1 /* $OpenBSD: auth2-pubkey.c,v 1.109 2021/07/23 03:37:52 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 <stdlib.h> 32 #include <errno.h> 33 #include <fcntl.h> 34 #ifdef HAVE_PATHS_H 35 # include <paths.h> 36 #endif 37 #include <pwd.h> 38 #include <signal.h> 39 #include <stdio.h> 40 #include <stdarg.h> 41 #include <string.h> 42 #include <time.h> 43 #include <unistd.h> 44 #include <limits.h> 45 46 #include "xmalloc.h" 47 #include "ssh.h" 48 #include "ssh2.h" 49 #include "packet.h" 50 #include "kex.h" 51 #include "sshbuf.h" 52 #include "log.h" 53 #include "misc.h" 54 #include "servconf.h" 55 #include "compat.h" 56 #include "sshkey.h" 57 #include "hostfile.h" 58 #include "auth.h" 59 #include "pathnames.h" 60 #include "uidswap.h" 61 #include "auth-options.h" 62 #include "canohost.h" 63 #ifdef GSSAPI 64 #include "ssh-gss.h" 65 #endif 66 #include "monitor_wrap.h" 67 #include "authfile.h" 68 #include "match.h" 69 #include "ssherr.h" 70 #include "channels.h" /* XXX for session.h */ 71 #include "session.h" /* XXX for child_set_env(); refactor? */ 72 #include "sk-api.h" 73 74 /* import */ 75 extern ServerOptions options; 76 77 static char * 78 format_key(const struct sshkey *key) 79 { 80 char *ret, *fp = sshkey_fingerprint(key, 81 options.fingerprint_hash, SSH_FP_DEFAULT); 82 83 xasprintf(&ret, "%s %s", sshkey_type(key), fp); 84 free(fp); 85 return ret; 86 } 87 88 static int 89 userauth_pubkey(struct ssh *ssh) 90 { 91 Authctxt *authctxt = ssh->authctxt; 92 struct passwd *pw = authctxt->pw; 93 struct sshbuf *b = NULL; 94 struct sshkey *key = NULL; 95 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 96 u_char *pkblob = NULL, *sig = NULL, have_sig; 97 size_t blen, slen; 98 int r, pktype; 99 int req_presence = 0, req_verify = 0, authenticated = 0; 100 struct sshauthopt *authopts = NULL; 101 struct sshkey_sig_details *sig_details = NULL; 102 103 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 104 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 105 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 106 fatal_fr(r, "parse packet"); 107 108 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) { 109 char *keystring; 110 struct sshbuf *pkbuf; 111 112 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL) 113 fatal_f("sshbuf_from failed"); 114 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL) 115 fatal_f("sshbuf_dtob64 failed"); 116 debug2_f("%s user %s %s public key %s %s", 117 authctxt->valid ? "valid" : "invalid", authctxt->user, 118 have_sig ? "attempting" : "querying", pkalg, keystring); 119 sshbuf_free(pkbuf); 120 free(keystring); 121 } 122 123 pktype = sshkey_type_from_name(pkalg); 124 if (pktype == KEY_UNSPEC) { 125 /* this is perfectly legal */ 126 verbose_f("unsupported public key algorithm: %s", pkalg); 127 goto done; 128 } 129 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 130 error_fr(r, "parse key"); 131 goto done; 132 } 133 if (key == NULL) { 134 error_f("cannot decode key: %s", pkalg); 135 goto done; 136 } 137 if (key->type != pktype) { 138 error_f("type mismatch for decoded key " 139 "(received %d, expected %d)", key->type, pktype); 140 goto done; 141 } 142 if (sshkey_type_plain(key->type) == KEY_RSA && 143 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 144 logit("Refusing RSA key because client uses unsafe " 145 "signature scheme"); 146 goto done; 147 } 148 if (auth2_key_already_used(authctxt, key)) { 149 logit("refusing previously-used %s key", sshkey_type(key)); 150 goto done; 151 } 152 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) { 153 logit_f("key type %s not in PubkeyAcceptedAlgorithms", 154 sshkey_ssh_name(key)); 155 goto done; 156 } 157 if ((r = sshkey_check_cert_sigtype(key, 158 options.ca_sign_algorithms)) != 0) { 159 logit_fr(r, "certificate signature algorithm %s", 160 (key->cert == NULL || key->cert->signature_type == NULL) ? 161 "(null)" : key->cert->signature_type); 162 goto done; 163 } 164 key_s = format_key(key); 165 if (sshkey_is_cert(key)) 166 ca_s = format_key(key->cert->signature_key); 167 168 if (have_sig) { 169 debug3_f("have %s signature for %s%s%s", pkalg, key_s, 170 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 171 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 172 (r = sshpkt_get_end(ssh)) != 0) 173 fatal_fr(r, "parse signature packet"); 174 if ((b = sshbuf_new()) == NULL) 175 fatal_f("sshbuf_new failed"); 176 if (ssh->compat & SSH_OLD_SESSIONID) { 177 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0) 178 fatal_fr(r, "put old session id"); 179 } else { 180 if ((r = sshbuf_put_stringb(b, 181 ssh->kex->session_id)) != 0) 182 fatal_fr(r, "put session id"); 183 } 184 if (!authctxt->valid || authctxt->user == NULL) { 185 debug2_f("disabled because of invalid user"); 186 goto done; 187 } 188 /* reconstruct packet */ 189 xasprintf(&userstyle, "%s%s%s", authctxt->user, 190 authctxt->style ? ":" : "", 191 authctxt->style ? authctxt->style : ""); 192 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 193 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 194 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 195 (r = sshbuf_put_cstring(b, "publickey")) != 0 || 196 (r = sshbuf_put_u8(b, have_sig)) != 0 || 197 (r = sshbuf_put_cstring(b, pkalg)) != 0 || 198 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 199 fatal_fr(r, "reconstruct packet"); 200 #ifdef DEBUG_PK 201 sshbuf_dump(b, stderr); 202 #endif 203 /* test for correct signature */ 204 authenticated = 0; 205 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && 206 PRIVSEP(sshkey_verify(key, sig, slen, 207 sshbuf_ptr(b), sshbuf_len(b), 208 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL, 209 ssh->compat, &sig_details)) == 0) { 210 authenticated = 1; 211 } 212 if (authenticated == 1 && sig_details != NULL) { 213 auth2_record_info(authctxt, "signature count = %u", 214 sig_details->sk_counter); 215 debug_f("sk_counter = %u, sk_flags = 0x%02x", 216 sig_details->sk_counter, sig_details->sk_flags); 217 req_presence = (options.pubkey_auth_options & 218 PUBKEYAUTH_TOUCH_REQUIRED) || 219 !authopts->no_require_user_presence; 220 if (req_presence && (sig_details->sk_flags & 221 SSH_SK_USER_PRESENCE_REQD) == 0) { 222 error("public key %s signature for %s%s from " 223 "%.128s port %d rejected: user presence " 224 "(authenticator touch) requirement " 225 "not met ", key_s, 226 authctxt->valid ? "" : "invalid user ", 227 authctxt->user, ssh_remote_ipaddr(ssh), 228 ssh_remote_port(ssh)); 229 authenticated = 0; 230 goto done; 231 } 232 req_verify = (options.pubkey_auth_options & 233 PUBKEYAUTH_VERIFY_REQUIRED) || 234 authopts->require_verify; 235 if (req_verify && (sig_details->sk_flags & 236 SSH_SK_USER_VERIFICATION_REQD) == 0) { 237 error("public key %s signature for %s%s from " 238 "%.128s port %d rejected: user " 239 "verification requirement not met ", key_s, 240 authctxt->valid ? "" : "invalid user ", 241 authctxt->user, ssh_remote_ipaddr(ssh), 242 ssh_remote_port(ssh)); 243 authenticated = 0; 244 goto done; 245 } 246 } 247 auth2_record_key(authctxt, authenticated, key); 248 } else { 249 debug_f("test pkalg %s pkblob %s%s%s", pkalg, key_s, 250 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 251 252 if ((r = sshpkt_get_end(ssh)) != 0) 253 fatal_fr(r, "parse packet"); 254 255 if (!authctxt->valid || authctxt->user == NULL) { 256 debug2_f("disabled because of invalid user"); 257 goto done; 258 } 259 /* XXX fake reply and always send PK_OK ? */ 260 /* 261 * XXX this allows testing whether a user is allowed 262 * to login: if you happen to have a valid pubkey this 263 * message is sent. the message is NEVER sent at all 264 * if a user is not allowed to login. is this an 265 * issue? -markus 266 */ 267 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 268 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 269 != 0 || 270 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 271 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 272 (r = sshpkt_send(ssh)) != 0 || 273 (r = ssh_packet_write_wait(ssh)) != 0) 274 fatal_fr(r, "send packet"); 275 authctxt->postponed = 1; 276 } 277 } 278 done: 279 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 280 debug_f("key options inconsistent with existing"); 281 authenticated = 0; 282 } 283 debug2_f("authenticated %d pkalg %s", authenticated, pkalg); 284 285 sshbuf_free(b); 286 sshauthopt_free(authopts); 287 sshkey_free(key); 288 free(userstyle); 289 free(pkalg); 290 free(pkblob); 291 free(key_s); 292 free(ca_s); 293 free(sig); 294 sshkey_sig_details_free(sig_details); 295 return authenticated; 296 } 297 298 static int 299 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 300 { 301 char *result; 302 u_int i; 303 304 /* XXX percent_expand() sequences for authorized_principals? */ 305 306 for (i = 0; i < cert->nprincipals; i++) { 307 if ((result = match_list(cert->principals[i], 308 principal_list, NULL)) != NULL) { 309 debug3("matched principal from key options \"%.100s\"", 310 result); 311 free(result); 312 return 1; 313 } 314 } 315 return 0; 316 } 317 318 /* 319 * Process a single authorized_principals format line. Returns 0 and sets 320 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 321 * log preamble for file/line information. 322 */ 323 static int 324 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 325 const char *loc, struct sshauthopt **authoptsp) 326 { 327 u_int i, found = 0; 328 char *ep, *line_opts; 329 const char *reason = NULL; 330 struct sshauthopt *opts = NULL; 331 332 if (authoptsp != NULL) 333 *authoptsp = NULL; 334 335 /* Trim trailing whitespace. */ 336 ep = cp + strlen(cp) - 1; 337 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 338 *ep-- = '\0'; 339 340 /* 341 * If the line has internal whitespace then assume it has 342 * key options. 343 */ 344 line_opts = NULL; 345 if ((ep = strrchr(cp, ' ')) != NULL || 346 (ep = strrchr(cp, '\t')) != NULL) { 347 for (; *ep == ' ' || *ep == '\t'; ep++) 348 ; 349 line_opts = cp; 350 cp = ep; 351 } 352 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 353 debug("%s: bad principals options: %s", loc, reason); 354 auth_debug_add("%s: bad principals options: %s", loc, reason); 355 return -1; 356 } 357 /* Check principals in cert against those on line */ 358 for (i = 0; i < cert->nprincipals; i++) { 359 if (strcmp(cp, cert->principals[i]) != 0) 360 continue; 361 debug3("%s: matched principal \"%.100s\"", 362 loc, cert->principals[i]); 363 found = 1; 364 } 365 if (found && authoptsp != NULL) { 366 *authoptsp = opts; 367 opts = NULL; 368 } 369 sshauthopt_free(opts); 370 return found ? 0 : -1; 371 } 372 373 static int 374 process_principals(struct ssh *ssh, FILE *f, const char *file, 375 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 376 { 377 char loc[256], *line = NULL, *cp, *ep; 378 size_t linesize = 0; 379 u_long linenum = 0; 380 u_int found_principal = 0; 381 382 if (authoptsp != NULL) 383 *authoptsp = NULL; 384 385 while (getline(&line, &linesize, f) != -1) { 386 linenum++; 387 /* Always consume entire input */ 388 if (found_principal) 389 continue; 390 391 /* Skip leading whitespace. */ 392 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 393 ; 394 /* Skip blank and comment lines. */ 395 if ((ep = strchr(cp, '#')) != NULL) 396 *ep = '\0'; 397 if (!*cp || *cp == '\n') 398 continue; 399 400 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 401 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 402 found_principal = 1; 403 } 404 free(line); 405 return found_principal; 406 } 407 408 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 409 410 static int 411 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 412 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 413 { 414 FILE *f; 415 int success; 416 417 if (authoptsp != NULL) 418 *authoptsp = NULL; 419 420 temporarily_use_uid(pw); 421 debug("trying authorized principals file %s", file); 422 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 423 restore_uid(); 424 return 0; 425 } 426 success = process_principals(ssh, f, file, cert, authoptsp); 427 fclose(f); 428 restore_uid(); 429 return success; 430 } 431 432 /* 433 * Checks whether principal is allowed in output of command. 434 * returns 1 if the principal is allowed or 0 otherwise. 435 */ 436 static int 437 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 438 const struct sshkey *key, struct sshauthopt **authoptsp) 439 { 440 struct passwd *runas_pw = NULL; 441 const struct sshkey_cert *cert = key->cert; 442 FILE *f = NULL; 443 int r, ok, found_principal = 0; 444 int i, ac = 0, uid_swapped = 0; 445 pid_t pid; 446 char *tmp, *username = NULL, *command = NULL, **av = NULL; 447 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 448 char serial_s[32], uidstr[32]; 449 void (*osigchld)(int); 450 451 if (authoptsp != NULL) 452 *authoptsp = NULL; 453 if (options.authorized_principals_command == NULL) 454 return 0; 455 if (options.authorized_principals_command_user == NULL) { 456 error("No user for AuthorizedPrincipalsCommand specified, " 457 "skipping"); 458 return 0; 459 } 460 461 /* 462 * NB. all returns later this function should go via "out" to 463 * ensure the original SIGCHLD handler is restored properly. 464 */ 465 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 466 467 /* Prepare and verify the user for the command */ 468 username = percent_expand(options.authorized_principals_command_user, 469 "u", user_pw->pw_name, (char *)NULL); 470 runas_pw = getpwnam(username); 471 if (runas_pw == NULL) { 472 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 473 username, strerror(errno)); 474 goto out; 475 } 476 477 /* Turn the command into an argument vector */ 478 if (argv_split(options.authorized_principals_command, 479 &ac, &av, 0) != 0) { 480 error("AuthorizedPrincipalsCommand \"%s\" contains " 481 "invalid quotes", options.authorized_principals_command); 482 goto out; 483 } 484 if (ac == 0) { 485 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 486 options.authorized_principals_command); 487 goto out; 488 } 489 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 490 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 491 error_f("sshkey_fingerprint failed"); 492 goto out; 493 } 494 if ((key_fp = sshkey_fingerprint(key, 495 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 496 error_f("sshkey_fingerprint failed"); 497 goto out; 498 } 499 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 500 error_fr(r, "sshkey_to_base64 failed"); 501 goto out; 502 } 503 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 504 error_fr(r, "sshkey_to_base64 failed"); 505 goto out; 506 } 507 snprintf(serial_s, sizeof(serial_s), "%llu", 508 (unsigned long long)cert->serial); 509 snprintf(uidstr, sizeof(uidstr), "%llu", 510 (unsigned long long)user_pw->pw_uid); 511 for (i = 1; i < ac; i++) { 512 tmp = percent_expand(av[i], 513 "U", uidstr, 514 "u", user_pw->pw_name, 515 "h", user_pw->pw_dir, 516 "t", sshkey_ssh_name(key), 517 "T", sshkey_ssh_name(cert->signature_key), 518 "f", key_fp, 519 "F", ca_fp, 520 "k", keytext, 521 "K", catext, 522 "i", cert->key_id, 523 "s", serial_s, 524 (char *)NULL); 525 if (tmp == NULL) 526 fatal_f("percent_expand failed"); 527 free(av[i]); 528 av[i] = tmp; 529 } 530 /* Prepare a printable command for logs, etc. */ 531 command = argv_assemble(ac, av); 532 533 if ((pid = subprocess("AuthorizedPrincipalsCommand", command, 534 ac, av, &f, 535 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 536 runas_pw, temporarily_use_uid, restore_uid)) == 0) 537 goto out; 538 539 uid_swapped = 1; 540 temporarily_use_uid(runas_pw); 541 542 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 543 544 fclose(f); 545 f = NULL; 546 547 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 548 goto out; 549 550 /* Read completed successfully */ 551 found_principal = ok; 552 out: 553 if (f != NULL) 554 fclose(f); 555 ssh_signal(SIGCHLD, osigchld); 556 for (i = 0; i < ac; i++) 557 free(av[i]); 558 free(av); 559 if (uid_swapped) 560 restore_uid(); 561 free(command); 562 free(username); 563 free(ca_fp); 564 free(key_fp); 565 free(catext); 566 free(keytext); 567 return found_principal; 568 } 569 570 /* 571 * Check a single line of an authorized_keys-format file. Returns 0 if key 572 * matches, -1 otherwise. Will return key/cert options via *authoptsp 573 * on success. "loc" is used as file/line location in log messages. 574 */ 575 static int 576 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 577 char *cp, const char *loc, struct sshauthopt **authoptsp) 578 { 579 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 580 struct sshkey *found = NULL; 581 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 582 char *key_options = NULL, *fp = NULL; 583 const char *reason = NULL; 584 int ret = -1; 585 586 if (authoptsp != NULL) 587 *authoptsp = NULL; 588 589 if ((found = sshkey_new(want_keytype)) == NULL) { 590 debug3_f("keytype %d failed", want_keytype); 591 goto out; 592 } 593 594 /* XXX djm: peek at key type in line and skip if unwanted */ 595 596 if (sshkey_read(found, &cp) != 0) { 597 /* no key? check for options */ 598 debug2("%s: check options: '%s'", loc, cp); 599 key_options = cp; 600 if (sshkey_advance_past_options(&cp) != 0) { 601 reason = "invalid key option string"; 602 goto fail_reason; 603 } 604 skip_space(&cp); 605 if (sshkey_read(found, &cp) != 0) { 606 /* still no key? advance to next line*/ 607 debug2("%s: advance: '%s'", loc, cp); 608 goto out; 609 } 610 } 611 /* Parse key options now; we need to know if this is a CA key */ 612 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 613 debug("%s: bad key options: %s", loc, reason); 614 auth_debug_add("%s: bad key options: %s", loc, reason); 615 goto out; 616 } 617 /* Ignore keys that don't match or incorrectly marked as CAs */ 618 if (sshkey_is_cert(key)) { 619 /* Certificate; check signature key against CA */ 620 if (!sshkey_equal(found, key->cert->signature_key) || 621 !keyopts->cert_authority) 622 goto out; 623 } else { 624 /* Plain key: check it against key found in file */ 625 if (!sshkey_equal(found, key) || keyopts->cert_authority) 626 goto out; 627 } 628 629 /* We have a candidate key, perform authorisation checks */ 630 if ((fp = sshkey_fingerprint(found, 631 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 632 fatal_f("fingerprint failed"); 633 634 debug("%s: matching %s found: %s %s", loc, 635 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 636 637 if (auth_authorise_keyopts(ssh, pw, keyopts, 638 sshkey_is_cert(key), loc) != 0) { 639 reason = "Refused by key options"; 640 goto fail_reason; 641 } 642 /* That's all we need for plain keys. */ 643 if (!sshkey_is_cert(key)) { 644 verbose("Accepted key %s %s found at %s", 645 sshkey_type(found), fp, loc); 646 finalopts = keyopts; 647 keyopts = NULL; 648 goto success; 649 } 650 651 /* 652 * Additional authorisation for certificates. 653 */ 654 655 /* Parse and check options present in certificate */ 656 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 657 reason = "Invalid certificate options"; 658 goto fail_reason; 659 } 660 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 661 reason = "Refused by certificate options"; 662 goto fail_reason; 663 } 664 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 665 goto fail_reason; 666 667 /* 668 * If the user has specified a list of principals as 669 * a key option, then prefer that list to matching 670 * their username in the certificate principals list. 671 */ 672 if (keyopts->cert_principals != NULL && 673 !match_principals_option(keyopts->cert_principals, key->cert)) { 674 reason = "Certificate does not contain an authorized principal"; 675 goto fail_reason; 676 } 677 if (sshkey_cert_check_authority_now(key, 0, 0, 0, 678 keyopts->cert_principals == NULL ? pw->pw_name : NULL, 679 &reason) != 0) 680 goto fail_reason; 681 682 verbose("Accepted certificate ID \"%s\" (serial %llu) " 683 "signed by CA %s %s found at %s", 684 key->cert->key_id, 685 (unsigned long long)key->cert->serial, 686 sshkey_type(found), fp, loc); 687 688 success: 689 if (finalopts == NULL) 690 fatal_f("internal error: missing options"); 691 if (authoptsp != NULL) { 692 *authoptsp = finalopts; 693 finalopts = NULL; 694 } 695 /* success */ 696 ret = 0; 697 goto out; 698 699 fail_reason: 700 error("%s", reason); 701 auth_debug_add("%s", reason); 702 out: 703 free(fp); 704 sshauthopt_free(keyopts); 705 sshauthopt_free(certopts); 706 sshauthopt_free(finalopts); 707 sshkey_free(found); 708 return ret; 709 } 710 711 /* 712 * Checks whether key is allowed in authorized_keys-format file, 713 * returns 1 if the key is allowed or 0 otherwise. 714 */ 715 static int 716 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 717 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 718 { 719 char *cp, *line = NULL, loc[256]; 720 size_t linesize = 0; 721 int found_key = 0; 722 u_long linenum = 0; 723 724 if (authoptsp != NULL) 725 *authoptsp = NULL; 726 727 while (getline(&line, &linesize, f) != -1) { 728 linenum++; 729 /* Always consume entire file */ 730 if (found_key) 731 continue; 732 733 /* Skip leading whitespace, empty and comment lines. */ 734 cp = line; 735 skip_space(&cp); 736 if (!*cp || *cp == '\n' || *cp == '#') 737 continue; 738 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 739 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 740 found_key = 1; 741 } 742 free(line); 743 return found_key; 744 } 745 746 /* Authenticate a certificate key against TrustedUserCAKeys */ 747 static int 748 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 749 struct sshauthopt **authoptsp) 750 { 751 char *ca_fp, *principals_file = NULL; 752 const char *reason; 753 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 754 struct sshauthopt *final_opts = NULL; 755 int r, ret = 0, found_principal = 0, use_authorized_principals; 756 757 if (authoptsp != NULL) 758 *authoptsp = NULL; 759 760 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 761 return 0; 762 763 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 764 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 765 return 0; 766 767 if ((r = sshkey_in_file(key->cert->signature_key, 768 options.trusted_user_ca_keys, 1, 0)) != 0) { 769 debug2_fr(r, "CA %s %s is not listed in %s", 770 sshkey_type(key->cert->signature_key), ca_fp, 771 options.trusted_user_ca_keys); 772 goto out; 773 } 774 /* 775 * If AuthorizedPrincipals is in use, then compare the certificate 776 * principals against the names in that file rather than matching 777 * against the username. 778 */ 779 if ((principals_file = authorized_principals_file(pw)) != NULL) { 780 if (match_principals_file(ssh, pw, principals_file, 781 key->cert, &principals_opts)) 782 found_principal = 1; 783 } 784 /* Try querying command if specified */ 785 if (!found_principal && match_principals_command(ssh, pw, key, 786 &principals_opts)) 787 found_principal = 1; 788 /* If principals file or command is specified, then require a match */ 789 use_authorized_principals = principals_file != NULL || 790 options.authorized_principals_command != NULL; 791 if (!found_principal && use_authorized_principals) { 792 reason = "Certificate does not contain an authorized principal"; 793 goto fail_reason; 794 } 795 if (use_authorized_principals && principals_opts == NULL) 796 fatal_f("internal error: missing principals_opts"); 797 if (sshkey_cert_check_authority_now(key, 0, 1, 0, 798 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 799 goto fail_reason; 800 801 /* Check authority from options in key and from principals file/cmd */ 802 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 803 reason = "Invalid certificate options"; 804 goto fail_reason; 805 } 806 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 807 reason = "Refused by certificate options"; 808 goto fail_reason; 809 } 810 if (principals_opts == NULL) { 811 final_opts = cert_opts; 812 cert_opts = NULL; 813 } else { 814 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 815 "principals") != 0) { 816 reason = "Refused by certificate principals options"; 817 goto fail_reason; 818 } 819 if ((final_opts = sshauthopt_merge(principals_opts, 820 cert_opts, &reason)) == NULL) { 821 fail_reason: 822 error("%s", reason); 823 auth_debug_add("%s", reason); 824 goto out; 825 } 826 } 827 828 /* Success */ 829 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 830 "%s CA %s via %s", key->cert->key_id, 831 (unsigned long long)key->cert->serial, 832 sshkey_type(key->cert->signature_key), ca_fp, 833 options.trusted_user_ca_keys); 834 if (authoptsp != NULL) { 835 *authoptsp = final_opts; 836 final_opts = NULL; 837 } 838 ret = 1; 839 out: 840 sshauthopt_free(principals_opts); 841 sshauthopt_free(cert_opts); 842 sshauthopt_free(final_opts); 843 free(principals_file); 844 free(ca_fp); 845 return ret; 846 } 847 848 /* 849 * Checks whether key is allowed in file. 850 * returns 1 if the key is allowed or 0 otherwise. 851 */ 852 static int 853 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 854 char *file, struct sshauthopt **authoptsp) 855 { 856 FILE *f; 857 int found_key = 0; 858 859 if (authoptsp != NULL) 860 *authoptsp = NULL; 861 862 /* Temporarily use the user's uid. */ 863 temporarily_use_uid(pw); 864 865 debug("trying public key file %s", file); 866 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 867 found_key = check_authkeys_file(ssh, pw, f, file, 868 key, authoptsp); 869 fclose(f); 870 } 871 872 restore_uid(); 873 return found_key; 874 } 875 876 /* 877 * Checks whether key is allowed in output of command. 878 * returns 1 if the key is allowed or 0 otherwise. 879 */ 880 static int 881 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 882 struct sshkey *key, struct sshauthopt **authoptsp) 883 { 884 struct passwd *runas_pw = NULL; 885 FILE *f = NULL; 886 int r, ok, found_key = 0; 887 int i, uid_swapped = 0, ac = 0; 888 pid_t pid; 889 char *username = NULL, *key_fp = NULL, *keytext = NULL; 890 char uidstr[32], *tmp, *command = NULL, **av = NULL; 891 void (*osigchld)(int); 892 893 if (authoptsp != NULL) 894 *authoptsp = NULL; 895 if (options.authorized_keys_command == NULL) 896 return 0; 897 if (options.authorized_keys_command_user == NULL) { 898 error("No user for AuthorizedKeysCommand specified, skipping"); 899 return 0; 900 } 901 902 /* 903 * NB. all returns later this function should go via "out" to 904 * ensure the original SIGCHLD handler is restored properly. 905 */ 906 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 907 908 /* Prepare and verify the user for the command */ 909 username = percent_expand(options.authorized_keys_command_user, 910 "u", user_pw->pw_name, (char *)NULL); 911 runas_pw = getpwnam(username); 912 if (runas_pw == NULL) { 913 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 914 username, strerror(errno)); 915 goto out; 916 } 917 918 /* Prepare AuthorizedKeysCommand */ 919 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 920 SSH_FP_DEFAULT)) == NULL) { 921 error_f("sshkey_fingerprint failed"); 922 goto out; 923 } 924 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 925 error_fr(r, "sshkey_to_base64 failed"); 926 goto out; 927 } 928 929 /* Turn the command into an argument vector */ 930 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) { 931 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 932 options.authorized_keys_command); 933 goto out; 934 } 935 if (ac == 0) { 936 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 937 options.authorized_keys_command); 938 goto out; 939 } 940 snprintf(uidstr, sizeof(uidstr), "%llu", 941 (unsigned long long)user_pw->pw_uid); 942 for (i = 1; i < ac; i++) { 943 tmp = percent_expand(av[i], 944 "U", uidstr, 945 "u", user_pw->pw_name, 946 "h", user_pw->pw_dir, 947 "t", sshkey_ssh_name(key), 948 "f", key_fp, 949 "k", keytext, 950 (char *)NULL); 951 if (tmp == NULL) 952 fatal_f("percent_expand failed"); 953 free(av[i]); 954 av[i] = tmp; 955 } 956 /* Prepare a printable command for logs, etc. */ 957 command = argv_assemble(ac, av); 958 959 /* 960 * If AuthorizedKeysCommand was run without arguments 961 * then fall back to the old behaviour of passing the 962 * target username as a single argument. 963 */ 964 if (ac == 1) { 965 av = xreallocarray(av, ac + 2, sizeof(*av)); 966 av[1] = xstrdup(user_pw->pw_name); 967 av[2] = NULL; 968 /* Fix up command too, since it is used in log messages */ 969 free(command); 970 xasprintf(&command, "%s %s", av[0], av[1]); 971 } 972 973 if ((pid = subprocess("AuthorizedKeysCommand", command, 974 ac, av, &f, 975 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 976 runas_pw, temporarily_use_uid, restore_uid)) == 0) 977 goto out; 978 979 uid_swapped = 1; 980 temporarily_use_uid(runas_pw); 981 982 ok = check_authkeys_file(ssh, user_pw, f, 983 options.authorized_keys_command, key, authoptsp); 984 985 fclose(f); 986 f = NULL; 987 988 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 989 goto out; 990 991 /* Read completed successfully */ 992 found_key = ok; 993 out: 994 if (f != NULL) 995 fclose(f); 996 ssh_signal(SIGCHLD, osigchld); 997 for (i = 0; i < ac; i++) 998 free(av[i]); 999 free(av); 1000 if (uid_swapped) 1001 restore_uid(); 1002 free(command); 1003 free(username); 1004 free(key_fp); 1005 free(keytext); 1006 return found_key; 1007 } 1008 1009 /* 1010 * Check whether key authenticates and authorises the user. 1011 */ 1012 int 1013 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1014 int auth_attempt, struct sshauthopt **authoptsp) 1015 { 1016 u_int success = 0, i; 1017 char *file; 1018 struct sshauthopt *opts = NULL; 1019 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 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1030 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1031 continue; 1032 file = expand_authorized_keys( 1033 options.authorized_keys_files[i], pw); 1034 success = user_key_allowed2(ssh, pw, key, file, &opts); 1035 free(file); 1036 if (!success) { 1037 sshauthopt_free(opts); 1038 opts = NULL; 1039 } 1040 } 1041 if (success) 1042 goto out; 1043 1044 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1045 goto out; 1046 sshauthopt_free(opts); 1047 opts = NULL; 1048 1049 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1050 goto out; 1051 sshauthopt_free(opts); 1052 opts = NULL; 1053 1054 out: 1055 if (success && authoptsp != NULL) { 1056 *authoptsp = opts; 1057 opts = NULL; 1058 } 1059 sshauthopt_free(opts); 1060 return success; 1061 } 1062 1063 Authmethod method_pubkey = { 1064 "publickey", 1065 userauth_pubkey, 1066 &options.pubkey_authentication 1067 }; 1068