1 /* $NetBSD: auth2-pubkey.c,v 1.29 2021/09/02 11:26:17 christos Exp $ */ 2 /* $OpenBSD: auth2-pubkey.c,v 1.109 2021/07/23 03:37:52 djm Exp $ */ 3 4 /* 5 * Copyright (c) 2000 Markus Friedl. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #include "includes.h" 29 __RCSID("$NetBSD: auth2-pubkey.c,v 1.29 2021/09/02 11:26:17 christos Exp $"); 30 #include <sys/types.h> 31 #include <sys/stat.h> 32 33 #include <stdlib.h> 34 #include <errno.h> 35 #include <fcntl.h> 36 #include <paths.h> 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 "digest.h" 70 71 #ifdef WITH_LDAP_PUBKEY 72 #include "ldapauth.h" 73 #endif 74 75 #include "ssherr.h" 76 #include "channels.h" /* XXX for session.h */ 77 #include "session.h" /* XXX for child_set_env(); refactor? */ 78 #include "sk-api.h" 79 80 /* import */ 81 extern ServerOptions options; 82 83 static char * 84 format_key(const struct sshkey *key) 85 { 86 char *ret, *fp = sshkey_fingerprint(key, 87 options.fingerprint_hash, SSH_FP_DEFAULT); 88 89 xasprintf(&ret, "%s %s", sshkey_type(key), fp); 90 free(fp); 91 return ret; 92 } 93 94 static int 95 userauth_pubkey(struct ssh *ssh) 96 { 97 Authctxt *authctxt = ssh->authctxt; 98 struct passwd *pw = authctxt->pw; 99 struct sshbuf *b = NULL; 100 struct sshkey *key = NULL; 101 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 102 u_char *pkblob = NULL, *sig = NULL, have_sig; 103 size_t blen, slen; 104 int r, pktype; 105 int req_presence = 0, req_verify = 0, authenticated = 0; 106 struct sshauthopt *authopts = NULL; 107 struct sshkey_sig_details *sig_details = NULL; 108 109 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 110 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 111 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 112 fatal_fr(r, "parse packet"); 113 114 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) { 115 char *keystring; 116 struct sshbuf *pkbuf; 117 118 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL) 119 fatal_f("sshbuf_from failed"); 120 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL) 121 fatal_f("sshbuf_dtob64 failed"); 122 debug2_f("%s user %s %s public key %s %s", 123 authctxt->valid ? "valid" : "invalid", authctxt->user, 124 have_sig ? "attempting" : "querying", pkalg, keystring); 125 sshbuf_free(pkbuf); 126 free(keystring); 127 } 128 129 pktype = sshkey_type_from_name(pkalg); 130 if (pktype == KEY_UNSPEC) { 131 /* this is perfectly legal */ 132 verbose_f("unsupported public key algorithm: %s", pkalg); 133 goto done; 134 } 135 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 136 error_fr(r, "parse key"); 137 goto done; 138 } 139 if (key == NULL) { 140 error_f("cannot decode key: %s", pkalg); 141 goto done; 142 } 143 if (key->type != pktype) { 144 error_f("type mismatch for decoded key " 145 "(received %d, expected %d)", key->type, pktype); 146 goto done; 147 } 148 if (sshkey_type_plain(key->type) == KEY_RSA && 149 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 150 logit("Refusing RSA key because client uses unsafe " 151 "signature scheme"); 152 goto done; 153 } 154 if (auth2_key_already_used(authctxt, key)) { 155 logit("refusing previously-used %s key", sshkey_type(key)); 156 goto done; 157 } 158 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) { 159 logit_f("key type %s not in PubkeyAcceptedAlgorithms", 160 sshkey_ssh_name(key)); 161 goto done; 162 } 163 if ((r = sshkey_check_cert_sigtype(key, 164 options.ca_sign_algorithms)) != 0) { 165 logit_fr(r, "certificate signature algorithm %s", 166 (key->cert == NULL || key->cert->signature_type == NULL) ? 167 "(null)" : key->cert->signature_type); 168 goto done; 169 } 170 key_s = format_key(key); 171 if (sshkey_is_cert(key)) 172 ca_s = format_key(key->cert->signature_key); 173 174 if (have_sig) { 175 debug3_f("have %s signature for %s%s%s", pkalg, key_s, 176 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 177 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 178 (r = sshpkt_get_end(ssh)) != 0) 179 fatal_fr(r, "parse signature packet"); 180 if ((b = sshbuf_new()) == NULL) 181 fatal_f("sshbuf_new failed"); 182 if (ssh->compat & SSH_OLD_SESSIONID) { 183 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0) 184 fatal_fr(r, "put old session id"); 185 } else { 186 if ((r = sshbuf_put_stringb(b, 187 ssh->kex->session_id)) != 0) 188 fatal_fr(r, "put session id"); 189 } 190 if (!authctxt->valid || authctxt->user == NULL) { 191 debug2_f("disabled because of invalid user"); 192 goto done; 193 } 194 /* reconstruct packet */ 195 xasprintf(&userstyle, "%s%s%s", authctxt->user, 196 authctxt->style ? ":" : "", 197 authctxt->style ? authctxt->style : ""); 198 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 199 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 200 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 201 (r = sshbuf_put_cstring(b, "publickey")) != 0 || 202 (r = sshbuf_put_u8(b, have_sig)) != 0 || 203 (r = sshbuf_put_cstring(b, pkalg)) != 0 || 204 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 205 fatal_fr(r, "reconstruct packet"); 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, &sig_details)) == 0) { 216 authenticated = 1; 217 } 218 if (authenticated == 1 && sig_details != NULL) { 219 auth2_record_info(authctxt, "signature count = %u", 220 sig_details->sk_counter); 221 debug_f("sk_counter = %u, sk_flags = 0x%02x", 222 sig_details->sk_counter, sig_details->sk_flags); 223 req_presence = (options.pubkey_auth_options & 224 PUBKEYAUTH_TOUCH_REQUIRED) || 225 !authopts->no_require_user_presence; 226 if (req_presence && (sig_details->sk_flags & 227 SSH_SK_USER_PRESENCE_REQD) == 0) { 228 error("public key %s signature for %s%s from " 229 "%.128s port %d rejected: user presence " 230 "(authenticator touch) requirement " 231 "not met ", key_s, 232 authctxt->valid ? "" : "invalid user ", 233 authctxt->user, ssh_remote_ipaddr(ssh), 234 ssh_remote_port(ssh)); 235 authenticated = 0; 236 goto done; 237 } 238 req_verify = (options.pubkey_auth_options & 239 PUBKEYAUTH_VERIFY_REQUIRED) || 240 authopts->require_verify; 241 if (req_verify && (sig_details->sk_flags & 242 SSH_SK_USER_VERIFICATION_REQD) == 0) { 243 error("public key %s signature for %s%s from " 244 "%.128s port %d rejected: user " 245 "verification requirement not met ", key_s, 246 authctxt->valid ? "" : "invalid user ", 247 authctxt->user, ssh_remote_ipaddr(ssh), 248 ssh_remote_port(ssh)); 249 authenticated = 0; 250 goto done; 251 } 252 } 253 auth2_record_key(authctxt, authenticated, key); 254 } else { 255 debug_f("test pkalg %s pkblob %s%s%s", pkalg, key_s, 256 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 257 258 if ((r = sshpkt_get_end(ssh)) != 0) 259 fatal_fr(r, "parse packet"); 260 261 if (!authctxt->valid || authctxt->user == NULL) { 262 debug2_f("disabled because of invalid user"); 263 goto done; 264 } 265 /* XXX fake reply and always send PK_OK ? */ 266 /* 267 * XXX this allows testing whether a user is allowed 268 * to login: if you happen to have a valid pubkey this 269 * message is sent. the message is NEVER sent at all 270 * if a user is not allowed to login. is this an 271 * issue? -markus 272 */ 273 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 274 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 275 != 0 || 276 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 277 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 278 (r = sshpkt_send(ssh)) != 0 || 279 (r = ssh_packet_write_wait(ssh)) < 0) 280 fatal_fr(r, "send packet"); 281 authctxt->postponed = 1; 282 } 283 } 284 done: 285 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 286 debug_f("key options inconsistent with existing"); 287 authenticated = 0; 288 } 289 debug2_f("authenticated %d pkalg %s", authenticated, pkalg); 290 291 sshbuf_free(b); 292 sshauthopt_free(authopts); 293 sshkey_free(key); 294 free(userstyle); 295 free(pkalg); 296 free(pkblob); 297 free(key_s); 298 free(ca_s); 299 free(sig); 300 sshkey_sig_details_free(sig_details); 301 return authenticated; 302 } 303 304 static int 305 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 306 { 307 char *result; 308 u_int i; 309 310 /* XXX percent_expand() sequences for authorized_principals? */ 311 312 for (i = 0; i < cert->nprincipals; i++) { 313 if ((result = match_list(cert->principals[i], 314 principal_list, NULL)) != NULL) { 315 debug3("matched principal from key options \"%.100s\"", 316 result); 317 free(result); 318 return 1; 319 } 320 } 321 return 0; 322 } 323 324 /* 325 * Process a single authorized_principals format line. Returns 0 and sets 326 * authoptsp is principal is authorised, -1 otherwise. "loc" is used as a 327 * log preamble for file/line information. 328 */ 329 static int 330 check_principals_line(struct ssh *ssh, char *cp, const struct sshkey_cert *cert, 331 const char *loc, struct sshauthopt **authoptsp) 332 { 333 u_int i, found = 0; 334 char *ep, *line_opts; 335 const char *reason = NULL; 336 struct sshauthopt *opts = NULL; 337 338 if (authoptsp != NULL) 339 *authoptsp = NULL; 340 341 /* Trim trailing whitespace. */ 342 ep = cp + strlen(cp) - 1; 343 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 344 *ep-- = '\0'; 345 346 /* 347 * If the line has internal whitespace then assume it has 348 * key options. 349 */ 350 line_opts = NULL; 351 if ((ep = strrchr(cp, ' ')) != NULL || 352 (ep = strrchr(cp, '\t')) != NULL) { 353 for (; *ep == ' ' || *ep == '\t'; ep++) 354 ; 355 line_opts = cp; 356 cp = ep; 357 } 358 if ((opts = sshauthopt_parse(line_opts, &reason)) == NULL) { 359 debug("%s: bad principals options: %s", loc, reason); 360 auth_debug_add("%s: bad principals options: %s", loc, reason); 361 return -1; 362 } 363 /* Check principals in cert against those on line */ 364 for (i = 0; i < cert->nprincipals; i++) { 365 if (strcmp(cp, cert->principals[i]) != 0) 366 continue; 367 debug3("%s: matched principal \"%.100s\"", 368 loc, cert->principals[i]); 369 found = 1; 370 } 371 if (found && authoptsp != NULL) { 372 *authoptsp = opts; 373 opts = NULL; 374 } 375 sshauthopt_free(opts); 376 return found ? 0 : -1; 377 } 378 379 static int 380 process_principals(struct ssh *ssh, FILE *f, const char *file, 381 const struct sshkey_cert *cert, struct sshauthopt **authoptsp) 382 { 383 char loc[256], *line = NULL, *cp, *ep; 384 size_t linesize = 0; 385 u_long linenum = 0; 386 u_int found_principal = 0; 387 388 if (authoptsp != NULL) 389 *authoptsp = NULL; 390 391 while (getline(&line, &linesize, f) != -1) { 392 linenum++; 393 /* Always consume entire input */ 394 if (found_principal) 395 continue; 396 397 /* Skip leading whitespace. */ 398 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 399 ; 400 /* Skip blank and comment lines. */ 401 if ((ep = strchr(cp, '#')) != NULL) 402 *ep = '\0'; 403 if (!*cp || *cp == '\n') 404 continue; 405 406 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 407 if (check_principals_line(ssh, cp, cert, loc, authoptsp) == 0) 408 found_principal = 1; 409 } 410 free(line); 411 return found_principal; 412 } 413 414 /* XXX remove pw args here and elsewhere once ssh->authctxt is guaranteed */ 415 416 static int 417 match_principals_file(struct ssh *ssh, struct passwd *pw, char *file, 418 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 419 { 420 FILE *f; 421 int success; 422 423 if (authoptsp != NULL) 424 *authoptsp = NULL; 425 426 temporarily_use_uid(pw); 427 debug("trying authorized principals file %s", file); 428 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 429 restore_uid(); 430 return 0; 431 } 432 success = process_principals(ssh, f, file, cert, authoptsp); 433 fclose(f); 434 restore_uid(); 435 return success; 436 } 437 438 /* 439 * Checks whether principal is allowed in output of command. 440 * returns 1 if the principal is allowed or 0 otherwise. 441 */ 442 static int 443 match_principals_command(struct ssh *ssh, struct passwd *user_pw, 444 const struct sshkey *key, struct sshauthopt **authoptsp) 445 { 446 struct passwd *runas_pw = NULL; 447 const struct sshkey_cert *cert = key->cert; 448 FILE *f = NULL; 449 int r, ok, found_principal = 0; 450 int i, ac = 0, uid_swapped = 0; 451 pid_t pid; 452 char *tmp, *username = NULL, *command = NULL, **av = NULL; 453 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 454 char serial_s[32], uidstr[32]; 455 void (*osigchld)(int); 456 457 if (authoptsp != NULL) 458 *authoptsp = NULL; 459 if (options.authorized_principals_command == NULL) 460 return 0; 461 if (options.authorized_principals_command_user == NULL) { 462 error("No user for AuthorizedPrincipalsCommand specified, " 463 "skipping"); 464 return 0; 465 } 466 467 /* 468 * NB. all returns later this function should go via "out" to 469 * ensure the original SIGCHLD handler is restored properly. 470 */ 471 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 472 473 /* Prepare and verify the user for the command */ 474 username = percent_expand(options.authorized_principals_command_user, 475 "u", user_pw->pw_name, (char *)NULL); 476 runas_pw = getpwnam(username); 477 if (runas_pw == NULL) { 478 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 479 username, strerror(errno)); 480 goto out; 481 } 482 483 /* Turn the command into an argument vector */ 484 if (argv_split(options.authorized_principals_command, 485 &ac, &av, 0) != 0) { 486 error("AuthorizedPrincipalsCommand \"%s\" contains " 487 "invalid quotes", options.authorized_principals_command); 488 goto out; 489 } 490 if (ac == 0) { 491 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 492 options.authorized_principals_command); 493 goto out; 494 } 495 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 496 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 497 error_f("sshkey_fingerprint failed"); 498 goto out; 499 } 500 if ((key_fp = sshkey_fingerprint(key, 501 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 502 error_f("sshkey_fingerprint failed"); 503 goto out; 504 } 505 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 506 error_fr(r, "sshkey_to_base64 failed"); 507 goto out; 508 } 509 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 510 error_fr(r, "sshkey_to_base64 failed"); 511 goto out; 512 } 513 snprintf(serial_s, sizeof(serial_s), "%llu", 514 (unsigned long long)cert->serial); 515 snprintf(uidstr, sizeof(uidstr), "%llu", 516 (unsigned long long)user_pw->pw_uid); 517 for (i = 1; i < ac; i++) { 518 tmp = percent_expand(av[i], 519 "U", uidstr, 520 "u", user_pw->pw_name, 521 "h", user_pw->pw_dir, 522 "t", sshkey_ssh_name(key), 523 "T", sshkey_ssh_name(cert->signature_key), 524 "f", key_fp, 525 "F", ca_fp, 526 "k", keytext, 527 "K", catext, 528 "i", cert->key_id, 529 "s", serial_s, 530 (char *)NULL); 531 if (tmp == NULL) 532 fatal_f("percent_expand failed"); 533 free(av[i]); 534 av[i] = tmp; 535 } 536 /* Prepare a printable command for logs, etc. */ 537 command = argv_assemble(ac, av); 538 539 if ((pid = subprocess("AuthorizedPrincipalsCommand", command, 540 ac, av, &f, 541 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 542 runas_pw, temporarily_use_uid, restore_uid)) == 0) 543 goto out; 544 545 uid_swapped = 1; 546 temporarily_use_uid(runas_pw); 547 548 ok = process_principals(ssh, f, "(command)", cert, authoptsp); 549 550 fclose(f); 551 f = NULL; 552 553 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 554 goto out; 555 556 /* Read completed successfully */ 557 found_principal = ok; 558 out: 559 if (f != NULL) 560 fclose(f); 561 ssh_signal(SIGCHLD, osigchld); 562 for (i = 0; i < ac; i++) 563 free(av[i]); 564 free(av); 565 if (uid_swapped) 566 restore_uid(); 567 free(command); 568 free(username); 569 free(ca_fp); 570 free(key_fp); 571 free(catext); 572 free(keytext); 573 return found_principal; 574 } 575 576 /* 577 * Check a single line of an authorized_keys-format file. Returns 0 if key 578 * matches, -1 otherwise. Will return key/cert options via *authoptsp 579 * on success. "loc" is used as file/line location in log messages. 580 */ 581 static int 582 check_authkey_line(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 583 char *cp, const char *loc, struct sshauthopt **authoptsp) 584 { 585 int want_keytype = sshkey_is_cert(key) ? KEY_UNSPEC : key->type; 586 struct sshkey *found = NULL; 587 struct sshauthopt *keyopts = NULL, *certopts = NULL, *finalopts = NULL; 588 char *key_options = NULL, *fp = NULL; 589 const char *reason = NULL; 590 int ret = -1; 591 592 if (authoptsp != NULL) 593 *authoptsp = NULL; 594 595 if ((found = sshkey_new(want_keytype)) == NULL) { 596 debug3_f("keytype %d failed", want_keytype); 597 goto out; 598 } 599 600 /* XXX djm: peek at key type in line and skip if unwanted */ 601 602 if (sshkey_read(found, &cp) != 0) { 603 /* no key? check for options */ 604 debug2("%s: check options: '%s'", loc, cp); 605 key_options = cp; 606 if (sshkey_advance_past_options(&cp) != 0) { 607 reason = "invalid key option string"; 608 goto fail_reason; 609 } 610 skip_space(&cp); 611 if (sshkey_read(found, &cp) != 0) { 612 /* still no key? advance to next line*/ 613 debug2("%s: advance: '%s'", loc, cp); 614 goto out; 615 } 616 } 617 /* Parse key options now; we need to know if this is a CA key */ 618 if ((keyopts = sshauthopt_parse(key_options, &reason)) == NULL) { 619 debug("%s: bad key options: %s", loc, reason); 620 auth_debug_add("%s: bad key options: %s", loc, reason); 621 goto out; 622 } 623 /* Ignore keys that don't match or incorrectly marked as CAs */ 624 if (sshkey_is_cert(key)) { 625 /* Certificate; check signature key against CA */ 626 if (!sshkey_equal(found, key->cert->signature_key) || 627 !keyopts->cert_authority) 628 goto out; 629 } else { 630 /* Plain key: check it against key found in file */ 631 if (!sshkey_equal(found, key) || keyopts->cert_authority) 632 goto out; 633 } 634 635 /* We have a candidate key, perform authorisation checks */ 636 if ((fp = sshkey_fingerprint(found, 637 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 638 fatal_f("fingerprint failed"); 639 640 debug("%s: matching %s found: %s %s", loc, 641 sshkey_is_cert(key) ? "CA" : "key", sshkey_type(found), fp); 642 643 if (auth_authorise_keyopts(ssh, pw, keyopts, 644 sshkey_is_cert(key), loc) != 0) { 645 reason = "Refused by key options"; 646 goto fail_reason; 647 } 648 /* That's all we need for plain keys. */ 649 if (!sshkey_is_cert(key)) { 650 verbose("Accepted key %s %s found at %s", 651 sshkey_type(found), fp, loc); 652 finalopts = keyopts; 653 keyopts = NULL; 654 goto success; 655 } 656 657 /* 658 * Additional authorisation for certificates. 659 */ 660 661 /* Parse and check options present in certificate */ 662 if ((certopts = sshauthopt_from_cert(key)) == NULL) { 663 reason = "Invalid certificate options"; 664 goto fail_reason; 665 } 666 if (auth_authorise_keyopts(ssh, pw, certopts, 0, loc) != 0) { 667 reason = "Refused by certificate options"; 668 goto fail_reason; 669 } 670 if ((finalopts = sshauthopt_merge(keyopts, certopts, &reason)) == NULL) 671 goto fail_reason; 672 673 /* 674 * If the user has specified a list of principals as 675 * a key option, then prefer that list to matching 676 * their username in the certificate principals list. 677 */ 678 if (keyopts->cert_principals != NULL && 679 !match_principals_option(keyopts->cert_principals, key->cert)) { 680 reason = "Certificate does not contain an authorized principal"; 681 goto fail_reason; 682 } 683 if (sshkey_cert_check_authority_now(key, 0, 0, 0, 684 keyopts->cert_principals == NULL ? pw->pw_name : NULL, 685 &reason) != 0) 686 goto fail_reason; 687 688 verbose("Accepted certificate ID \"%s\" (serial %llu) " 689 "signed by CA %s %s found at %s", 690 key->cert->key_id, 691 (unsigned long long)key->cert->serial, 692 sshkey_type(found), fp, loc); 693 694 success: 695 if (finalopts == NULL) 696 fatal_f("internal error: missing options"); 697 if (authoptsp != NULL) { 698 *authoptsp = finalopts; 699 finalopts = NULL; 700 } 701 /* success */ 702 ret = 0; 703 goto out; 704 705 fail_reason: 706 error("%s", reason); 707 auth_debug_add("%s", reason); 708 out: 709 free(fp); 710 sshauthopt_free(keyopts); 711 sshauthopt_free(certopts); 712 sshauthopt_free(finalopts); 713 sshkey_free(found); 714 return ret; 715 } 716 717 /* 718 * Checks whether key is allowed in authorized_keys-format file, 719 * returns 1 if the key is allowed or 0 otherwise. 720 */ 721 static int 722 check_authkeys_file(struct ssh *ssh, struct passwd *pw, FILE *f, 723 char *file, struct sshkey *key, struct sshauthopt **authoptsp) 724 { 725 char *cp, *line = NULL, loc[256]; 726 size_t linesize = 0; 727 int found_key = 0; 728 u_long linenum = 0; 729 struct sshauthopt *opts = NULL; 730 #ifdef WITH_LDAP_PUBKEY 731 struct sshkey *found = NULL; 732 ldap_key_t * k; 733 unsigned int i = 0; 734 const char *reason; 735 #endif 736 737 #ifdef WITH_LDAP_PUBKEY 738 found_key = 0; 739 /* allocate a new key type */ 740 found = sshkey_new(key->type); 741 742 /* first check if the options is enabled, then try.. */ 743 if (options.lpk.on) { 744 debug("[LDAP] trying LDAP first uid=%s",pw->pw_name); 745 if (ldap_ismember(&options.lpk, pw->pw_name) > 0) { 746 if ((k = ldap_getuserkey(&options.lpk, pw->pw_name)) != NULL) { 747 /* Skip leading whitespace, empty and comment lines. */ 748 for (i = 0 ; i < k->num ; i++) { 749 /* dont forget if multiple keys to reset options */ 750 char *xoptions = NULL; 751 752 for (cp = (char *)k->keys[i]->bv_val; *cp == ' ' || *cp == '\t'; cp++) 753 ; 754 if (!*cp || *cp == '\n' || *cp == '#') 755 continue; 756 757 if (sshkey_read(found, &cp) != 0) { 758 /* no key? check if there are options for this key */ 759 int quoted = 0; 760 debug2("[LDAP] user_key_allowed: check options: '%s'", cp); 761 xoptions = cp; 762 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 763 if (*cp == '\\' && cp[1] == '"') 764 cp++; /* Skip both */ 765 else if (*cp == '"') 766 quoted = !quoted; 767 } 768 /* Skip remaining whitespace. */ 769 for (; *cp == ' ' || *cp == '\t'; cp++) 770 ; 771 if (sshkey_read(found, &cp) != 0) { 772 debug2("[LDAP] user_key_allowed: advance: '%s'", cp); 773 /* still no key? advance to next line*/ 774 continue; 775 } 776 } 777 if ((opts = sshauthopt_parse(xoptions, &reason)) == NULL) { 778 debug("[LDAP] %s: bad principals options: %s", xoptions, reason); 779 auth_debug_add("[LDAP] %s: bad principals options: %s", xoptions, reason); 780 continue; 781 } 782 783 784 if (sshkey_equal(found, key)) { 785 found_key = 1; 786 debug("[LDAP] matching key found"); 787 char *fp = sshkey_fingerprint(found, SSH_FP_HASH_DEFAULT, SSH_FP_HEX); 788 verbose("[LDAP] Found matching %s key: %s", sshkey_type(found), fp); 789 790 /* restoring memory */ 791 ldap_keys_free(k); 792 free(fp); 793 restore_uid(); 794 sshkey_free(found); 795 return found_key; 796 break; 797 } 798 }/* end of LDAP for() */ 799 } else { 800 logit("[LDAP] no keys found for '%s'!", pw->pw_name); 801 } 802 } else { 803 logit("[LDAP] '%s' is not in '%s'", pw->pw_name, options.lpk.sgroup); 804 } 805 } 806 #endif 807 808 if (authoptsp != NULL) 809 *authoptsp = opts; 810 811 while (getline(&line, &linesize, f) != -1) { 812 linenum++; 813 /* Always consume entire file */ 814 if (found_key) 815 continue; 816 817 /* Skip leading whitespace, empty and comment lines. */ 818 cp = line; 819 skip_space(&cp); 820 if (!*cp || *cp == '\n' || *cp == '#') 821 continue; 822 snprintf(loc, sizeof(loc), "%.200s:%lu", file, linenum); 823 if (check_authkey_line(ssh, pw, key, cp, loc, authoptsp) == 0) 824 found_key = 1; 825 } 826 free(line); 827 return found_key; 828 } 829 830 /* Authenticate a certificate key against TrustedUserCAKeys */ 831 static int 832 user_cert_trusted_ca(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 833 struct sshauthopt **authoptsp) 834 { 835 char *ca_fp, *principals_file = NULL; 836 const char *reason; 837 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 838 struct sshauthopt *final_opts = NULL; 839 int r, ret = 0, found_principal = 0, use_authorized_principals; 840 841 if (authoptsp != NULL) 842 *authoptsp = NULL; 843 844 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 845 return 0; 846 847 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 848 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 849 return 0; 850 851 if ((r = sshkey_in_file(key->cert->signature_key, 852 options.trusted_user_ca_keys, 1, 0)) != 0) { 853 debug2_fr(r, "CA %s %s is not listed in %s", 854 sshkey_type(key->cert->signature_key), ca_fp, 855 options.trusted_user_ca_keys); 856 goto out; 857 } 858 /* 859 * If AuthorizedPrincipals is in use, then compare the certificate 860 * principals against the names in that file rather than matching 861 * against the username. 862 */ 863 if ((principals_file = authorized_principals_file(pw)) != NULL) { 864 if (match_principals_file(ssh, pw, principals_file, 865 key->cert, &principals_opts)) 866 found_principal = 1; 867 } 868 /* Try querying command if specified */ 869 if (!found_principal && match_principals_command(ssh, pw, key, 870 &principals_opts)) 871 found_principal = 1; 872 /* If principals file or command is specified, then require a match */ 873 use_authorized_principals = principals_file != NULL || 874 options.authorized_principals_command != NULL; 875 if (!found_principal && use_authorized_principals) { 876 reason = "Certificate does not contain an authorized principal"; 877 goto fail_reason; 878 } 879 if (use_authorized_principals && principals_opts == NULL) 880 fatal_f("internal error: missing principals_opts"); 881 if (sshkey_cert_check_authority_now(key, 0, 1, 0, 882 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 883 goto fail_reason; 884 885 /* Check authority from options in key and from principals file/cmd */ 886 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 887 reason = "Invalid certificate options"; 888 goto fail_reason; 889 } 890 if (auth_authorise_keyopts(ssh, pw, cert_opts, 0, "cert") != 0) { 891 reason = "Refused by certificate options"; 892 goto fail_reason; 893 } 894 if (principals_opts == NULL) { 895 final_opts = cert_opts; 896 cert_opts = NULL; 897 } else { 898 if (auth_authorise_keyopts(ssh, pw, principals_opts, 0, 899 "principals") != 0) { 900 reason = "Refused by certificate principals options"; 901 goto fail_reason; 902 } 903 if ((final_opts = sshauthopt_merge(principals_opts, 904 cert_opts, &reason)) == NULL) { 905 fail_reason: 906 error("%s", reason); 907 auth_debug_add("%s", reason); 908 goto out; 909 } 910 } 911 912 /* Success */ 913 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 914 "%s CA %s via %s", key->cert->key_id, 915 (unsigned long long)key->cert->serial, 916 sshkey_type(key->cert->signature_key), ca_fp, 917 options.trusted_user_ca_keys); 918 if (authoptsp != NULL) { 919 *authoptsp = final_opts; 920 final_opts = NULL; 921 } 922 ret = 1; 923 out: 924 sshauthopt_free(principals_opts); 925 sshauthopt_free(cert_opts); 926 sshauthopt_free(final_opts); 927 free(principals_file); 928 free(ca_fp); 929 return ret; 930 } 931 932 /* 933 * Checks whether key is allowed in file. 934 * returns 1 if the key is allowed or 0 otherwise. 935 */ 936 static int 937 user_key_allowed2(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 938 char *file, struct sshauthopt **authoptsp) 939 { 940 FILE *f; 941 int found_key = 0; 942 943 if (authoptsp != NULL) 944 *authoptsp = NULL; 945 946 /* Temporarily use the user's uid. */ 947 temporarily_use_uid(pw); 948 949 debug("trying public key file %s", file); 950 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 951 found_key = check_authkeys_file(ssh, pw, f, file, 952 key, authoptsp); 953 fclose(f); 954 } 955 956 restore_uid(); 957 return found_key; 958 } 959 960 /* 961 * Checks whether key is allowed in output of command. 962 * returns 1 if the key is allowed or 0 otherwise. 963 */ 964 static int 965 user_key_command_allowed2(struct ssh *ssh, struct passwd *user_pw, 966 struct sshkey *key, struct sshauthopt **authoptsp) 967 { 968 struct passwd *runas_pw = NULL; 969 FILE *f = NULL; 970 int r, ok, found_key = 0; 971 int i, uid_swapped = 0, ac = 0; 972 pid_t pid; 973 char *username = NULL, *key_fp = NULL, *keytext = NULL; 974 char uidstr[32], *tmp, *command = NULL, **av = NULL; 975 void (*osigchld)(int); 976 977 if (authoptsp != NULL) 978 *authoptsp = NULL; 979 if (options.authorized_keys_command == NULL) 980 return 0; 981 if (options.authorized_keys_command_user == NULL) { 982 error("No user for AuthorizedKeysCommand specified, skipping"); 983 return 0; 984 } 985 986 /* 987 * NB. all returns later this function should go via "out" to 988 * ensure the original SIGCHLD handler is restored properly. 989 */ 990 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 991 992 /* Prepare and verify the user for the command */ 993 username = percent_expand(options.authorized_keys_command_user, 994 "u", user_pw->pw_name, (char *)NULL); 995 runas_pw = getpwnam(username); 996 if (runas_pw == NULL) { 997 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 998 username, strerror(errno)); 999 goto out; 1000 } 1001 1002 /* Prepare AuthorizedKeysCommand */ 1003 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 1004 SSH_FP_DEFAULT)) == NULL) { 1005 error_f("sshkey_fingerprint failed"); 1006 goto out; 1007 } 1008 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 1009 error_fr(r, "sshkey_to_base64 failed"); 1010 goto out; 1011 } 1012 1013 /* Turn the command into an argument vector */ 1014 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) { 1015 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 1016 options.authorized_keys_command); 1017 goto out; 1018 } 1019 if (ac == 0) { 1020 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 1021 options.authorized_keys_command); 1022 goto out; 1023 } 1024 snprintf(uidstr, sizeof(uidstr), "%llu", 1025 (unsigned long long)user_pw->pw_uid); 1026 for (i = 1; i < ac; i++) { 1027 tmp = percent_expand(av[i], 1028 "U", uidstr, 1029 "u", user_pw->pw_name, 1030 "h", user_pw->pw_dir, 1031 "t", sshkey_ssh_name(key), 1032 "f", key_fp, 1033 "k", keytext, 1034 (char *)NULL); 1035 if (tmp == NULL) 1036 fatal_f("percent_expand failed"); 1037 free(av[i]); 1038 av[i] = tmp; 1039 } 1040 /* Prepare a printable command for logs, etc. */ 1041 command = argv_assemble(ac, av); 1042 1043 /* 1044 * If AuthorizedKeysCommand was run without arguments 1045 * then fall back to the old behaviour of passing the 1046 * target username as a single argument. 1047 */ 1048 if (ac == 1) { 1049 av = xreallocarray(av, ac + 2, sizeof(*av)); 1050 av[1] = xstrdup(user_pw->pw_name); 1051 av[2] = NULL; 1052 /* Fix up command too, since it is used in log messages */ 1053 free(command); 1054 xasprintf(&command, "%s %s", av[0], av[1]); 1055 } 1056 1057 if ((pid = subprocess("AuthorizedKeysCommand", command, 1058 ac, av, &f, 1059 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 1060 runas_pw, temporarily_use_uid, restore_uid)) == 0) 1061 goto out; 1062 1063 uid_swapped = 1; 1064 temporarily_use_uid(runas_pw); 1065 1066 ok = check_authkeys_file(ssh, user_pw, f, 1067 options.authorized_keys_command, key, authoptsp); 1068 1069 fclose(f); 1070 f = NULL; 1071 1072 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 1073 goto out; 1074 1075 /* Read completed successfully */ 1076 found_key = ok; 1077 out: 1078 if (f != NULL) 1079 fclose(f); 1080 ssh_signal(SIGCHLD, osigchld); 1081 for (i = 0; i < ac; i++) 1082 free(av[i]); 1083 free(av); 1084 if (uid_swapped) 1085 restore_uid(); 1086 free(command); 1087 free(username); 1088 free(key_fp); 1089 free(keytext); 1090 return found_key; 1091 } 1092 1093 /* 1094 * Check whether key authenticates and authorises the user. 1095 */ 1096 int 1097 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 1098 int auth_attempt, struct sshauthopt **authoptsp) 1099 { 1100 u_int success = 0, i; 1101 char *file; 1102 struct sshauthopt *opts = NULL; 1103 1104 if (authoptsp != NULL) 1105 *authoptsp = NULL; 1106 1107 if (auth_key_is_revoked(key)) 1108 return 0; 1109 if (sshkey_is_cert(key) && 1110 auth_key_is_revoked(key->cert->signature_key)) 1111 return 0; 1112 1113 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1114 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1115 continue; 1116 file = expand_authorized_keys( 1117 options.authorized_keys_files[i], pw); 1118 success = user_key_allowed2(ssh, pw, key, file, &opts); 1119 free(file); 1120 if (!success) { 1121 sshauthopt_free(opts); 1122 opts = NULL; 1123 } 1124 } 1125 if (success) 1126 goto out; 1127 1128 if ((success = user_cert_trusted_ca(ssh, pw, key, &opts)) != 0) 1129 goto out; 1130 sshauthopt_free(opts); 1131 opts = NULL; 1132 1133 if ((success = user_key_command_allowed2(ssh, pw, key, &opts)) != 0) 1134 goto out; 1135 sshauthopt_free(opts); 1136 opts = NULL; 1137 1138 out: 1139 if (success && authoptsp != NULL) { 1140 *authoptsp = opts; 1141 opts = NULL; 1142 } 1143 sshauthopt_free(opts); 1144 return success; 1145 } 1146 1147 Authmethod method_pubkey = { 1148 "publickey", 1149 userauth_pubkey, 1150 &options.pubkey_authentication 1151 }; 1152