
 424 /* Appends an arbitrary precision integer to packet data. */
 425
 426 void
 427 packet_put_bignum(BIGNUM * value)
 428 {
 429         buffer_put_bignum(&outgoing_packet, value);
 430 }
 431 void
 432 packet_put_bignum2(BIGNUM * value)
 433 {
 434         buffer_put_bignum2(&outgoing_packet, value);
 435 }
 436
 437 /*
 438  * Finalizes and sends the packet.  If the encryption key has been set,
 439  * encrypts the packet before sending.
 440  */
 441
 442 void
 443 packet_send1()
 444 {
 445         char buf[8], *cp;
 446         int i, padding, len;
 447         unsigned int checksum;
 448         u_int32_t rand = 0;
 449
 450         /*
 451          * If using packet compression, compress the payload of the outgoing
 452          * packet.
 453          */
 454         if (packet_compression) {
 455                 buffer_clear(&compression_buffer);
 456                 /* Skip padding. */
 457                 buffer_consume(&outgoing_packet, 8);
 458                 /* padding */
 459                 buffer_append(&compression_buffer, "\0\0\0\0\0\0\0\0", 8);
 460                 buffer_compress(&outgoing_packet, &compression_buffer);
 461                 buffer_clear(&outgoing_packet);
 462                 buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
 463                               buffer_len(&compression_buffer));
 464         }
 465         /* Compute packet length without padding (add checksum, remove padding). */
 466         len = buffer_len(&outgoing_packet) + 4 - 8;
 467
 468         /* Insert padding. Initialized to zero in packet_start1() */
 469         padding = 8 - len % 8;
 470         if (cipher_type != SSH_CIPHER_NONE) {
 471                 cp = buffer_ptr(&outgoing_packet);
 472                 for (i = 0; i < padding; i++) {
 473                         if (i % 4 == 0)
 474                                 rand = arc4random();
 475                         cp[7 - i] = rand & 0xff;
 476                         rand >>= 8;
 477                 }
 478         }
 479         buffer_consume(&outgoing_packet, 8 - padding);
 480
 481         /* Add check bytes. */
 482         checksum = crc32((unsigned char *) buffer_ptr(&outgoing_packet),
 483                          buffer_len(&outgoing_packet));
 484         PUT_32BIT(buf, checksum);
 485         buffer_append(&outgoing_packet, buf, 4);
 486
 487 #ifdef PACKET_DEBUG
 488         fprintf(stderr, "packet_send plain: ");
 489         buffer_dump(&outgoing_packet);
 490 #endif
 491
 492         /* Append to output. */
 493         PUT_32BIT(buf, len);
 494         buffer_append(&output, buf, 4);
 495         buffer_append_space(&output, &cp, buffer_len(&outgoing_packet));
 496         packet_encrypt(&send_context, cp, buffer_ptr(&outgoing_packet),
 497                        buffer_len(&outgoing_packet));
 498
 499 #ifdef PACKET_DEBUG
 500         fprintf(stderr, "encrypted: ");
 501         buffer_dump(&output);
 502 #endif
 503
 504         buffer_clear(&outgoing_packet);
 505
 506         /*
 507          * Note that the packet is now only buffered in output.  It won\'t be
 508          * actually sent until packet_write_wait or packet_write_poll is
 509          * called.
 510          */
 511 }
 512
 513 /*
 514  * Finalize packet in SSH2 format (compress, mac, encrypt, enqueue)
 515  */
 516 void
 517 packet_send2()
 518 {
 519         unsigned char *macbuf = NULL;
 520         char *cp;
 521         unsigned int packet_length = 0;
 522         unsigned int i, padlen, len;
 523         u_int32_t rand = 0;
 524         static unsigned int seqnr = 0;
 525         int type;
 526         Enc *enc   = NULL;
 527         Mac *mac   = NULL;
 528         Comp *comp = NULL;
 529         int block_size;
 530
 531         if (kex != NULL) {
 532                 enc  = &kex->enc[MODE_OUT];
 533                 mac  = &kex->mac[MODE_OUT];
 534                 comp = &kex->comp[MODE_OUT];
 535         }
 536         block_size = enc ? enc->block_size : 8;
 537
 538         cp = buffer_ptr(&outgoing_packet);
 539         type = cp[5] & 0xff;
 540
 541 #ifdef PACKET_DEBUG
 542         fprintf(stderr, "plain:     ");
 543         buffer_dump(&outgoing_packet);
 544 #endif
 545
 546         if (comp && comp->enabled) {
 547                 len = buffer_len(&outgoing_packet);
 548                 /* skip header, compress only payload */
 549                 buffer_consume(&outgoing_packet, 5);
 550                 buffer_clear(&compression_buffer);
 551                 buffer_compress(&outgoing_packet, &compression_buffer);
 552                 buffer_clear(&outgoing_packet);
 553                 buffer_append(&outgoing_packet, "\0\0\0\0\0", 5);
 554                 buffer_append(&outgoing_packet, buffer_ptr(&compression_buffer),
 555                     buffer_len(&compression_buffer));
 556                 DBG(debug("compression: raw %d compressed %d", len,
 557                     buffer_len(&outgoing_packet)));
 558         }
 559
 560         /* sizeof (packet_len + pad_len + payload) */
 561         len = buffer_len(&outgoing_packet);
 562
 563         /*
 564          * calc size of padding, alloc space, get random data,
 565          * minimum padding is 4 bytes
 566          */
 567         padlen = block_size - (len % block_size);
 568         if (padlen < 4)
 569                 padlen += block_size;
 570         buffer_append_space(&outgoing_packet, &cp, padlen);
 571         if (enc && enc->type != SSH_CIPHER_NONE) {
 572                 /* random padding */
 573                 for (i = 0; i < padlen; i++) {
 574                         if (i % 4 == 0)
 575                                 rand = arc4random();
 576                         cp[i] = rand & 0xff;
 577                         rand <<= 8;
 578                 }
 579         } else {
 580                 /* clear padding */
 581                 memset(cp, 0, padlen);
 582         }
 583         /* packet_length includes payload, padding and padding length field */
 584         packet_length = buffer_len(&outgoing_packet) - 4;
 585         cp = buffer_ptr(&outgoing_packet);
 586         PUT_32BIT(cp, packet_length);
 587         cp[4] = padlen & 0xff;
 588         DBG(debug("send: len %d (includes padlen %d)", packet_length+4, padlen));
 589
 590         /* compute MAC over seqnr and packet(length fields, payload, padding) */
 591         if (mac && mac->enabled) {
 592                 macbuf = hmac( mac->md, seqnr,
 593                     (unsigned char *) buffer_ptr(&outgoing_packet),
 594                     buffer_len(&outgoing_packet),
 595                     mac->key, mac->key_len
 596                 );
 597                 DBG(debug("done calc HMAC out #%d", seqnr));
 598         }
 599         /* encrypt packet and append to output buffer. */
 600         buffer_append_space(&output, &cp, buffer_len(&outgoing_packet));
 601         packet_encrypt(&send_context, cp, buffer_ptr(&outgoing_packet),
 602             buffer_len(&outgoing_packet));
 603         /* append unencrypted MAC */
 604         if (mac && mac->enabled)
 605                 buffer_append(&output, (char *)macbuf, mac->mac_len);
 606 #ifdef PACKET_DEBUG
 607         fprintf(stderr, "encrypted: ");
 608         buffer_dump(&output);
 609 #endif
 610         /* increment sequence number for outgoing packets */
 611         if (++seqnr == 0)
 612                 log("outgoing seqnr wraps around");
 613         buffer_clear(&outgoing_packet);
 614
 615         if (type == SSH2_MSG_NEWKEYS) {
 616                 if (kex==NULL || mac==NULL || enc==NULL || comp==NULL)
 617                         fatal("packet_send2: no KEX");
 618                 if (mac->md != NULL)
 619                         mac->enabled = 1;
 620                 DBG(debug("cipher_set_key_iv send_context"));
 621                 cipher_set_key_iv(&send_context, enc->type,
 622                     enc->key, enc->key_len,
 623                     enc->iv, enc->iv_len);
 624                 clear_enc_keys(enc, kex->we_need);
 625                 if (comp->type != 0 && comp->enabled == 0) {
 626                         comp->enabled = 1;
 627                         if (! packet_compression)
 628                                 packet_start_compression(6);
 629                 }
 630         }
 631 }
 632
 633 void
 634 packet_send()
 635 {
 636         if (use_ssh2_packet_format)
 637                 packet_send2();
 638         else
 639                 packet_send1();
 640         DBG(debug("packet_send done"));
 641 }
 642
 643 /*
 644  * Waits until a packet has been received, and returns its type.  Note that
 645  * no other data is processed until this returns, so this function should not
 646  * be used during the interactive session.
 647  */
 648
 649 int
 650 packet_read(int *payload_len_ptr)
 651 {
 652         int type, len;
 653         fd_set set;
 654         char buf[8192];
 655         DBG(debug("packet_read()"));
 656
 657         /* Since we are blocking, ensure that all written packets have been sent. */
 658         packet_write_wait();
 659
 660         /* Stay in the loop until we have received a complete packet. */
 661         for (;;) {
 662                 /* Try to read a packet from the buffer. */
 663                 type = packet_read_poll(payload_len_ptr);
 664                 if (!use_ssh2_packet_format && (
 665                     type == SSH_SMSG_SUCCESS
 666                     || type == SSH_SMSG_FAILURE
 667                     || type == SSH_CMSG_EOF
 668                     || type == SSH_CMSG_EXIT_CONFIRMATION))
 669                         packet_integrity_check(*payload_len_ptr, 0, type);
 670                 /* If we got a packet, return it. */
 671                 if (type != SSH_MSG_NONE)
 672                         return type;
 673                 /*
 674                  * Otherwise, wait for some data to arrive, add it to the
 675                  * buffer, and try again.
 676                  */
 677                 FD_ZERO(&set);
 678                 FD_SET(connection_in, &set);
 679
 680                 /* Wait for some data to arrive. */
 681                 select(connection_in + 1, &set, NULL, NULL, NULL);
 682
 683                 /* Read data from the socket. */
 684                 len = read(connection_in, buf, sizeof(buf));
 685                 if (len == 0) {
 686                         log("Connection closed by %.200s", get_remote_ipaddr());
 687                         fatal_cleanup();
 688                 }
 689                 if (len < 0)
 690                         fatal("Read from socket failed: %.100s", strerror(errno));
 691                 /* Append it to the buffer. */
 692                 packet_process_incoming(buf, len);
 693         }
 694         /* NOTREACHED */
 695 }
 696
 697 /*
 698  * Waits until a packet has been received, verifies that its type matches
 699  * that given, and gives a fatal error and exits if there is a mismatch.
 700  */
 701
 702 void
 703 packet_read_expect(int *payload_len_ptr, int expected_type)
 704 {
 705         int type;
 706
 707         type = packet_read(payload_len_ptr);
 708         if (type != expected_type)
 709                 packet_disconnect("Protocol error: expected packet type %d, got %d",
 710                     expected_type, type);
 711 }
 712
 713 /* Checks if a full packet is available in the data received so far via
 714  * packet_process_incoming.  If so, reads the packet; otherwise returns
 715  * SSH_MSG_NONE.  This does not wait for data from the connection.
 716  *
 717  * SSH_MSG_DISCONNECT is handled specially here.  Also,
 718  * SSH_MSG_IGNORE messages are skipped by this function and are never returned
 719  * to higher levels.
 720  *
 721  * The returned payload_len does include space consumed by:
 722  *      Packet length
 723  *      Padding
 724  *      Packet type
 725  *      Check bytes
 726  */
 727
 728 int
 729 packet_read_poll1(int *payload_len_ptr)
 730 {
 731         unsigned int len, padded_len;
 732         unsigned char *ucp;
 733         char buf[8], *cp;
 734         unsigned int checksum, stored_checksum;
 735
 736         /* Check if input size is less than minimum packet size. */
 737         if (buffer_len(&input) < 4 + 8)
 738                 return SSH_MSG_NONE;
 739         /* Get length of incoming packet. */
 740         ucp = (unsigned char *) buffer_ptr(&input);
 741         len = GET_32BIT(ucp);
 742         if (len < 1 + 2 + 2 || len > 256 * 1024)
 743                 packet_disconnect("Bad packet length %d.", len);
 744         padded_len = (len + 8) & ~7;
 745
 746         /* Check if the packet has been entirely received. */
 747         if (buffer_len(&input) < 4 + padded_len)
 748                 return SSH_MSG_NONE;
 749
 750         /* The entire packet is in buffer. */
 751
 752         /* Consume packet length. */
 753         buffer_consume(&input, 4);
 754
 755         /* Copy data to incoming_packet. */
 756         buffer_clear(&incoming_packet);
 757         buffer_append_space(&incoming_packet, &cp, padded_len);
 758         packet_decrypt(&receive_context, cp, buffer_ptr(&input), padded_len);
 759         buffer_consume(&input, padded_len);
 760
 761 #ifdef PACKET_DEBUG
 762         fprintf(stderr, "read_poll plain: ");
 763         buffer_dump(&incoming_packet);
 764 #endif
 765
 766         /* Compute packet checksum. */
 767         checksum = crc32((unsigned char *) buffer_ptr(&incoming_packet),
 768             buffer_len(&incoming_packet) - 4);
 769
 770         /* Skip padding. */
 771         buffer_consume(&incoming_packet, 8 - len % 8);
 772
 773         /* Test check bytes. */
 774
 775         if (len != buffer_len(&incoming_packet))
 776                 packet_disconnect("packet_read_poll: len %d != buffer_len %d.",
 777                     len, buffer_len(&incoming_packet));
 778
 779         ucp = (unsigned char *) buffer_ptr(&incoming_packet) + len - 4;
 780         stored_checksum = GET_32BIT(ucp);
 781         if (checksum != stored_checksum)
 782                 packet_disconnect("Corrupted check bytes on input.");
 783         buffer_consume_end(&incoming_packet, 4);
 784
 785         /* If using packet compression, decompress the packet. */
 786         if (packet_compression) {
 787                 buffer_clear(&compression_buffer);
 788                 buffer_uncompress(&incoming_packet, &compression_buffer);
 789                 buffer_clear(&incoming_packet);
 790                 buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
 791                     buffer_len(&compression_buffer));
 792         }
 793         /* Get packet type. */
 794         buffer_get(&incoming_packet, &buf[0], 1);
 795
 796         /* Return length of payload (without type field). */
 797         *payload_len_ptr = buffer_len(&incoming_packet);
 798
 799         /* Return type. */
 800         return (unsigned char) buf[0];
 801 }
 802
 803 int
 804 packet_read_poll2(int *payload_len_ptr)
 805 {
 806         unsigned int padlen, need;
 807         unsigned char buf[8], *macbuf;
 808         unsigned char *ucp;
 809         char *cp;
 810         static unsigned int packet_length = 0;
 811         static unsigned int seqnr = 0;
 812         int type;
 813         int maclen, block_size;
 814         Enc *enc   = NULL;
 815         Mac *mac   = NULL;
 816         Comp *comp = NULL;
 817
 818         if (kex != NULL) {
 819                 enc  = &kex->enc[MODE_IN];
 820                 mac  = &kex->mac[MODE_IN];
 821                 comp = &kex->comp[MODE_IN];
 822         }
 823         maclen = mac && mac->enabled ? mac->mac_len : 0;
 824         block_size = enc ? enc->block_size : 8;
 825
 826         if (packet_length == 0) {
 827                 /*
 828                  * check if input size is less than the cipher block size,
 829                  * decrypt first block and extract length of incoming packet
 830                  */
 831                 if (buffer_len(&input) < block_size)
 832                         return SSH_MSG_NONE;
 833                 buffer_clear(&incoming_packet);
 834                 buffer_append_space(&incoming_packet, &cp, block_size);
 835                 packet_decrypt(&receive_context, cp, buffer_ptr(&input),
 836                     block_size);
 837                 ucp = (unsigned char *) buffer_ptr(&incoming_packet);
 838                 packet_length = GET_32BIT(ucp);
 839                 if (packet_length < 1 + 4 || packet_length > 256 * 1024) {
 840                         buffer_dump(&incoming_packet);
 841                         packet_disconnect("Bad packet length %d.", packet_length);
 842                 }
 843                 DBG(debug("input: packet len %d", packet_length+4));
 844                 buffer_consume(&input, block_size);
 845         }
 846         /* we have a partial packet of block_size bytes */
 847         need = 4 + packet_length - block_size;
 848         DBG(debug("partial packet %d, need %d, maclen %d", block_size,
 849             need, maclen));
 850         if (need % block_size != 0)
 851                 fatal("padding error: need %d block %d mod %d",
 852                     need, block_size, need % block_size);
 853         /*
 854          * check if the entire packet has been received and
 855          * decrypt into incoming_packet
 856          */
 857         if (buffer_len(&input) < need + maclen)
 858                 return SSH_MSG_NONE;
 859 #ifdef PACKET_DEBUG
 860         fprintf(stderr, "read_poll enc/full: ");
 861         buffer_dump(&input);
 862 #endif
 863         buffer_append_space(&incoming_packet, &cp, need);
 864         packet_decrypt(&receive_context, cp, buffer_ptr(&input), need);
 865         buffer_consume(&input, need);
 866         /*
 867          * compute MAC over seqnr and packet,
 868          * increment sequence number for incoming packet
 869          */
 870         if (mac && mac->enabled) {
 871                 macbuf = hmac( mac->md, seqnr,
 872                     (unsigned char *) buffer_ptr(&incoming_packet),
 873                     buffer_len(&incoming_packet),
 874                     mac->key, mac->key_len
 875                 );
 876                 if (memcmp(macbuf, buffer_ptr(&input), mac->mac_len) != 0)
 877                         packet_disconnect("Corrupted HMAC on input.");
 878                 DBG(debug("HMAC #%d ok", seqnr));
 879                 buffer_consume(&input, mac->mac_len);
 880         }
 881         if (++seqnr == 0)
 882                 log("incoming seqnr wraps around");
 883
 884         /* get padlen */
 885         cp = buffer_ptr(&incoming_packet) + 4;
 886         padlen = *cp & 0xff;
 887         DBG(debug("input: padlen %d", padlen));
 888         if (padlen < 4)
 889                 packet_disconnect("Corrupted padlen %d on input.", padlen);
 890
 891         /* skip packet size + padlen, discard padding */
 892         buffer_consume(&incoming_packet, 4 + 1);
 893         buffer_consume_end(&incoming_packet, padlen);
 894
 895         DBG(debug("input: len before de-compress %d", buffer_len(&incoming_packet)));
 896         if (comp && comp->enabled) {
 897                 buffer_clear(&compression_buffer);
 898                 buffer_uncompress(&incoming_packet, &compression_buffer);
 899                 buffer_clear(&incoming_packet);
 900                 buffer_append(&incoming_packet, buffer_ptr(&compression_buffer),
 901                     buffer_len(&compression_buffer));
 902                 DBG(debug("input: len after de-compress %d", buffer_len(&incoming_packet)));
 903         }
 904         /*
 905          * get packet type, implies consume.
 906          * return length of payload (without type field)
 907          */
 908         buffer_get(&incoming_packet, (char *)&buf[0], 1);
 909         *payload_len_ptr = buffer_len(&incoming_packet);
 910
 911         /* reset for next packet */
 912         packet_length = 0;
 913
 914         /* extract packet type */
 915         type = (unsigned char)buf[0];
 916
 917         if (type == SSH2_MSG_NEWKEYS) {
 918                 if (kex==NULL || mac==NULL || enc==NULL || comp==NULL)
 919                         fatal("packet_read_poll2: no KEX");
 920                 if (mac->md != NULL)
 921                         mac->enabled = 1;
 922                 DBG(debug("cipher_set_key_iv receive_context"));
 923                 cipher_set_key_iv(&receive_context, enc->type,
 924                     enc->key, enc->key_len,
 925                     enc->iv, enc->iv_len);
 926                 clear_enc_keys(enc, kex->we_need);
 927                 if (comp->type != 0 && comp->enabled == 0) {
 928                         comp->enabled = 1;
 929                         if (! packet_compression)
 930                                 packet_start_compression(6);
 931                 }
 932         }
 933
 934 #ifdef PACKET_DEBUG
 935         fprintf(stderr, "read/plain[%d]:\r\n",type);
 936         buffer_dump(&incoming_packet);
 937 #endif
 938         return (unsigned char)type;
 939 }
 940
 941 int
 942 packet_read_poll(int *payload_len_ptr)
 943 {
 944         char *msg;
 945         for (;;) {
 946                 int type = use_ssh2_packet_format ?
 947                     packet_read_poll2(payload_len_ptr):
 948                     packet_read_poll1(payload_len_ptr);
 949
 950                 if(compat20) {
 951                         int reason;
 952                         if (type != 0)
 953                                 DBG(debug("received packet type %d", type));
 954                         switch(type) {
 955                         case SSH2_MSG_IGNORE:
 956                                 break;
 957                         case SSH2_MSG_DEBUG:
 958                                 packet_get_char();
 959                                 msg = packet_get_string(NULL);
 960                                 debug("Remote: %.900s", msg);
 961                                 xfree(msg);
 962                                 msg = packet_get_string(NULL);
 963                                 xfree(msg);
 964                                 break;
 965                         case SSH2_MSG_DISCONNECT:
 966                                 reason = packet_get_int();
 967                                 msg = packet_get_string(NULL);
 968                                 log("Received disconnect: %d: %.900s", reason, msg);
 969                                 xfree(msg);
 970                                 fatal_cleanup();
 971                                 break;
 972                         default:
 973                                 return type;
 974                                 break;
 975                         }
 976                 } else {
 977                         switch(type) {
 978                         case SSH_MSG_IGNORE:
 979                                 break;
 980                         case SSH_MSG_DEBUG:
 981                                 msg = packet_get_string(NULL);
 982                                 debug("Remote: %.900s", msg);
 983                                 xfree(msg);
 984                                 break;
 985                         case SSH_MSG_DISCONNECT:
 986                                 msg = packet_get_string(NULL);
 987                                 log("Received disconnect: %.900s", msg);
 988                                 fatal_cleanup();
 989                                 xfree(msg);
 990                                 break;
 991                         default:
 992                                 if (type != 0)
 993                                         DBG(debug("received packet type %d", type));
 994                                 return type;
 995                                 break;
 996                         }
 997                 }
 998         }
 999 }
1000
1001 /*
1002  * Buffers the given amount of input characters.  This is intended to be used
1003  * together with packet_read_poll.
1004  */
1005
1006 void
1007 packet_process_incoming(const char *buf, unsigned int len)
1008 {
1009         buffer_append(&input, buf, len);
1010 }
1011
1012 /* Returns a character from the packet. */
1013
1014 unsigned int
1015 packet_get_char()
1016 {
1017         char ch;
1018         buffer_get(&incoming_packet, &ch, 1);
1019         return (unsigned char) ch;
1020 }
1021
1022 /* Returns an integer from the packet data. */
1023
1024 unsigned int
1025 packet_get_int()
1026 {
1027         return buffer_get_int(&incoming_packet);
1028 }
1029
1030 /*
1031  * Returns an arbitrary precision integer from the packet data.  The integer
1032  * must have been initialized before this call.
1033  */
1034
1035 void
1036 packet_get_bignum(BIGNUM * value, int *length_ptr)
1037 {
1038         *length_ptr = buffer_get_bignum(&incoming_packet, value);
1039 }
1040
1041 void
1042 packet_get_bignum2(BIGNUM * value, int *length_ptr)
1043 {
1044         *length_ptr = buffer_get_bignum2(&incoming_packet, value);
1045 }
1046
1047 char *
1048 packet_get_raw(int *length_ptr)
1049 {
1050         int bytes = buffer_len(&incoming_packet);
1051         if (length_ptr != NULL)
1052                 *length_ptr = bytes;
1053         return buffer_ptr(&incoming_packet);
1054 }
1055
1056 int
1057 packet_remaining(void)
1058 {
1059         return buffer_len(&incoming_packet);
1060 }
1061
1062 /*
1063  * Returns a string from the packet data.  The string is allocated using
1064  * xmalloc; it is the responsibility of the calling program to free it when
1065  * no longer needed.  The length_ptr argument may be NULL, or point to an
1066  * integer into which the length of the string is stored.
1067  */
1068
1069 char *
1070 packet_get_string(unsigned int *length_ptr)
1071 {
1072         return buffer_get_string(&incoming_packet, length_ptr);
1073 }
1074
1075 /*
1076  * Sends a diagnostic message from the server to the client.  This message
1077  * can be sent at any time (but not while constructing another message). The
1078  * message is printed immediately, but only if the client is being executed
1079  * in verbose mode.  These messages are primarily intended to ease debugging
1080  * authentication problems.   The length of the formatted message must not
1081  * exceed 1024 bytes.  This will automatically call packet_write_wait.
1082  */
1083
1084 void
1085 packet_send_debug(const char *fmt,...)
1086 {
1087         char buf[1024];
1088         va_list args;
1089
1090         va_start(args, fmt);
1091         vsnprintf(buf, sizeof(buf), fmt, args);
1092         va_end(args);
1093
1094         if (compat20) {
1095                 packet_start(SSH2_MSG_DEBUG);
1096                 packet_put_char(0);     /* bool: always display */
1097                 packet_put_cstring(buf);
1098                 packet_put_cstring("");
1099         } else {
1100                 packet_start(SSH_MSG_DEBUG);
1101                 packet_put_cstring(buf);
1102         }
1103         packet_send();
1104         packet_write_wait();
1105 }
1106
1107 /*
1108  * Logs the error plus constructs and sends a disconnect packet, closes the
1109  * connection, and exits.  This function never returns. The error message
1110  * should not contain a newline.  The length of the formatted message must
1111  * not exceed 1024 bytes.
1112  */
1113
1114 void
1115 packet_disconnect(const char *fmt,...)
1116 {
1117         char buf[1024];
1118         va_list args;
1119         static int disconnecting = 0;
1120         if (disconnecting)      /* Guard against recursive invocations. */
1121                 fatal("packet_disconnect called recursively.");
1122         disconnecting = 1;
1123
1124         /*
1125          * Format the message.  Note that the caller must make sure the
1126          * message is of limited size.
1127          */
1128         va_start(args, fmt);
1129         vsnprintf(buf, sizeof(buf), fmt, args);
1130         va_end(args);
1131
1132         /* Send the disconnect message to the other side, and wait for it to get sent. */
1133         if (compat20) {
1134                 packet_start(SSH2_MSG_DISCONNECT);
1135                 packet_put_int(SSH2_DISCONNECT_PROTOCOL_ERROR);
1136                 packet_put_cstring(buf);
1137                 packet_put_cstring("");
1138         } else {
1139                 packet_start(SSH_MSG_DISCONNECT);
1140                 packet_put_string(buf, strlen(buf));
1141         }
1142         packet_send();
1143         packet_write_wait();
1144
1145         /* Stop listening for connections. */
1146         channel_stop_listening();
1147
1148         /* Close the connection. */
1149         packet_close();
1150
1151         /* Display the error locally and exit. */
1152         log("Disconnecting: %.100s", buf);
1153         fatal_cleanup();
1154 }
1155
1156 /* Checks if there is any buffered output, and tries to write some of the output. */
1157
1158 void
1159 packet_write_poll()
1160 {
1161         int len = buffer_len(&output);
1162         if (len > 0) {
1163                 len = write(connection_out, buffer_ptr(&output), len);
1164                 if (len <= 0) {
1165                         if (errno == EAGAIN)
1166                                 return;
1167                         else
1168                                 fatal("Write failed: %.100s", strerror(errno));
1169                 }
1170                 buffer_consume(&output, len);
1171         }
1172 }
1173
1174 /*
1175  * Calls packet_write_poll repeatedly until all pending output data has been
1176  * written.
1177  */
1178
1179 void
1180 packet_write_wait()
1181 {
1182         packet_write_poll();
1183         while (packet_have_data_to_write()) {
1184                 fd_set set;
1185                 FD_ZERO(&set);
1186                 FD_SET(connection_out, &set);
1187                 select(connection_out + 1, NULL, &set, NULL, NULL);
1188                 packet_write_poll();
1189         }
1190 }
1191
1192 /* Returns true if there is buffered data to write to the connection. */
1193
1194 int
1195 packet_have_data_to_write()
1196 {
1197         return buffer_len(&output) != 0;
1198 }
1199
1200 /* Returns true if there is not too much data to write to the connection. */
1201
1202 int
1203 packet_not_very_much_data_to_write()
1204 {
1205         if (interactive_mode)
1206                 return buffer_len(&output) < 16384;
1207         else
1208                 return buffer_len(&output) < 128 * 1024;
1209 }
1210
1211 /* Informs that the current session is interactive.  Sets IP flags for that. */
1212
1213 void
1214 packet_set_interactive(int interactive, int keepalives)
1215 {
1216         int on = 1;
1217
1218         /* Record that we are in interactive mode. */
1219         interactive_mode = interactive;
1220
1221         /* Only set socket options if using a socket.  */
1222         if (!packet_connection_is_on_socket())
1223                 return;
1224         if (keepalives) {
1225                 /* Set keepalives if requested. */
1226                 if (setsockopt(connection_in, SOL_SOCKET, SO_KEEPALIVE, (void *) &on,
1227                     sizeof(on)) < 0)
1228                         error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));
1229         }
1230         /*
1231          * IPTOS_LOWDELAY, TCP_NODELAY and IPTOS_THROUGHPUT are IPv4 only
1232          */
1233         if (!packet_connection_is_ipv4())
1234                 return;
1235         if (interactive) {
1236                 /*
1237                  * Set IP options for an interactive connection.  Use
1238                  * IPTOS_LOWDELAY and TCP_NODELAY.
1239                  */
1240 #if defined(IP_TOS) && !defined(IP_TOS_IS_BROKEN)
1241                 int lowdelay = IPTOS_LOWDELAY;
1242                 if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *) &lowdelay,
1243                     sizeof(lowdelay)) < 0)
1244                         error("setsockopt IPTOS_LOWDELAY: %.100s", strerror(errno));
1245 #endif
1246                 if (setsockopt(connection_in, IPPROTO_TCP, TCP_NODELAY, (void *) &on,
1247                     sizeof(on)) < 0)
1248                         error("setsockopt TCP_NODELAY: %.100s", strerror(errno));
1249         } else {
1250                 /*
1251                  * Set IP options for a non-interactive connection.  Use
1252                  * IPTOS_THROUGHPUT.
1253                  */
1254 #if defined(IP_TOS) && !defined(IP_TOS_IS_BROKEN)
1255                 int throughput = IPTOS_THROUGHPUT;
1256                 if (setsockopt(connection_in, IPPROTO_IP, IP_TOS, (void *) &throughput,
1257                     sizeof(throughput)) < 0)
1258                         error("setsockopt IPTOS_THROUGHPUT: %.100s", strerror(errno));
1259 #endif
1260         }
1261 }
1262
1263 /* Returns true if the current connection is interactive. */
1264
1265 int
1266 packet_is_interactive()
1267 {
1268         return interactive_mode;
1269 }
1270
1271 int
1272 packet_set_maxsize(int s)
1273 {
1274         static int called = 0;
1275         if (called) {
1276                 log("packet_set_maxsize: called twice: old %d new %d",
1277                     max_packet_size, s);
1278                 return -1;
1279         }
1280         if (s < 4 * 1024 || s > 1024 * 1024) {
1281                 log("packet_set_maxsize: bad size %d", s);
1282                 return -1;
1283         }
1284         log("packet_set_maxsize: setting to %d", s);
1285         max_packet_size = s;
1286         return s;
1287 }