1 /* $OpenBSD: auth2-pubkey.c,v 1.41 2014/07/15 15:54:14 millert 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 #include <sys/wait.h> 31 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 45 #include "xmalloc.h" 46 #include "ssh.h" 47 #include "ssh2.h" 48 #include "packet.h" 49 #include "buffer.h" 50 #include "log.h" 51 #include "misc.h" 52 #include "servconf.h" 53 #include "compat.h" 54 #include "key.h" 55 #include "hostfile.h" 56 #include "auth.h" 57 #include "pathnames.h" 58 #include "uidswap.h" 59 #include "auth-options.h" 60 #include "canohost.h" 61 #ifdef GSSAPI 62 #include "ssh-gss.h" 63 #endif 64 #include "monitor_wrap.h" 65 #include "authfile.h" 66 #include "match.h" 67 68 /* import */ 69 extern ServerOptions options; 70 extern u_char *session_id2; 71 extern u_int session_id2_len; 72 73 static int 74 userauth_pubkey(Authctxt *authctxt) 75 { 76 Buffer b; 77 Key *key = NULL; 78 char *pkalg, *userstyle; 79 u_char *pkblob, *sig; 80 u_int alen, blen, slen; 81 int have_sig, pktype; 82 int authenticated = 0; 83 84 if (!authctxt->valid) { 85 debug2("userauth_pubkey: disabled because of invalid user"); 86 return 0; 87 } 88 have_sig = packet_get_char(); 89 if (datafellows & SSH_BUG_PKAUTH) { 90 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 91 /* no explicit pkalg given */ 92 pkblob = packet_get_string(&blen); 93 buffer_init(&b); 94 buffer_append(&b, pkblob, blen); 95 /* so we have to extract the pkalg from the pkblob */ 96 pkalg = buffer_get_string(&b, &alen); 97 buffer_free(&b); 98 } else { 99 pkalg = packet_get_string(&alen); 100 pkblob = packet_get_string(&blen); 101 } 102 pktype = key_type_from_name(pkalg); 103 if (pktype == KEY_UNSPEC) { 104 /* this is perfectly legal */ 105 logit("userauth_pubkey: unsupported public key algorithm: %s", 106 pkalg); 107 goto done; 108 } 109 key = key_from_blob(pkblob, blen); 110 if (key == NULL) { 111 error("userauth_pubkey: cannot decode key: %s", pkalg); 112 goto done; 113 } 114 if (key->type != pktype) { 115 error("userauth_pubkey: type mismatch for decoded key " 116 "(received %d, expected %d)", key->type, pktype); 117 goto done; 118 } 119 if (key_type_plain(key->type) == KEY_RSA && 120 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 121 logit("Refusing RSA key because client uses unsafe " 122 "signature scheme"); 123 goto done; 124 } 125 if (have_sig) { 126 sig = packet_get_string(&slen); 127 packet_check_eom(); 128 buffer_init(&b); 129 if (datafellows & SSH_OLD_SESSIONID) { 130 buffer_append(&b, session_id2, session_id2_len); 131 } else { 132 buffer_put_string(&b, session_id2, session_id2_len); 133 } 134 /* reconstruct packet */ 135 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 136 xasprintf(&userstyle, "%s%s%s", authctxt->user, 137 authctxt->style ? ":" : "", 138 authctxt->style ? authctxt->style : ""); 139 buffer_put_cstring(&b, userstyle); 140 free(userstyle); 141 buffer_put_cstring(&b, 142 datafellows & SSH_BUG_PKSERVICE ? 143 "ssh-userauth" : 144 authctxt->service); 145 if (datafellows & SSH_BUG_PKAUTH) { 146 buffer_put_char(&b, have_sig); 147 } else { 148 buffer_put_cstring(&b, "publickey"); 149 buffer_put_char(&b, have_sig); 150 buffer_put_cstring(&b, pkalg); 151 } 152 buffer_put_string(&b, pkblob, blen); 153 #ifdef DEBUG_PK 154 buffer_dump(&b); 155 #endif 156 pubkey_auth_info(authctxt, key, NULL); 157 158 /* test for correct signature */ 159 authenticated = 0; 160 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 161 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 162 buffer_len(&b))) == 1) 163 authenticated = 1; 164 buffer_free(&b); 165 free(sig); 166 } else { 167 debug("test whether pkalg/pkblob are acceptable"); 168 packet_check_eom(); 169 170 /* XXX fake reply and always send PK_OK ? */ 171 /* 172 * XXX this allows testing whether a user is allowed 173 * to login: if you happen to have a valid pubkey this 174 * message is sent. the message is NEVER sent at all 175 * if a user is not allowed to login. is this an 176 * issue? -markus 177 */ 178 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 179 packet_start(SSH2_MSG_USERAUTH_PK_OK); 180 packet_put_string(pkalg, alen); 181 packet_put_string(pkblob, blen); 182 packet_send(); 183 packet_write_wait(); 184 authctxt->postponed = 1; 185 } 186 } 187 if (authenticated != 1) 188 auth_clear_options(); 189 done: 190 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 191 if (key != NULL) 192 key_free(key); 193 free(pkalg); 194 free(pkblob); 195 return authenticated; 196 } 197 198 void 199 pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...) 200 { 201 char *fp, *extra; 202 va_list ap; 203 int i; 204 205 extra = NULL; 206 if (fmt != NULL) { 207 va_start(ap, fmt); 208 i = vasprintf(&extra, fmt, ap); 209 va_end(ap); 210 if (i < 0 || extra == NULL) 211 fatal("%s: vasprintf failed", __func__); 212 } 213 214 if (key_is_cert(key)) { 215 fp = key_fingerprint(key->cert->signature_key, 216 SSH_FP_MD5, SSH_FP_HEX); 217 auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s", 218 key_type(key), key->cert->key_id, 219 (unsigned long long)key->cert->serial, 220 key_type(key->cert->signature_key), fp, 221 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 222 free(fp); 223 } else { 224 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 225 auth_info(authctxt, "%s %s%s%s", key_type(key), fp, 226 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 227 free(fp); 228 } 229 free(extra); 230 } 231 232 static int 233 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 234 { 235 char *result; 236 u_int i; 237 238 /* XXX percent_expand() sequences for authorized_principals? */ 239 240 for (i = 0; i < cert->nprincipals; i++) { 241 if ((result = match_list(cert->principals[i], 242 principal_list, NULL)) != NULL) { 243 debug3("matched principal from key options \"%.100s\"", 244 result); 245 free(result); 246 return 1; 247 } 248 } 249 return 0; 250 } 251 252 static int 253 match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert) 254 { 255 FILE *f; 256 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 257 u_long linenum = 0; 258 u_int i; 259 260 temporarily_use_uid(pw); 261 debug("trying authorized principals file %s", file); 262 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 263 restore_uid(); 264 return 0; 265 } 266 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 267 /* Skip leading whitespace. */ 268 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 269 ; 270 /* Skip blank and comment lines. */ 271 if ((ep = strchr(cp, '#')) != NULL) 272 *ep = '\0'; 273 if (!*cp || *cp == '\n') 274 continue; 275 /* Trim trailing whitespace. */ 276 ep = cp + strlen(cp) - 1; 277 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 278 *ep-- = '\0'; 279 /* 280 * If the line has internal whitespace then assume it has 281 * key options. 282 */ 283 line_opts = NULL; 284 if ((ep = strrchr(cp, ' ')) != NULL || 285 (ep = strrchr(cp, '\t')) != NULL) { 286 for (; *ep == ' ' || *ep == '\t'; ep++) 287 ; 288 line_opts = cp; 289 cp = ep; 290 } 291 for (i = 0; i < cert->nprincipals; i++) { 292 if (strcmp(cp, cert->principals[i]) == 0) { 293 debug3("matched principal \"%.100s\" " 294 "from file \"%s\" on line %lu", 295 cert->principals[i], file, linenum); 296 if (auth_parse_options(pw, line_opts, 297 file, linenum) != 1) 298 continue; 299 fclose(f); 300 restore_uid(); 301 return 1; 302 } 303 } 304 } 305 fclose(f); 306 restore_uid(); 307 return 0; 308 } 309 310 /* 311 * Checks whether key is allowed in authorized_keys-format file, 312 * returns 1 if the key is allowed or 0 otherwise. 313 */ 314 static int 315 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw) 316 { 317 char line[SSH_MAX_PUBKEY_BYTES]; 318 const char *reason; 319 int found_key = 0; 320 u_long linenum = 0; 321 Key *found; 322 char *fp; 323 324 found_key = 0; 325 326 found = NULL; 327 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 328 char *cp, *key_options = NULL; 329 if (found != NULL) 330 key_free(found); 331 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 332 auth_clear_options(); 333 334 /* Skip leading whitespace, empty and comment lines. */ 335 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 336 ; 337 if (!*cp || *cp == '\n' || *cp == '#') 338 continue; 339 340 if (key_read(found, &cp) != 1) { 341 /* no key? check if there are options for this key */ 342 int quoted = 0; 343 debug2("user_key_allowed: check options: '%s'", cp); 344 key_options = cp; 345 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 346 if (*cp == '\\' && cp[1] == '"') 347 cp++; /* Skip both */ 348 else if (*cp == '"') 349 quoted = !quoted; 350 } 351 /* Skip remaining whitespace. */ 352 for (; *cp == ' ' || *cp == '\t'; cp++) 353 ; 354 if (key_read(found, &cp) != 1) { 355 debug2("user_key_allowed: advance: '%s'", cp); 356 /* still no key? advance to next line*/ 357 continue; 358 } 359 } 360 if (key_is_cert(key)) { 361 if (!key_equal(found, key->cert->signature_key)) 362 continue; 363 if (auth_parse_options(pw, key_options, file, 364 linenum) != 1) 365 continue; 366 if (!key_is_cert_authority) 367 continue; 368 fp = key_fingerprint(found, SSH_FP_MD5, 369 SSH_FP_HEX); 370 debug("matching CA found: file %s, line %lu, %s %s", 371 file, linenum, key_type(found), fp); 372 /* 373 * If the user has specified a list of principals as 374 * a key option, then prefer that list to matching 375 * their username in the certificate principals list. 376 */ 377 if (authorized_principals != NULL && 378 !match_principals_option(authorized_principals, 379 key->cert)) { 380 reason = "Certificate does not contain an " 381 "authorized principal"; 382 fail_reason: 383 free(fp); 384 error("%s", reason); 385 auth_debug_add("%s", reason); 386 continue; 387 } 388 if (key_cert_check_authority(key, 0, 0, 389 authorized_principals == NULL ? pw->pw_name : NULL, 390 &reason) != 0) 391 goto fail_reason; 392 if (auth_cert_options(key, pw) != 0) { 393 free(fp); 394 continue; 395 } 396 verbose("Accepted certificate ID \"%s\" " 397 "signed by %s CA %s via %s", key->cert->key_id, 398 key_type(found), fp, file); 399 free(fp); 400 found_key = 1; 401 break; 402 } else if (key_equal(found, key)) { 403 if (auth_parse_options(pw, key_options, file, 404 linenum) != 1) 405 continue; 406 if (key_is_cert_authority) 407 continue; 408 found_key = 1; 409 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 410 debug("matching key found: file %s, line %lu %s %s", 411 file, linenum, key_type(found), fp); 412 free(fp); 413 break; 414 } 415 } 416 if (found != NULL) 417 key_free(found); 418 if (!found_key) 419 debug2("key not found"); 420 return found_key; 421 } 422 423 /* Authenticate a certificate key against TrustedUserCAKeys */ 424 static int 425 user_cert_trusted_ca(struct passwd *pw, Key *key) 426 { 427 char *ca_fp, *principals_file = NULL; 428 const char *reason; 429 int ret = 0; 430 431 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 432 return 0; 433 434 ca_fp = key_fingerprint(key->cert->signature_key, 435 SSH_FP_MD5, SSH_FP_HEX); 436 437 if (key_in_file(key->cert->signature_key, 438 options.trusted_user_ca_keys, 1) != 1) { 439 debug2("%s: CA %s %s is not listed in %s", __func__, 440 key_type(key->cert->signature_key), ca_fp, 441 options.trusted_user_ca_keys); 442 goto out; 443 } 444 /* 445 * If AuthorizedPrincipals is in use, then compare the certificate 446 * principals against the names in that file rather than matching 447 * against the username. 448 */ 449 if ((principals_file = authorized_principals_file(pw)) != NULL) { 450 if (!match_principals_file(principals_file, pw, key->cert)) { 451 reason = "Certificate does not contain an " 452 "authorized principal"; 453 fail_reason: 454 error("%s", reason); 455 auth_debug_add("%s", reason); 456 goto out; 457 } 458 } 459 if (key_cert_check_authority(key, 0, 1, 460 principals_file == NULL ? pw->pw_name : NULL, &reason) != 0) 461 goto fail_reason; 462 if (auth_cert_options(key, pw) != 0) 463 goto out; 464 465 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", 466 key->cert->key_id, key_type(key->cert->signature_key), ca_fp, 467 options.trusted_user_ca_keys); 468 ret = 1; 469 470 out: 471 free(principals_file); 472 free(ca_fp); 473 return ret; 474 } 475 476 /* 477 * Checks whether key is allowed in file. 478 * returns 1 if the key is allowed or 0 otherwise. 479 */ 480 static int 481 user_key_allowed2(struct passwd *pw, Key *key, char *file) 482 { 483 FILE *f; 484 int found_key = 0; 485 486 /* Temporarily use the user's uid. */ 487 temporarily_use_uid(pw); 488 489 debug("trying public key file %s", file); 490 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 491 found_key = check_authkeys_file(f, file, key, pw); 492 fclose(f); 493 } 494 495 restore_uid(); 496 return found_key; 497 } 498 499 /* 500 * Checks whether key is allowed in output of command. 501 * returns 1 if the key is allowed or 0 otherwise. 502 */ 503 static int 504 user_key_command_allowed2(struct passwd *user_pw, Key *key) 505 { 506 FILE *f; 507 int ok, found_key = 0; 508 struct passwd *pw; 509 struct stat st; 510 int status, devnull, p[2], i; 511 pid_t pid; 512 char *username, errmsg[512]; 513 514 if (options.authorized_keys_command == NULL || 515 options.authorized_keys_command[0] != '/') 516 return 0; 517 518 if (options.authorized_keys_command_user == NULL) { 519 error("No user for AuthorizedKeysCommand specified, skipping"); 520 return 0; 521 } 522 523 username = percent_expand(options.authorized_keys_command_user, 524 "u", user_pw->pw_name, (char *)NULL); 525 pw = getpwnam(username); 526 if (pw == NULL) { 527 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 528 username, strerror(errno)); 529 free(username); 530 return 0; 531 } 532 free(username); 533 534 temporarily_use_uid(pw); 535 536 if (stat(options.authorized_keys_command, &st) < 0) { 537 error("Could not stat AuthorizedKeysCommand \"%s\": %s", 538 options.authorized_keys_command, strerror(errno)); 539 goto out; 540 } 541 if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0, 542 errmsg, sizeof(errmsg)) != 0) { 543 error("Unsafe AuthorizedKeysCommand: %s", errmsg); 544 goto out; 545 } 546 547 if (pipe(p) != 0) { 548 error("%s: pipe: %s", __func__, strerror(errno)); 549 goto out; 550 } 551 552 debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"", 553 options.authorized_keys_command, user_pw->pw_name, pw->pw_name); 554 555 /* 556 * Don't want to call this in the child, where it can fatal() and 557 * run cleanup_exit() code. 558 */ 559 restore_uid(); 560 561 switch ((pid = fork())) { 562 case -1: /* error */ 563 error("%s: fork: %s", __func__, strerror(errno)); 564 close(p[0]); 565 close(p[1]); 566 return 0; 567 case 0: /* child */ 568 for (i = 0; i < NSIG; i++) 569 signal(i, SIG_DFL); 570 571 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { 572 error("%s: open %s: %s", __func__, _PATH_DEVNULL, 573 strerror(errno)); 574 _exit(1); 575 } 576 /* Keep stderr around a while longer to catch errors */ 577 if (dup2(devnull, STDIN_FILENO) == -1 || 578 dup2(p[1], STDOUT_FILENO) == -1) { 579 error("%s: dup2: %s", __func__, strerror(errno)); 580 _exit(1); 581 } 582 closefrom(STDERR_FILENO + 1); 583 584 /* Don't use permanently_set_uid() here to avoid fatal() */ 585 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) { 586 error("setresgid %u: %s", (u_int)pw->pw_gid, 587 strerror(errno)); 588 _exit(1); 589 } 590 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) { 591 error("setresuid %u: %s", (u_int)pw->pw_uid, 592 strerror(errno)); 593 _exit(1); 594 } 595 /* stdin is pointed to /dev/null at this point */ 596 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) { 597 error("%s: dup2: %s", __func__, strerror(errno)); 598 _exit(1); 599 } 600 601 execl(options.authorized_keys_command, 602 options.authorized_keys_command, user_pw->pw_name, NULL); 603 604 error("AuthorizedKeysCommand %s exec failed: %s", 605 options.authorized_keys_command, strerror(errno)); 606 _exit(127); 607 default: /* parent */ 608 break; 609 } 610 611 temporarily_use_uid(pw); 612 613 close(p[1]); 614 if ((f = fdopen(p[0], "r")) == NULL) { 615 error("%s: fdopen: %s", __func__, strerror(errno)); 616 close(p[0]); 617 /* Don't leave zombie child */ 618 kill(pid, SIGTERM); 619 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) 620 ; 621 goto out; 622 } 623 ok = check_authkeys_file(f, options.authorized_keys_command, key, pw); 624 fclose(f); 625 626 while (waitpid(pid, &status, 0) == -1) { 627 if (errno != EINTR) { 628 error("%s: waitpid: %s", __func__, strerror(errno)); 629 goto out; 630 } 631 } 632 if (WIFSIGNALED(status)) { 633 error("AuthorizedKeysCommand %s exited on signal %d", 634 options.authorized_keys_command, WTERMSIG(status)); 635 goto out; 636 } else if (WEXITSTATUS(status) != 0) { 637 error("AuthorizedKeysCommand %s returned status %d", 638 options.authorized_keys_command, WEXITSTATUS(status)); 639 goto out; 640 } 641 found_key = ok; 642 out: 643 restore_uid(); 644 return found_key; 645 } 646 647 /* 648 * Check whether key authenticates and authorises the user. 649 */ 650 int 651 user_key_allowed(struct passwd *pw, Key *key) 652 { 653 u_int success, i; 654 char *file; 655 656 if (auth_key_is_revoked(key)) 657 return 0; 658 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 659 return 0; 660 661 success = user_cert_trusted_ca(pw, key); 662 if (success) 663 return success; 664 665 success = user_key_command_allowed2(pw, key); 666 if (success > 0) 667 return success; 668 669 for (i = 0; !success && i < options.num_authkeys_files; i++) { 670 671 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 672 continue; 673 file = expand_authorized_keys( 674 options.authorized_keys_files[i], pw); 675 676 success = user_key_allowed2(pw, key, file); 677 free(file); 678 } 679 680 return success; 681 } 682 683 Authmethod method_pubkey = { 684 "publickey", 685 userauth_pubkey, 686 &options.pubkey_authentication 687 }; 688