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