1 /* $OpenBSD: ssh_api.c,v 1.27 2021/04/03 06:18:41 djm Exp $ */ 2 /* 3 * Copyright (c) 2012 Markus Friedl. All rights reserved. 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 #include "includes.h" 19 20 #include <sys/types.h> 21 22 #include <stdio.h> 23 #include <stdlib.h> 24 25 #include "ssh_api.h" 26 #include "compat.h" 27 #include "log.h" 28 #include "authfile.h" 29 #include "sshkey.h" 30 #include "misc.h" 31 #include "ssh2.h" 32 #include "version.h" 33 #include "myproposal.h" 34 #include "ssherr.h" 35 #include "sshbuf.h" 36 37 #include "openbsd-compat/openssl-compat.h" 38 39 #include <string.h> 40 41 int _ssh_exchange_banner(struct ssh *); 42 int _ssh_send_banner(struct ssh *, struct sshbuf *); 43 int _ssh_read_banner(struct ssh *, struct sshbuf *); 44 int _ssh_order_hostkeyalgs(struct ssh *); 45 int _ssh_verify_host_key(struct sshkey *, struct ssh *); 46 struct sshkey *_ssh_host_public_key(int, int, struct ssh *); 47 struct sshkey *_ssh_host_private_key(int, int, struct ssh *); 48 int _ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *, 49 u_char **, size_t *, const u_char *, size_t, const char *); 50 51 /* 52 * stubs for the server side implementation of kex. 53 * disable privsep so our stubs will never be called. 54 */ 55 int use_privsep = 0; 56 int mm_sshkey_sign(struct sshkey *, u_char **, u_int *, 57 const u_char *, u_int, const char *, const char *, const char *, u_int); 58 59 #ifdef WITH_OPENSSL 60 DH *mm_choose_dh(int, int, int); 61 #endif 62 63 int 64 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp, 65 const u_char *data, u_int datalen, const char *alg, 66 const char *sk_provider, const char *sk_pin, u_int compat) 67 { 68 return (-1); 69 } 70 71 #ifdef WITH_OPENSSL 72 DH * 73 mm_choose_dh(int min, int nbits, int max) 74 { 75 return (NULL); 76 } 77 #endif 78 79 /* API */ 80 81 int 82 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params) 83 { 84 char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT }; 85 struct ssh *ssh; 86 char **proposal; 87 static int called; 88 int r; 89 90 if (!called) { 91 seed_rng(); 92 called = 1; 93 } 94 95 if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL) 96 return SSH_ERR_ALLOC_FAIL; 97 if (is_server) 98 ssh_packet_set_server(ssh); 99 100 /* Initialize key exchange */ 101 proposal = kex_params ? kex_params->proposal : myproposal; 102 if ((r = kex_ready(ssh, proposal)) != 0) { 103 ssh_free(ssh); 104 return r; 105 } 106 ssh->kex->server = is_server; 107 if (is_server) { 108 #ifdef WITH_OPENSSL 109 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server; 110 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server; 111 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server; 112 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server; 113 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server; 114 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server; 115 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server; 116 # ifdef OPENSSL_HAS_ECC 117 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server; 118 # endif 119 #endif /* WITH_OPENSSL */ 120 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server; 121 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server; 122 ssh->kex->load_host_public_key=&_ssh_host_public_key; 123 ssh->kex->load_host_private_key=&_ssh_host_private_key; 124 ssh->kex->sign=&_ssh_host_key_sign; 125 } else { 126 #ifdef WITH_OPENSSL 127 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client; 128 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client; 129 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client; 130 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client; 131 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client; 132 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client; 133 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client; 134 # ifdef OPENSSL_HAS_ECC 135 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client; 136 # endif 137 #endif /* WITH_OPENSSL */ 138 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client; 139 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client; 140 ssh->kex->verify_host_key =&_ssh_verify_host_key; 141 } 142 *sshp = ssh; 143 return 0; 144 } 145 146 void 147 ssh_free(struct ssh *ssh) 148 { 149 struct key_entry *k; 150 151 if (ssh == NULL) 152 return; 153 154 /* 155 * we've only created the public keys variants in case we 156 * are a acting as a server. 157 */ 158 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) { 159 TAILQ_REMOVE(&ssh->public_keys, k, next); 160 if (ssh->kex && ssh->kex->server) 161 sshkey_free(k->key); 162 free(k); 163 } 164 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) { 165 TAILQ_REMOVE(&ssh->private_keys, k, next); 166 free(k); 167 } 168 ssh_packet_close(ssh); 169 free(ssh); 170 } 171 172 void 173 ssh_set_app_data(struct ssh *ssh, void *app_data) 174 { 175 ssh->app_data = app_data; 176 } 177 178 void * 179 ssh_get_app_data(struct ssh *ssh) 180 { 181 return ssh->app_data; 182 } 183 184 /* Returns < 0 on error, 0 otherwise */ 185 int 186 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key) 187 { 188 struct sshkey *pubkey = NULL; 189 struct key_entry *k = NULL, *k_prv = NULL; 190 int r; 191 192 if (ssh->kex->server) { 193 if ((r = sshkey_from_private(key, &pubkey)) != 0) 194 return r; 195 if ((k = malloc(sizeof(*k))) == NULL || 196 (k_prv = malloc(sizeof(*k_prv))) == NULL) { 197 free(k); 198 sshkey_free(pubkey); 199 return SSH_ERR_ALLOC_FAIL; 200 } 201 k_prv->key = key; 202 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next); 203 204 /* add the public key, too */ 205 k->key = pubkey; 206 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 207 r = 0; 208 } else { 209 if ((k = malloc(sizeof(*k))) == NULL) 210 return SSH_ERR_ALLOC_FAIL; 211 k->key = key; 212 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 213 r = 0; 214 } 215 216 return r; 217 } 218 219 int 220 ssh_set_verify_host_key_callback(struct ssh *ssh, 221 int (*cb)(struct sshkey *, struct ssh *)) 222 { 223 if (cb == NULL || ssh->kex == NULL) 224 return SSH_ERR_INVALID_ARGUMENT; 225 226 ssh->kex->verify_host_key = cb; 227 228 return 0; 229 } 230 231 int 232 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len) 233 { 234 return sshbuf_put(ssh_packet_get_input(ssh), data, len); 235 } 236 237 int 238 ssh_packet_next(struct ssh *ssh, u_char *typep) 239 { 240 int r; 241 u_int32_t seqnr; 242 u_char type; 243 244 /* 245 * Try to read a packet. Return SSH_MSG_NONE if no packet or not 246 * enough data. 247 */ 248 *typep = SSH_MSG_NONE; 249 if (sshbuf_len(ssh->kex->client_version) == 0 || 250 sshbuf_len(ssh->kex->server_version) == 0) 251 return _ssh_exchange_banner(ssh); 252 /* 253 * If we enough data and a dispatch function then 254 * call the function and get the next packet. 255 * Otherwise return the packet type to the caller so it 256 * can decide how to go on. 257 * 258 * We will only call the dispatch function for: 259 * 20-29 Algorithm negotiation 260 * 30-49 Key exchange method specific (numbers can be reused for 261 * different authentication methods) 262 */ 263 for (;;) { 264 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0) 265 return r; 266 if (type > 0 && type < DISPATCH_MAX && 267 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX && 268 ssh->dispatch[type] != NULL) { 269 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0) 270 return r; 271 } else { 272 *typep = type; 273 return 0; 274 } 275 } 276 } 277 278 const u_char * 279 ssh_packet_payload(struct ssh *ssh, size_t *lenp) 280 { 281 return sshpkt_ptr(ssh, lenp); 282 } 283 284 int 285 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len) 286 { 287 int r; 288 289 if ((r = sshpkt_start(ssh, type)) != 0 || 290 (r = sshpkt_put(ssh, data, len)) != 0 || 291 (r = sshpkt_send(ssh)) != 0) 292 return r; 293 return 0; 294 } 295 296 const u_char * 297 ssh_output_ptr(struct ssh *ssh, size_t *len) 298 { 299 struct sshbuf *output = ssh_packet_get_output(ssh); 300 301 *len = sshbuf_len(output); 302 return sshbuf_ptr(output); 303 } 304 305 int 306 ssh_output_consume(struct ssh *ssh, size_t len) 307 { 308 return sshbuf_consume(ssh_packet_get_output(ssh), len); 309 } 310 311 int 312 ssh_output_space(struct ssh *ssh, size_t len) 313 { 314 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len)); 315 } 316 317 int 318 ssh_input_space(struct ssh *ssh, size_t len) 319 { 320 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len)); 321 } 322 323 /* Read other side's version identification. */ 324 int 325 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner) 326 { 327 struct sshbuf *input = ssh_packet_get_input(ssh); 328 const char *mismatch = "Protocol mismatch.\r\n"; 329 const u_char *s = sshbuf_ptr(input); 330 u_char c; 331 char *cp = NULL, *remote_version = NULL; 332 int r = 0, remote_major, remote_minor, expect_nl; 333 size_t n, j; 334 335 for (j = n = 0;;) { 336 sshbuf_reset(banner); 337 expect_nl = 0; 338 for (;;) { 339 if (j >= sshbuf_len(input)) 340 return 0; /* insufficient data in input buf */ 341 c = s[j++]; 342 if (c == '\r') { 343 expect_nl = 1; 344 continue; 345 } 346 if (c == '\n') 347 break; 348 if (expect_nl) 349 goto bad; 350 if ((r = sshbuf_put_u8(banner, c)) != 0) 351 return r; 352 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN) 353 goto bad; 354 } 355 if (sshbuf_len(banner) >= 4 && 356 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0) 357 break; 358 debug_f("%.*s", (int)sshbuf_len(banner), 359 sshbuf_ptr(banner)); 360 /* Accept lines before banner only on client */ 361 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) { 362 bad: 363 if ((r = sshbuf_put(ssh_packet_get_output(ssh), 364 mismatch, strlen(mismatch))) != 0) 365 return r; 366 return SSH_ERR_NO_PROTOCOL_VERSION; 367 } 368 } 369 if ((r = sshbuf_consume(input, j)) != 0) 370 return r; 371 372 /* XXX remote version must be the same size as banner for sscanf */ 373 if ((cp = sshbuf_dup_string(banner)) == NULL || 374 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) { 375 r = SSH_ERR_ALLOC_FAIL; 376 goto out; 377 } 378 379 /* 380 * Check that the versions match. In future this might accept 381 * several versions and set appropriate flags to handle them. 382 */ 383 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n", 384 &remote_major, &remote_minor, remote_version) != 3) { 385 r = SSH_ERR_INVALID_FORMAT; 386 goto out; 387 } 388 debug("Remote protocol version %d.%d, remote software version %.100s", 389 remote_major, remote_minor, remote_version); 390 391 compat_banner(ssh, remote_version); 392 if (remote_major == 1 && remote_minor == 99) { 393 remote_major = 2; 394 remote_minor = 0; 395 } 396 if (remote_major != 2) 397 r = SSH_ERR_PROTOCOL_MISMATCH; 398 399 debug("Remote version string %.100s", cp); 400 out: 401 free(cp); 402 free(remote_version); 403 return r; 404 } 405 406 /* Send our own protocol version identification. */ 407 int 408 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner) 409 { 410 char *cp; 411 int r; 412 413 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0) 414 return r; 415 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0) 416 return r; 417 /* Remove trailing \r\n */ 418 if ((r = sshbuf_consume_end(banner, 2)) != 0) 419 return r; 420 if ((cp = sshbuf_dup_string(banner)) == NULL) 421 return SSH_ERR_ALLOC_FAIL; 422 debug("Local version string %.100s", cp); 423 free(cp); 424 return 0; 425 } 426 427 int 428 _ssh_exchange_banner(struct ssh *ssh) 429 { 430 struct kex *kex = ssh->kex; 431 int r; 432 433 /* 434 * if _ssh_read_banner() cannot parse a full version string 435 * it will return NULL and we end up calling it again. 436 */ 437 438 r = 0; 439 if (kex->server) { 440 if (sshbuf_len(ssh->kex->server_version) == 0) 441 r = _ssh_send_banner(ssh, ssh->kex->server_version); 442 if (r == 0 && 443 sshbuf_len(ssh->kex->server_version) != 0 && 444 sshbuf_len(ssh->kex->client_version) == 0) 445 r = _ssh_read_banner(ssh, ssh->kex->client_version); 446 } else { 447 if (sshbuf_len(ssh->kex->server_version) == 0) 448 r = _ssh_read_banner(ssh, ssh->kex->server_version); 449 if (r == 0 && 450 sshbuf_len(ssh->kex->server_version) != 0 && 451 sshbuf_len(ssh->kex->client_version) == 0) 452 r = _ssh_send_banner(ssh, ssh->kex->client_version); 453 } 454 if (r != 0) 455 return r; 456 /* start initial kex as soon as we have exchanged the banners */ 457 if (sshbuf_len(ssh->kex->server_version) != 0 && 458 sshbuf_len(ssh->kex->client_version) != 0) { 459 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 || 460 (r = kex_send_kexinit(ssh)) != 0) 461 return r; 462 } 463 return 0; 464 } 465 466 struct sshkey * 467 _ssh_host_public_key(int type, int nid, struct ssh *ssh) 468 { 469 struct key_entry *k; 470 471 debug3_f("need %d", type); 472 TAILQ_FOREACH(k, &ssh->public_keys, next) { 473 debug3_f("check %s", sshkey_type(k->key)); 474 if (k->key->type == type && 475 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 476 return (k->key); 477 } 478 return (NULL); 479 } 480 481 struct sshkey * 482 _ssh_host_private_key(int type, int nid, struct ssh *ssh) 483 { 484 struct key_entry *k; 485 486 debug3_f("need %d", type); 487 TAILQ_FOREACH(k, &ssh->private_keys, next) { 488 debug3_f("check %s", sshkey_type(k->key)); 489 if (k->key->type == type && 490 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 491 return (k->key); 492 } 493 return (NULL); 494 } 495 496 int 497 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh) 498 { 499 struct key_entry *k; 500 501 debug3_f("need %s", sshkey_type(hostkey)); 502 TAILQ_FOREACH(k, &ssh->public_keys, next) { 503 debug3_f("check %s", sshkey_type(k->key)); 504 if (sshkey_equal_public(hostkey, k->key)) 505 return (0); /* ok */ 506 } 507 return (-1); /* failed */ 508 } 509 510 /* offer hostkey algorithms in kexinit depending on registered keys */ 511 int 512 _ssh_order_hostkeyalgs(struct ssh *ssh) 513 { 514 struct key_entry *k; 515 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL; 516 char **proposal; 517 size_t maxlen; 518 int ktype, r; 519 520 /* XXX we de-serialize ssh->kex->my, modify it, and change it */ 521 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0) 522 return r; 523 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS]; 524 if ((oavail = avail = strdup(orig)) == NULL) { 525 r = SSH_ERR_ALLOC_FAIL; 526 goto out; 527 } 528 maxlen = strlen(avail) + 1; 529 if ((replace = calloc(1, maxlen)) == NULL) { 530 r = SSH_ERR_ALLOC_FAIL; 531 goto out; 532 } 533 *replace = '\0'; 534 while ((alg = strsep(&avail, ",")) && *alg != '\0') { 535 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC) 536 continue; 537 TAILQ_FOREACH(k, &ssh->public_keys, next) { 538 if (k->key->type == ktype || 539 (sshkey_is_cert(k->key) && k->key->type == 540 sshkey_type_plain(ktype))) { 541 if (*replace != '\0') 542 strlcat(replace, ",", maxlen); 543 strlcat(replace, alg, maxlen); 544 break; 545 } 546 } 547 } 548 if (*replace != '\0') { 549 debug2_f("orig/%d %s", ssh->kex->server, orig); 550 debug2_f("replace/%d %s", ssh->kex->server, replace); 551 free(orig); 552 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace; 553 replace = NULL; /* owned by proposal */ 554 r = kex_prop2buf(ssh->kex->my, proposal); 555 } 556 out: 557 free(oavail); 558 free(replace); 559 kex_prop_free(proposal); 560 return r; 561 } 562 563 int 564 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey, 565 struct sshkey *pubkey, u_char **signature, size_t *slen, 566 const u_char *data, size_t dlen, const char *alg) 567 { 568 return sshkey_sign(privkey, signature, slen, data, dlen, 569 alg, NULL, NULL, ssh->compat); 570 } 571