1 /* $OpenBSD: auth2-pubkey.c,v 1.87 2019/01/22 11:26:16 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 #include "includes.h" 27 28 #include <sys/types.h> 29 #include <sys/stat.h> 30 31 #include <errno.h> 32 #include <fcntl.h> 33 #ifdef HAVE_PATHS_H 34 # include <paths.h> 35 #endif 36 #include <pwd.h> 37 #include <signal.h> 38 #include <stdio.h> 39 #include <stdarg.h> 40 #include <string.h> 41 #include <time.h> 42 #include <unistd.h> 43 #include <limits.h> 44 45 #include "xmalloc.h" 46 #include "ssh.h" 47 #include "ssh2.h" 48 #include "packet.h" 49 #include "sshbuf.h" 50 #include "log.h" 51 #include "misc.h" 52 #include "servconf.h" 53 #include "compat.h" 54 #include "sshkey.h" 55 #include "hostfile.h" 56 #include "auth.h" 57 #include "pathnames.h" 58 #include "uidswap.h" 59 #include "auth-options.h" 60 #include "canohost.h" 61 #ifdef GSSAPI 62 #include "ssh-gss.h" 63 #endif 64 #include "monitor_wrap.h" 65 #include "authfile.h" 66 #include "match.h" 67 #include "ssherr.h" 68 #include "channels.h" /* XXX for session.h */ 69 #include "session.h" /* XXX for child_set_env(); refactor? */ 70 71 /* import */ 72 extern ServerOptions options; 73 extern u_char *session_id2; 74 extern u_int session_id2_len; 75 76 static char * 77 format_key(const struct sshkey *key) 78 { 79 char *ret, *fp = sshkey_fingerprint(key, 80 options.fingerprint_hash, SSH_FP_DEFAULT); 81 82 xasprintf(&ret, "%s %s", sshkey_type(key), fp); 83 free(fp); 84 return ret; 85 } 86 87 static int 88 userauth_pubkey(struct ssh *ssh) 89 { 90 Authctxt *authctxt = ssh->authctxt; 91 struct passwd *pw = authctxt->pw; 92 struct sshbuf *b = NULL; 93 struct sshkey *key = NULL; 94 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 95 u_char *pkblob = NULL, *sig = NULL, have_sig; 96 size_t blen, slen; 97 int r, pktype; 98 int authenticated = 0; 99 struct sshauthopt *authopts = 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(pkbuf)) == 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)) == 0) { 216 authenticated = 1; 217 } 218 auth2_record_key(authctxt, authenticated, key); 219 } else { 220 debug("%s: test pkalg %s pkblob %s%s%s", 221 __func__, pkalg, key_s, 222 ca_s == NULL ? "" : " CA ", 223 ca_s == NULL ? "" : ca_s); 224 225 if ((r = sshpkt_get_end(ssh)) != 0) 226 fatal("%s: %s", __func__, ssh_err(r)); 227 228 if (!authctxt->valid || authctxt->user == NULL) { 229 debug2("%s: disabled because of invalid user", 230 __func__); 231 goto done; 232 } 233 /* XXX fake reply and always send PK_OK ? */ 234 /* 235 * XXX this allows testing whether a user is allowed 236 * to login: if you happen to have a valid pubkey this 237 * message is sent. the message is NEVER sent at all 238 * if a user is not allowed to login. is this an 239 * issue? -markus 240 */ 241 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 242 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 243 != 0 || 244 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 245 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 246 (r = sshpkt_send(ssh)) != 0 || 247 (r = ssh_packet_write_wait(ssh)) != 0) 248 fatal("%s: %s", __func__, ssh_err(r)); 249 authctxt->postponed = 1; 250 } 251 } 252 done: 253 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 254 debug("%s: key options inconsistent with existing", __func__); 255 authenticated = 0; 256 } 257 debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg); 258 259 sshbuf_free(b); 260 sshauthopt_free(authopts); 261 sshkey_free(key); 262 free(userstyle); 263 free(pkalg); 264 free(pkblob); 265 free(key_s); 266 free(ca_s); 267 free(sig); 268 return authenticated; 269 } 270 271 static int 272 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 273 { 274 char *result; 275 u_int i; 276 277 /* XXX percent_expand() sequences for authorized_principals? */ 278 279 for (i = 0; i < cert->nprincipals; i++) { 280 if ((result = match_list(cert->principals[i], 281 principal_list, NULL)) != NULL) { 282 debug3("matched principal from key options \"%.100s\"", 283 result); 284 free(result); 285 return 1; 286 } 287 } 288 return 0; 289 } 290 291 /* 292 * Process a single authorized_principals format line. Returns 0 and sets 293 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 294 * log preamble for file/line information. 295 */ 296 static int 297 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 298 const char *loc, struct sshauthopt **authoptsp) 299 { 300 u_int i, found = 0; 301 char *ep, *line_opts; 302 const char *reason = NULL; 303 struct sshauthopt *opts = NULL; 304 305 if (authoptsp != NULL) 306 *authoptsp = NULL; 307 308 /* Trim trailing whitespace. */ 309 ep = cp + strlen(cp) - 1; 310 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 311 *ep-- = '\0'; 312 313 /* 314 * If the line has internal whitespace then assume it has 315 * key options. 316 */ 317 line_opts = NULL; 318 if ((ep = strrchr(cp, ' ')) != NULL || 319 (ep = strrchr(cp, '\t')) != NULL) { 320 for (; *ep == ' ' || *ep == '\t'; ep++) 321 ; 322 line_opts = cp; 323 cp = ep; 324 } 325 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 326 debug("%s: bad principals options: %s", loc, reason); 327 auth_debug_add("%s: bad principals options: %s", loc, reason); 328 return -1; 329 } 330 /* Check principals in cert against those on line */ 331 for (i = 0; i < cert->nprincipals; i++) { 332 if (strcmp(cp, cert->principals[i]) != 0) 333 continue; 334 debug3("%s: matched principal \"%.100s\"", 335 loc, cert->principals[i]); 336 found = 1; 337 } 338 if (found && authoptsp != NULL) { 339 *authoptsp = opts; 340 opts = NULL; 341 } 342 sshauthopt_free(opts); 343 return found ? 0 : -1; 344 } 345 346 static int 347 process_principals(struct ssh *ssh, FILE *f, const char *file, 348 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 349 { 350 char loc[256], *line = NULL, *cp, *ep; 351 size_t linesize = 0; 352 u_long linenum = 0; 353 u_int found_principal = 0; 354 355 if (authoptsp != NULL) 356 *authoptsp = NULL; 357 358 while (getline(&line, &linesize, f) != -1) { 359 linenum++; 360 /* Always consume entire input */ 361 if (found_principal) 362 continue; 363 364 /* Skip leading whitespace. */ 365 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 366 ; 367 /* Skip blank and comment lines. */ 368 if ((ep = strchr(cp, '#')) != NULL) 369 *ep = '\0'; 370 if (!*cp || *cp == '\n') 371 continue; 372 373 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 374 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 375 found_principal = 1; 376 } 377 free(line); 378 return found_principal; 379 } 380 381 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 382 383 static int 384 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 385 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 386 { 387 FILE *f; 388 int success; 389 390 if (authoptsp != NULL) 391 *authoptsp = NULL; 392 393 temporarily_use_uid(pw); 394 debug("trying authorized principals file %s", file); 395 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 396 restore_uid(); 397 return 0; 398 } 399 success = process_principals(ssh, f, file, cert, authoptsp); 400 fclose(f); 401 restore_uid(); 402 return success; 403 } 404 405 /* 406 * Checks whether principal is allowed in output of command. 407 * returns 1 if the principal is allowed or 0 otherwise. 408 */ 409 static int 410 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 411 const struct sshkey *key, struct sshauthopt **authoptsp) 412 { 413 struct passwd *runas_pw = NULL; 414 const struct sshkey_cert *cert = key->cert; 415 FILE *f = NULL; 416 int r, ok, found_principal = 0; 417 int i, ac = 0, uid_swapped = 0; 418 pid_t pid; 419 char *tmp, *username = NULL, *command = NULL, **av = NULL; 420 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 421 char serial_s[16], uidstr[32]; 422 void (*osigchld)(int); 423 424 if (authoptsp != NULL) 425 *authoptsp = NULL; 426 if (options.authorized_principals_command == NULL) 427 return 0; 428 if (options.authorized_principals_command_user == NULL) { 429 error("No user for AuthorizedPrincipalsCommand specified, " 430 "skipping"); 431 return 0; 432 } 433 434 /* 435 * NB. all returns later this function should go via "out" to 436 * ensure the original SIGCHLD handler is restored properly. 437 */ 438 osigchld = signal(SIGCHLD, SIG_DFL); 439 440 /* Prepare and verify the user for the command */ 441 username = percent_expand(options.authorized_principals_command_user, 442 "u", user_pw->pw_name, (char *)NULL); 443 runas_pw = getpwnam(username); 444 if (runas_pw == NULL) { 445 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 446 username, strerror(errno)); 447 goto out; 448 } 449 450 /* Turn the command into an argument vector */ 451 if (argv_split(options.authorized_principals_command, &ac, &av) != 0) { 452 error("AuthorizedPrincipalsCommand \"%s\" contains " 453 "invalid quotes", command); 454 goto out; 455 } 456 if (ac == 0) { 457 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 458 command); 459 goto out; 460 } 461 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 462 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 463 error("%s: sshkey_fingerprint failed", __func__); 464 goto out; 465 } 466 if ((key_fp = sshkey_fingerprint(key, 467 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 468 error("%s: sshkey_fingerprint failed", __func__); 469 goto out; 470 } 471 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 472 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 473 goto out; 474 } 475 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 476 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 477 goto out; 478 } 479 snprintf(serial_s, sizeof(serial_s), "%llu", 480 (unsigned long long)cert->serial); 481 snprintf(uidstr, sizeof(uidstr), "%llu", 482 (unsigned long long)user_pw->pw_uid); 483 for (i = 1; i < ac; i++) { 484 tmp = percent_expand(av[i], 485 "U", uidstr, 486 "u", user_pw->pw_name, 487 "h", user_pw->pw_dir, 488 "t", sshkey_ssh_name(key), 489 "T", sshkey_ssh_name(cert->signature_key), 490 "f", key_fp, 491 "F", ca_fp, 492 "k", keytext, 493 "K", catext, 494 "i", cert->key_id, 495 "s", serial_s, 496 (char *)NULL); 497 if (tmp == NULL) 498 fatal("%s: percent_expand failed", __func__); 499 free(av[i]); 500 av[i] = tmp; 501 } 502 /* Prepare a printable command for logs, etc. */ 503 command = argv_assemble(ac, av); 504 505 if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command, 506 ac, av, &f, 507 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 508 goto out; 509 510 uid_swapped = 1; 511 temporarily_use_uid(runas_pw); 512 513 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 514 515 fclose(f); 516 f = NULL; 517 518 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 519 goto out; 520 521 /* Read completed successfully */ 522 found_principal = ok; 523 out: 524 if (f != NULL) 525 fclose(f); 526 signal(SIGCHLD, osigchld); 527 for (i = 0; i < ac; i++) 528 free(av[i]); 529 free(av); 530 if (uid_swapped) 531 restore_uid(); 532 free(command); 533 free(username); 534 free(ca_fp); 535 free(key_fp); 536 free(catext); 537 free(keytext); 538 return found_principal; 539 } 540 541 static void 542 skip_space(char **cpp) 543 { 544 char *cp; 545 546 for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++) 547 ; 548 *cpp = cp; 549 } 550 551 /* 552 * Advanced *cpp past the end of key options, defined as the first unquoted 553 * whitespace character. Returns 0 on success or -1 on failure (e.g. 554 * unterminated quotes). 555 */ 556 static int 557 advance_past_options(char **cpp) 558 { 559 char *cp = *cpp; 560 int quoted = 0; 561 562 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 563 if (*cp == '\\' && cp[1] == '"') 564 cp++; /* Skip both */ 565 else if (*cp == '"') 566 quoted = !quoted; 567 } 568 *cpp = cp; 569 /* return failure for unterminated quotes */ 570 return (*cp == '\0' && quoted) ? -1 : 0; 571 } 572 573 /* 574 * Check a single line of an authorized_keys-format file. Returns 0 if key 575 * matches, -1 otherwise. Will return key/cert options via *authoptsp 576 * on success. "loc" is used as file/line location in log messages. 577 */ 578 static int 579 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 580 char *cp, const char *loc, struct sshauthopt **authoptsp) 581 { 582 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 583 struct sshkey *found = NULL; 584 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 585 char *key_options = NULL, *fp = NULL; 586 const char *reason = NULL; 587 int ret = -1; 588 589 if (authoptsp != NULL) 590 *authoptsp = NULL; 591 592 if ((found = sshkey_new(want_keytype)) == NULL) { 593 debug3("%s: keytype %d failed", __func__, want_keytype); 594 goto out; 595 } 596 597 /* XXX djm: peek at key type in line and skip if unwanted */ 598 599 if (sshkey_read(found, &cp) != 0) { 600 /* no key? check for options */ 601 debug2("%s: check options: '%s'", loc, cp); 602 key_options = cp; 603 if (advance_past_options(&cp) != 0) { 604 reason = "invalid key option string"; 605 goto fail_reason; 606 } 607 skip_space(&cp); 608 if (sshkey_read(found, &cp) != 0) { 609 /* still no key? advance to next line*/ 610 debug2("%s: advance: '%s'", loc, cp); 611 goto out; 612 } 613 } 614 /* Parse key options now; we need to know if this is a CA key */ 615 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 616 debug("%s: bad key options: %s", loc, reason); 617 auth_debug_add("%s: bad key options: %s", loc, reason); 618 goto out; 619 } 620 /* Ignore keys that don't match or incorrectly marked as CAs */ 621 if (sshkey_is_cert(key)) { 622 /* Certificate; check signature key against CA */ 623 if (!sshkey_equal(found, key->cert->signature_key) || 624 !keyopts->cert_authority) 625 goto out; 626 } else { 627 /* Plain key: check it against key found in file */ 628 if (!sshkey_equal(found, key) || keyopts->cert_authority) 629 goto out; 630 } 631 632 /* We have a candidate key, perform authorisation checks */ 633 if ((fp = sshkey_fingerprint(found, 634 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 635 fatal("%s: fingerprint failed", __func__); 636 637 debug("%s: matching %s found: %s %s", loc, 638 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 639 640 if (auth_authorise_keyopts(ssh, pw, keyopts, 641 sshkey_is_cert(key), loc) != 0) { 642 reason = "Refused by key options"; 643 goto fail_reason; 644 } 645 /* That's all we need for plain keys. */ 646 if (!sshkey_is_cert(key)) { 647 verbose("Accepted key %s %s found at %s", 648 sshkey_type(found), fp, loc); 649 finalopts = keyopts; 650 keyopts = NULL; 651 goto success; 652 } 653 654 /* 655 * Additional authorisation for certificates. 656 */ 657 658 /* Parse and check options present in certificate */ 659 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 660 reason = "Invalid certificate options"; 661 goto fail_reason; 662 } 663 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 664 reason = "Refused by certificate options"; 665 goto fail_reason; 666 } 667 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 668 goto fail_reason; 669 670 /* 671 * If the user has specified a list of principals as 672 * a key option, then prefer that list to matching 673 * their username in the certificate principals list. 674 */ 675 if (keyopts->cert_principals != NULL && 676 !match_principals_option(keyopts->cert_principals, key->cert)) { 677 reason = "Certificate does not contain an authorized principal"; 678 goto fail_reason; 679 } 680 if (sshkey_cert_check_authority(key, 0, 0, 681 keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0) 682 goto fail_reason; 683 684 verbose("Accepted certificate ID \"%s\" (serial %llu) " 685 "signed by CA %s %s found at %s", 686 key->cert->key_id, 687 (unsigned long long)key->cert->serial, 688 sshkey_type(found), fp, loc); 689 690 success: 691 if (finalopts == NULL) 692 fatal("%s: internal error: missing options", __func__); 693 if (authoptsp != NULL) { 694 *authoptsp = finalopts; 695 finalopts = NULL; 696 } 697 /* success */ 698 ret = 0; 699 goto out; 700 701 fail_reason: 702 error("%s", reason); 703 auth_debug_add("%s", reason); 704 out: 705 free(fp); 706 sshauthopt_free(keyopts); 707 sshauthopt_free(certopts); 708 sshauthopt_free(finalopts); 709 sshkey_free(found); 710 return ret; 711 } 712 713 /* 714 * Checks whether key is allowed in authorized_keys-format file, 715 * returns 1 if the key is allowed or 0 otherwise. 716 */ 717 static int 718 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 719 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 720 { 721 char *cp, *line = NULL, loc[256]; 722 size_t linesize = 0; 723 int found_key = 0; 724 u_long linenum = 0; 725 726 if (authoptsp != NULL) 727 *authoptsp = NULL; 728 729 while (getline(&line, &linesize, f) != -1) { 730 linenum++; 731 /* Always consume entire file */ 732 if (found_key) 733 continue; 734 735 /* Skip leading whitespace, empty and comment lines. */ 736 cp = line; 737 skip_space(&cp); 738 if (!*cp || *cp == '\n' || *cp == '#') 739 continue; 740 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 741 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 742 found_key = 1; 743 } 744 free(line); 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("%s: CA %s %s is not listed in %s: %s", __func__, 772 sshkey_type(key->cert->signature_key), ca_fp, 773 options.trusted_user_ca_keys, ssh_err(r)); 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("%s: internal error: missing principals_opts", __func__); 799 if (sshkey_cert_check_authority(key, 0, 1, 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 = 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("%s: sshkey_fingerprint failed", __func__); 924 goto out; 925 } 926 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 927 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 928 goto out; 929 } 930 931 /* Turn the command into an argument vector */ 932 if (argv_split(options.authorized_keys_command, &ac, &av) != 0) { 933 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 934 command); 935 goto out; 936 } 937 if (ac == 0) { 938 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 939 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("%s: percent_expand failed", __func__); 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", runas_pw, command, 976 ac, av, &f, 977 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 978 goto out; 979 980 uid_swapped = 1; 981 temporarily_use_uid(runas_pw); 982 983 ok = check_authkeys_file(ssh, user_pw, f, 984 options.authorized_keys_command, key, authoptsp); 985 986 fclose(f); 987 f = NULL; 988 989 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 990 goto out; 991 992 /* Read completed successfully */ 993 found_key = ok; 994 out: 995 if (f != NULL) 996 fclose(f); 997 signal(SIGCHLD, osigchld); 998 for (i = 0; i < ac; i++) 999 free(av[i]); 1000 free(av); 1001 if (uid_swapped) 1002 restore_uid(); 1003 free(command); 1004 free(username); 1005 free(key_fp); 1006 free(keytext); 1007 return found_key; 1008 } 1009 1010 /* 1011 * Check whether key authenticates and authorises the user. 1012 */ 1013 int 1014 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1015 int auth_attempt, struct sshauthopt **authoptsp) 1016 { 1017 u_int success, i; 1018 char *file; 1019 struct sshauthopt *opts = NULL; 1020 if (authoptsp != NULL) 1021 *authoptsp = NULL; 1022 1023 if (auth_key_is_revoked(key)) 1024 return 0; 1025 if (sshkey_is_cert(key) && 1026 auth_key_is_revoked(key->cert->signature_key)) 1027 return 0; 1028 1029 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1030 goto out; 1031 sshauthopt_free(opts); 1032 opts = NULL; 1033 1034 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1035 goto out; 1036 sshauthopt_free(opts); 1037 opts = NULL; 1038 1039 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1040 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1041 continue; 1042 file = expand_authorized_keys( 1043 options.authorized_keys_files[i], pw); 1044 success = user_key_allowed2(ssh, pw, key, file, &opts); 1045 free(file); 1046 } 1047 1048 out: 1049 if (success && authoptsp != NULL) { 1050 *authoptsp = opts; 1051 opts = NULL; 1052 } 1053 sshauthopt_free(opts); 1054 return success; 1055 } 1056 1057 Authmethod method_pubkey = { 1058 "publickey", 1059 userauth_pubkey, 1060 &options.pubkey_authentication 1061 }; 1062