1 /* $OpenBSD: auth2-pubkey.c,v 1.106 2021/01/27 10:05:28 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 "kex.h" 48 #include "sshbuf.h" 49 #include "log.h" 50 #include "misc.h" 51 #include "servconf.h" 52 #include "compat.h" 53 #include "sshkey.h" 54 #include "hostfile.h" 55 #include "auth.h" 56 #include "pathnames.h" 57 #include "uidswap.h" 58 #include "auth-options.h" 59 #include "canohost.h" 60 #ifdef GSSAPI 61 #include "ssh-gss.h" 62 #endif 63 #include "monitor_wrap.h" 64 #include "authfile.h" 65 #include "match.h" 66 #include "ssherr.h" 67 #include "channels.h" /* XXX for session.h */ 68 #include "session.h" /* XXX for child_set_env(); refactor? */ 69 #include "sk-api.h" 70 71 /* import */ 72 extern ServerOptions options; 73 74 static char * 75 format_key(const struct sshkey *key) 76 { 77 char *ret, *fp = sshkey_fingerprint(key, 78 options.fingerprint_hash, SSH_FP_DEFAULT); 79 80 xasprintf(&ret, "%s %s", sshkey_type(key), fp); 81 free(fp); 82 return ret; 83 } 84 85 static int 86 userauth_pubkey(struct ssh *ssh) 87 { 88 Authctxt *authctxt = ssh->authctxt; 89 struct passwd *pw = authctxt->pw; 90 struct sshbuf *b = NULL; 91 struct sshkey *key = NULL; 92 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 93 u_char *pkblob = NULL, *sig = NULL, have_sig; 94 size_t blen, slen; 95 int r, pktype; 96 int req_presence = 0, req_verify = 0, authenticated = 0; 97 struct sshauthopt *authopts = NULL; 98 struct sshkey_sig_details *sig_details = NULL; 99 100 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 101 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 102 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 103 fatal_fr(r, "parse packet"); 104 105 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) { 106 char *keystring; 107 struct sshbuf *pkbuf; 108 109 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL) 110 fatal_f("sshbuf_from failed"); 111 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL) 112 fatal_f("sshbuf_dtob64 failed"); 113 debug2_f("%s user %s %s public key %s %s", 114 authctxt->valid ? "valid" : "invalid", authctxt->user, 115 have_sig ? "attempting" : "querying", pkalg, keystring); 116 sshbuf_free(pkbuf); 117 free(keystring); 118 } 119 120 pktype = sshkey_type_from_name(pkalg); 121 if (pktype == KEY_UNSPEC) { 122 /* this is perfectly legal */ 123 verbose_f("unsupported public key algorithm: %s", pkalg); 124 goto done; 125 } 126 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 127 error_fr(r, "parse key"); 128 goto done; 129 } 130 if (key == NULL) { 131 error_f("cannot decode key: %s", pkalg); 132 goto done; 133 } 134 if (key->type != pktype) { 135 error_f("type mismatch for decoded key " 136 "(received %d, expected %d)", key->type, pktype); 137 goto done; 138 } 139 if (sshkey_type_plain(key->type) == KEY_RSA && 140 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 141 logit("Refusing RSA key because client uses unsafe " 142 "signature scheme"); 143 goto done; 144 } 145 if (auth2_key_already_used(authctxt, key)) { 146 logit("refusing previously-used %s key", sshkey_type(key)); 147 goto done; 148 } 149 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) { 150 logit_f("key type %s not in PubkeyAcceptedAlgorithms", 151 sshkey_ssh_name(key)); 152 goto done; 153 } 154 if ((r = sshkey_check_cert_sigtype(key, 155 options.ca_sign_algorithms)) != 0) { 156 logit_fr(r, "certificate signature algorithm %s", 157 (key->cert == NULL || key->cert->signature_type == NULL) ? 158 "(null)" : key->cert->signature_type); 159 goto done; 160 } 161 key_s = format_key(key); 162 if (sshkey_is_cert(key)) 163 ca_s = format_key(key->cert->signature_key); 164 165 if (have_sig) { 166 debug3_f("have %s signature for %s%s%s", pkalg, key_s, 167 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 168 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 169 (r = sshpkt_get_end(ssh)) != 0) 170 fatal_fr(r, "parse signature packet"); 171 if ((b = sshbuf_new()) == NULL) 172 fatal_f("sshbuf_new failed"); 173 if (ssh->compat & SSH_OLD_SESSIONID) { 174 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0) 175 fatal_fr(r, "put old session id"); 176 } else { 177 if ((r = sshbuf_put_stringb(b, 178 ssh->kex->session_id)) != 0) 179 fatal_fr(r, "put session id"); 180 } 181 if (!authctxt->valid || authctxt->user == NULL) { 182 debug2_f("disabled because of invalid user"); 183 goto done; 184 } 185 /* reconstruct packet */ 186 xasprintf(&userstyle, "%s%s%s", authctxt->user, 187 authctxt->style ? ":" : "", 188 authctxt->style ? authctxt->style : ""); 189 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 190 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 191 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 192 (r = sshbuf_put_cstring(b, "publickey")) != 0 || 193 (r = sshbuf_put_u8(b, have_sig)) != 0 || 194 (r = sshbuf_put_cstring(b, pkalg)) != 0 || 195 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 196 fatal_fr(r, "reconstruct packet"); 197 #ifdef DEBUG_PK 198 sshbuf_dump(b, stderr); 199 #endif 200 /* test for correct signature */ 201 authenticated = 0; 202 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && 203 PRIVSEP(sshkey_verify(key, sig, slen, 204 sshbuf_ptr(b), sshbuf_len(b), 205 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL, 206 ssh->compat, &sig_details)) == 0) { 207 authenticated = 1; 208 } 209 if (authenticated == 1 && sig_details != NULL) { 210 auth2_record_info(authctxt, "signature count = %u", 211 sig_details->sk_counter); 212 debug_f("sk_counter = %u, sk_flags = 0x%02x", 213 sig_details->sk_counter, sig_details->sk_flags); 214 req_presence = (options.pubkey_auth_options & 215 PUBKEYAUTH_TOUCH_REQUIRED) || 216 !authopts->no_require_user_presence; 217 if (req_presence && (sig_details->sk_flags & 218 SSH_SK_USER_PRESENCE_REQD) == 0) { 219 error("public key %s signature for %s%s from " 220 "%.128s port %d rejected: user presence " 221 "(authenticator touch) requirement " 222 "not met ", key_s, 223 authctxt->valid ? "" : "invalid user ", 224 authctxt->user, ssh_remote_ipaddr(ssh), 225 ssh_remote_port(ssh)); 226 authenticated = 0; 227 goto done; 228 } 229 req_verify = (options.pubkey_auth_options & 230 PUBKEYAUTH_VERIFY_REQUIRED) || 231 authopts->require_verify; 232 if (req_verify && (sig_details->sk_flags & 233 SSH_SK_USER_VERIFICATION_REQD) == 0) { 234 error("public key %s signature for %s%s from " 235 "%.128s port %d rejected: user " 236 "verification requirement not met ", key_s, 237 authctxt->valid ? "" : "invalid user ", 238 authctxt->user, ssh_remote_ipaddr(ssh), 239 ssh_remote_port(ssh)); 240 authenticated = 0; 241 goto done; 242 } 243 } 244 auth2_record_key(authctxt, authenticated, key); 245 } else { 246 debug_f("test pkalg %s pkblob %s%s%s", pkalg, key_s, 247 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 248 249 if ((r = sshpkt_get_end(ssh)) != 0) 250 fatal_fr(r, "parse packet"); 251 252 if (!authctxt->valid || authctxt->user == NULL) { 253 debug2_f("disabled because of invalid user"); 254 goto done; 255 } 256 /* XXX fake reply and always send PK_OK ? */ 257 /* 258 * XXX this allows testing whether a user is allowed 259 * to login: if you happen to have a valid pubkey this 260 * message is sent. the message is NEVER sent at all 261 * if a user is not allowed to login. is this an 262 * issue? -markus 263 */ 264 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 265 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 266 != 0 || 267 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 268 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 269 (r = sshpkt_send(ssh)) != 0 || 270 (r = ssh_packet_write_wait(ssh)) != 0) 271 fatal_fr(r, "send packet"); 272 authctxt->postponed = 1; 273 } 274 } 275 done: 276 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 277 debug_f("key options inconsistent with existing"); 278 authenticated = 0; 279 } 280 debug2_f("authenticated %d pkalg %s", authenticated, pkalg); 281 282 sshbuf_free(b); 283 sshauthopt_free(authopts); 284 sshkey_free(key); 285 free(userstyle); 286 free(pkalg); 287 free(pkblob); 288 free(key_s); 289 free(ca_s); 290 free(sig); 291 sshkey_sig_details_free(sig_details); 292 return authenticated; 293 } 294 295 static int 296 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 297 { 298 char *result; 299 u_int i; 300 301 /* XXX percent_expand() sequences for authorized_principals? */ 302 303 for (i = 0; i < cert->nprincipals; i++) { 304 if ((result = match_list(cert->principals[i], 305 principal_list, NULL)) != NULL) { 306 debug3("matched principal from key options \"%.100s\"", 307 result); 308 free(result); 309 return 1; 310 } 311 } 312 return 0; 313 } 314 315 /* 316 * Process a single authorized_principals format line. Returns 0 and sets 317 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 318 * log preamble for file/line information. 319 */ 320 static int 321 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 322 const char *loc, struct sshauthopt **authoptsp) 323 { 324 u_int i, found = 0; 325 char *ep, *line_opts; 326 const char *reason = NULL; 327 struct sshauthopt *opts = NULL; 328 329 if (authoptsp != NULL) 330 *authoptsp = NULL; 331 332 /* Trim trailing whitespace. */ 333 ep = cp + strlen(cp) - 1; 334 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 335 *ep-- = '\0'; 336 337 /* 338 * If the line has internal whitespace then assume it has 339 * key options. 340 */ 341 line_opts = NULL; 342 if ((ep = strrchr(cp, ' ')) != NULL || 343 (ep = strrchr(cp, '\t')) != NULL) { 344 for (; *ep == ' ' || *ep == '\t'; ep++) 345 ; 346 line_opts = cp; 347 cp = ep; 348 } 349 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 350 debug("%s: bad principals options: %s", loc, reason); 351 auth_debug_add("%s: bad principals options: %s", loc, reason); 352 return -1; 353 } 354 /* Check principals in cert against those on line */ 355 for (i = 0; i < cert->nprincipals; i++) { 356 if (strcmp(cp, cert->principals[i]) != 0) 357 continue; 358 debug3("%s: matched principal \"%.100s\"", 359 loc, cert->principals[i]); 360 found = 1; 361 } 362 if (found && authoptsp != NULL) { 363 *authoptsp = opts; 364 opts = NULL; 365 } 366 sshauthopt_free(opts); 367 return found ? 0 : -1; 368 } 369 370 static int 371 process_principals(struct ssh *ssh, FILE *f, const char *file, 372 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 373 { 374 char loc[256], *line = NULL, *cp, *ep; 375 size_t linesize = 0; 376 u_long linenum = 0; 377 u_int found_principal = 0; 378 379 if (authoptsp != NULL) 380 *authoptsp = NULL; 381 382 while (getline(&line, &linesize, f) != -1) { 383 linenum++; 384 /* Always consume entire input */ 385 if (found_principal) 386 continue; 387 388 /* Skip leading whitespace. */ 389 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 390 ; 391 /* Skip blank and comment lines. */ 392 if ((ep = strchr(cp, '#')) != NULL) 393 *ep = '\0'; 394 if (!*cp || *cp == '\n') 395 continue; 396 397 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 398 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 399 found_principal = 1; 400 } 401 free(line); 402 return found_principal; 403 } 404 405 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 406 407 static int 408 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 409 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 410 { 411 FILE *f; 412 int success; 413 414 if (authoptsp != NULL) 415 *authoptsp = NULL; 416 417 temporarily_use_uid(pw); 418 debug("trying authorized principals file %s", file); 419 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 420 restore_uid(); 421 return 0; 422 } 423 success = process_principals(ssh, f, file, cert, authoptsp); 424 fclose(f); 425 restore_uid(); 426 return success; 427 } 428 429 /* 430 * Checks whether principal is allowed in output of command. 431 * returns 1 if the principal is allowed or 0 otherwise. 432 */ 433 static int 434 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 435 const struct sshkey *key, struct sshauthopt **authoptsp) 436 { 437 struct passwd *runas_pw = NULL; 438 const struct sshkey_cert *cert = key->cert; 439 FILE *f = NULL; 440 int r, ok, found_principal = 0; 441 int i, ac = 0, uid_swapped = 0; 442 pid_t pid; 443 char *tmp, *username = NULL, *command = NULL, **av = NULL; 444 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 445 char serial_s[32], uidstr[32]; 446 void (*osigchld)(int); 447 448 if (authoptsp != NULL) 449 *authoptsp = NULL; 450 if (options.authorized_principals_command == NULL) 451 return 0; 452 if (options.authorized_principals_command_user == NULL) { 453 error("No user for AuthorizedPrincipalsCommand specified, " 454 "skipping"); 455 return 0; 456 } 457 458 /* 459 * NB. all returns later this function should go via "out" to 460 * ensure the original SIGCHLD handler is restored properly. 461 */ 462 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 463 464 /* Prepare and verify the user for the command */ 465 username = percent_expand(options.authorized_principals_command_user, 466 "u", user_pw->pw_name, (char *)NULL); 467 runas_pw = getpwnam(username); 468 if (runas_pw == NULL) { 469 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 470 username, strerror(errno)); 471 goto out; 472 } 473 474 /* Turn the command into an argument vector */ 475 if (argv_split(options.authorized_principals_command, &ac, &av) != 0) { 476 error("AuthorizedPrincipalsCommand \"%s\" contains " 477 "invalid quotes", options.authorized_principals_command); 478 goto out; 479 } 480 if (ac == 0) { 481 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 482 options.authorized_principals_command); 483 goto out; 484 } 485 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 486 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 487 error_f("sshkey_fingerprint failed"); 488 goto out; 489 } 490 if ((key_fp = sshkey_fingerprint(key, 491 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 492 error_f("sshkey_fingerprint failed"); 493 goto out; 494 } 495 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 496 error_fr(r, "sshkey_to_base64 failed"); 497 goto out; 498 } 499 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 500 error_fr(r, "sshkey_to_base64 failed"); 501 goto out; 502 } 503 snprintf(serial_s, sizeof(serial_s), "%llu", 504 (unsigned long long)cert->serial); 505 snprintf(uidstr, sizeof(uidstr), "%llu", 506 (unsigned long long)user_pw->pw_uid); 507 for (i = 1; i < ac; i++) { 508 tmp = percent_expand(av[i], 509 "U", uidstr, 510 "u", user_pw->pw_name, 511 "h", user_pw->pw_dir, 512 "t", sshkey_ssh_name(key), 513 "T", sshkey_ssh_name(cert->signature_key), 514 "f", key_fp, 515 "F", ca_fp, 516 "k", keytext, 517 "K", catext, 518 "i", cert->key_id, 519 "s", serial_s, 520 (char *)NULL); 521 if (tmp == NULL) 522 fatal_f("percent_expand failed"); 523 free(av[i]); 524 av[i] = tmp; 525 } 526 /* Prepare a printable command for logs, etc. */ 527 command = argv_assemble(ac, av); 528 529 if ((pid = subprocess("AuthorizedPrincipalsCommand", command, 530 ac, av, &f, 531 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 532 runas_pw, temporarily_use_uid, restore_uid)) == 0) 533 goto out; 534 535 uid_swapped = 1; 536 temporarily_use_uid(runas_pw); 537 538 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 539 540 fclose(f); 541 f = NULL; 542 543 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 544 goto out; 545 546 /* Read completed successfully */ 547 found_principal = ok; 548 out: 549 if (f != NULL) 550 fclose(f); 551 ssh_signal(SIGCHLD, osigchld); 552 for (i = 0; i < ac; i++) 553 free(av[i]); 554 free(av); 555 if (uid_swapped) 556 restore_uid(); 557 free(command); 558 free(username); 559 free(ca_fp); 560 free(key_fp); 561 free(catext); 562 free(keytext); 563 return found_principal; 564 } 565 566 /* 567 * Check a single line of an authorized_keys-format file. Returns 0 if key 568 * matches, -1 otherwise. Will return key/cert options via *authoptsp 569 * on success. "loc" is used as file/line location in log messages. 570 */ 571 static int 572 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 573 char *cp, const char *loc, struct sshauthopt **authoptsp) 574 { 575 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 576 struct sshkey *found = NULL; 577 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 578 char *key_options = NULL, *fp = NULL; 579 const char *reason = NULL; 580 int ret = -1; 581 582 if (authoptsp != NULL) 583 *authoptsp = NULL; 584 585 if ((found = sshkey_new(want_keytype)) == NULL) { 586 debug3_f("keytype %d failed", want_keytype); 587 goto out; 588 } 589 590 /* XXX djm: peek at key type in line and skip if unwanted */ 591 592 if (sshkey_read(found, &cp) != 0) { 593 /* no key? check for options */ 594 debug2("%s: check options: '%s'", loc, cp); 595 key_options = cp; 596 if (sshkey_advance_past_options(&cp) != 0) { 597 reason = "invalid key option string"; 598 goto fail_reason; 599 } 600 skip_space(&cp); 601 if (sshkey_read(found, &cp) != 0) { 602 /* still no key? advance to next line*/ 603 debug2("%s: advance: '%s'", loc, cp); 604 goto out; 605 } 606 } 607 /* Parse key options now; we need to know if this is a CA key */ 608 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 609 debug("%s: bad key options: %s", loc, reason); 610 auth_debug_add("%s: bad key options: %s", loc, reason); 611 goto out; 612 } 613 /* Ignore keys that don't match or incorrectly marked as CAs */ 614 if (sshkey_is_cert(key)) { 615 /* Certificate; check signature key against CA */ 616 if (!sshkey_equal(found, key->cert->signature_key) || 617 !keyopts->cert_authority) 618 goto out; 619 } else { 620 /* Plain key: check it against key found in file */ 621 if (!sshkey_equal(found, key) || keyopts->cert_authority) 622 goto out; 623 } 624 625 /* We have a candidate key, perform authorisation checks */ 626 if ((fp = sshkey_fingerprint(found, 627 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 628 fatal_f("fingerprint failed"); 629 630 debug("%s: matching %s found: %s %s", loc, 631 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 632 633 if (auth_authorise_keyopts(ssh, pw, keyopts, 634 sshkey_is_cert(key), loc) != 0) { 635 reason = "Refused by key options"; 636 goto fail_reason; 637 } 638 /* That's all we need for plain keys. */ 639 if (!sshkey_is_cert(key)) { 640 verbose("Accepted key %s %s found at %s", 641 sshkey_type(found), fp, loc); 642 finalopts = keyopts; 643 keyopts = NULL; 644 goto success; 645 } 646 647 /* 648 * Additional authorisation for certificates. 649 */ 650 651 /* Parse and check options present in certificate */ 652 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 653 reason = "Invalid certificate options"; 654 goto fail_reason; 655 } 656 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 657 reason = "Refused by certificate options"; 658 goto fail_reason; 659 } 660 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 661 goto fail_reason; 662 663 /* 664 * If the user has specified a list of principals as 665 * a key option, then prefer that list to matching 666 * their username in the certificate principals list. 667 */ 668 if (keyopts->cert_principals != NULL && 669 !match_principals_option(keyopts->cert_principals, key->cert)) { 670 reason = "Certificate does not contain an authorized principal"; 671 goto fail_reason; 672 } 673 if (sshkey_cert_check_authority(key, 0, 0, 0, 674 keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0) 675 goto fail_reason; 676 677 verbose("Accepted certificate ID \"%s\" (serial %llu) " 678 "signed by CA %s %s found at %s", 679 key->cert->key_id, 680 (unsigned long long)key->cert->serial, 681 sshkey_type(found), fp, loc); 682 683 success: 684 if (finalopts == NULL) 685 fatal_f("internal error: missing options"); 686 if (authoptsp != NULL) { 687 *authoptsp = finalopts; 688 finalopts = NULL; 689 } 690 /* success */ 691 ret = 0; 692 goto out; 693 694 fail_reason: 695 error("%s", reason); 696 auth_debug_add("%s", reason); 697 out: 698 free(fp); 699 sshauthopt_free(keyopts); 700 sshauthopt_free(certopts); 701 sshauthopt_free(finalopts); 702 sshkey_free(found); 703 return ret; 704 } 705 706 /* 707 * Checks whether key is allowed in authorized_keys-format file, 708 * returns 1 if the key is allowed or 0 otherwise. 709 */ 710 static int 711 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 712 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 713 { 714 char *cp, *line = NULL, loc[256]; 715 size_t linesize = 0; 716 int found_key = 0; 717 u_long linenum = 0; 718 719 if (authoptsp != NULL) 720 *authoptsp = NULL; 721 722 while (getline(&line, &linesize, f) != -1) { 723 linenum++; 724 /* Always consume entire file */ 725 if (found_key) 726 continue; 727 728 /* Skip leading whitespace, empty and comment lines. */ 729 cp = line; 730 skip_space(&cp); 731 if (!*cp || *cp == '\n' || *cp == '#') 732 continue; 733 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 734 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 735 found_key = 1; 736 } 737 free(line); 738 return found_key; 739 } 740 741 /* Authenticate a certificate key against TrustedUserCAKeys */ 742 static int 743 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 744 struct sshauthopt **authoptsp) 745 { 746 char *ca_fp, *principals_file = NULL; 747 const char *reason; 748 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 749 struct sshauthopt *final_opts = NULL; 750 int r, ret = 0, found_principal = 0, use_authorized_principals; 751 752 if (authoptsp != NULL) 753 *authoptsp = NULL; 754 755 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 756 return 0; 757 758 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 759 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 760 return 0; 761 762 if ((r = sshkey_in_file(key->cert->signature_key, 763 options.trusted_user_ca_keys, 1, 0)) != 0) { 764 debug2_fr(r, "CA %s %s is not listed in %s", 765 sshkey_type(key->cert->signature_key), ca_fp, 766 options.trusted_user_ca_keys); 767 goto out; 768 } 769 /* 770 * If AuthorizedPrincipals is in use, then compare the certificate 771 * principals against the names in that file rather than matching 772 * against the username. 773 */ 774 if ((principals_file = authorized_principals_file(pw)) != NULL) { 775 if (match_principals_file(ssh, pw, principals_file, 776 key->cert, &principals_opts)) 777 found_principal = 1; 778 } 779 /* Try querying command if specified */ 780 if (!found_principal && match_principals_command(ssh, pw, key, 781 &principals_opts)) 782 found_principal = 1; 783 /* If principals file or command is specified, then require a match */ 784 use_authorized_principals = principals_file != NULL || 785 options.authorized_principals_command != NULL; 786 if (!found_principal && use_authorized_principals) { 787 reason = "Certificate does not contain an authorized principal"; 788 goto fail_reason; 789 } 790 if (use_authorized_principals && principals_opts == NULL) 791 fatal_f("internal error: missing principals_opts"); 792 if (sshkey_cert_check_authority(key, 0, 1, 0, 793 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 794 goto fail_reason; 795 796 /* Check authority from options in key and from principals file/cmd */ 797 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 798 reason = "Invalid certificate options"; 799 goto fail_reason; 800 } 801 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 802 reason = "Refused by certificate options"; 803 goto fail_reason; 804 } 805 if (principals_opts == NULL) { 806 final_opts = cert_opts; 807 cert_opts = NULL; 808 } else { 809 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 810 "principals") != 0) { 811 reason = "Refused by certificate principals options"; 812 goto fail_reason; 813 } 814 if ((final_opts = sshauthopt_merge(principals_opts, 815 cert_opts, &reason)) == NULL) { 816 fail_reason: 817 error("%s", reason); 818 auth_debug_add("%s", reason); 819 goto out; 820 } 821 } 822 823 /* Success */ 824 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 825 "%s CA %s via %s", key->cert->key_id, 826 (unsigned long long)key->cert->serial, 827 sshkey_type(key->cert->signature_key), ca_fp, 828 options.trusted_user_ca_keys); 829 if (authoptsp != NULL) { 830 *authoptsp = final_opts; 831 final_opts = NULL; 832 } 833 ret = 1; 834 out: 835 sshauthopt_free(principals_opts); 836 sshauthopt_free(cert_opts); 837 sshauthopt_free(final_opts); 838 free(principals_file); 839 free(ca_fp); 840 return ret; 841 } 842 843 /* 844 * Checks whether key is allowed in file. 845 * returns 1 if the key is allowed or 0 otherwise. 846 */ 847 static int 848 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 849 char *file, struct sshauthopt **authoptsp) 850 { 851 FILE *f; 852 int found_key = 0; 853 854 if (authoptsp != NULL) 855 *authoptsp = NULL; 856 857 /* Temporarily use the user's uid. */ 858 temporarily_use_uid(pw); 859 860 debug("trying public key file %s", file); 861 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 862 found_key = check_authkeys_file(ssh, pw, f, file, 863 key, authoptsp); 864 fclose(f); 865 } 866 867 restore_uid(); 868 return found_key; 869 } 870 871 /* 872 * Checks whether key is allowed in output of command. 873 * returns 1 if the key is allowed or 0 otherwise. 874 */ 875 static int 876 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 877 struct sshkey *key, struct sshauthopt **authoptsp) 878 { 879 struct passwd *runas_pw = NULL; 880 FILE *f = NULL; 881 int r, ok, found_key = 0; 882 int i, uid_swapped = 0, ac = 0; 883 pid_t pid; 884 char *username = NULL, *key_fp = NULL, *keytext = NULL; 885 char uidstr[32], *tmp, *command = NULL, **av = NULL; 886 void (*osigchld)(int); 887 888 if (authoptsp != NULL) 889 *authoptsp = NULL; 890 if (options.authorized_keys_command == NULL) 891 return 0; 892 if (options.authorized_keys_command_user == NULL) { 893 error("No user for AuthorizedKeysCommand specified, skipping"); 894 return 0; 895 } 896 897 /* 898 * NB. all returns later this function should go via "out" to 899 * ensure the original SIGCHLD handler is restored properly. 900 */ 901 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 902 903 /* Prepare and verify the user for the command */ 904 username = percent_expand(options.authorized_keys_command_user, 905 "u", user_pw->pw_name, (char *)NULL); 906 runas_pw = getpwnam(username); 907 if (runas_pw == NULL) { 908 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 909 username, strerror(errno)); 910 goto out; 911 } 912 913 /* Prepare AuthorizedKeysCommand */ 914 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 915 SSH_FP_DEFAULT)) == NULL) { 916 error_f("sshkey_fingerprint failed"); 917 goto out; 918 } 919 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 920 error_fr(r, "sshkey_to_base64 failed"); 921 goto out; 922 } 923 924 /* Turn the command into an argument vector */ 925 if (argv_split(options.authorized_keys_command, &ac, &av) != 0) { 926 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 927 options.authorized_keys_command); 928 goto out; 929 } 930 if (ac == 0) { 931 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 932 options.authorized_keys_command); 933 goto out; 934 } 935 snprintf(uidstr, sizeof(uidstr), "%llu", 936 (unsigned long long)user_pw->pw_uid); 937 for (i = 1; i < ac; i++) { 938 tmp = percent_expand(av[i], 939 "U", uidstr, 940 "u", user_pw->pw_name, 941 "h", user_pw->pw_dir, 942 "t", sshkey_ssh_name(key), 943 "f", key_fp, 944 "k", keytext, 945 (char *)NULL); 946 if (tmp == NULL) 947 fatal_f("percent_expand failed"); 948 free(av[i]); 949 av[i] = tmp; 950 } 951 /* Prepare a printable command for logs, etc. */ 952 command = argv_assemble(ac, av); 953 954 /* 955 * If AuthorizedKeysCommand was run without arguments 956 * then fall back to the old behaviour of passing the 957 * target username as a single argument. 958 */ 959 if (ac == 1) { 960 av = xreallocarray(av, ac + 2, sizeof(*av)); 961 av[1] = xstrdup(user_pw->pw_name); 962 av[2] = NULL; 963 /* Fix up command too, since it is used in log messages */ 964 free(command); 965 xasprintf(&command, "%s %s", av[0], av[1]); 966 } 967 968 if ((pid = subprocess("AuthorizedKeysCommand", command, 969 ac, av, &f, 970 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 971 runas_pw, temporarily_use_uid, restore_uid)) == 0) 972 goto out; 973 974 uid_swapped = 1; 975 temporarily_use_uid(runas_pw); 976 977 ok = check_authkeys_file(ssh, user_pw, f, 978 options.authorized_keys_command, key, authoptsp); 979 980 fclose(f); 981 f = NULL; 982 983 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 984 goto out; 985 986 /* Read completed successfully */ 987 found_key = ok; 988 out: 989 if (f != NULL) 990 fclose(f); 991 ssh_signal(SIGCHLD, osigchld); 992 for (i = 0; i < ac; i++) 993 free(av[i]); 994 free(av); 995 if (uid_swapped) 996 restore_uid(); 997 free(command); 998 free(username); 999 free(key_fp); 1000 free(keytext); 1001 return found_key; 1002 } 1003 1004 /* 1005 * Check whether key authenticates and authorises the user. 1006 */ 1007 int 1008 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1009 int auth_attempt, struct sshauthopt **authoptsp) 1010 { 1011 u_int success = 0, i; 1012 char *file; 1013 struct sshauthopt *opts = NULL; 1014 1015 if (authoptsp != NULL) 1016 *authoptsp = NULL; 1017 1018 if (auth_key_is_revoked(key)) 1019 return 0; 1020 if (sshkey_is_cert(key) && 1021 auth_key_is_revoked(key->cert->signature_key)) 1022 return 0; 1023 1024 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1025 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1026 continue; 1027 file = expand_authorized_keys( 1028 options.authorized_keys_files[i], pw); 1029 success = user_key_allowed2(ssh, pw, key, file, &opts); 1030 free(file); 1031 if (!success) { 1032 sshauthopt_free(opts); 1033 opts = NULL; 1034 } 1035 } 1036 if (success) 1037 goto out; 1038 1039 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1040 goto out; 1041 sshauthopt_free(opts); 1042 opts = NULL; 1043 1044 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1045 goto out; 1046 sshauthopt_free(opts); 1047 opts = NULL; 1048 1049 out: 1050 if (success && authoptsp != NULL) { 1051 *authoptsp = opts; 1052 opts = NULL; 1053 } 1054 sshauthopt_free(opts); 1055 return success; 1056 } 1057 1058 Authmethod method_pubkey = { 1059 "publickey", 1060 userauth_pubkey, 1061 &options.pubkey_authentication 1062 }; 1063