1 /* $OpenBSD: auth2-pubkey.c,v 1.110 2021/09/29 01:33:32 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, nonblank = 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 nonblank++; 398 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 399 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 400 found_principal = 1; 401 } 402 debug2_f("%s: processed %lu/%lu lines", file, nonblank, linenum); 403 free(line); 404 return found_principal; 405 } 406 407 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 408 409 static int 410 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 411 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 412 { 413 FILE *f; 414 int success; 415 416 if (authoptsp != NULL) 417 *authoptsp = NULL; 418 419 temporarily_use_uid(pw); 420 debug("trying authorized principals file %s", file); 421 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 422 restore_uid(); 423 return 0; 424 } 425 success = process_principals(ssh, f, file, cert, authoptsp); 426 fclose(f); 427 restore_uid(); 428 return success; 429 } 430 431 /* 432 * Checks whether principal is allowed in output of command. 433 * returns 1 if the principal is allowed or 0 otherwise. 434 */ 435 static int 436 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 437 const struct sshkey *key, struct sshauthopt **authoptsp) 438 { 439 struct passwd *runas_pw = NULL; 440 const struct sshkey_cert *cert = key->cert; 441 FILE *f = NULL; 442 int r, ok, found_principal = 0; 443 int i, ac = 0, uid_swapped = 0; 444 pid_t pid; 445 char *tmp, *username = NULL, *command = NULL, **av = NULL; 446 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 447 char serial_s[32], uidstr[32]; 448 void (*osigchld)(int); 449 450 if (authoptsp != NULL) 451 *authoptsp = NULL; 452 if (options.authorized_principals_command == NULL) 453 return 0; 454 if (options.authorized_principals_command_user == NULL) { 455 error("No user for AuthorizedPrincipalsCommand specified, " 456 "skipping"); 457 return 0; 458 } 459 460 /* 461 * NB. all returns later this function should go via "out" to 462 * ensure the original SIGCHLD handler is restored properly. 463 */ 464 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 465 466 /* Prepare and verify the user for the command */ 467 username = percent_expand(options.authorized_principals_command_user, 468 "u", user_pw->pw_name, (char *)NULL); 469 runas_pw = getpwnam(username); 470 if (runas_pw == NULL) { 471 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 472 username, strerror(errno)); 473 goto out; 474 } 475 476 /* Turn the command into an argument vector */ 477 if (argv_split(options.authorized_principals_command, 478 &ac, &av, 0) != 0) { 479 error("AuthorizedPrincipalsCommand \"%s\" contains " 480 "invalid quotes", options.authorized_principals_command); 481 goto out; 482 } 483 if (ac == 0) { 484 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 485 options.authorized_principals_command); 486 goto out; 487 } 488 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 489 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 490 error_f("sshkey_fingerprint failed"); 491 goto out; 492 } 493 if ((key_fp = sshkey_fingerprint(key, 494 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 495 error_f("sshkey_fingerprint failed"); 496 goto out; 497 } 498 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 499 error_fr(r, "sshkey_to_base64 failed"); 500 goto out; 501 } 502 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 503 error_fr(r, "sshkey_to_base64 failed"); 504 goto out; 505 } 506 snprintf(serial_s, sizeof(serial_s), "%llu", 507 (unsigned long long)cert->serial); 508 snprintf(uidstr, sizeof(uidstr), "%llu", 509 (unsigned long long)user_pw->pw_uid); 510 for (i = 1; i < ac; i++) { 511 tmp = percent_expand(av[i], 512 "U", uidstr, 513 "u", user_pw->pw_name, 514 "h", user_pw->pw_dir, 515 "t", sshkey_ssh_name(key), 516 "T", sshkey_ssh_name(cert->signature_key), 517 "f", key_fp, 518 "F", ca_fp, 519 "k", keytext, 520 "K", catext, 521 "i", cert->key_id, 522 "s", serial_s, 523 (char *)NULL); 524 if (tmp == NULL) 525 fatal_f("percent_expand failed"); 526 free(av[i]); 527 av[i] = tmp; 528 } 529 /* Prepare a printable command for logs, etc. */ 530 command = argv_assemble(ac, av); 531 532 if ((pid = subprocess("AuthorizedPrincipalsCommand", command, 533 ac, av, &f, 534 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 535 runas_pw, temporarily_use_uid, restore_uid)) == 0) 536 goto out; 537 538 uid_swapped = 1; 539 temporarily_use_uid(runas_pw); 540 541 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 542 543 fclose(f); 544 f = NULL; 545 546 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 547 goto out; 548 549 /* Read completed successfully */ 550 found_principal = ok; 551 out: 552 if (f != NULL) 553 fclose(f); 554 ssh_signal(SIGCHLD, osigchld); 555 for (i = 0; i < ac; i++) 556 free(av[i]); 557 free(av); 558 if (uid_swapped) 559 restore_uid(); 560 free(command); 561 free(username); 562 free(ca_fp); 563 free(key_fp); 564 free(catext); 565 free(keytext); 566 return found_principal; 567 } 568 569 /* 570 * Check a single line of an authorized_keys-format file. Returns 0 if key 571 * matches, -1 otherwise. Will return key/cert options via *authoptsp 572 * on success. "loc" is used as file/line location in log messages. 573 */ 574 static int 575 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 576 char *cp, const char *loc, struct sshauthopt **authoptsp) 577 { 578 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 579 struct sshkey *found = NULL; 580 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 581 char *key_options = NULL, *fp = NULL; 582 const char *reason = NULL; 583 int ret = -1; 584 585 if (authoptsp != NULL) 586 *authoptsp = NULL; 587 588 if ((found = sshkey_new(want_keytype)) == NULL) { 589 debug3_f("keytype %d failed", want_keytype); 590 goto out; 591 } 592 593 /* XXX djm: peek at key type in line and skip if unwanted */ 594 595 if (sshkey_read(found, &cp) != 0) { 596 /* no key? check for options */ 597 debug2("%s: check options: '%s'", loc, cp); 598 key_options = cp; 599 if (sshkey_advance_past_options(&cp) != 0) { 600 reason = "invalid key option string"; 601 goto fail_reason; 602 } 603 skip_space(&cp); 604 if (sshkey_read(found, &cp) != 0) { 605 /* still no key? advance to next line*/ 606 debug2("%s: advance: '%s'", loc, cp); 607 goto out; 608 } 609 } 610 /* Parse key options now; we need to know if this is a CA key */ 611 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 612 debug("%s: bad key options: %s", loc, reason); 613 auth_debug_add("%s: bad key options: %s", loc, reason); 614 goto out; 615 } 616 /* Ignore keys that don't match or incorrectly marked as CAs */ 617 if (sshkey_is_cert(key)) { 618 /* Certificate; check signature key against CA */ 619 if (!sshkey_equal(found, key->cert->signature_key) || 620 !keyopts->cert_authority) 621 goto out; 622 } else { 623 /* Plain key: check it against key found in file */ 624 if (!sshkey_equal(found, key) || keyopts->cert_authority) 625 goto out; 626 } 627 628 /* We have a candidate key, perform authorisation checks */ 629 if ((fp = sshkey_fingerprint(found, 630 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 631 fatal_f("fingerprint failed"); 632 633 debug("%s: matching %s found: %s %s", loc, 634 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 635 636 if (auth_authorise_keyopts(ssh, pw, keyopts, 637 sshkey_is_cert(key), loc) != 0) { 638 reason = "Refused by key options"; 639 goto fail_reason; 640 } 641 /* That's all we need for plain keys. */ 642 if (!sshkey_is_cert(key)) { 643 verbose("Accepted key %s %s found at %s", 644 sshkey_type(found), fp, loc); 645 finalopts = keyopts; 646 keyopts = NULL; 647 goto success; 648 } 649 650 /* 651 * Additional authorisation for certificates. 652 */ 653 654 /* Parse and check options present in certificate */ 655 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 656 reason = "Invalid certificate options"; 657 goto fail_reason; 658 } 659 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 660 reason = "Refused by certificate options"; 661 goto fail_reason; 662 } 663 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 664 goto fail_reason; 665 666 /* 667 * If the user has specified a list of principals as 668 * a key option, then prefer that list to matching 669 * their username in the certificate principals list. 670 */ 671 if (keyopts->cert_principals != NULL && 672 !match_principals_option(keyopts->cert_principals, key->cert)) { 673 reason = "Certificate does not contain an authorized principal"; 674 goto fail_reason; 675 } 676 if (sshkey_cert_check_authority_now(key, 0, 0, 0, 677 keyopts->cert_principals == NULL ? pw->pw_name : NULL, 678 &reason) != 0) 679 goto fail_reason; 680 681 verbose("Accepted certificate ID \"%s\" (serial %llu) " 682 "signed by CA %s %s found at %s", 683 key->cert->key_id, 684 (unsigned long long)key->cert->serial, 685 sshkey_type(found), fp, loc); 686 687 success: 688 if (finalopts == NULL) 689 fatal_f("internal error: missing options"); 690 if (authoptsp != NULL) { 691 *authoptsp = finalopts; 692 finalopts = NULL; 693 } 694 /* success */ 695 ret = 0; 696 goto out; 697 698 fail_reason: 699 error("%s", reason); 700 auth_debug_add("%s", reason); 701 out: 702 free(fp); 703 sshauthopt_free(keyopts); 704 sshauthopt_free(certopts); 705 sshauthopt_free(finalopts); 706 sshkey_free(found); 707 return ret; 708 } 709 710 /* 711 * Checks whether key is allowed in authorized_keys-format file, 712 * returns 1 if the key is allowed or 0 otherwise. 713 */ 714 static int 715 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 716 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 717 { 718 char *cp, *line = NULL, loc[256]; 719 size_t linesize = 0; 720 int found_key = 0; 721 u_long linenum = 0, nonblank = 0; 722 723 if (authoptsp != NULL) 724 *authoptsp = NULL; 725 726 while (getline(&line, &linesize, f) != -1) { 727 linenum++; 728 /* Always consume entire file */ 729 if (found_key) 730 continue; 731 732 /* Skip leading whitespace, empty and comment lines. */ 733 cp = line; 734 skip_space(&cp); 735 if (!*cp || *cp == '\n' || *cp == '#') 736 continue; 737 738 nonblank++; 739 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 740 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 741 found_key = 1; 742 } 743 free(line); 744 debug2_f("%s: processed %lu/%lu lines", file, nonblank, linenum); 745 return found_key; 746 } 747 748 /* Authenticate a certificate key against TrustedUserCAKeys */ 749 static int 750 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 751 struct sshauthopt **authoptsp) 752 { 753 char *ca_fp, *principals_file = NULL; 754 const char *reason; 755 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 756 struct sshauthopt *final_opts = NULL; 757 int r, ret = 0, found_principal = 0, use_authorized_principals; 758 759 if (authoptsp != NULL) 760 *authoptsp = NULL; 761 762 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 763 return 0; 764 765 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 766 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 767 return 0; 768 769 if ((r = sshkey_in_file(key->cert->signature_key, 770 options.trusted_user_ca_keys, 1, 0)) != 0) { 771 debug2_fr(r, "CA %s %s is not listed in %s", 772 sshkey_type(key->cert->signature_key), ca_fp, 773 options.trusted_user_ca_keys); 774 goto out; 775 } 776 /* 777 * If AuthorizedPrincipals is in use, then compare the certificate 778 * principals against the names in that file rather than matching 779 * against the username. 780 */ 781 if ((principals_file = authorized_principals_file(pw)) != NULL) { 782 if (match_principals_file(ssh, pw, principals_file, 783 key->cert, &principals_opts)) 784 found_principal = 1; 785 } 786 /* Try querying command if specified */ 787 if (!found_principal && match_principals_command(ssh, pw, key, 788 &principals_opts)) 789 found_principal = 1; 790 /* If principals file or command is specified, then require a match */ 791 use_authorized_principals = principals_file != NULL || 792 options.authorized_principals_command != NULL; 793 if (!found_principal && use_authorized_principals) { 794 reason = "Certificate does not contain an authorized principal"; 795 goto fail_reason; 796 } 797 if (use_authorized_principals && principals_opts == NULL) 798 fatal_f("internal error: missing principals_opts"); 799 if (sshkey_cert_check_authority_now(key, 0, 1, 0, 800 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 801 goto fail_reason; 802 803 /* Check authority from options in key and from principals file/cmd */ 804 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 805 reason = "Invalid certificate options"; 806 goto fail_reason; 807 } 808 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 809 reason = "Refused by certificate options"; 810 goto fail_reason; 811 } 812 if (principals_opts == NULL) { 813 final_opts = cert_opts; 814 cert_opts = NULL; 815 } else { 816 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 817 "principals") != 0) { 818 reason = "Refused by certificate principals options"; 819 goto fail_reason; 820 } 821 if ((final_opts = sshauthopt_merge(principals_opts, 822 cert_opts, &reason)) == NULL) { 823 fail_reason: 824 error("%s", reason); 825 auth_debug_add("%s", reason); 826 goto out; 827 } 828 } 829 830 /* Success */ 831 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 832 "%s CA %s via %s", key->cert->key_id, 833 (unsigned long long)key->cert->serial, 834 sshkey_type(key->cert->signature_key), ca_fp, 835 options.trusted_user_ca_keys); 836 if (authoptsp != NULL) { 837 *authoptsp = final_opts; 838 final_opts = NULL; 839 } 840 ret = 1; 841 out: 842 sshauthopt_free(principals_opts); 843 sshauthopt_free(cert_opts); 844 sshauthopt_free(final_opts); 845 free(principals_file); 846 free(ca_fp); 847 return ret; 848 } 849 850 /* 851 * Checks whether key is allowed in file. 852 * returns 1 if the key is allowed or 0 otherwise. 853 */ 854 static int 855 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 856 char *file, struct sshauthopt **authoptsp) 857 { 858 FILE *f; 859 int found_key = 0; 860 861 if (authoptsp != NULL) 862 *authoptsp = NULL; 863 864 /* Temporarily use the user's uid. */ 865 temporarily_use_uid(pw); 866 867 debug("trying public key file %s", file); 868 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 869 found_key = check_authkeys_file(ssh, pw, f, file, 870 key, authoptsp); 871 fclose(f); 872 } 873 874 restore_uid(); 875 return found_key; 876 } 877 878 /* 879 * Checks whether key is allowed in output of command. 880 * returns 1 if the key is allowed or 0 otherwise. 881 */ 882 static int 883 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 884 struct sshkey *key, struct sshauthopt **authoptsp) 885 { 886 struct passwd *runas_pw = NULL; 887 FILE *f = NULL; 888 int r, ok, found_key = 0; 889 int i, uid_swapped = 0, ac = 0; 890 pid_t pid; 891 char *username = NULL, *key_fp = NULL, *keytext = NULL; 892 char uidstr[32], *tmp, *command = NULL, **av = NULL; 893 void (*osigchld)(int); 894 895 if (authoptsp != NULL) 896 *authoptsp = NULL; 897 if (options.authorized_keys_command == NULL) 898 return 0; 899 if (options.authorized_keys_command_user == NULL) { 900 error("No user for AuthorizedKeysCommand specified, skipping"); 901 return 0; 902 } 903 904 /* 905 * NB. all returns later this function should go via "out" to 906 * ensure the original SIGCHLD handler is restored properly. 907 */ 908 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 909 910 /* Prepare and verify the user for the command */ 911 username = percent_expand(options.authorized_keys_command_user, 912 "u", user_pw->pw_name, (char *)NULL); 913 runas_pw = getpwnam(username); 914 if (runas_pw == NULL) { 915 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 916 username, strerror(errno)); 917 goto out; 918 } 919 920 /* Prepare AuthorizedKeysCommand */ 921 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 922 SSH_FP_DEFAULT)) == NULL) { 923 error_f("sshkey_fingerprint failed"); 924 goto out; 925 } 926 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 927 error_fr(r, "sshkey_to_base64 failed"); 928 goto out; 929 } 930 931 /* Turn the command into an argument vector */ 932 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) { 933 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 934 options.authorized_keys_command); 935 goto out; 936 } 937 if (ac == 0) { 938 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 939 options.authorized_keys_command); 940 goto out; 941 } 942 snprintf(uidstr, sizeof(uidstr), "%llu", 943 (unsigned long long)user_pw->pw_uid); 944 for (i = 1; i < ac; i++) { 945 tmp = percent_expand(av[i], 946 "U", uidstr, 947 "u", user_pw->pw_name, 948 "h", user_pw->pw_dir, 949 "t", sshkey_ssh_name(key), 950 "f", key_fp, 951 "k", keytext, 952 (char *)NULL); 953 if (tmp == NULL) 954 fatal_f("percent_expand failed"); 955 free(av[i]); 956 av[i] = tmp; 957 } 958 /* Prepare a printable command for logs, etc. */ 959 command = argv_assemble(ac, av); 960 961 /* 962 * If AuthorizedKeysCommand was run without arguments 963 * then fall back to the old behaviour of passing the 964 * target username as a single argument. 965 */ 966 if (ac == 1) { 967 av = xreallocarray(av, ac + 2, sizeof(*av)); 968 av[1] = xstrdup(user_pw->pw_name); 969 av[2] = NULL; 970 /* Fix up command too, since it is used in log messages */ 971 free(command); 972 xasprintf(&command, "%s %s", av[0], av[1]); 973 } 974 975 if ((pid = subprocess("AuthorizedKeysCommand", command, 976 ac, av, &f, 977 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 978 runas_pw, temporarily_use_uid, restore_uid)) == 0) 979 goto out; 980 981 uid_swapped = 1; 982 temporarily_use_uid(runas_pw); 983 984 ok = check_authkeys_file(ssh, user_pw, f, 985 options.authorized_keys_command, key, authoptsp); 986 987 fclose(f); 988 f = NULL; 989 990 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 991 goto out; 992 993 /* Read completed successfully */ 994 found_key = ok; 995 out: 996 if (f != NULL) 997 fclose(f); 998 ssh_signal(SIGCHLD, osigchld); 999 for (i = 0; i < ac; i++) 1000 free(av[i]); 1001 free(av); 1002 if (uid_swapped) 1003 restore_uid(); 1004 free(command); 1005 free(username); 1006 free(key_fp); 1007 free(keytext); 1008 return found_key; 1009 } 1010 1011 /* 1012 * Check whether key authenticates and authorises the user. 1013 */ 1014 int 1015 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1016 int auth_attempt, struct sshauthopt **authoptsp) 1017 { 1018 u_int success = 0, i; 1019 char *file; 1020 struct sshauthopt *opts = NULL; 1021 1022 if (authoptsp != NULL) 1023 *authoptsp = NULL; 1024 1025 if (auth_key_is_revoked(key)) 1026 return 0; 1027 if (sshkey_is_cert(key) && 1028 auth_key_is_revoked(key->cert->signature_key)) 1029 return 0; 1030 1031 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1032 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1033 continue; 1034 file = expand_authorized_keys( 1035 options.authorized_keys_files[i], pw); 1036 success = user_key_allowed2(ssh, pw, key, file, &opts); 1037 free(file); 1038 if (!success) { 1039 sshauthopt_free(opts); 1040 opts = NULL; 1041 } 1042 } 1043 if (success) 1044 goto out; 1045 1046 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1047 goto out; 1048 sshauthopt_free(opts); 1049 opts = NULL; 1050 1051 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1052 goto out; 1053 sshauthopt_free(opts); 1054 opts = NULL; 1055 1056 out: 1057 if (success && authoptsp != NULL) { 1058 *authoptsp = opts; 1059 opts = NULL; 1060 } 1061 sshauthopt_free(opts); 1062 return success; 1063 } 1064 1065 Authmethod method_pubkey = { 1066 "publickey", 1067 userauth_pubkey, 1068 &options.pubkey_authentication 1069 }; 1070