1 /* $OpenBSD: ssh_api.c,v 1.28 2024/01/09 21:39:14 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 char *populated[PROPOSAL_MAX]; 86 struct ssh *ssh; 87 char **proposal; 88 static int called; 89 int r; 90 91 if (!called) { 92 seed_rng(); 93 called = 1; 94 } 95 96 if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL) 97 return SSH_ERR_ALLOC_FAIL; 98 if (is_server) 99 ssh_packet_set_server(ssh); 100 101 /* Initialize key exchange */ 102 proposal = kex_params ? kex_params->proposal : myproposal; 103 kex_proposal_populate_entries(ssh, populated, 104 proposal[PROPOSAL_KEX_ALGS], 105 proposal[PROPOSAL_ENC_ALGS_CTOS], 106 proposal[PROPOSAL_MAC_ALGS_CTOS], 107 proposal[PROPOSAL_COMP_ALGS_CTOS], 108 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS]); 109 r = kex_ready(ssh, populated); 110 kex_proposal_free_entries(populated); 111 if (r != 0) { 112 ssh_free(ssh); 113 return r; 114 } 115 116 ssh->kex->server = is_server; 117 if (is_server) { 118 #ifdef WITH_OPENSSL 119 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server; 120 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server; 121 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server; 122 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server; 123 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server; 124 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server; 125 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server; 126 # ifdef OPENSSL_HAS_ECC 127 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server; 128 # endif 129 #endif /* WITH_OPENSSL */ 130 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server; 131 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server; 132 ssh->kex->load_host_public_key=&_ssh_host_public_key; 133 ssh->kex->load_host_private_key=&_ssh_host_private_key; 134 ssh->kex->sign=&_ssh_host_key_sign; 135 } else { 136 #ifdef WITH_OPENSSL 137 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client; 138 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client; 139 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client; 140 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client; 141 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client; 142 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client; 143 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client; 144 # ifdef OPENSSL_HAS_ECC 145 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client; 146 # endif 147 #endif /* WITH_OPENSSL */ 148 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client; 149 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client; 150 ssh->kex->verify_host_key =&_ssh_verify_host_key; 151 } 152 *sshp = ssh; 153 return 0; 154 } 155 156 void 157 ssh_free(struct ssh *ssh) 158 { 159 struct key_entry *k; 160 161 if (ssh == NULL) 162 return; 163 164 /* 165 * we've only created the public keys variants in case we 166 * are a acting as a server. 167 */ 168 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) { 169 TAILQ_REMOVE(&ssh->public_keys, k, next); 170 if (ssh->kex && ssh->kex->server) 171 sshkey_free(k->key); 172 free(k); 173 } 174 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) { 175 TAILQ_REMOVE(&ssh->private_keys, k, next); 176 free(k); 177 } 178 ssh_packet_close(ssh); 179 free(ssh); 180 } 181 182 void 183 ssh_set_app_data(struct ssh *ssh, void *app_data) 184 { 185 ssh->app_data = app_data; 186 } 187 188 void * 189 ssh_get_app_data(struct ssh *ssh) 190 { 191 return ssh->app_data; 192 } 193 194 /* Returns < 0 on error, 0 otherwise */ 195 int 196 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key) 197 { 198 struct sshkey *pubkey = NULL; 199 struct key_entry *k = NULL, *k_prv = NULL; 200 int r; 201 202 if (ssh->kex->server) { 203 if ((r = sshkey_from_private(key, &pubkey)) != 0) 204 return r; 205 if ((k = malloc(sizeof(*k))) == NULL || 206 (k_prv = malloc(sizeof(*k_prv))) == NULL) { 207 free(k); 208 sshkey_free(pubkey); 209 return SSH_ERR_ALLOC_FAIL; 210 } 211 k_prv->key = key; 212 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next); 213 214 /* add the public key, too */ 215 k->key = pubkey; 216 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 217 r = 0; 218 } else { 219 if ((k = malloc(sizeof(*k))) == NULL) 220 return SSH_ERR_ALLOC_FAIL; 221 k->key = key; 222 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 223 r = 0; 224 } 225 226 return r; 227 } 228 229 int 230 ssh_set_verify_host_key_callback(struct ssh *ssh, 231 int (*cb)(struct sshkey *, struct ssh *)) 232 { 233 if (cb == NULL || ssh->kex == NULL) 234 return SSH_ERR_INVALID_ARGUMENT; 235 236 ssh->kex->verify_host_key = cb; 237 238 return 0; 239 } 240 241 int 242 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len) 243 { 244 return sshbuf_put(ssh_packet_get_input(ssh), data, len); 245 } 246 247 int 248 ssh_packet_next(struct ssh *ssh, u_char *typep) 249 { 250 int r; 251 u_int32_t seqnr; 252 u_char type; 253 254 /* 255 * Try to read a packet. Return SSH_MSG_NONE if no packet or not 256 * enough data. 257 */ 258 *typep = SSH_MSG_NONE; 259 if (sshbuf_len(ssh->kex->client_version) == 0 || 260 sshbuf_len(ssh->kex->server_version) == 0) 261 return _ssh_exchange_banner(ssh); 262 /* 263 * If we enough data and a dispatch function then 264 * call the function and get the next packet. 265 * Otherwise return the packet type to the caller so it 266 * can decide how to go on. 267 * 268 * We will only call the dispatch function for: 269 * 20-29 Algorithm negotiation 270 * 30-49 Key exchange method specific (numbers can be reused for 271 * different authentication methods) 272 */ 273 for (;;) { 274 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0) 275 return r; 276 if (type > 0 && type < DISPATCH_MAX && 277 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX && 278 ssh->dispatch[type] != NULL) { 279 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0) 280 return r; 281 } else { 282 *typep = type; 283 return 0; 284 } 285 } 286 } 287 288 const u_char * 289 ssh_packet_payload(struct ssh *ssh, size_t *lenp) 290 { 291 return sshpkt_ptr(ssh, lenp); 292 } 293 294 int 295 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len) 296 { 297 int r; 298 299 if ((r = sshpkt_start(ssh, type)) != 0 || 300 (r = sshpkt_put(ssh, data, len)) != 0 || 301 (r = sshpkt_send(ssh)) != 0) 302 return r; 303 return 0; 304 } 305 306 const u_char * 307 ssh_output_ptr(struct ssh *ssh, size_t *len) 308 { 309 struct sshbuf *output = ssh_packet_get_output(ssh); 310 311 *len = sshbuf_len(output); 312 return sshbuf_ptr(output); 313 } 314 315 int 316 ssh_output_consume(struct ssh *ssh, size_t len) 317 { 318 return sshbuf_consume(ssh_packet_get_output(ssh), len); 319 } 320 321 int 322 ssh_output_space(struct ssh *ssh, size_t len) 323 { 324 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len)); 325 } 326 327 int 328 ssh_input_space(struct ssh *ssh, size_t len) 329 { 330 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len)); 331 } 332 333 /* Read other side's version identification. */ 334 int 335 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner) 336 { 337 struct sshbuf *input = ssh_packet_get_input(ssh); 338 const char *mismatch = "Protocol mismatch.\r\n"; 339 const u_char *s = sshbuf_ptr(input); 340 u_char c; 341 char *cp = NULL, *remote_version = NULL; 342 int r = 0, remote_major, remote_minor, expect_nl; 343 size_t n, j; 344 345 for (j = n = 0;;) { 346 sshbuf_reset(banner); 347 expect_nl = 0; 348 for (;;) { 349 if (j >= sshbuf_len(input)) 350 return 0; /* insufficient data in input buf */ 351 c = s[j++]; 352 if (c == '\r') { 353 expect_nl = 1; 354 continue; 355 } 356 if (c == '\n') 357 break; 358 if (expect_nl) 359 goto bad; 360 if ((r = sshbuf_put_u8(banner, c)) != 0) 361 return r; 362 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN) 363 goto bad; 364 } 365 if (sshbuf_len(banner) >= 4 && 366 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0) 367 break; 368 debug_f("%.*s", (int)sshbuf_len(banner), 369 sshbuf_ptr(banner)); 370 /* Accept lines before banner only on client */ 371 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) { 372 bad: 373 if ((r = sshbuf_put(ssh_packet_get_output(ssh), 374 mismatch, strlen(mismatch))) != 0) 375 return r; 376 return SSH_ERR_NO_PROTOCOL_VERSION; 377 } 378 } 379 if ((r = sshbuf_consume(input, j)) != 0) 380 return r; 381 382 /* XXX remote version must be the same size as banner for sscanf */ 383 if ((cp = sshbuf_dup_string(banner)) == NULL || 384 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) { 385 r = SSH_ERR_ALLOC_FAIL; 386 goto out; 387 } 388 389 /* 390 * Check that the versions match. In future this might accept 391 * several versions and set appropriate flags to handle them. 392 */ 393 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n", 394 &remote_major, &remote_minor, remote_version) != 3) { 395 r = SSH_ERR_INVALID_FORMAT; 396 goto out; 397 } 398 debug("Remote protocol version %d.%d, remote software version %.100s", 399 remote_major, remote_minor, remote_version); 400 401 compat_banner(ssh, remote_version); 402 if (remote_major == 1 && remote_minor == 99) { 403 remote_major = 2; 404 remote_minor = 0; 405 } 406 if (remote_major != 2) 407 r = SSH_ERR_PROTOCOL_MISMATCH; 408 409 debug("Remote version string %.100s", cp); 410 out: 411 free(cp); 412 free(remote_version); 413 return r; 414 } 415 416 /* Send our own protocol version identification. */ 417 int 418 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner) 419 { 420 char *cp; 421 int r; 422 423 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0) 424 return r; 425 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0) 426 return r; 427 /* Remove trailing \r\n */ 428 if ((r = sshbuf_consume_end(banner, 2)) != 0) 429 return r; 430 if ((cp = sshbuf_dup_string(banner)) == NULL) 431 return SSH_ERR_ALLOC_FAIL; 432 debug("Local version string %.100s", cp); 433 free(cp); 434 return 0; 435 } 436 437 int 438 _ssh_exchange_banner(struct ssh *ssh) 439 { 440 struct kex *kex = ssh->kex; 441 int r; 442 443 /* 444 * if _ssh_read_banner() cannot parse a full version string 445 * it will return NULL and we end up calling it again. 446 */ 447 448 r = 0; 449 if (kex->server) { 450 if (sshbuf_len(ssh->kex->server_version) == 0) 451 r = _ssh_send_banner(ssh, ssh->kex->server_version); 452 if (r == 0 && 453 sshbuf_len(ssh->kex->server_version) != 0 && 454 sshbuf_len(ssh->kex->client_version) == 0) 455 r = _ssh_read_banner(ssh, ssh->kex->client_version); 456 } else { 457 if (sshbuf_len(ssh->kex->server_version) == 0) 458 r = _ssh_read_banner(ssh, ssh->kex->server_version); 459 if (r == 0 && 460 sshbuf_len(ssh->kex->server_version) != 0 && 461 sshbuf_len(ssh->kex->client_version) == 0) 462 r = _ssh_send_banner(ssh, ssh->kex->client_version); 463 } 464 if (r != 0) 465 return r; 466 /* start initial kex as soon as we have exchanged the banners */ 467 if (sshbuf_len(ssh->kex->server_version) != 0 && 468 sshbuf_len(ssh->kex->client_version) != 0) { 469 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 || 470 (r = kex_send_kexinit(ssh)) != 0) 471 return r; 472 } 473 return 0; 474 } 475 476 struct sshkey * 477 _ssh_host_public_key(int type, int nid, struct ssh *ssh) 478 { 479 struct key_entry *k; 480 481 debug3_f("need %d", type); 482 TAILQ_FOREACH(k, &ssh->public_keys, next) { 483 debug3_f("check %s", sshkey_type(k->key)); 484 if (k->key->type == type && 485 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 486 return (k->key); 487 } 488 return (NULL); 489 } 490 491 struct sshkey * 492 _ssh_host_private_key(int type, int nid, struct ssh *ssh) 493 { 494 struct key_entry *k; 495 496 debug3_f("need %d", type); 497 TAILQ_FOREACH(k, &ssh->private_keys, next) { 498 debug3_f("check %s", sshkey_type(k->key)); 499 if (k->key->type == type && 500 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 501 return (k->key); 502 } 503 return (NULL); 504 } 505 506 int 507 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh) 508 { 509 struct key_entry *k; 510 511 debug3_f("need %s", sshkey_type(hostkey)); 512 TAILQ_FOREACH(k, &ssh->public_keys, next) { 513 debug3_f("check %s", sshkey_type(k->key)); 514 if (sshkey_equal_public(hostkey, k->key)) 515 return (0); /* ok */ 516 } 517 return (-1); /* failed */ 518 } 519 520 /* offer hostkey algorithms in kexinit depending on registered keys */ 521 int 522 _ssh_order_hostkeyalgs(struct ssh *ssh) 523 { 524 struct key_entry *k; 525 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL; 526 char **proposal; 527 size_t maxlen; 528 int ktype, r; 529 530 /* XXX we de-serialize ssh->kex->my, modify it, and change it */ 531 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0) 532 return r; 533 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS]; 534 if ((oavail = avail = strdup(orig)) == NULL) { 535 r = SSH_ERR_ALLOC_FAIL; 536 goto out; 537 } 538 maxlen = strlen(avail) + 1; 539 if ((replace = calloc(1, maxlen)) == NULL) { 540 r = SSH_ERR_ALLOC_FAIL; 541 goto out; 542 } 543 *replace = '\0'; 544 while ((alg = strsep(&avail, ",")) && *alg != '\0') { 545 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC) 546 continue; 547 TAILQ_FOREACH(k, &ssh->public_keys, next) { 548 if (k->key->type == ktype || 549 (sshkey_is_cert(k->key) && k->key->type == 550 sshkey_type_plain(ktype))) { 551 if (*replace != '\0') 552 strlcat(replace, ",", maxlen); 553 strlcat(replace, alg, maxlen); 554 break; 555 } 556 } 557 } 558 if (*replace != '\0') { 559 debug2_f("orig/%d %s", ssh->kex->server, orig); 560 debug2_f("replace/%d %s", ssh->kex->server, replace); 561 free(orig); 562 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace; 563 replace = NULL; /* owned by proposal */ 564 r = kex_prop2buf(ssh->kex->my, proposal); 565 } 566 out: 567 free(oavail); 568 free(replace); 569 kex_prop_free(proposal); 570 return r; 571 } 572 573 int 574 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey, 575 struct sshkey *pubkey, u_char **signature, size_t *slen, 576 const u_char *data, size_t dlen, const char *alg) 577 { 578 return sshkey_sign(privkey, signature, slen, data, dlen, 579 alg, NULL, NULL, ssh->compat); 580 } 581