1 /* 2 * Dropbear - a SSH2 server 3 * 4 * Copyright (c) 2002,2003 Matt Johnston 5 * All rights reserved. 6 * 7 * Permission is hereby granted, free of charge, to any person obtaining a copy 8 * of this software and associated documentation files (the "Software"), to deal 9 * in the Software without restriction, including without limitation the rights 10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 11 * copies of the Software, and to permit persons to whom the Software is 12 * furnished to do so, subject to the following conditions: 13 * 14 * The above copyright notice and this permission notice shall be included in 15 * all copies or substantial portions of the Software. 16 * 17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 23 * SOFTWARE. */ 24 25 #include "includes.h" 26 #include "packet.h" 27 #include "session.h" 28 #include "dbutil.h" 29 #include "ssh.h" 30 #include "algo.h" 31 #include "buffer.h" 32 #include "kex.h" 33 #include "random.h" 34 #include "service.h" 35 #include "auth.h" 36 #include "channel.h" 37 38 static void read_packet_init(); 39 static void writemac(buffer * outputbuffer, buffer * clearwritebuf); 40 static int checkmac(buffer* hashbuf, buffer* readbuf); 41 42 #define ZLIB_COMPRESS_INCR 20 /* this is 12 bytes + 0.1% of 8000 bytes */ 43 #define ZLIB_DECOMPRESS_INCR 100 44 #ifndef DISABLE_ZLIB 45 static buffer* buf_decompress(buffer* buf, unsigned int len); 46 static void buf_compress(buffer * dest, buffer * src, unsigned int len); 47 #endif 48 49 /* non-blocking function writing out a current encrypted packet */ 50 void write_packet() { 51 52 int len, written; 53 buffer * writebuf = NULL; 54 55 TRACE(("enter write_packet")) 56 dropbear_assert(!isempty(&ses.writequeue)); 57 58 /* Get the next buffer in the queue of encrypted packets to write*/ 59 writebuf = (buffer*)examine(&ses.writequeue); 60 61 len = writebuf->len - writebuf->pos; 62 dropbear_assert(len > 0); 63 /* Try to write as much as possible */ 64 written = write(ses.sock, buf_getptr(writebuf, len), len); 65 66 if (written < 0) { 67 if (errno == EINTR) { 68 TRACE(("leave writepacket: EINTR")) 69 return; 70 } else { 71 dropbear_exit("error writing"); 72 } 73 } 74 75 if (written == 0) { 76 ses.remoteclosed(); 77 } 78 79 if (written == len) { 80 /* We've finished with the packet, free it */ 81 dequeue(&ses.writequeue); 82 buf_free(writebuf); 83 writebuf = NULL; 84 } else { 85 /* More packet left to write, leave it in the queue for later */ 86 buf_incrpos(writebuf, written); 87 } 88 89 TRACE(("leave write_packet")) 90 } 91 92 /* Non-blocking function reading available portion of a packet into the 93 * ses's buffer, decrypting the length if encrypted, decrypting the 94 * full portion if possible */ 95 void read_packet() { 96 97 int len; 98 unsigned int maxlen; 99 unsigned char blocksize; 100 101 TRACE(("enter read_packet")) 102 blocksize = ses.keys->recv_algo_crypt->blocksize; 103 104 if (ses.readbuf == NULL || ses.readbuf->len < blocksize) { 105 /* In the first blocksize of a packet */ 106 107 /* Read the first blocksize of the packet, so we can decrypt it and 108 * find the length of the whole packet */ 109 read_packet_init(); 110 111 /* If we don't have the length of decryptreadbuf, we didn't read 112 * a whole blocksize and should exit */ 113 if (ses.decryptreadbuf->len == 0) { 114 TRACE(("leave read_packet: packetinit done")) 115 return; 116 } 117 } 118 119 /* Attempt to read the remainder of the packet, note that there 120 * mightn't be any available (EAGAIN) */ 121 dropbear_assert(ses.readbuf != NULL); 122 maxlen = ses.readbuf->len - ses.readbuf->pos; 123 len = read(ses.sock, buf_getptr(ses.readbuf, maxlen), maxlen); 124 125 if (len == 0) { 126 ses.remoteclosed(); 127 } 128 129 if (len < 0) { 130 if (errno == EINTR || errno == EAGAIN) { 131 TRACE(("leave read_packet: EINTR or EAGAIN")) 132 return; 133 } else { 134 dropbear_exit("error reading: %s", strerror(errno)); 135 } 136 } 137 138 buf_incrpos(ses.readbuf, len); 139 140 if ((unsigned int)len == maxlen) { 141 /* The whole packet has been read */ 142 decrypt_packet(); 143 /* The main select() loop process_packet() to 144 * handle the packet contents... */ 145 } 146 TRACE(("leave read_packet")) 147 } 148 149 /* Function used to read the initial portion of a packet, and determine the 150 * length. Only called during the first BLOCKSIZE of a packet. */ 151 static void read_packet_init() { 152 153 unsigned int maxlen; 154 int len; 155 unsigned char blocksize; 156 unsigned char macsize; 157 158 159 blocksize = ses.keys->recv_algo_crypt->blocksize; 160 macsize = ses.keys->recv_algo_mac->hashsize; 161 162 if (ses.readbuf == NULL) { 163 /* start of a new packet */ 164 ses.readbuf = buf_new(INIT_READBUF); 165 dropbear_assert(ses.decryptreadbuf == NULL); 166 ses.decryptreadbuf = buf_new(blocksize); 167 } 168 169 maxlen = blocksize - ses.readbuf->pos; 170 171 /* read the rest of the packet if possible */ 172 len = read(ses.sock, buf_getwriteptr(ses.readbuf, maxlen), 173 maxlen); 174 if (len == 0) { 175 ses.remoteclosed(); 176 } 177 if (len < 0) { 178 if (errno == EINTR) { 179 TRACE(("leave read_packet_init: EINTR")) 180 return; 181 } 182 dropbear_exit("error reading: %s", strerror(errno)); 183 } 184 185 buf_incrwritepos(ses.readbuf, len); 186 187 if ((unsigned int)len != maxlen) { 188 /* don't have enough bytes to determine length, get next time */ 189 return; 190 } 191 192 /* now we have the first block, need to get packet length, so we decrypt 193 * the first block (only need first 4 bytes) */ 194 buf_setpos(ses.readbuf, 0); 195 if (ses.keys->recv_algo_crypt->cipherdesc == NULL) { 196 /* copy it */ 197 memcpy(buf_getwriteptr(ses.decryptreadbuf, blocksize), 198 buf_getptr(ses.readbuf, blocksize), 199 blocksize); 200 } else { 201 /* decrypt it */ 202 if (cbc_decrypt(buf_getptr(ses.readbuf, blocksize), 203 buf_getwriteptr(ses.decryptreadbuf,blocksize), 204 blocksize, 205 &ses.keys->recv_symmetric_struct) != CRYPT_OK) { 206 dropbear_exit("error decrypting"); 207 } 208 } 209 buf_setlen(ses.decryptreadbuf, blocksize); 210 len = buf_getint(ses.decryptreadbuf) + 4 + macsize; 211 212 buf_setpos(ses.readbuf, blocksize); 213 214 /* check packet length */ 215 if ((len > MAX_PACKET_LEN) || 216 (len < MIN_PACKET_LEN + macsize) || 217 ((len - macsize) % blocksize != 0)) { 218 dropbear_exit("bad packet size %d", len); 219 } 220 221 buf_resize(ses.readbuf, len); 222 buf_setlen(ses.readbuf, len); 223 224 } 225 226 /* handle the received packet */ 227 void decrypt_packet() { 228 229 unsigned char blocksize; 230 unsigned char macsize; 231 unsigned int padlen; 232 unsigned int len; 233 234 TRACE(("enter decrypt_packet")) 235 blocksize = ses.keys->recv_algo_crypt->blocksize; 236 macsize = ses.keys->recv_algo_mac->hashsize; 237 238 ses.kexstate.datarecv += ses.readbuf->len; 239 240 /* we've already decrypted the first blocksize in read_packet_init */ 241 buf_setpos(ses.readbuf, blocksize); 242 243 buf_resize(ses.decryptreadbuf, ses.readbuf->len - macsize); 244 buf_setlen(ses.decryptreadbuf, ses.decryptreadbuf->size); 245 buf_setpos(ses.decryptreadbuf, blocksize); 246 247 /* decrypt if encryption is set, memcpy otherwise */ 248 if (ses.keys->recv_algo_crypt->cipherdesc == NULL) { 249 /* copy it */ 250 len = ses.readbuf->len - macsize - blocksize; 251 memcpy(buf_getwriteptr(ses.decryptreadbuf, len), 252 buf_getptr(ses.readbuf, len), len); 253 } else { 254 /* decrypt */ 255 while (ses.readbuf->pos < ses.readbuf->len - macsize) { 256 if (cbc_decrypt(buf_getptr(ses.readbuf, blocksize), 257 buf_getwriteptr(ses.decryptreadbuf, blocksize), 258 blocksize, 259 &ses.keys->recv_symmetric_struct) != CRYPT_OK) { 260 dropbear_exit("error decrypting"); 261 } 262 buf_incrpos(ses.readbuf, blocksize); 263 buf_incrwritepos(ses.decryptreadbuf, blocksize); 264 } 265 } 266 267 /* check the hmac */ 268 buf_setpos(ses.readbuf, ses.readbuf->len - macsize); 269 if (checkmac(ses.readbuf, ses.decryptreadbuf) != DROPBEAR_SUCCESS) { 270 dropbear_exit("Integrity error"); 271 } 272 273 /* readbuf no longer required */ 274 buf_free(ses.readbuf); 275 ses.readbuf = NULL; 276 277 /* get padding length */ 278 buf_setpos(ses.decryptreadbuf, PACKET_PADDING_OFF); 279 padlen = buf_getbyte(ses.decryptreadbuf); 280 281 /* payload length */ 282 /* - 4 - 1 is for LEN and PADLEN values */ 283 len = ses.decryptreadbuf->len - padlen - 4 - 1; 284 if ((len > MAX_PAYLOAD_LEN) || (len < 1)) { 285 dropbear_exit("bad packet size"); 286 } 287 288 buf_setpos(ses.decryptreadbuf, PACKET_PAYLOAD_OFF); 289 290 #ifndef DISABLE_ZLIB 291 if (ses.keys->recv_algo_comp == DROPBEAR_COMP_ZLIB) { 292 /* decompress */ 293 ses.payload = buf_decompress(ses.decryptreadbuf, len); 294 295 } else 296 #endif 297 { 298 /* copy payload */ 299 ses.payload = buf_new(len); 300 memcpy(ses.payload->data, buf_getptr(ses.decryptreadbuf, len), len); 301 buf_incrlen(ses.payload, len); 302 } 303 304 buf_free(ses.decryptreadbuf); 305 ses.decryptreadbuf = NULL; 306 buf_setpos(ses.payload, 0); 307 308 ses.recvseq++; 309 310 TRACE(("leave decrypt_packet")) 311 } 312 313 /* Checks the mac in hashbuf, for the data in readbuf. 314 * Returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */ 315 static int checkmac(buffer* macbuf, buffer* sourcebuf) { 316 317 unsigned int macsize; 318 hmac_state hmac; 319 unsigned char tempbuf[MAX_MAC_LEN]; 320 unsigned long bufsize; 321 unsigned int len; 322 323 macsize = ses.keys->recv_algo_mac->hashsize; 324 if (macsize == 0) { 325 return DROPBEAR_SUCCESS; 326 } 327 328 /* calculate the mac */ 329 if (hmac_init(&hmac, 330 find_hash(ses.keys->recv_algo_mac->hashdesc->name), 331 ses.keys->recvmackey, 332 ses.keys->recv_algo_mac->keysize) 333 != CRYPT_OK) { 334 dropbear_exit("HMAC error"); 335 } 336 337 /* sequence number */ 338 STORE32H(ses.recvseq, tempbuf); 339 if (hmac_process(&hmac, tempbuf, 4) != CRYPT_OK) { 340 dropbear_exit("HMAC error"); 341 } 342 343 buf_setpos(sourcebuf, 0); 344 len = sourcebuf->len; 345 if (hmac_process(&hmac, buf_getptr(sourcebuf, len), len) != CRYPT_OK) { 346 dropbear_exit("HMAC error"); 347 } 348 349 bufsize = sizeof(tempbuf); 350 if (hmac_done(&hmac, tempbuf, &bufsize) != CRYPT_OK) { 351 dropbear_exit("HMAC error"); 352 } 353 354 /* compare the hash */ 355 if (memcmp(tempbuf, buf_getptr(macbuf, macsize), macsize) != 0) { 356 return DROPBEAR_FAILURE; 357 } else { 358 return DROPBEAR_SUCCESS; 359 } 360 } 361 362 #ifndef DISABLE_ZLIB 363 /* returns a pointer to a newly created buffer */ 364 static buffer* buf_decompress(buffer* buf, unsigned int len) { 365 366 int result; 367 buffer * ret; 368 z_streamp zstream; 369 370 zstream = ses.keys->recv_zstream; 371 ret = buf_new(len); 372 373 zstream->avail_in = len; 374 zstream->next_in = buf_getptr(buf, len); 375 376 /* decompress the payload, incrementally resizing the output buffer */ 377 while (1) { 378 379 zstream->avail_out = ret->size - ret->pos; 380 zstream->next_out = buf_getwriteptr(ret, zstream->avail_out); 381 382 result = inflate(zstream, Z_SYNC_FLUSH); 383 384 buf_setlen(ret, ret->size - zstream->avail_out); 385 buf_setpos(ret, ret->len); 386 387 if (result != Z_BUF_ERROR && result != Z_OK) { 388 dropbear_exit("zlib error"); 389 } 390 391 if (zstream->avail_in == 0 && 392 (zstream->avail_out != 0 || result == Z_BUF_ERROR)) { 393 /* we can only exit if avail_out hasn't all been used, 394 * and there's no remaining input */ 395 return ret; 396 } 397 398 if (zstream->avail_out == 0) { 399 buf_resize(ret, ret->size + ZLIB_DECOMPRESS_INCR); 400 } 401 } 402 } 403 #endif 404 405 406 407 408 /* encrypt the writepayload, putting into writebuf, ready for write_packet() 409 * to put on the wire */ 410 void encrypt_packet() { 411 412 unsigned char padlen; 413 unsigned char blocksize, macsize; 414 buffer * writebuf; /* the packet which will go on the wire */ 415 buffer * clearwritebuf; /* unencrypted, possibly compressed */ 416 417 TRACE(("enter encrypt_packet()")) 418 TRACE(("encrypt_packet type is %d", ses.writepayload->data[0])) 419 blocksize = ses.keys->trans_algo_crypt->blocksize; 420 macsize = ses.keys->trans_algo_mac->hashsize; 421 422 /* Encrypted packet len is payload+5, then worst case is if we are 3 away 423 * from a blocksize multiple. In which case we need to pad to the 424 * multiple, then add another blocksize (or MIN_PACKET_LEN) */ 425 clearwritebuf = buf_new((ses.writepayload->len+4+1) + MIN_PACKET_LEN + 3 426 #ifndef DISABLE_ZLIB 427 + ZLIB_COMPRESS_INCR /* bit of a kludge, but we can't know len*/ 428 #endif 429 ); 430 buf_setlen(clearwritebuf, PACKET_PAYLOAD_OFF); 431 buf_setpos(clearwritebuf, PACKET_PAYLOAD_OFF); 432 433 buf_setpos(ses.writepayload, 0); 434 435 #ifndef DISABLE_ZLIB 436 /* compression */ 437 if (ses.keys->trans_algo_comp == DROPBEAR_COMP_ZLIB) { 438 buf_compress(clearwritebuf, ses.writepayload, ses.writepayload->len); 439 } else 440 #endif 441 { 442 memcpy(buf_getwriteptr(clearwritebuf, ses.writepayload->len), 443 buf_getptr(ses.writepayload, ses.writepayload->len), 444 ses.writepayload->len); 445 buf_incrwritepos(clearwritebuf, ses.writepayload->len); 446 } 447 448 /* finished with payload */ 449 buf_setpos(ses.writepayload, 0); 450 buf_setlen(ses.writepayload, 0); 451 452 /* length of padding - packet length must be a multiple of blocksize, 453 * with a minimum of 4 bytes of padding */ 454 padlen = blocksize - (clearwritebuf->len) % blocksize; 455 if (padlen < 4) { 456 padlen += blocksize; 457 } 458 /* check for min packet length */ 459 if (clearwritebuf->len + padlen < MIN_PACKET_LEN) { 460 padlen += blocksize; 461 } 462 463 buf_setpos(clearwritebuf, 0); 464 /* packet length excluding the packetlength uint32 */ 465 buf_putint(clearwritebuf, clearwritebuf->len + padlen - 4); 466 467 /* padding len */ 468 buf_putbyte(clearwritebuf, padlen); 469 /* actual padding */ 470 buf_setpos(clearwritebuf, clearwritebuf->len); 471 buf_incrlen(clearwritebuf, padlen); 472 genrandom(buf_getptr(clearwritebuf, padlen), padlen); 473 474 /* do the actual encryption */ 475 buf_setpos(clearwritebuf, 0); 476 /* create a new writebuffer, this is freed when it has been put on the 477 * wire by writepacket() */ 478 writebuf = buf_new(clearwritebuf->len + macsize); 479 480 if (ses.keys->trans_algo_crypt->cipherdesc == NULL) { 481 /* copy it */ 482 memcpy(buf_getwriteptr(writebuf, clearwritebuf->len), 483 buf_getptr(clearwritebuf, clearwritebuf->len), 484 clearwritebuf->len); 485 buf_incrwritepos(writebuf, clearwritebuf->len); 486 } else { 487 /* encrypt it */ 488 while (clearwritebuf->pos < clearwritebuf->len) { 489 if (cbc_encrypt(buf_getptr(clearwritebuf, blocksize), 490 buf_getwriteptr(writebuf, blocksize), 491 blocksize, 492 &ses.keys->trans_symmetric_struct) != CRYPT_OK) { 493 dropbear_exit("error encrypting"); 494 } 495 buf_incrpos(clearwritebuf, blocksize); 496 buf_incrwritepos(writebuf, blocksize); 497 } 498 } 499 500 /* now add a hmac and we're done */ 501 writemac(writebuf, clearwritebuf); 502 503 /* clearwritebuf is finished with */ 504 buf_free(clearwritebuf); 505 clearwritebuf = NULL; 506 507 /* enqueue the packet for sending */ 508 buf_setpos(writebuf, 0); 509 enqueue(&ses.writequeue, (void*)writebuf); 510 511 /* Update counts */ 512 ses.kexstate.datatrans += writebuf->len; 513 ses.transseq++; 514 515 TRACE(("leave encrypt_packet()")) 516 } 517 518 519 /* Create the packet mac, and append H(seqno|clearbuf) to the output */ 520 static void writemac(buffer * outputbuffer, buffer * clearwritebuf) { 521 522 unsigned int macsize; 523 unsigned char seqbuf[4]; 524 unsigned char tempbuf[MAX_MAC_LEN]; 525 unsigned long bufsize; 526 hmac_state hmac; 527 528 TRACE(("enter writemac")) 529 530 macsize = ses.keys->trans_algo_mac->hashsize; 531 if (macsize > 0) { 532 /* calculate the mac */ 533 if (hmac_init(&hmac, 534 find_hash(ses.keys->trans_algo_mac->hashdesc->name), 535 ses.keys->transmackey, 536 ses.keys->trans_algo_mac->keysize) != CRYPT_OK) { 537 dropbear_exit("HMAC error"); 538 } 539 540 /* sequence number */ 541 STORE32H(ses.transseq, seqbuf); 542 if (hmac_process(&hmac, seqbuf, 4) != CRYPT_OK) { 543 dropbear_exit("HMAC error"); 544 } 545 546 /* the actual contents */ 547 buf_setpos(clearwritebuf, 0); 548 if (hmac_process(&hmac, 549 buf_getptr(clearwritebuf, 550 clearwritebuf->len), 551 clearwritebuf->len) != CRYPT_OK) { 552 dropbear_exit("HMAC error"); 553 } 554 555 bufsize = sizeof(tempbuf); 556 if (hmac_done(&hmac, tempbuf, &bufsize) 557 != CRYPT_OK) { 558 dropbear_exit("HMAC error"); 559 } 560 buf_putbytes(outputbuffer, tempbuf, macsize); 561 } 562 TRACE(("leave writemac")) 563 } 564 565 #ifndef DISABLE_ZLIB 566 /* compresses len bytes from src, outputting to dest (starting from the 567 * respective current positions. */ 568 static void buf_compress(buffer * dest, buffer * src, unsigned int len) { 569 570 unsigned int endpos = src->pos + len; 571 int result; 572 573 TRACE(("enter buf_compress")) 574 575 while (1) { 576 577 ses.keys->trans_zstream->avail_in = endpos - src->pos; 578 ses.keys->trans_zstream->next_in = 579 buf_getptr(src, ses.keys->trans_zstream->avail_in); 580 581 ses.keys->trans_zstream->avail_out = dest->size - dest->pos; 582 ses.keys->trans_zstream->next_out = 583 buf_getwriteptr(dest, ses.keys->trans_zstream->avail_out); 584 585 result = deflate(ses.keys->trans_zstream, Z_SYNC_FLUSH); 586 587 buf_setpos(src, endpos - ses.keys->trans_zstream->avail_in); 588 buf_setlen(dest, dest->size - ses.keys->trans_zstream->avail_out); 589 buf_setpos(dest, dest->len); 590 591 if (result != Z_OK) { 592 dropbear_exit("zlib error"); 593 } 594 595 if (ses.keys->trans_zstream->avail_in == 0) { 596 break; 597 } 598 599 dropbear_assert(ses.keys->trans_zstream->avail_out == 0); 600 601 /* the buffer has been filled, we must extend. This only happens in 602 * unusual circumstances where the data grows in size after deflate(), 603 * but it is possible */ 604 buf_resize(dest, dest->size + ZLIB_COMPRESS_INCR); 605 606 } 607 TRACE(("leave buf_compress")) 608 } 609 #endif 610
