1 /* $OpenBSD: auth2-pubkey.c,v 1.77 2018/03/03 03:15:51 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 "buffer.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; 93 struct sshkey *key = NULL; 94 char *pkalg, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 95 u_char *pkblob, *sig, have_sig; 96 size_t blen, slen; 97 int r, pktype; 98 int authenticated = 0; 99 struct sshauthopt *authopts = NULL; 100 101 if (!authctxt->valid) { 102 debug2("%s: disabled because of invalid user", __func__); 103 return 0; 104 } 105 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 106 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 107 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 108 fatal("%s: parse request failed: %s", __func__, ssh_err(r)); 109 pktype = sshkey_type_from_name(pkalg); 110 if (pktype == KEY_UNSPEC) { 111 /* this is perfectly legal */ 112 logit("%s: unsupported public key algorithm: %s", 113 __func__, pkalg); 114 goto done; 115 } 116 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 117 error("%s: could not parse key: %s", __func__, ssh_err(r)); 118 goto done; 119 } 120 if (key == NULL) { 121 error("%s: cannot decode key: %s", __func__, pkalg); 122 goto done; 123 } 124 if (key->type != pktype) { 125 error("%s: type mismatch for decoded key " 126 "(received %d, expected %d)", __func__, key->type, pktype); 127 goto done; 128 } 129 if (sshkey_type_plain(key->type) == KEY_RSA && 130 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 131 logit("Refusing RSA key because client uses unsafe " 132 "signature scheme"); 133 goto done; 134 } 135 if (auth2_key_already_used(authctxt, key)) { 136 logit("refusing previously-used %s key", sshkey_type(key)); 137 goto done; 138 } 139 if (match_pattern_list(sshkey_ssh_name(key), 140 options.pubkey_key_types, 0) != 1) { 141 logit("%s: key type %s not in PubkeyAcceptedKeyTypes", 142 __func__, sshkey_ssh_name(key)); 143 goto done; 144 } 145 146 key_s = format_key(key); 147 if (sshkey_is_cert(key)) 148 ca_s = format_key(key->cert->signature_key); 149 150 if (have_sig) { 151 debug3("%s: have %s signature for %s%s%s", 152 __func__, pkalg, key_s, 153 ca_s == NULL ? "" : " CA ", 154 ca_s == NULL ? "" : ca_s); 155 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 156 (r = sshpkt_get_end(ssh)) != 0) 157 fatal("%s: %s", __func__, ssh_err(r)); 158 if ((b = sshbuf_new()) == NULL) 159 fatal("%s: sshbuf_new failed", __func__); 160 if (ssh->compat & SSH_OLD_SESSIONID) { 161 if ((r = sshbuf_put(b, session_id2, 162 session_id2_len)) != 0) 163 fatal("%s: sshbuf_put session id: %s", 164 __func__, ssh_err(r)); 165 } else { 166 if ((r = sshbuf_put_string(b, session_id2, 167 session_id2_len)) != 0) 168 fatal("%s: sshbuf_put_string session id: %s", 169 __func__, ssh_err(r)); 170 } 171 /* reconstruct packet */ 172 xasprintf(&userstyle, "%s%s%s", authctxt->user, 173 authctxt->style ? ":" : "", 174 authctxt->style ? authctxt->style : ""); 175 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 176 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 177 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 178 (r = sshbuf_put_cstring(b, "publickey")) != 0 || 179 (r = sshbuf_put_u8(b, have_sig)) != 0 || 180 (r = sshbuf_put_cstring(b, pkalg) != 0) || 181 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 182 fatal("%s: build packet failed: %s", 183 __func__, ssh_err(r)); 184 #ifdef DEBUG_PK 185 sshbuf_dump(b, stderr); 186 #endif 187 188 /* test for correct signature */ 189 authenticated = 0; 190 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && 191 PRIVSEP(sshkey_verify(key, sig, slen, sshbuf_ptr(b), 192 sshbuf_len(b), NULL, ssh->compat)) == 0) { 193 authenticated = 1; 194 } 195 sshbuf_free(b); 196 free(sig); 197 auth2_record_key(authctxt, authenticated, key); 198 } else { 199 debug("%s: test pkalg %s pkblob %s%s%s", 200 __func__, pkalg, key_s, 201 ca_s == NULL ? "" : " CA ", 202 ca_s == NULL ? "" : ca_s); 203 204 if ((r = sshpkt_get_end(ssh)) != 0) 205 fatal("%s: %s", __func__, ssh_err(r)); 206 207 /* XXX fake reply and always send PK_OK ? */ 208 /* 209 * XXX this allows testing whether a user is allowed 210 * to login: if you happen to have a valid pubkey this 211 * message is sent. the message is NEVER sent at all 212 * if a user is not allowed to login. is this an 213 * issue? -markus 214 */ 215 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 216 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 217 != 0 || 218 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 219 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 220 (r = sshpkt_send(ssh)) != 0) 221 fatal("%s: %s", __func__, ssh_err(r)); 222 ssh_packet_write_wait(ssh); 223 authctxt->postponed = 1; 224 } 225 } 226 done: 227 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 228 debug("%s: key options inconsistent with existing", __func__); 229 authenticated = 0; 230 } 231 debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg); 232 233 sshauthopt_free(authopts); 234 sshkey_free(key); 235 free(userstyle); 236 free(pkalg); 237 free(pkblob); 238 free(key_s); 239 free(ca_s); 240 return authenticated; 241 } 242 243 static int 244 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 245 { 246 char *result; 247 u_int i; 248 249 /* XXX percent_expand() sequences for authorized_principals? */ 250 251 for (i = 0; i < cert->nprincipals; i++) { 252 if ((result = match_list(cert->principals[i], 253 principal_list, NULL)) != NULL) { 254 debug3("matched principal from key options \"%.100s\"", 255 result); 256 free(result); 257 return 1; 258 } 259 } 260 return 0; 261 } 262 263 /* 264 * Process a single authorized_principals format line. Returns 0 and sets 265 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 266 * log preamble for file/line information. 267 */ 268 static int 269 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 270 const char *loc, struct sshauthopt **authoptsp) 271 { 272 u_int i, found = 0; 273 char *ep, *line_opts; 274 const char *reason = NULL; 275 struct sshauthopt *opts = NULL; 276 277 if (authoptsp != NULL) 278 *authoptsp = NULL; 279 280 /* Trim trailing whitespace. */ 281 ep = cp + strlen(cp) - 1; 282 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 283 *ep-- = '\0'; 284 285 /* 286 * If the line has internal whitespace then assume it has 287 * key options. 288 */ 289 line_opts = NULL; 290 if ((ep = strrchr(cp, ' ')) != NULL || 291 (ep = strrchr(cp, '\t')) != NULL) { 292 for (; *ep == ' ' || *ep == '\t'; ep++) 293 ; 294 line_opts = cp; 295 cp = ep; 296 } 297 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 298 debug("%s: bad principals options: %s", loc, reason); 299 auth_debug_add("%s: bad principals options: %s", loc, reason); 300 return -1; 301 } 302 /* Check principals in cert against those on line */ 303 for (i = 0; i < cert->nprincipals; i++) { 304 if (strcmp(cp, cert->principals[i]) != 0) 305 continue; 306 debug3("%s: matched principal \"%.100s\"", 307 loc, cert->principals[i]); 308 found = 1; 309 } 310 if (found && authoptsp != NULL) { 311 *authoptsp = opts; 312 opts = NULL; 313 } 314 sshauthopt_free(opts); 315 return found ? 0 : -1; 316 } 317 318 static int 319 process_principals(struct ssh *ssh, FILE *f, const char *file, 320 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 321 { 322 char loc[256], line[SSH_MAX_PUBKEY_BYTES], *cp, *ep; 323 u_long linenum = 0; 324 u_int found_principal = 0; 325 326 if (authoptsp != NULL) 327 *authoptsp = NULL; 328 329 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 330 /* Always consume entire input */ 331 if (found_principal) 332 continue; 333 334 /* Skip leading whitespace. */ 335 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 336 ; 337 /* Skip blank and comment lines. */ 338 if ((ep = strchr(cp, '#')) != NULL) 339 *ep = '\0'; 340 if (!*cp || *cp == '\n') 341 continue; 342 343 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 344 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 345 found_principal = 1; 346 } 347 return found_principal; 348 } 349 350 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 351 352 static int 353 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 354 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 355 { 356 FILE *f; 357 int success; 358 359 if (authoptsp != NULL) 360 *authoptsp = NULL; 361 362 temporarily_use_uid(pw); 363 debug("trying authorized principals file %s", file); 364 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 365 restore_uid(); 366 return 0; 367 } 368 success = process_principals(ssh, f, file, cert, authoptsp); 369 fclose(f); 370 restore_uid(); 371 return success; 372 } 373 374 /* 375 * Checks whether principal is allowed in output of command. 376 * returns 1 if the principal is allowed or 0 otherwise. 377 */ 378 static int 379 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 380 const struct sshkey *key, struct sshauthopt **authoptsp) 381 { 382 struct passwd *runas_pw = NULL; 383 const struct sshkey_cert *cert = key->cert; 384 FILE *f = NULL; 385 int r, ok, found_principal = 0; 386 int i, ac = 0, uid_swapped = 0; 387 pid_t pid; 388 char *tmp, *username = NULL, *command = NULL, **av = NULL; 389 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 390 char serial_s[16]; 391 void (*osigchld)(int); 392 393 if (authoptsp != NULL) 394 *authoptsp = NULL; 395 if (options.authorized_principals_command == NULL) 396 return 0; 397 if (options.authorized_principals_command_user == NULL) { 398 error("No user for AuthorizedPrincipalsCommand specified, " 399 "skipping"); 400 return 0; 401 } 402 403 /* 404 * NB. all returns later this function should go via "out" to 405 * ensure the original SIGCHLD handler is restored properly. 406 */ 407 osigchld = signal(SIGCHLD, SIG_DFL); 408 409 /* Prepare and verify the user for the command */ 410 username = percent_expand(options.authorized_principals_command_user, 411 "u", user_pw->pw_name, (char *)NULL); 412 runas_pw = getpwnam(username); 413 if (runas_pw == NULL) { 414 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 415 username, strerror(errno)); 416 goto out; 417 } 418 419 /* Turn the command into an argument vector */ 420 if (argv_split(options.authorized_principals_command, &ac, &av) != 0) { 421 error("AuthorizedPrincipalsCommand \"%s\" contains " 422 "invalid quotes", command); 423 goto out; 424 } 425 if (ac == 0) { 426 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 427 command); 428 goto out; 429 } 430 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 431 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 432 error("%s: sshkey_fingerprint failed", __func__); 433 goto out; 434 } 435 if ((key_fp = sshkey_fingerprint(key, 436 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 437 error("%s: sshkey_fingerprint failed", __func__); 438 goto out; 439 } 440 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 441 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 442 goto out; 443 } 444 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 445 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 446 goto out; 447 } 448 snprintf(serial_s, sizeof(serial_s), "%llu", 449 (unsigned long long)cert->serial); 450 for (i = 1; i < ac; i++) { 451 tmp = percent_expand(av[i], 452 "u", user_pw->pw_name, 453 "h", user_pw->pw_dir, 454 "t", sshkey_ssh_name(key), 455 "T", sshkey_ssh_name(cert->signature_key), 456 "f", key_fp, 457 "F", ca_fp, 458 "k", keytext, 459 "K", catext, 460 "i", cert->key_id, 461 "s", serial_s, 462 (char *)NULL); 463 if (tmp == NULL) 464 fatal("%s: percent_expand failed", __func__); 465 free(av[i]); 466 av[i] = tmp; 467 } 468 /* Prepare a printable command for logs, etc. */ 469 command = argv_assemble(ac, av); 470 471 if ((pid = subprocess("AuthorizedPrincipalsCommand", runas_pw, command, 472 ac, av, &f, 473 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 474 goto out; 475 476 uid_swapped = 1; 477 temporarily_use_uid(runas_pw); 478 479 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 480 481 fclose(f); 482 f = NULL; 483 484 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 485 goto out; 486 487 /* Read completed successfully */ 488 found_principal = ok; 489 out: 490 if (f != NULL) 491 fclose(f); 492 signal(SIGCHLD, osigchld); 493 for (i = 0; i < ac; i++) 494 free(av[i]); 495 free(av); 496 if (uid_swapped) 497 restore_uid(); 498 free(command); 499 free(username); 500 free(ca_fp); 501 free(key_fp); 502 free(catext); 503 free(keytext); 504 return found_principal; 505 } 506 507 static void 508 skip_space(char **cpp) 509 { 510 char *cp; 511 512 for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++) 513 ; 514 *cpp = cp; 515 } 516 517 /* 518 * Advanced *cpp past the end of key options, defined as the first unquoted 519 * whitespace character. Returns 0 on success or -1 on failure (e.g. 520 * unterminated quotes). 521 */ 522 static int 523 advance_past_options(char **cpp) 524 { 525 char *cp = *cpp; 526 int quoted = 0; 527 528 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 529 if (*cp == '\\' && cp[1] == '"') 530 cp++; /* Skip both */ 531 else if (*cp == '"') 532 quoted = !quoted; 533 } 534 *cpp = cp; 535 /* return failure for unterminated quotes */ 536 return (*cp == '\0' && quoted) ? -1 : 0; 537 } 538 539 /* 540 * Check a single line of an authorized_keys-format file. Returns 0 if key 541 * matches, -1 otherwise. Will return key/cert options via *authoptsp 542 * on success. "loc" is used as file/line location in log messages. 543 */ 544 static int 545 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 546 char *cp, const char *loc, struct sshauthopt **authoptsp) 547 { 548 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 549 struct sshkey *found = NULL; 550 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 551 char *key_options = NULL, *fp = NULL; 552 const char *reason = NULL; 553 int ret = -1; 554 555 if (authoptsp != NULL) 556 *authoptsp = NULL; 557 558 if ((found = sshkey_new(want_keytype)) == NULL) { 559 debug3("%s: keytype %d failed", __func__, want_keytype); 560 goto out; 561 } 562 563 /* XXX djm: peek at key type in line and skip if unwanted */ 564 565 if (sshkey_read(found, &cp) != 0) { 566 /* no key? check for options */ 567 debug2("%s: check options: '%s'", loc, cp); 568 key_options = cp; 569 if (advance_past_options(&cp) != 0) { 570 reason = "invalid key option string"; 571 goto fail_reason; 572 } 573 skip_space(&cp); 574 if (sshkey_read(found, &cp) != 0) { 575 /* still no key? advance to next line*/ 576 debug2("%s: advance: '%s'", loc, cp); 577 goto out; 578 } 579 } 580 /* Parse key options now; we need to know if this is a CA key */ 581 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 582 debug("%s: bad key options: %s", loc, reason); 583 auth_debug_add("%s: bad key options: %s", loc, reason); 584 goto out; 585 } 586 /* Ignore keys that don't match or incorrectly marked as CAs */ 587 if (sshkey_is_cert(key)) { 588 /* Certificate; check signature key against CA */ 589 if (!sshkey_equal(found, key->cert->signature_key) || 590 !keyopts->cert_authority) 591 goto out; 592 } else { 593 /* Plain key: check it against key found in file */ 594 if (!sshkey_equal(found, key) || keyopts->cert_authority) 595 goto out; 596 } 597 598 /* We have a candidate key, perform authorisation checks */ 599 if ((fp = sshkey_fingerprint(found, 600 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 601 fatal("%s: fingerprint failed", __func__); 602 603 debug("%s: matching %s found: %s %s", loc, 604 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 605 606 if (auth_authorise_keyopts(ssh, pw, keyopts, 607 sshkey_is_cert(key), loc) != 0) { 608 reason = "Refused by key options"; 609 goto fail_reason; 610 } 611 /* That's all we need for plain keys. */ 612 if (!sshkey_is_cert(key)) { 613 verbose("Accepted key %s %s found at %s", 614 sshkey_type(found), fp, loc); 615 finalopts = keyopts; 616 keyopts = NULL; 617 goto success; 618 } 619 620 /* 621 * Additional authorisation for certificates. 622 */ 623 624 /* Parse and check options present in certificate */ 625 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 626 reason = "Invalid certificate options"; 627 goto fail_reason; 628 } 629 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 630 reason = "Refused by certificate options"; 631 goto fail_reason; 632 } 633 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 634 goto fail_reason; 635 636 /* 637 * If the user has specified a list of principals as 638 * a key option, then prefer that list to matching 639 * their username in the certificate principals list. 640 */ 641 if (keyopts->cert_principals != NULL && 642 !match_principals_option(keyopts->cert_principals, key->cert)) { 643 reason = "Certificate does not contain an authorized principal"; 644 goto fail_reason; 645 } 646 if (sshkey_cert_check_authority(key, 0, 0, 647 keyopts->cert_principals == NULL ? pw->pw_name : NULL, &reason) != 0) 648 goto fail_reason; 649 650 verbose("Accepted certificate ID \"%s\" (serial %llu) " 651 "signed by CA %s %s found at %s", 652 key->cert->key_id, 653 (unsigned long long)key->cert->serial, 654 sshkey_type(found), fp, loc); 655 656 success: 657 if (finalopts == NULL) 658 fatal("%s: internal error: missing options", __func__); 659 if (authoptsp != NULL) { 660 *authoptsp = finalopts; 661 finalopts = NULL; 662 } 663 /* success */ 664 ret = 0; 665 goto out; 666 667 fail_reason: 668 error("%s", reason); 669 auth_debug_add("%s", reason); 670 out: 671 free(fp); 672 sshauthopt_free(keyopts); 673 sshauthopt_free(certopts); 674 sshauthopt_free(finalopts); 675 sshkey_free(found); 676 return ret; 677 } 678 679 /* 680 * Checks whether key is allowed in authorized_keys-format file, 681 * returns 1 if the key is allowed or 0 otherwise. 682 */ 683 static int 684 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 685 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 686 { 687 char *cp, line[SSH_MAX_PUBKEY_BYTES], loc[256]; 688 int found_key = 0; 689 u_long linenum = 0; 690 691 if (authoptsp != NULL) 692 *authoptsp = NULL; 693 694 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 695 /* Always consume entire file */ 696 if (found_key) 697 continue; 698 699 /* Skip leading whitespace, empty and comment lines. */ 700 cp = line; 701 skip_space(&cp); 702 if (!*cp || *cp == '\n' || *cp == '#') 703 continue; 704 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 705 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 706 found_key = 1; 707 } 708 return found_key; 709 } 710 711 /* Authenticate a certificate key against TrustedUserCAKeys */ 712 static int 713 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 714 struct sshauthopt **authoptsp) 715 { 716 char *ca_fp, *principals_file = NULL; 717 const char *reason; 718 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 719 struct sshauthopt *final_opts = NULL; 720 int r, ret = 0, found_principal = 0, use_authorized_principals; 721 722 if (authoptsp != NULL) 723 *authoptsp = NULL; 724 725 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 726 return 0; 727 728 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 729 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 730 return 0; 731 732 if ((r = sshkey_in_file(key->cert->signature_key, 733 options.trusted_user_ca_keys, 1, 0)) != 0) { 734 debug2("%s: CA %s %s is not listed in %s: %s", __func__, 735 sshkey_type(key->cert->signature_key), ca_fp, 736 options.trusted_user_ca_keys, ssh_err(r)); 737 goto out; 738 } 739 /* 740 * If AuthorizedPrincipals is in use, then compare the certificate 741 * principals against the names in that file rather than matching 742 * against the username. 743 */ 744 if ((principals_file = authorized_principals_file(pw)) != NULL) { 745 if (match_principals_file(ssh, pw, principals_file, 746 key->cert, &principals_opts)) 747 found_principal = 1; 748 } 749 /* Try querying command if specified */ 750 if (!found_principal && match_principals_command(ssh, pw, key, 751 &principals_opts)) 752 found_principal = 1; 753 /* If principals file or command is specified, then require a match */ 754 use_authorized_principals = principals_file != NULL || 755 options.authorized_principals_command != NULL; 756 if (!found_principal && use_authorized_principals) { 757 reason = "Certificate does not contain an authorized principal"; 758 goto fail_reason; 759 } 760 if (use_authorized_principals && principals_opts == NULL) 761 fatal("%s: internal error: missing principals_opts", __func__); 762 if (sshkey_cert_check_authority(key, 0, 1, 763 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 764 goto fail_reason; 765 766 /* Check authority from options in key and from principals file/cmd */ 767 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 768 reason = "Invalid certificate options"; 769 goto fail_reason; 770 } 771 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 772 reason = "Refused by certificate options"; 773 goto fail_reason; 774 } 775 if (principals_opts == NULL) { 776 final_opts = cert_opts; 777 cert_opts = NULL; 778 } else { 779 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 780 "principals") != 0) { 781 reason = "Refused by certificate principals options"; 782 goto fail_reason; 783 } 784 if ((final_opts = sshauthopt_merge(principals_opts, 785 cert_opts, &reason)) == NULL) { 786 fail_reason: 787 error("%s", reason); 788 auth_debug_add("%s", reason); 789 goto out; 790 } 791 } 792 793 /* Success */ 794 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 795 "%s CA %s via %s", key->cert->key_id, 796 (unsigned long long)key->cert->serial, 797 sshkey_type(key->cert->signature_key), ca_fp, 798 options.trusted_user_ca_keys); 799 if (authoptsp != NULL) { 800 *authoptsp = final_opts; 801 final_opts = NULL; 802 } 803 ret = 1; 804 out: 805 sshauthopt_free(principals_opts); 806 sshauthopt_free(cert_opts); 807 sshauthopt_free(final_opts); 808 free(principals_file); 809 free(ca_fp); 810 return ret; 811 } 812 813 /* 814 * Checks whether key is allowed in file. 815 * returns 1 if the key is allowed or 0 otherwise. 816 */ 817 static int 818 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 819 char *file, struct sshauthopt **authoptsp) 820 { 821 FILE *f; 822 int found_key = 0; 823 824 if (authoptsp != NULL) 825 *authoptsp = NULL; 826 827 /* Temporarily use the user's uid. */ 828 temporarily_use_uid(pw); 829 830 debug("trying public key file %s", file); 831 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 832 found_key = check_authkeys_file(ssh, pw, f, file, 833 key, authoptsp); 834 fclose(f); 835 } 836 837 restore_uid(); 838 return found_key; 839 } 840 841 /* 842 * Checks whether key is allowed in output of command. 843 * returns 1 if the key is allowed or 0 otherwise. 844 */ 845 static int 846 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 847 struct sshkey *key, struct sshauthopt **authoptsp) 848 { 849 struct passwd *runas_pw = NULL; 850 FILE *f = NULL; 851 int r, ok, found_key = 0; 852 int i, uid_swapped = 0, ac = 0; 853 pid_t pid; 854 char *username = NULL, *key_fp = NULL, *keytext = NULL; 855 char *tmp, *command = NULL, **av = NULL; 856 void (*osigchld)(int); 857 858 if (authoptsp != NULL) 859 *authoptsp = NULL; 860 if (options.authorized_keys_command == NULL) 861 return 0; 862 if (options.authorized_keys_command_user == NULL) { 863 error("No user for AuthorizedKeysCommand specified, skipping"); 864 return 0; 865 } 866 867 /* 868 * NB. all returns later this function should go via "out" to 869 * ensure the original SIGCHLD handler is restored properly. 870 */ 871 osigchld = signal(SIGCHLD, SIG_DFL); 872 873 /* Prepare and verify the user for the command */ 874 username = percent_expand(options.authorized_keys_command_user, 875 "u", user_pw->pw_name, (char *)NULL); 876 runas_pw = getpwnam(username); 877 if (runas_pw == NULL) { 878 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 879 username, strerror(errno)); 880 goto out; 881 } 882 883 /* Prepare AuthorizedKeysCommand */ 884 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 885 SSH_FP_DEFAULT)) == NULL) { 886 error("%s: sshkey_fingerprint failed", __func__); 887 goto out; 888 } 889 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 890 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 891 goto out; 892 } 893 894 /* Turn the command into an argument vector */ 895 if (argv_split(options.authorized_keys_command, &ac, &av) != 0) { 896 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 897 command); 898 goto out; 899 } 900 if (ac == 0) { 901 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 902 command); 903 goto out; 904 } 905 for (i = 1; i < ac; i++) { 906 tmp = percent_expand(av[i], 907 "u", user_pw->pw_name, 908 "h", user_pw->pw_dir, 909 "t", sshkey_ssh_name(key), 910 "f", key_fp, 911 "k", keytext, 912 (char *)NULL); 913 if (tmp == NULL) 914 fatal("%s: percent_expand failed", __func__); 915 free(av[i]); 916 av[i] = tmp; 917 } 918 /* Prepare a printable command for logs, etc. */ 919 command = argv_assemble(ac, av); 920 921 /* 922 * If AuthorizedKeysCommand was run without arguments 923 * then fall back to the old behaviour of passing the 924 * target username as a single argument. 925 */ 926 if (ac == 1) { 927 av = xreallocarray(av, ac + 2, sizeof(*av)); 928 av[1] = xstrdup(user_pw->pw_name); 929 av[2] = NULL; 930 /* Fix up command too, since it is used in log messages */ 931 free(command); 932 xasprintf(&command, "%s %s", av[0], av[1]); 933 } 934 935 if ((pid = subprocess("AuthorizedKeysCommand", runas_pw, command, 936 ac, av, &f, 937 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD)) == 0) 938 goto out; 939 940 uid_swapped = 1; 941 temporarily_use_uid(runas_pw); 942 943 ok = check_authkeys_file(ssh, user_pw, f, 944 options.authorized_keys_command, key, authoptsp); 945 946 fclose(f); 947 f = NULL; 948 949 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 950 goto out; 951 952 /* Read completed successfully */ 953 found_key = ok; 954 out: 955 if (f != NULL) 956 fclose(f); 957 signal(SIGCHLD, osigchld); 958 for (i = 0; i < ac; i++) 959 free(av[i]); 960 free(av); 961 if (uid_swapped) 962 restore_uid(); 963 free(command); 964 free(username); 965 free(key_fp); 966 free(keytext); 967 return found_key; 968 } 969 970 /* 971 * Check whether key authenticates and authorises the user. 972 */ 973 int 974 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 975 int auth_attempt, struct sshauthopt **authoptsp) 976 { 977 u_int success, i; 978 char *file; 979 struct sshauthopt *opts = NULL; 980 if (authoptsp != NULL) 981 *authoptsp = NULL; 982 983 if (auth_key_is_revoked(key)) 984 return 0; 985 if (sshkey_is_cert(key) && 986 auth_key_is_revoked(key->cert->signature_key)) 987 return 0; 988 989 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 990 goto out; 991 sshauthopt_free(opts); 992 opts = NULL; 993 994 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 995 goto out; 996 sshauthopt_free(opts); 997 opts = NULL; 998 999 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1000 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1001 continue; 1002 file = expand_authorized_keys( 1003 options.authorized_keys_files[i], pw); 1004 success = user_key_allowed2(ssh, pw, key, file, &opts); 1005 free(file); 1006 } 1007 1008 out: 1009 if (success && authoptsp != NULL) { 1010 *authoptsp = opts; 1011 opts = NULL; 1012 } 1013 sshauthopt_free(opts); 1014 return success; 1015 } 1016 1017 Authmethod method_pubkey = { 1018 "publickey", 1019 userauth_pubkey, 1020 &options.pubkey_authentication 1021 }; 1022