1 /* $NetBSD: ssh_api.c,v 1.13 2021/04/19 14:40:15 christos Exp $ */ 2 /* $OpenBSD: ssh_api.c,v 1.27 2021/04/03 06:18:41 djm Exp $ */ 3 4 /* 5 * Copyright (c) 2012 Markus Friedl. All rights reserved. 6 * 7 * Permission to use, copy, modify, and distribute this software for any 8 * purpose with or without fee is hereby granted, provided that the above 9 * copyright notice and this permission notice appear in all copies. 10 * 11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 18 */ 19 20 #include "includes.h" 21 __RCSID("$NetBSD: ssh_api.c,v 1.13 2021/04/19 14:40:15 christos Exp $"); 22 23 #include <sys/types.h> 24 25 #include <stdio.h> 26 #include <stdlib.h> 27 28 #include "ssh_api.h" 29 #include "compat.h" 30 #include "log.h" 31 #include "authfile.h" 32 #include "sshkey.h" 33 #include "misc.h" 34 #include "ssh2.h" 35 #include "version.h" 36 #include "myproposal.h" 37 #include "ssherr.h" 38 #include "sshbuf.h" 39 40 #include <string.h> 41 42 int _ssh_exchange_banner(struct ssh *); 43 int _ssh_send_banner(struct ssh *, struct sshbuf *); 44 int _ssh_read_banner(struct ssh *, struct sshbuf *); 45 int _ssh_order_hostkeyalgs(struct ssh *); 46 int _ssh_verify_host_key(struct sshkey *, struct ssh *); 47 struct sshkey *_ssh_host_public_key(int, int, struct ssh *); 48 struct sshkey *_ssh_host_private_key(int, int, struct ssh *); 49 int _ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *, 50 u_char **, size_t *, const u_char *, size_t, const char *); 51 52 /* 53 * stubs for the server side implementation of kex. 54 * disable privsep so our stubs will never be called. 55 */ 56 int use_privsep = 0; 57 int mm_sshkey_sign(struct sshkey *, u_char **, u_int *, 58 const u_char *, u_int, const char *, const char *, const char *, u_int); 59 60 #ifdef WITH_OPENSSL 61 DH *mm_choose_dh(int, int, int); 62 #endif 63 64 int 65 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp, 66 const u_char *data, u_int datalen, const char *alg, 67 const char *sk_provider, const char *sk_pin, u_int compat) 68 { 69 return (-1); 70 } 71 72 #ifdef WITH_OPENSSL 73 DH * 74 mm_choose_dh(int min, int nbits, int max) 75 { 76 return (NULL); 77 } 78 #endif 79 80 /* API */ 81 82 int 83 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params) 84 { 85 const char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT }; 86 struct ssh *ssh; 87 const char **proposal; 88 static int called; 89 int r; 90 91 if (!called) { 92 #ifdef WITH_OPENSSL 93 OpenSSL_add_all_algorithms(); 94 #endif 95 called = 1; 96 } 97 98 if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL) 99 return SSH_ERR_ALLOC_FAIL; 100 if (is_server) 101 ssh_packet_set_server(ssh); 102 103 /* Initialize key exchange */ 104 proposal = kex_params ? __UNCONST(kex_params->proposal) : myproposal; 105 if ((r = kex_ready(ssh, proposal)) != 0) { 106 ssh_free(ssh); 107 return r; 108 } 109 ssh->kex->server = is_server; 110 if (is_server) { 111 #ifdef WITH_OPENSSL 112 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server; 113 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server; 114 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server; 115 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server; 116 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server; 117 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server; 118 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server; 119 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server; 120 #endif /* WITH_OPENSSL */ 121 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server; 122 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server; 123 ssh->kex->load_host_public_key=&_ssh_host_public_key; 124 ssh->kex->load_host_private_key=&_ssh_host_private_key; 125 ssh->kex->sign=&_ssh_host_key_sign; 126 } else { 127 #ifdef WITH_OPENSSL 128 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client; 129 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client; 130 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client; 131 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client; 132 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client; 133 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client; 134 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client; 135 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client; 136 #endif /* WITH_OPENSSL */ 137 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client; 138 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client; 139 ssh->kex->verify_host_key =&_ssh_verify_host_key; 140 } 141 *sshp = ssh; 142 return 0; 143 } 144 145 void 146 ssh_free(struct ssh *ssh) 147 { 148 struct key_entry *k; 149 150 if (ssh == NULL) 151 return; 152 153 /* 154 * we've only created the public keys variants in case we 155 * are a acting as a server. 156 */ 157 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) { 158 TAILQ_REMOVE(&ssh->public_keys, k, next); 159 if (ssh->kex && ssh->kex->server) 160 sshkey_free(k->key); 161 free(k); 162 } 163 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) { 164 TAILQ_REMOVE(&ssh->private_keys, k, next); 165 free(k); 166 } 167 ssh_packet_close(ssh); 168 free(ssh); 169 } 170 171 void 172 ssh_set_app_data(struct ssh *ssh, void *app_data) 173 { 174 ssh->app_data = app_data; 175 } 176 177 void * 178 ssh_get_app_data(struct ssh *ssh) 179 { 180 return ssh->app_data; 181 } 182 183 /* Returns < 0 on error, 0 otherwise */ 184 int 185 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key) 186 { 187 struct sshkey *pubkey = NULL; 188 struct key_entry *k = NULL, *k_prv = NULL; 189 int r; 190 191 if (ssh->kex->server) { 192 if ((r = sshkey_from_private(key, &pubkey)) != 0) 193 return r; 194 if ((k = malloc(sizeof(*k))) == NULL || 195 (k_prv = malloc(sizeof(*k_prv))) == NULL) { 196 free(k); 197 sshkey_free(pubkey); 198 return SSH_ERR_ALLOC_FAIL; 199 } 200 k_prv->key = key; 201 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next); 202 203 /* add the public key, too */ 204 k->key = pubkey; 205 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 206 r = 0; 207 } else { 208 if ((k = malloc(sizeof(*k))) == NULL) 209 return SSH_ERR_ALLOC_FAIL; 210 k->key = key; 211 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next); 212 r = 0; 213 } 214 215 return r; 216 } 217 218 int 219 ssh_set_verify_host_key_callback(struct ssh *ssh, 220 int (*cb)(struct sshkey *, struct ssh *)) 221 { 222 if (cb == NULL || ssh->kex == NULL) 223 return SSH_ERR_INVALID_ARGUMENT; 224 225 ssh->kex->verify_host_key = cb; 226 227 return 0; 228 } 229 230 int 231 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len) 232 { 233 return sshbuf_put(ssh_packet_get_input(ssh), data, len); 234 } 235 236 int 237 ssh_packet_next(struct ssh *ssh, u_char *typep) 238 { 239 int r; 240 u_int32_t seqnr; 241 u_char type; 242 243 /* 244 * Try to read a packet. Return SSH_MSG_NONE if no packet or not 245 * enough data. 246 */ 247 *typep = SSH_MSG_NONE; 248 if (sshbuf_len(ssh->kex->client_version) == 0 || 249 sshbuf_len(ssh->kex->server_version) == 0) 250 return _ssh_exchange_banner(ssh); 251 /* 252 * If we enough data and a dispatch function then 253 * call the function and get the next packet. 254 * Otherwise return the packet type to the caller so it 255 * can decide how to go on. 256 * 257 * We will only call the dispatch function for: 258 * 20-29 Algorithm negotiation 259 * 30-49 Key exchange method specific (numbers can be reused for 260 * different authentication methods) 261 */ 262 for (;;) { 263 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0) 264 return r; 265 if (type > 0 && type < DISPATCH_MAX && 266 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX && 267 ssh->dispatch[type] != NULL) { 268 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0) 269 return r; 270 } else { 271 *typep = type; 272 return 0; 273 } 274 } 275 } 276 277 const u_char * 278 ssh_packet_payload(struct ssh *ssh, size_t *lenp) 279 { 280 return sshpkt_ptr(ssh, lenp); 281 } 282 283 int 284 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len) 285 { 286 int r; 287 288 if ((r = sshpkt_start(ssh, type)) != 0 || 289 (r = sshpkt_put(ssh, data, len)) != 0 || 290 (r = sshpkt_send(ssh)) != 0) 291 return r; 292 return 0; 293 } 294 295 const u_char * 296 ssh_output_ptr(struct ssh *ssh, size_t *len) 297 { 298 struct sshbuf *output = ssh_packet_get_output(ssh); 299 300 *len = sshbuf_len(output); 301 return sshbuf_ptr(output); 302 } 303 304 int 305 ssh_output_consume(struct ssh *ssh, size_t len) 306 { 307 return sshbuf_consume(ssh_packet_get_output(ssh), len); 308 } 309 310 int 311 ssh_output_space(struct ssh *ssh, size_t len) 312 { 313 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len)); 314 } 315 316 int 317 ssh_input_space(struct ssh *ssh, size_t len) 318 { 319 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len)); 320 } 321 322 /* Read other side's version identification. */ 323 int 324 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner) 325 { 326 struct sshbuf *input = ssh_packet_get_input(ssh); 327 const char *mismatch = "Protocol mismatch.\r\n"; 328 const u_char *s = sshbuf_ptr(input); 329 u_char c; 330 char *cp = NULL, *remote_version = NULL; 331 int r = 0, remote_major, remote_minor, expect_nl; 332 size_t n, j; 333 334 for (j = n = 0;;) { 335 sshbuf_reset(banner); 336 expect_nl = 0; 337 for (;;) { 338 if (j >= sshbuf_len(input)) 339 return 0; /* insufficient data in input buf */ 340 c = s[j++]; 341 if (c == '\r') { 342 expect_nl = 1; 343 continue; 344 } 345 if (c == '\n') 346 break; 347 if (expect_nl) 348 goto bad; 349 if ((r = sshbuf_put_u8(banner, c)) != 0) 350 return r; 351 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN) 352 goto bad; 353 } 354 if (sshbuf_len(banner) >= 4 && 355 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0) 356 break; 357 debug_f("%.*s", (int)sshbuf_len(banner), 358 sshbuf_ptr(banner)); 359 /* Accept lines before banner only on client */ 360 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) { 361 bad: 362 if ((r = sshbuf_put(ssh_packet_get_output(ssh), 363 mismatch, strlen(mismatch))) != 0) 364 return r; 365 return SSH_ERR_NO_PROTOCOL_VERSION; 366 } 367 } 368 if ((r = sshbuf_consume(input, j)) != 0) 369 return r; 370 371 /* XXX remote version must be the same size as banner for sscanf */ 372 if ((cp = sshbuf_dup_string(banner)) == NULL || 373 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) { 374 r = SSH_ERR_ALLOC_FAIL; 375 goto out; 376 } 377 378 /* 379 * Check that the versions match. In future this might accept 380 * several versions and set appropriate flags to handle them. 381 */ 382 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n", 383 &remote_major, &remote_minor, remote_version) != 3) { 384 r = SSH_ERR_INVALID_FORMAT; 385 goto out; 386 } 387 debug("Remote protocol version %d.%d, remote software version %.100s", 388 remote_major, remote_minor, remote_version); 389 390 compat_banner(ssh, remote_version); 391 if (remote_major == 1 && remote_minor == 99) { 392 remote_major = 2; 393 remote_minor = 0; 394 } 395 if (remote_major != 2) 396 r = SSH_ERR_PROTOCOL_MISMATCH; 397 398 debug("Remote version string %.100s", cp); 399 out: 400 free(cp); 401 free(remote_version); 402 return r; 403 } 404 405 /* Send our own protocol version identification. */ 406 int 407 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner) 408 { 409 char *cp; 410 int r; 411 412 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0) 413 return r; 414 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0) 415 return r; 416 /* Remove trailing \r\n */ 417 if ((r = sshbuf_consume_end(banner, 2)) != 0) 418 return r; 419 if ((cp = sshbuf_dup_string(banner)) == NULL) 420 return SSH_ERR_ALLOC_FAIL; 421 debug("Local version string %.100s", cp); 422 free(cp); 423 return 0; 424 } 425 426 int 427 _ssh_exchange_banner(struct ssh *ssh) 428 { 429 struct kex *kex = ssh->kex; 430 int r; 431 432 /* 433 * if _ssh_read_banner() cannot parse a full version string 434 * it will return NULL and we end up calling it again. 435 */ 436 437 r = 0; 438 if (kex->server) { 439 if (sshbuf_len(ssh->kex->server_version) == 0) 440 r = _ssh_send_banner(ssh, ssh->kex->server_version); 441 if (r == 0 && 442 sshbuf_len(ssh->kex->server_version) != 0 && 443 sshbuf_len(ssh->kex->client_version) == 0) 444 r = _ssh_read_banner(ssh, ssh->kex->client_version); 445 } else { 446 if (sshbuf_len(ssh->kex->server_version) == 0) 447 r = _ssh_read_banner(ssh, ssh->kex->server_version); 448 if (r == 0 && 449 sshbuf_len(ssh->kex->server_version) != 0 && 450 sshbuf_len(ssh->kex->client_version) == 0) 451 r = _ssh_send_banner(ssh, ssh->kex->client_version); 452 } 453 if (r != 0) 454 return r; 455 /* start initial kex as soon as we have exchanged the banners */ 456 if (sshbuf_len(ssh->kex->server_version) != 0 && 457 sshbuf_len(ssh->kex->client_version) != 0) { 458 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 || 459 (r = kex_send_kexinit(ssh)) != 0) 460 return r; 461 } 462 return 0; 463 } 464 465 struct sshkey * 466 _ssh_host_public_key(int type, int nid, struct ssh *ssh) 467 { 468 struct key_entry *k; 469 470 debug3_f("need %d", type); 471 TAILQ_FOREACH(k, &ssh->public_keys, next) { 472 debug3_f("check %s", sshkey_type(k->key)); 473 if (k->key->type == type && 474 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 475 return (k->key); 476 } 477 return (NULL); 478 } 479 480 struct sshkey * 481 _ssh_host_private_key(int type, int nid, struct ssh *ssh) 482 { 483 struct key_entry *k; 484 485 debug3_f("need %d", type); 486 TAILQ_FOREACH(k, &ssh->private_keys, next) { 487 debug3_f("check %s", sshkey_type(k->key)); 488 if (k->key->type == type && 489 (type != KEY_ECDSA || k->key->ecdsa_nid == nid)) 490 return (k->key); 491 } 492 return (NULL); 493 } 494 495 int 496 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh) 497 { 498 struct key_entry *k; 499 500 debug3_f("need %s", sshkey_type(hostkey)); 501 TAILQ_FOREACH(k, &ssh->public_keys, next) { 502 debug3_f("check %s", sshkey_type(k->key)); 503 if (sshkey_equal_public(hostkey, k->key)) 504 return (0); /* ok */ 505 } 506 return (-1); /* failed */ 507 } 508 509 /* offer hostkey algorithms in kexinit depending on registered keys */ 510 int 511 _ssh_order_hostkeyalgs(struct ssh *ssh) 512 { 513 struct key_entry *k; 514 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL; 515 char **proposal; 516 size_t maxlen; 517 int ktype, r; 518 519 /* XXX we de-serialize ssh->kex->my, modify it, and change it */ 520 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0) 521 return r; 522 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS]; 523 if ((oavail = avail = strdup(orig)) == NULL) { 524 r = SSH_ERR_ALLOC_FAIL; 525 goto out; 526 } 527 maxlen = strlen(avail) + 1; 528 if ((replace = calloc(1, maxlen)) == NULL) { 529 r = SSH_ERR_ALLOC_FAIL; 530 goto out; 531 } 532 *replace = '\0'; 533 while ((alg = strsep(&avail, ",")) && *alg != '\0') { 534 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC) 535 continue; 536 TAILQ_FOREACH(k, &ssh->public_keys, next) { 537 if (k->key->type == ktype || 538 (sshkey_is_cert(k->key) && k->key->type == 539 sshkey_type_plain(ktype))) { 540 if (*replace != '\0') 541 strlcat(replace, ",", maxlen); 542 strlcat(replace, alg, maxlen); 543 break; 544 } 545 } 546 } 547 if (*replace != '\0') { 548 debug2_f("orig/%d %s", ssh->kex->server, orig); 549 debug2_f("replace/%d %s", ssh->kex->server, replace); 550 free(orig); 551 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace; 552 replace = NULL; /* owned by proposal */ 553 r = kex_prop2buf(ssh->kex->my, (const char **)(void *)proposal); 554 } 555 out: 556 free(oavail); 557 free(replace); 558 kex_prop_free(proposal); 559 return r; 560 } 561 562 int 563 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey, 564 struct sshkey *pubkey, u_char **signature, size_t *slen, 565 const u_char *data, size_t dlen, const char *alg) 566 { 567 return sshkey_sign(privkey, signature, slen, data, dlen, 568 alg, NULL, NULL, ssh->compat); 569 } 570