1 /* $OpenBSD: auth2-pubkey.c,v 1.117 2022/09/17 10:34:29 djm Exp $ */ 2 /* 3 * Copyright (c) 2000 Markus Friedl. All rights reserved. 4 * Copyright (c) 2010 Damien Miller. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 29 #include <sys/types.h> 30 31 #include <stdlib.h> 32 #include <errno.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 "kex.h" 50 #include "sshbuf.h" 51 #include "log.h" 52 #include "misc.h" 53 #include "servconf.h" 54 #include "compat.h" 55 #include "sshkey.h" 56 #include "hostfile.h" 57 #include "auth.h" 58 #include "pathnames.h" 59 #include "uidswap.h" 60 #include "auth-options.h" 61 #include "canohost.h" 62 #ifdef GSSAPI 63 #include "ssh-gss.h" 64 #endif 65 #include "monitor_wrap.h" 66 #include "authfile.h" 67 #include "match.h" 68 #include "ssherr.h" 69 #include "channels.h" /* XXX for session.h */ 70 #include "session.h" /* XXX for child_set_env(); refactor? */ 71 #include "sk-api.h" 72 73 /* import */ 74 extern ServerOptions options; 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, const char *method) 89 { 90 Authctxt *authctxt = ssh->authctxt; 91 struct passwd *pw = authctxt->pw; 92 struct sshbuf *b = NULL; 93 struct sshkey *key = NULL, *hostkey = NULL; 94 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL; 95 u_char *pkblob = NULL, *sig = NULL, have_sig; 96 size_t blen, slen; 97 int hostbound, r, pktype; 98 int req_presence = 0, req_verify = 0, authenticated = 0; 99 struct sshauthopt *authopts = NULL; 100 struct sshkey_sig_details *sig_details = NULL; 101 102 hostbound = strcmp(method, "publickey-hostbound-v00@openssh.com") == 0; 103 104 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 || 105 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 || 106 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0) 107 fatal_fr(r, "parse %s packet", method); 108 109 /* hostbound auth includes the hostkey offered at initial KEX */ 110 if (hostbound) { 111 if ((r = sshpkt_getb_froms(ssh, &b)) != 0 || 112 (r = sshkey_fromb(b, &hostkey)) != 0) 113 fatal_fr(r, "parse %s hostkey", method); 114 if (ssh->kex->initial_hostkey == NULL) 115 fatal_f("internal error: initial hostkey not recorded"); 116 if (!sshkey_equal(hostkey, ssh->kex->initial_hostkey)) 117 fatal_f("%s packet contained wrong host key", method); 118 sshbuf_free(b); 119 b = NULL; 120 } 121 122 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) { 123 char *keystring; 124 struct sshbuf *pkbuf; 125 126 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL) 127 fatal_f("sshbuf_from failed"); 128 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL) 129 fatal_f("sshbuf_dtob64 failed"); 130 debug2_f("%s user %s %s public key %s %s", 131 authctxt->valid ? "valid" : "invalid", authctxt->user, 132 have_sig ? "attempting" : "querying", pkalg, keystring); 133 sshbuf_free(pkbuf); 134 free(keystring); 135 } 136 137 pktype = sshkey_type_from_name(pkalg); 138 if (pktype == KEY_UNSPEC) { 139 /* this is perfectly legal */ 140 verbose_f("unsupported public key algorithm: %s", pkalg); 141 goto done; 142 } 143 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 144 error_fr(r, "parse key"); 145 goto done; 146 } 147 if (key == NULL) { 148 error_f("cannot decode key: %s", pkalg); 149 goto done; 150 } 151 if (key->type != pktype) { 152 error_f("type mismatch for decoded key " 153 "(received %d, expected %d)", key->type, pktype); 154 goto done; 155 } 156 if (sshkey_type_plain(key->type) == KEY_RSA && 157 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 158 logit("Refusing RSA key because client uses unsafe " 159 "signature scheme"); 160 goto done; 161 } 162 if (auth2_key_already_used(authctxt, key)) { 163 logit("refusing previously-used %s key", sshkey_type(key)); 164 goto done; 165 } 166 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) { 167 logit_f("signature algorithm %s not in " 168 "PubkeyAcceptedAlgorithms", pkalg); 169 goto done; 170 } 171 if ((r = sshkey_check_cert_sigtype(key, 172 options.ca_sign_algorithms)) != 0) { 173 logit_fr(r, "certificate signature algorithm %s", 174 (key->cert == NULL || key->cert->signature_type == NULL) ? 175 "(null)" : key->cert->signature_type); 176 goto done; 177 } 178 if ((r = sshkey_check_rsa_length(key, 179 options.required_rsa_size)) != 0) { 180 logit_r(r, "refusing %s key", sshkey_type(key)); 181 goto done; 182 } 183 key_s = format_key(key); 184 if (sshkey_is_cert(key)) 185 ca_s = format_key(key->cert->signature_key); 186 187 if (have_sig) { 188 debug3_f("%s have %s signature for %s%s%s", 189 method, pkalg, key_s, 190 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 191 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 || 192 (r = sshpkt_get_end(ssh)) != 0) 193 fatal_fr(r, "parse signature packet"); 194 if ((b = sshbuf_new()) == NULL) 195 fatal_f("sshbuf_new failed"); 196 if (ssh->compat & SSH_OLD_SESSIONID) { 197 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0) 198 fatal_fr(r, "put old session id"); 199 } else { 200 if ((r = sshbuf_put_stringb(b, 201 ssh->kex->session_id)) != 0) 202 fatal_fr(r, "put session id"); 203 } 204 if (!authctxt->valid || authctxt->user == NULL) { 205 debug2_f("disabled because of invalid user"); 206 goto done; 207 } 208 /* reconstruct packet */ 209 xasprintf(&userstyle, "%s%s%s", authctxt->user, 210 authctxt->style ? ":" : "", 211 authctxt->style ? authctxt->style : ""); 212 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 213 (r = sshbuf_put_cstring(b, userstyle)) != 0 || 214 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 215 (r = sshbuf_put_cstring(b, method)) != 0 || 216 (r = sshbuf_put_u8(b, have_sig)) != 0 || 217 (r = sshbuf_put_cstring(b, pkalg)) != 0 || 218 (r = sshbuf_put_string(b, pkblob, blen)) != 0) 219 fatal_fr(r, "reconstruct %s packet", method); 220 if (hostbound && 221 (r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0) 222 fatal_fr(r, "reconstruct %s packet", method); 223 #ifdef DEBUG_PK 224 sshbuf_dump(b, stderr); 225 #endif 226 /* test for correct signature */ 227 authenticated = 0; 228 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) && 229 PRIVSEP(sshkey_verify(key, sig, slen, 230 sshbuf_ptr(b), sshbuf_len(b), 231 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL, 232 ssh->compat, &sig_details)) == 0) { 233 authenticated = 1; 234 } 235 if (authenticated == 1 && sig_details != NULL) { 236 auth2_record_info(authctxt, "signature count = %u", 237 sig_details->sk_counter); 238 debug_f("sk_counter = %u, sk_flags = 0x%02x", 239 sig_details->sk_counter, sig_details->sk_flags); 240 req_presence = (options.pubkey_auth_options & 241 PUBKEYAUTH_TOUCH_REQUIRED) || 242 !authopts->no_require_user_presence; 243 if (req_presence && (sig_details->sk_flags & 244 SSH_SK_USER_PRESENCE_REQD) == 0) { 245 error("public key %s signature for %s%s from " 246 "%.128s port %d rejected: user presence " 247 "(authenticator touch) requirement " 248 "not met ", key_s, 249 authctxt->valid ? "" : "invalid user ", 250 authctxt->user, ssh_remote_ipaddr(ssh), 251 ssh_remote_port(ssh)); 252 authenticated = 0; 253 goto done; 254 } 255 req_verify = (options.pubkey_auth_options & 256 PUBKEYAUTH_VERIFY_REQUIRED) || 257 authopts->require_verify; 258 if (req_verify && (sig_details->sk_flags & 259 SSH_SK_USER_VERIFICATION_REQD) == 0) { 260 error("public key %s signature for %s%s from " 261 "%.128s port %d rejected: user " 262 "verification requirement not met ", key_s, 263 authctxt->valid ? "" : "invalid user ", 264 authctxt->user, ssh_remote_ipaddr(ssh), 265 ssh_remote_port(ssh)); 266 authenticated = 0; 267 goto done; 268 } 269 } 270 auth2_record_key(authctxt, authenticated, key); 271 } else { 272 debug_f("%s test pkalg %s pkblob %s%s%s", method, pkalg, key_s, 273 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s); 274 275 if ((r = sshpkt_get_end(ssh)) != 0) 276 fatal_fr(r, "parse packet"); 277 278 if (!authctxt->valid || authctxt->user == NULL) { 279 debug2_f("disabled because of invalid user"); 280 goto done; 281 } 282 /* XXX fake reply and always send PK_OK ? */ 283 /* 284 * XXX this allows testing whether a user is allowed 285 * to login: if you happen to have a valid pubkey this 286 * message is sent. the message is NEVER sent at all 287 * if a user is not allowed to login. is this an 288 * issue? -markus 289 */ 290 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) { 291 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK)) 292 != 0 || 293 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 || 294 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 || 295 (r = sshpkt_send(ssh)) != 0 || 296 (r = ssh_packet_write_wait(ssh)) != 0) 297 fatal_fr(r, "send packet"); 298 authctxt->postponed = 1; 299 } 300 } 301 done: 302 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) { 303 debug_f("key options inconsistent with existing"); 304 authenticated = 0; 305 } 306 debug2_f("authenticated %d pkalg %s", authenticated, pkalg); 307 308 sshbuf_free(b); 309 sshauthopt_free(authopts); 310 sshkey_free(key); 311 sshkey_free(hostkey); 312 free(userstyle); 313 free(pkalg); 314 free(pkblob); 315 free(key_s); 316 free(ca_s); 317 free(sig); 318 sshkey_sig_details_free(sig_details); 319 return authenticated; 320 } 321 322 static int 323 match_principals_file(struct passwd *pw, char *file, 324 struct sshkey_cert *cert, struct sshauthopt **authoptsp) 325 { 326 FILE *f; 327 int success; 328 329 if (authoptsp != NULL) 330 *authoptsp = NULL; 331 332 temporarily_use_uid(pw); 333 debug("trying authorized principals file %s", file); 334 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 335 restore_uid(); 336 return 0; 337 } 338 success = auth_process_principals(f, file, cert, authoptsp); 339 fclose(f); 340 restore_uid(); 341 return success; 342 } 343 344 /* 345 * Checks whether principal is allowed in output of command. 346 * returns 1 if the principal is allowed or 0 otherwise. 347 */ 348 static int 349 match_principals_command(struct passwd *user_pw, 350 const struct sshkey *key, struct sshauthopt **authoptsp) 351 { 352 struct passwd *runas_pw = NULL; 353 const struct sshkey_cert *cert = key->cert; 354 FILE *f = NULL; 355 int r, ok, found_principal = 0; 356 int i, ac = 0, uid_swapped = 0; 357 pid_t pid; 358 char *tmp, *username = NULL, *command = NULL, **av = NULL; 359 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL; 360 char serial_s[32], uidstr[32]; 361 void (*osigchld)(int); 362 363 if (authoptsp != NULL) 364 *authoptsp = NULL; 365 if (options.authorized_principals_command == NULL) 366 return 0; 367 if (options.authorized_principals_command_user == NULL) { 368 error("No user for AuthorizedPrincipalsCommand specified, " 369 "skipping"); 370 return 0; 371 } 372 373 /* 374 * NB. all returns later this function should go via "out" to 375 * ensure the original SIGCHLD handler is restored properly. 376 */ 377 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 378 379 /* Prepare and verify the user for the command */ 380 username = percent_expand(options.authorized_principals_command_user, 381 "u", user_pw->pw_name, (char *)NULL); 382 runas_pw = getpwnam(username); 383 if (runas_pw == NULL) { 384 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 385 username, strerror(errno)); 386 goto out; 387 } 388 389 /* Turn the command into an argument vector */ 390 if (argv_split(options.authorized_principals_command, 391 &ac, &av, 0) != 0) { 392 error("AuthorizedPrincipalsCommand \"%s\" contains " 393 "invalid quotes", options.authorized_principals_command); 394 goto out; 395 } 396 if (ac == 0) { 397 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 398 options.authorized_principals_command); 399 goto out; 400 } 401 if ((ca_fp = sshkey_fingerprint(cert->signature_key, 402 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 403 error_f("sshkey_fingerprint failed"); 404 goto out; 405 } 406 if ((key_fp = sshkey_fingerprint(key, 407 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) { 408 error_f("sshkey_fingerprint failed"); 409 goto out; 410 } 411 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) { 412 error_fr(r, "sshkey_to_base64 failed"); 413 goto out; 414 } 415 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 416 error_fr(r, "sshkey_to_base64 failed"); 417 goto out; 418 } 419 snprintf(serial_s, sizeof(serial_s), "%llu", 420 (unsigned long long)cert->serial); 421 snprintf(uidstr, sizeof(uidstr), "%llu", 422 (unsigned long long)user_pw->pw_uid); 423 for (i = 1; i < ac; i++) { 424 tmp = percent_expand(av[i], 425 "U", uidstr, 426 "u", user_pw->pw_name, 427 "h", user_pw->pw_dir, 428 "t", sshkey_ssh_name(key), 429 "T", sshkey_ssh_name(cert->signature_key), 430 "f", key_fp, 431 "F", ca_fp, 432 "k", keytext, 433 "K", catext, 434 "i", cert->key_id, 435 "s", serial_s, 436 (char *)NULL); 437 if (tmp == NULL) 438 fatal_f("percent_expand failed"); 439 free(av[i]); 440 av[i] = tmp; 441 } 442 /* Prepare a printable command for logs, etc. */ 443 command = argv_assemble(ac, av); 444 445 if ((pid = subprocess("AuthorizedPrincipalsCommand", command, 446 ac, av, &f, 447 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 448 runas_pw, temporarily_use_uid, restore_uid)) == 0) 449 goto out; 450 451 uid_swapped = 1; 452 temporarily_use_uid(runas_pw); 453 454 ok = auth_process_principals(f, "(command)", cert, authoptsp); 455 456 fclose(f); 457 f = NULL; 458 459 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0) 460 goto out; 461 462 /* Read completed successfully */ 463 found_principal = ok; 464 out: 465 if (f != NULL) 466 fclose(f); 467 ssh_signal(SIGCHLD, osigchld); 468 for (i = 0; i < ac; i++) 469 free(av[i]); 470 free(av); 471 if (uid_swapped) 472 restore_uid(); 473 free(command); 474 free(username); 475 free(ca_fp); 476 free(key_fp); 477 free(catext); 478 free(keytext); 479 return found_principal; 480 } 481 482 /* Authenticate a certificate key against TrustedUserCAKeys */ 483 static int 484 user_cert_trusted_ca(struct passwd *pw, struct sshkey *key, 485 const char *remote_ip, const char *remote_host, 486 struct sshauthopt **authoptsp) 487 { 488 char *ca_fp, *principals_file = NULL; 489 const char *reason; 490 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL; 491 struct sshauthopt *final_opts = NULL; 492 int r, ret = 0, found_principal = 0, use_authorized_principals; 493 494 if (authoptsp != NULL) 495 *authoptsp = NULL; 496 497 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL) 498 return 0; 499 500 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 501 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 502 return 0; 503 504 if ((r = sshkey_in_file(key->cert->signature_key, 505 options.trusted_user_ca_keys, 1, 0)) != 0) { 506 debug2_fr(r, "CA %s %s is not listed in %s", 507 sshkey_type(key->cert->signature_key), ca_fp, 508 options.trusted_user_ca_keys); 509 goto out; 510 } 511 /* 512 * If AuthorizedPrincipals is in use, then compare the certificate 513 * principals against the names in that file rather than matching 514 * against the username. 515 */ 516 if ((principals_file = authorized_principals_file(pw)) != NULL) { 517 if (match_principals_file(pw, principals_file, 518 key->cert, &principals_opts)) 519 found_principal = 1; 520 } 521 /* Try querying command if specified */ 522 if (!found_principal && match_principals_command(pw, key, 523 &principals_opts)) 524 found_principal = 1; 525 /* If principals file or command is specified, then require a match */ 526 use_authorized_principals = principals_file != NULL || 527 options.authorized_principals_command != NULL; 528 if (!found_principal && use_authorized_principals) { 529 reason = "Certificate does not contain an authorized principal"; 530 goto fail_reason; 531 } 532 if (use_authorized_principals && principals_opts == NULL) 533 fatal_f("internal error: missing principals_opts"); 534 if (sshkey_cert_check_authority_now(key, 0, 1, 0, 535 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 536 goto fail_reason; 537 538 /* Check authority from options in key and from principals file/cmd */ 539 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) { 540 reason = "Invalid certificate options"; 541 goto fail_reason; 542 } 543 if (auth_authorise_keyopts(pw, cert_opts, 0, 544 remote_ip, remote_host, "cert") != 0) { 545 reason = "Refused by certificate options"; 546 goto fail_reason; 547 } 548 if (principals_opts == NULL) { 549 final_opts = cert_opts; 550 cert_opts = NULL; 551 } else { 552 if (auth_authorise_keyopts(pw, principals_opts, 0, 553 remote_ip, remote_host, "principals") != 0) { 554 reason = "Refused by certificate principals options"; 555 goto fail_reason; 556 } 557 if ((final_opts = sshauthopt_merge(principals_opts, 558 cert_opts, &reason)) == NULL) { 559 fail_reason: 560 error("%s", reason); 561 auth_debug_add("%s", reason); 562 goto out; 563 } 564 } 565 566 /* Success */ 567 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 568 "%s CA %s via %s", key->cert->key_id, 569 (unsigned long long)key->cert->serial, 570 sshkey_type(key->cert->signature_key), ca_fp, 571 options.trusted_user_ca_keys); 572 if (authoptsp != NULL) { 573 *authoptsp = final_opts; 574 final_opts = NULL; 575 } 576 ret = 1; 577 out: 578 sshauthopt_free(principals_opts); 579 sshauthopt_free(cert_opts); 580 sshauthopt_free(final_opts); 581 free(principals_file); 582 free(ca_fp); 583 return ret; 584 } 585 586 /* 587 * Checks whether key is allowed in file. 588 * returns 1 if the key is allowed or 0 otherwise. 589 */ 590 static int 591 user_key_allowed2(struct passwd *pw, struct sshkey *key, 592 char *file, const char *remote_ip, const char *remote_host, 593 struct sshauthopt **authoptsp) 594 { 595 FILE *f; 596 int found_key = 0; 597 598 if (authoptsp != NULL) 599 *authoptsp = NULL; 600 601 /* Temporarily use the user's uid. */ 602 temporarily_use_uid(pw); 603 604 debug("trying public key file %s", file); 605 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 606 found_key = auth_check_authkeys_file(pw, f, file, 607 key, remote_ip, remote_host, authoptsp); 608 fclose(f); 609 } 610 611 restore_uid(); 612 return found_key; 613 } 614 615 /* 616 * Checks whether key is allowed in output of command. 617 * returns 1 if the key is allowed or 0 otherwise. 618 */ 619 static int 620 user_key_command_allowed2(struct passwd *user_pw, struct sshkey *key, 621 const char *remote_ip, const char *remote_host, 622 struct sshauthopt **authoptsp) 623 { 624 struct passwd *runas_pw = NULL; 625 FILE *f = NULL; 626 int r, ok, found_key = 0; 627 int i, uid_swapped = 0, ac = 0; 628 pid_t pid; 629 char *username = NULL, *key_fp = NULL, *keytext = NULL; 630 char uidstr[32], *tmp, *command = NULL, **av = NULL; 631 void (*osigchld)(int); 632 633 if (authoptsp != NULL) 634 *authoptsp = NULL; 635 if (options.authorized_keys_command == NULL) 636 return 0; 637 if (options.authorized_keys_command_user == NULL) { 638 error("No user for AuthorizedKeysCommand specified, skipping"); 639 return 0; 640 } 641 642 /* 643 * NB. all returns later this function should go via "out" to 644 * ensure the original SIGCHLD handler is restored properly. 645 */ 646 osigchld = ssh_signal(SIGCHLD, SIG_DFL); 647 648 /* Prepare and verify the user for the command */ 649 username = percent_expand(options.authorized_keys_command_user, 650 "u", user_pw->pw_name, (char *)NULL); 651 runas_pw = getpwnam(username); 652 if (runas_pw == NULL) { 653 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 654 username, strerror(errno)); 655 goto out; 656 } 657 658 /* Prepare AuthorizedKeysCommand */ 659 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 660 SSH_FP_DEFAULT)) == NULL) { 661 error_f("sshkey_fingerprint failed"); 662 goto out; 663 } 664 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 665 error_fr(r, "sshkey_to_base64 failed"); 666 goto out; 667 } 668 669 /* Turn the command into an argument vector */ 670 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) { 671 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 672 options.authorized_keys_command); 673 goto out; 674 } 675 if (ac == 0) { 676 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 677 options.authorized_keys_command); 678 goto out; 679 } 680 snprintf(uidstr, sizeof(uidstr), "%llu", 681 (unsigned long long)user_pw->pw_uid); 682 for (i = 1; i < ac; i++) { 683 tmp = percent_expand(av[i], 684 "U", uidstr, 685 "u", user_pw->pw_name, 686 "h", user_pw->pw_dir, 687 "t", sshkey_ssh_name(key), 688 "f", key_fp, 689 "k", keytext, 690 (char *)NULL); 691 if (tmp == NULL) 692 fatal_f("percent_expand failed"); 693 free(av[i]); 694 av[i] = tmp; 695 } 696 /* Prepare a printable command for logs, etc. */ 697 command = argv_assemble(ac, av); 698 699 /* 700 * If AuthorizedKeysCommand was run without arguments 701 * then fall back to the old behaviour of passing the 702 * target username as a single argument. 703 */ 704 if (ac == 1) { 705 av = xreallocarray(av, ac + 2, sizeof(*av)); 706 av[1] = xstrdup(user_pw->pw_name); 707 av[2] = NULL; 708 /* Fix up command too, since it is used in log messages */ 709 free(command); 710 xasprintf(&command, "%s %s", av[0], av[1]); 711 } 712 713 if ((pid = subprocess("AuthorizedKeysCommand", command, 714 ac, av, &f, 715 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD, 716 runas_pw, temporarily_use_uid, restore_uid)) == 0) 717 goto out; 718 719 uid_swapped = 1; 720 temporarily_use_uid(runas_pw); 721 722 ok = auth_check_authkeys_file(user_pw, f, 723 options.authorized_keys_command, key, remote_ip, 724 remote_host, authoptsp); 725 726 fclose(f); 727 f = NULL; 728 729 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0) 730 goto out; 731 732 /* Read completed successfully */ 733 found_key = ok; 734 out: 735 if (f != NULL) 736 fclose(f); 737 ssh_signal(SIGCHLD, osigchld); 738 for (i = 0; i < ac; i++) 739 free(av[i]); 740 free(av); 741 if (uid_swapped) 742 restore_uid(); 743 free(command); 744 free(username); 745 free(key_fp); 746 free(keytext); 747 return found_key; 748 } 749 750 /* 751 * Check whether key authenticates and authorises the user. 752 */ 753 int 754 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key, 755 int auth_attempt, struct sshauthopt **authoptsp) 756 { 757 u_int success = 0, i; 758 char *file; 759 struct sshauthopt *opts = NULL; 760 const char *remote_ip = ssh_remote_ipaddr(ssh); 761 const char *remote_host = auth_get_canonical_hostname(ssh, 762 options.use_dns); 763 764 if (authoptsp != NULL) 765 *authoptsp = NULL; 766 767 if (auth_key_is_revoked(key)) 768 return 0; 769 if (sshkey_is_cert(key) && 770 auth_key_is_revoked(key->cert->signature_key)) 771 return 0; 772 773 for (i = 0; !success && i < options.num_authkeys_files; i++) { 774 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 775 continue; 776 file = expand_authorized_keys( 777 options.authorized_keys_files[i], pw); 778 success = user_key_allowed2(pw, key, file, 779 remote_ip, remote_host, &opts); 780 free(file); 781 if (!success) { 782 sshauthopt_free(opts); 783 opts = NULL; 784 } 785 } 786 if (success) 787 goto out; 788 789 if ((success = user_cert_trusted_ca(pw, key, remote_ip, remote_host, 790 &opts)) != 0) 791 goto out; 792 sshauthopt_free(opts); 793 opts = NULL; 794 795 if ((success = user_key_command_allowed2(pw, key, remote_ip, 796 remote_host, &opts)) != 0) 797 goto out; 798 sshauthopt_free(opts); 799 opts = NULL; 800 801 out: 802 if (success && authoptsp != NULL) { 803 *authoptsp = opts; 804 opts = NULL; 805 } 806 sshauthopt_free(opts); 807 return success; 808 } 809 810 Authmethod method_pubkey = { 811 "publickey", 812 "publickey-hostbound-v00@openssh.com", 813 userauth_pubkey, 814 &options.pubkey_authentication 815 }; 816