1 /* $OpenBSD: auth2-pubkey.c,v 1.100 2020/08/27 01:07:09 djm Exp $ */ 2 /* 3 * Copyright (c) 2000 Markus Friedl. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 */ 25 26 27 #include <sys/types.h> 28 #include <sys/stat.h> 29 30 #include <stdlib.h> 31 #include <errno.h> 32 #include <fcntl.h> 33 #include <paths.h> 34 #include <pwd.h> 35 #include <signal.h> 36 #include <stdio.h> 37 #include <stdarg.h> 38 #include <string.h> 39 #include <time.h> 40 #include <unistd.h> 41 #include <limits.h> 42 43 #include "xmalloc.h" 44 #include "ssh.h" 45 #include "ssh2.h" 46 #include "packet.h" 47 #include "sshbuf.h" 48 #include "log.h" 49 #include "misc.h" 50 #include "servconf.h" 51 #include "compat.h" 52 #include "sshkey.h" 53 #include "hostfile.h" 54 #include "auth.h" 55 #include "pathnames.h" 56 #include "uidswap.h" 57 #include "auth-options.h" 58 #include "canohost.h" 59 #ifdef GSSAPI 60 #include "ssh-gss.h" 61 #endif 62 #include "monitor_wrap.h" 63 #include "authfile.h" 64 #include "match.h" 65 #include "ssherr.h" 66 #include "channels.h" /* XXX for session.h */ 67 #include "session.h" /* XXX for child_set_env(); refactor? */ 68 #include "sk-api.h" 69 70 /* import */ 71 extern ServerOptions options; 72 extern u_char *session_id2; 73 extern u_int session_id2_len; 74 75 static char * 76 format_key(const struct sshkey *key) 77 { 78 char *ret, *fp = sshkey_fingerprint(key, 79 options.fingerprint_hash, SSH_FP_DEFAULT); 80 81 xasprintf(&ret, "%s %s", sshkey_type(key), fp); 82 free(fp); 83 return ret; 84 } 85 86 static int 87 userauth_pubkey(struct ssh *ssh) 88 { 89 Authctxt *authctxt = ssh->authctxt; 90 struct passwd *pw = authctxt->pw; 91 struct sshbuf *b = NULL; 92 struct sshkey *key = NULL; 93 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 94 u_char *pkblob = NULL, *sig = NULL, have_sig; 95 size_t blen, slen; 96 int r, pktype; 97 int req_presence = 0, req_verify = 0, authenticated = 0; 98 struct sshauthopt *authopts = NULL; 99 struct sshkey_sig_details *sig_details = NULL; 100 101 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 102 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 103 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 104 fatal("%s: parse request failed: %s", __func__, ssh_err(r)); 105 106 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) { 107 char *keystring; 108 struct sshbuf *pkbuf; 109 110 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL) 111 fatal("%s: sshbuf_from failed", __func__); 112 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL) 113 fatal("%s: sshbuf_dtob64 failed", __func__); 114 debug2("%s: %s user %s %s public key %s %s", __func__, 115 authctxt->valid ? "valid" : "invalid", authctxt->user, 116 have_sig ? "attempting" : "querying", pkalg, keystring); 117 sshbuf_free(pkbuf); 118 free(keystring); 119 } 120 121 pktype = sshkey_type_from_name(pkalg); 122 if (pktype == KEY_UNSPEC) { 123 /* this is perfectly legal */ 124 verbose("%s: unsupported public key algorithm: %s", 125 __func__, pkalg); 126 goto done; 127 } 128 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 129 error("%s: could not parse key: %s", __func__, ssh_err(r)); 130 goto done; 131 } 132 if (key == NULL) { 133 error("%s: cannot decode key: %s", __func__, pkalg); 134 goto done; 135 } 136 if (key->type != pktype) { 137 error("%s: type mismatch for decoded key " 138 "(received %d, expected %d)", __func__, key->type, pktype); 139 goto done; 140 } 141 if (sshkey_type_plain(key->type) == KEY_RSA && 142 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 143 logit("Refusing RSA key because client uses unsafe " 144 "signature scheme"); 145 goto done; 146 } 147 if (auth2_key_already_used(authctxt, key)) { 148 logit("refusing previously-used %s key", sshkey_type(key)); 149 goto done; 150 } 151 if (match_pattern_list(pkalg, options.pubkey_key_types, 0) != 1) { 152 logit("%s: key type %s not in PubkeyAcceptedKeyTypes", 153 __func__, sshkey_ssh_name(key)); 154 goto done; 155 } 156 if ((r = sshkey_check_cert_sigtype(key, 157 options.ca_sign_algorithms)) != 0) { 158 logit("%s: certificate signature algorithm %s: %s", __func__, 159 (key->cert == NULL || key->cert->signature_type == NULL) ? 160 "(null)" : key->cert->signature_type, ssh_err(r)); 161 goto done; 162 } 163 key_s = format_key(key); 164 if (sshkey_is_cert(key)) 165 ca_s = format_key(key->cert->signature_key); 166 167 if (have_sig) { 168 debug3("%s: have %s signature for %s%s%s", 169 __func__, pkalg, key_s, 170 ca_s == NULL ? "" : " CA ", 171 ca_s == NULL ? "" : ca_s); 172 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 173 (r = sshpkt_get_end(ssh)) != 0) 174 fatal("%s: %s", __func__, ssh_err(r)); 175 if ((b = sshbuf_new()) == NULL) 176 fatal("%s: sshbuf_new failed", __func__); 177 if (ssh->compat & SSH_OLD_SESSIONID) { 178 if ((r = sshbuf_put(b, session_id2, 179 session_id2_len)) != 0) 180 fatal("%s: sshbuf_put session id: %s", 181 __func__, ssh_err(r)); 182 } else { 183 if ((r = sshbuf_put_string(b, session_id2, 184 session_id2_len)) != 0) 185 fatal("%s: sshbuf_put_string session id: %s", 186 __func__, ssh_err(r)); 187 } 188 if (!authctxt->valid || authctxt->user == NULL) { 189 debug2("%s: disabled because of invalid user", 190 __func__); 191 goto done; 192 } 193 /* reconstruct packet */ 194 xasprintf(&userstyle, "%s%s%s", authctxt->user, 195 authctxt->style ? ":" : "", 196 authctxt->style ? authctxt->style : ""); 197 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 198 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 199 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 200 (r = sshbuf_put_cstring(b, "publickey")) != 0 || 201 (r = sshbuf_put_u8(b, have_sig)) != 0 || 202 (r = sshbuf_put_cstring(b, pkalg)) != 0 || 203 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 204 fatal("%s: build packet failed: %s", 205 __func__, ssh_err(r)); 206 #ifdef DEBUG_PK 207 sshbuf_dump(b, stderr); 208 #endif 209 /* test for correct signature */ 210 authenticated = 0; 211 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && 212 PRIVSEP(sshkey_verify(key, sig, slen, 213 sshbuf_ptr(b), sshbuf_len(b), 214 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL, 215 ssh->compat, &sig_details)) == 0) { 216 authenticated = 1; 217 } 218 if (authenticated == 1 && sig_details != NULL) { 219 auth2_record_info(authctxt, "signature count = %u", 220 sig_details->sk_counter); 221 debug("%s: sk_counter = %u, sk_flags = 0x%02x", 222 __func__, sig_details->sk_counter, 223 sig_details->sk_flags); 224 req_presence = (options.pubkey_auth_options & 225 PUBKEYAUTH_TOUCH_REQUIRED) || 226 !authopts->no_require_user_presence; 227 if (req_presence && (sig_details->sk_flags & 228 SSH_SK_USER_PRESENCE_REQD) == 0) { 229 error("public key %s signature for %s%s from " 230 "%.128s port %d rejected: user presence " 231 "(authenticator touch) requirement " 232 "not met ", key_s, 233 authctxt->valid ? "" : "invalid user ", 234 authctxt->user, ssh_remote_ipaddr(ssh), 235 ssh_remote_port(ssh)); 236 authenticated = 0; 237 goto done; 238 } 239 req_verify = (options.pubkey_auth_options & 240 PUBKEYAUTH_VERIFY_REQUIRED) || 241 authopts->require_verify; 242 if (req_verify && (sig_details->sk_flags & 243 SSH_SK_USER_VERIFICATION_REQD) == 0) { 244 error("public key %s signature for %s%s from " 245 "%.128s port %d rejected: user " 246 "verification requirement not met ", key_s, 247 authctxt->valid ? "" : "invalid user ", 248 authctxt->user, ssh_remote_ipaddr(ssh), 249 ssh_remote_port(ssh)); 250 authenticated = 0; 251 goto done; 252 } 253 } 254 auth2_record_key(authctxt, authenticated, key); 255 } else { 256 debug("%s: test pkalg %s pkblob %s%s%s", 257 __func__, pkalg, key_s, 258 ca_s == NULL ? "" : " CA ", 259 ca_s == NULL ? "" : ca_s); 260 261 if ((r = sshpkt_get_end(ssh)) != 0) 262 fatal("%s: %s", __func__, ssh_err(r)); 263 264 if (!authctxt->valid || authctxt->user == NULL) { 265 debug2("%s: disabled because of invalid user", 266 __func__); 267 goto done; 268 } 269 /* XXX fake reply and always send PK_OK ? */ 270 /* 271 * XXX this allows testing whether a user is allowed 272 * to login: if you happen to have a valid pubkey this 273 * message is sent. the message is NEVER sent at all 274 * if a user is not allowed to login. is this an 275 * issue? -markus 276 */ 277 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 278 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 279 != 0 || 280 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 281 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 282 (r = sshpkt_send(ssh)) != 0 || 283 (r = ssh_packet_write_wait(ssh)) != 0) 284 fatal("%s: %s", __func__, ssh_err(r)); 285 authctxt->postponed = 1; 286 } 287 } 288 done: 289 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 290 debug("%s: key options inconsistent with existing", __func__); 291 authenticated = 0; 292 } 293 debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg); 294 295 sshbuf_free(b); 296 sshauthopt_free(authopts); 297 sshkey_free(key); 298 free(userstyle); 299 free(pkalg); 300 free(pkblob); 301 free(key_s); 302 free(ca_s); 303 free(sig); 304 sshkey_sig_details_free(sig_details); 305 return authenticated; 306 } 307 308 static int 309 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 310 { 311 char *result; 312 u_int i; 313 314 /* XXX percent_expand() sequences for authorized_principals? */ 315 316 for (i = 0; i < cert->nprincipals; i++) { 317 if ((result = match_list(cert->principals[i], 318 principal_list, NULL)) != NULL) { 319 debug3("matched principal from key options \"%.100s\"", 320 result); 321 free(result); 322 return 1; 323 } 324 } 325 return 0; 326 } 327 328 /* 329 * Process a single authorized_principals format line. Returns 0 and sets 330 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 331 * log preamble for file/line information. 332 */ 333 static int 334 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 335 const char *loc, struct sshauthopt **authoptsp) 336 { 337 u_int i, found = 0; 338 char *ep, *line_opts; 339 const char *reason = NULL; 340 struct sshauthopt *opts = NULL; 341 342 if (authoptsp != NULL) 343 *authoptsp = NULL; 344 345 /* Trim trailing whitespace. */ 346 ep = cp + strlen(cp) - 1; 347 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 348 *ep-- = '\0'; 349 350 /* 351 * If the line has internal whitespace then assume it has 352 * key options. 353 */ 354 line_opts = NULL; 355 if ((ep = strrchr(cp, ' ')) != NULL || 356 (ep = strrchr(cp, '\t')) != NULL) { 357 for (; *ep == ' ' || *ep == '\t'; ep++) 358 ; 359 line_opts = cp; 360 cp = ep; 361 } 362 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 363 debug("%s: bad principals options: %s", loc, reason); 364 auth_debug_add("%s: bad principals options: %s", loc, reason); 365 return -1; 366 } 367 /* Check principals in cert against those on line */ 368 for (i = 0; i < cert->nprincipals; i++) { 369 if (strcmp(cp, cert->principals[i]) != 0) 370 continue; 371 debug3("%s: matched principal \"%.100s\"", 372 loc, cert->principals[i]); 373 found = 1; 374 } 375 if (found && authoptsp != NULL) { 376 *authoptsp = opts; 377 opts = NULL; 378 } 379 sshauthopt_free(opts); 380 return found ? 0 : -1; 381 } 382 383 static int 384 process_principals(struct ssh *ssh, FILE *f, const char *file, 385 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 386 { 387 char loc[256], *line = NULL, *cp, *ep; 388 size_t linesize = 0; 389 u_long linenum = 0; 390 u_int found_principal = 0; 391 392 if (authoptsp != NULL) 393 *authoptsp = NULL; 394 395 while (getline(&line, &linesize, f) != -1) { 396 linenum++; 397 /* Always consume entire input */ 398 if (found_principal) 399 continue; 400 401 /* Skip leading whitespace. */ 402 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 403 ; 404 /* Skip blank and comment lines. */ 405 if ((ep = strchr(cp, '#')) != NULL) 406 *ep = '\0'; 407 if (!*cp || *cp == '\n') 408 continue; 409 410 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 411 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 412 found_principal = 1; 413 } 414 free(line); 415 return found_principal; 416 } 417 418 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 419 420 static int 421 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 422 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 423 { 424 FILE *f; 425 int success; 426 427 if (authoptsp != NULL) 428 *authoptsp = NULL; 429 430 temporarily_use_uid(pw); 431 debug("trying authorized principals file %s", file); 432 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 433 restore_uid(); 434 return 0; 435 } 436 success = process_principals(ssh, f, file, cert, authoptsp); 437 fclose(f); 438 restore_uid(); 439 return success; 440 } 441 442 /* 443 * Checks whether principal is allowed in output of command. 444 * returns 1 if the principal is allowed or 0 otherwise. 445 */ 446 static int 447 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 448 const struct sshkey *key, struct sshauthopt **authoptsp) 449 { 450 struct passwd *runas_pw = NULL; 451 const struct sshkey_cert *cert = key->cert; 452 FILE *f = NULL; 453 int r, ok, found_principal = 0; 454 int i, ac = 0, uid_swapped = 0; 455 pid_t pid; 456 char *tmp, *username = NULL, *command = NULL, **av = NULL; 457 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 458 char serial_s[32], uidstr[32]; 459 void (*osigchld)(int); 460 461 if (authoptsp != NULL) 462 *authoptsp = NULL; 463 if (options.authorized_principals_command == NULL) 464 return 0; 465 if (options.authorized_principals_command_user == NULL) { 466 error("No user for AuthorizedPrincipalsCommand specified, " 467 "skipping"); 468 return 0; 469 } 470 471 /* 472 * NB. all returns later this function should go via "out" to 473 * ensure the original SIGCHLD handler is restored properly. 474 */ 475 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 476 477 /* Prepare and verify the user for the command */ 478 username = percent_expand(options.authorized_principals_command_user, 479 "u", user_pw->pw_name, (char *)NULL); 480 runas_pw = getpwnam(username); 481 if (runas_pw == NULL) { 482 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 483 username, strerror(errno)); 484 goto out; 485 } 486 487 /* Turn the command into an argument vector */ 488 if (argv_split(options.authorized_principals_command, &ac, &av) != 0) { 489 error("AuthorizedPrincipalsCommand \"%s\" contains " 490 "invalid quotes", options.authorized_principals_command); 491 goto out; 492 } 493 if (ac == 0) { 494 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 495 options.authorized_principals_command); 496 goto out; 497 } 498 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 499 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 500 error("%s: sshkey_fingerprint failed", __func__); 501 goto out; 502 } 503 if ((key_fp = sshkey_fingerprint(key, 504 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 505 error("%s: sshkey_fingerprint failed", __func__); 506 goto out; 507 } 508 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 509 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 510 goto out; 511 } 512 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 513 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 514 goto out; 515 } 516 snprintf(serial_s, sizeof(serial_s), "%llu", 517 (unsigned long long)cert->serial); 518 snprintf(uidstr, sizeof(uidstr), "%llu", 519 (unsigned long long)user_pw->pw_uid); 520 for (i = 1; i < ac; i++) { 521 tmp = percent_expand(av[i], 522 "U", uidstr, 523 "u", user_pw->pw_name, 524 "h", user_pw->pw_dir, 525 "t", sshkey_ssh_name(key), 526 "T", sshkey_ssh_name(cert->signature_key), 527 "f", key_fp, 528 "F", ca_fp, 529 "k", keytext, 530 "K", catext, 531 "i", cert->key_id, 532 "s", serial_s, 533 (char *)NULL); 534 if (tmp == NULL) 535 fatal("%s: percent_expand failed", __func__); 536 free(av[i]); 537 av[i] = tmp; 538 } 539 /* Prepare a printable command for logs, etc. */ 540 command = argv_assemble(ac, av); 541 542 if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command, 543 ac, av, &f, 544 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 545 goto out; 546 547 uid_swapped = 1; 548 temporarily_use_uid(runas_pw); 549 550 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 551 552 fclose(f); 553 f = NULL; 554 555 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 556 goto out; 557 558 /* Read completed successfully */ 559 found_principal = ok; 560 out: 561 if (f != NULL) 562 fclose(f); 563 ssh_signal(SIGCHLD, osigchld); 564 for (i = 0; i < ac; i++) 565 free(av[i]); 566 free(av); 567 if (uid_swapped) 568 restore_uid(); 569 free(command); 570 free(username); 571 free(ca_fp); 572 free(key_fp); 573 free(catext); 574 free(keytext); 575 return found_principal; 576 } 577 578 /* 579 * Check a single line of an authorized_keys-format file. Returns 0 if key 580 * matches, -1 otherwise. Will return key/cert options via *authoptsp 581 * on success. "loc" is used as file/line location in log messages. 582 */ 583 static int 584 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 585 char *cp, const char *loc, struct sshauthopt **authoptsp) 586 { 587 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 588 struct sshkey *found = NULL; 589 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 590 char *key_options = NULL, *fp = NULL; 591 const char *reason = NULL; 592 int ret = -1; 593 594 if (authoptsp != NULL) 595 *authoptsp = NULL; 596 597 if ((found = sshkey_new(want_keytype)) == NULL) { 598 debug3("%s: keytype %d failed", __func__, want_keytype); 599 goto out; 600 } 601 602 /* XXX djm: peek at key type in line and skip if unwanted */ 603 604 if (sshkey_read(found, &cp) != 0) { 605 /* no key? check for options */ 606 debug2("%s: check options: '%s'", loc, cp); 607 key_options = cp; 608 if (sshkey_advance_past_options(&cp) != 0) { 609 reason = "invalid key option string"; 610 goto fail_reason; 611 } 612 skip_space(&cp); 613 if (sshkey_read(found, &cp) != 0) { 614 /* still no key? advance to next line*/ 615 debug2("%s: advance: '%s'", loc, cp); 616 goto out; 617 } 618 } 619 /* Parse key options now; we need to know if this is a CA key */ 620 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 621 debug("%s: bad key options: %s", loc, reason); 622 auth_debug_add("%s: bad key options: %s", loc, reason); 623 goto out; 624 } 625 /* Ignore keys that don't match or incorrectly marked as CAs */ 626 if (sshkey_is_cert(key)) { 627 /* Certificate; check signature key against CA */ 628 if (!sshkey_equal(found, key->cert->signature_key) || 629 !keyopts->cert_authority) 630 goto out; 631 } else { 632 /* Plain key: check it against key found in file */ 633 if (!sshkey_equal(found, key) || keyopts->cert_authority) 634 goto out; 635 } 636 637 /* We have a candidate key, perform authorisation checks */ 638 if ((fp = sshkey_fingerprint(found, 639 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 640 fatal("%s: fingerprint failed", __func__); 641 642 debug("%s: matching %s found: %s %s", loc, 643 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 644 645 if (auth_authorise_keyopts(ssh, pw, keyopts, 646 sshkey_is_cert(key), loc) != 0) { 647 reason = "Refused by key options"; 648 goto fail_reason; 649 } 650 /* That's all we need for plain keys. */ 651 if (!sshkey_is_cert(key)) { 652 verbose("Accepted key %s %s found at %s", 653 sshkey_type(found), fp, loc); 654 finalopts = keyopts; 655 keyopts = NULL; 656 goto success; 657 } 658 659 /* 660 * Additional authorisation for certificates. 661 */ 662 663 /* Parse and check options present in certificate */ 664 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 665 reason = "Invalid certificate options"; 666 goto fail_reason; 667 } 668 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 669 reason = "Refused by certificate options"; 670 goto fail_reason; 671 } 672 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 673 goto fail_reason; 674 675 /* 676 * If the user has specified a list of principals as 677 * a key option, then prefer that list to matching 678 * their username in the certificate principals list. 679 */ 680 if (keyopts->cert_principals != NULL && 681 !match_principals_option(keyopts->cert_principals, key->cert)) { 682 reason = "Certificate does not contain an authorized principal"; 683 goto fail_reason; 684 } 685 if (sshkey_cert_check_authority(key, 0, 0, 686 keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0) 687 goto fail_reason; 688 689 verbose("Accepted certificate ID \"%s\" (serial %llu) " 690 "signed by CA %s %s found at %s", 691 key->cert->key_id, 692 (unsigned long long)key->cert->serial, 693 sshkey_type(found), fp, loc); 694 695 success: 696 if (finalopts == NULL) 697 fatal("%s: internal error: missing options", __func__); 698 if (authoptsp != NULL) { 699 *authoptsp = finalopts; 700 finalopts = NULL; 701 } 702 /* success */ 703 ret = 0; 704 goto out; 705 706 fail_reason: 707 error("%s", reason); 708 auth_debug_add("%s", reason); 709 out: 710 free(fp); 711 sshauthopt_free(keyopts); 712 sshauthopt_free(certopts); 713 sshauthopt_free(finalopts); 714 sshkey_free(found); 715 return ret; 716 } 717 718 /* 719 * Checks whether key is allowed in authorized_keys-format file, 720 * returns 1 if the key is allowed or 0 otherwise. 721 */ 722 static int 723 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 724 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 725 { 726 char *cp, *line = NULL, loc[256]; 727 size_t linesize = 0; 728 int found_key = 0; 729 u_long linenum = 0; 730 731 if (authoptsp != NULL) 732 *authoptsp = NULL; 733 734 while (getline(&line, &linesize, f) != -1) { 735 linenum++; 736 /* Always consume entire file */ 737 if (found_key) 738 continue; 739 740 /* Skip leading whitespace, empty and comment lines. */ 741 cp = line; 742 skip_space(&cp); 743 if (!*cp || *cp == '\n' || *cp == '#') 744 continue; 745 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 746 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 747 found_key = 1; 748 } 749 free(line); 750 return found_key; 751 } 752 753 /* Authenticate a certificate key against TrustedUserCAKeys */ 754 static int 755 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 756 struct sshauthopt **authoptsp) 757 { 758 char *ca_fp, *principals_file = NULL; 759 const char *reason; 760 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 761 struct sshauthopt *final_opts = NULL; 762 int r, ret = 0, found_principal = 0, use_authorized_principals; 763 764 if (authoptsp != NULL) 765 *authoptsp = NULL; 766 767 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 768 return 0; 769 770 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 771 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 772 return 0; 773 774 if ((r = sshkey_in_file(key->cert->signature_key, 775 options.trusted_user_ca_keys, 1, 0)) != 0) { 776 debug2("%s: CA %s %s is not listed in %s: %s", __func__, 777 sshkey_type(key->cert->signature_key), ca_fp, 778 options.trusted_user_ca_keys, ssh_err(r)); 779 goto out; 780 } 781 /* 782 * If AuthorizedPrincipals is in use, then compare the certificate 783 * principals against the names in that file rather than matching 784 * against the username. 785 */ 786 if ((principals_file = authorized_principals_file(pw)) != NULL) { 787 if (match_principals_file(ssh, pw, principals_file, 788 key->cert, &principals_opts)) 789 found_principal = 1; 790 } 791 /* Try querying command if specified */ 792 if (!found_principal && match_principals_command(ssh, pw, key, 793 &principals_opts)) 794 found_principal = 1; 795 /* If principals file or command is specified, then require a match */ 796 use_authorized_principals = principals_file != NULL || 797 options.authorized_principals_command != NULL; 798 if (!found_principal && use_authorized_principals) { 799 reason = "Certificate does not contain an authorized principal"; 800 goto fail_reason; 801 } 802 if (use_authorized_principals && principals_opts == NULL) 803 fatal("%s: internal error: missing principals_opts", __func__); 804 if (sshkey_cert_check_authority(key, 0, 1, 805 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 806 goto fail_reason; 807 808 /* Check authority from options in key and from principals file/cmd */ 809 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 810 reason = "Invalid certificate options"; 811 goto fail_reason; 812 } 813 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 814 reason = "Refused by certificate options"; 815 goto fail_reason; 816 } 817 if (principals_opts == NULL) { 818 final_opts = cert_opts; 819 cert_opts = NULL; 820 } else { 821 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 822 "principals") != 0) { 823 reason = "Refused by certificate principals options"; 824 goto fail_reason; 825 } 826 if ((final_opts = sshauthopt_merge(principals_opts, 827 cert_opts, &reason)) == NULL) { 828 fail_reason: 829 error("%s", reason); 830 auth_debug_add("%s", reason); 831 goto out; 832 } 833 } 834 835 /* Success */ 836 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 837 "%s CA %s via %s", key->cert->key_id, 838 (unsigned long long)key->cert->serial, 839 sshkey_type(key->cert->signature_key), ca_fp, 840 options.trusted_user_ca_keys); 841 if (authoptsp != NULL) { 842 *authoptsp = final_opts; 843 final_opts = NULL; 844 } 845 ret = 1; 846 out: 847 sshauthopt_free(principals_opts); 848 sshauthopt_free(cert_opts); 849 sshauthopt_free(final_opts); 850 free(principals_file); 851 free(ca_fp); 852 return ret; 853 } 854 855 /* 856 * Checks whether key is allowed in file. 857 * returns 1 if the key is allowed or 0 otherwise. 858 */ 859 static int 860 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 861 char *file, struct sshauthopt **authoptsp) 862 { 863 FILE *f; 864 int found_key = 0; 865 866 if (authoptsp != NULL) 867 *authoptsp = NULL; 868 869 /* Temporarily use the user's uid. */ 870 temporarily_use_uid(pw); 871 872 debug("trying public key file %s", file); 873 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 874 found_key = check_authkeys_file(ssh, pw, f, file, 875 key, authoptsp); 876 fclose(f); 877 } 878 879 restore_uid(); 880 return found_key; 881 } 882 883 /* 884 * Checks whether key is allowed in output of command. 885 * returns 1 if the key is allowed or 0 otherwise. 886 */ 887 static int 888 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 889 struct sshkey *key, struct sshauthopt **authoptsp) 890 { 891 struct passwd *runas_pw = NULL; 892 FILE *f = NULL; 893 int r, ok, found_key = 0; 894 int i, uid_swapped = 0, ac = 0; 895 pid_t pid; 896 char *username = NULL, *key_fp = NULL, *keytext = NULL; 897 char uidstr[32], *tmp, *command = NULL, **av = NULL; 898 void (*osigchld)(int); 899 900 if (authoptsp != NULL) 901 *authoptsp = NULL; 902 if (options.authorized_keys_command == NULL) 903 return 0; 904 if (options.authorized_keys_command_user == NULL) { 905 error("No user for AuthorizedKeysCommand specified, skipping"); 906 return 0; 907 } 908 909 /* 910 * NB. all returns later this function should go via "out" to 911 * ensure the original SIGCHLD handler is restored properly. 912 */ 913 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 914 915 /* Prepare and verify the user for the command */ 916 username = percent_expand(options.authorized_keys_command_user, 917 "u", user_pw->pw_name, (char *)NULL); 918 runas_pw = getpwnam(username); 919 if (runas_pw == NULL) { 920 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 921 username, strerror(errno)); 922 goto out; 923 } 924 925 /* Prepare AuthorizedKeysCommand */ 926 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 927 SSH_FP_DEFAULT)) == NULL) { 928 error("%s: sshkey_fingerprint failed", __func__); 929 goto out; 930 } 931 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 932 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 933 goto out; 934 } 935 936 /* Turn the command into an argument vector */ 937 if (argv_split(options.authorized_keys_command, &ac, &av) != 0) { 938 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 939 command); 940 goto out; 941 } 942 if (ac == 0) { 943 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 944 command); 945 goto out; 946 } 947 snprintf(uidstr, sizeof(uidstr), "%llu", 948 (unsigned long long)user_pw->pw_uid); 949 for (i = 1; i < ac; i++) { 950 tmp = percent_expand(av[i], 951 "U", uidstr, 952 "u", user_pw->pw_name, 953 "h", user_pw->pw_dir, 954 "t", sshkey_ssh_name(key), 955 "f", key_fp, 956 "k", keytext, 957 (char *)NULL); 958 if (tmp == NULL) 959 fatal("%s: percent_expand failed", __func__); 960 free(av[i]); 961 av[i] = tmp; 962 } 963 /* Prepare a printable command for logs, etc. */ 964 command = argv_assemble(ac, av); 965 966 /* 967 * If AuthorizedKeysCommand was run without arguments 968 * then fall back to the old behaviour of passing the 969 * target username as a single argument. 970 */ 971 if (ac == 1) { 972 av = xreallocarray(av, ac + 2, sizeof(*av)); 973 av[1] = xstrdup(user_pw->pw_name); 974 av[2] = NULL; 975 /* Fix up command too, since it is used in log messages */ 976 free(command); 977 xasprintf(&command, "%s %s", av[0], av[1]); 978 } 979 980 if ((pid = subprocess("AuthorizedKeysCommand", runas_pw, command, 981 ac, av, &f, 982 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 983 goto out; 984 985 uid_swapped = 1; 986 temporarily_use_uid(runas_pw); 987 988 ok = check_authkeys_file(ssh, user_pw, f, 989 options.authorized_keys_command, key, authoptsp); 990 991 fclose(f); 992 f = NULL; 993 994 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 995 goto out; 996 997 /* Read completed successfully */ 998 found_key = ok; 999 out: 1000 if (f != NULL) 1001 fclose(f); 1002 ssh_signal(SIGCHLD, osigchld); 1003 for (i = 0; i < ac; i++) 1004 free(av[i]); 1005 free(av); 1006 if (uid_swapped) 1007 restore_uid(); 1008 free(command); 1009 free(username); 1010 free(key_fp); 1011 free(keytext); 1012 return found_key; 1013 } 1014 1015 /* 1016 * Check whether key authenticates and authorises the user. 1017 */ 1018 int 1019 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1020 int auth_attempt, struct sshauthopt **authoptsp) 1021 { 1022 u_int success = 0, i; 1023 char *file; 1024 struct sshauthopt *opts = NULL; 1025 1026 if (authoptsp != NULL) 1027 *authoptsp = NULL; 1028 1029 if (auth_key_is_revoked(key)) 1030 return 0; 1031 if (sshkey_is_cert(key) && 1032 auth_key_is_revoked(key->cert->signature_key)) 1033 return 0; 1034 1035 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1036 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1037 continue; 1038 file = expand_authorized_keys( 1039 options.authorized_keys_files[i], pw); 1040 success = user_key_allowed2(ssh, pw, key, file, &opts); 1041 free(file); 1042 if (!success) { 1043 sshauthopt_free(opts); 1044 opts = NULL; 1045 } 1046 } 1047 if (success) 1048 goto out; 1049 1050 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1051 goto out; 1052 sshauthopt_free(opts); 1053 opts = NULL; 1054 1055 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1056 goto out; 1057 sshauthopt_free(opts); 1058 opts = NULL; 1059 1060 out: 1061 if (success && authoptsp != NULL) { 1062 *authoptsp = opts; 1063 opts = NULL; 1064 } 1065 sshauthopt_free(opts); 1066 return success; 1067 } 1068 1069 Authmethod method_pubkey = { 1070 "publickey", 1071 userauth_pubkey, 1072 &options.pubkey_authentication 1073 }; 1074