1 /* $OpenBSD: auth2-pubkey.c,v 1.38 2013/06/21 00:34:49 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 #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 "servconf.h" 52 #include "compat.h" 53 #include "key.h" 54 #include "hostfile.h" 55 #include "auth.h" 56 #include "pathnames.h" 57 #include "uidswap.h" 58 #include "auth-options.h" 59 #include "canohost.h" 60 #ifdef GSSAPI 61 #include "ssh-gss.h" 62 #endif 63 #include "monitor_wrap.h" 64 #include "misc.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 (have_sig) { 120 sig = packet_get_string(&slen); 121 packet_check_eom(); 122 buffer_init(&b); 123 if (datafellows & SSH_OLD_SESSIONID) { 124 buffer_append(&b, session_id2, session_id2_len); 125 } else { 126 buffer_put_string(&b, session_id2, session_id2_len); 127 } 128 /* reconstruct packet */ 129 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 130 xasprintf(&userstyle, "%s%s%s", authctxt->user, 131 authctxt->style ? ":" : "", 132 authctxt->style ? authctxt->style : ""); 133 buffer_put_cstring(&b, userstyle); 134 free(userstyle); 135 buffer_put_cstring(&b, 136 datafellows & SSH_BUG_PKSERVICE ? 137 "ssh-userauth" : 138 authctxt->service); 139 if (datafellows & SSH_BUG_PKAUTH) { 140 buffer_put_char(&b, have_sig); 141 } else { 142 buffer_put_cstring(&b, "publickey"); 143 buffer_put_char(&b, have_sig); 144 buffer_put_cstring(&b, pkalg); 145 } 146 buffer_put_string(&b, pkblob, blen); 147 #ifdef DEBUG_PK 148 buffer_dump(&b); 149 #endif 150 pubkey_auth_info(authctxt, key, NULL); 151 152 /* test for correct signature */ 153 authenticated = 0; 154 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 155 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 156 buffer_len(&b))) == 1) 157 authenticated = 1; 158 buffer_free(&b); 159 free(sig); 160 } else { 161 debug("test whether pkalg/pkblob are acceptable"); 162 packet_check_eom(); 163 164 /* XXX fake reply and always send PK_OK ? */ 165 /* 166 * XXX this allows testing whether a user is allowed 167 * to login: if you happen to have a valid pubkey this 168 * message is sent. the message is NEVER sent at all 169 * if a user is not allowed to login. is this an 170 * issue? -markus 171 */ 172 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 173 packet_start(SSH2_MSG_USERAUTH_PK_OK); 174 packet_put_string(pkalg, alen); 175 packet_put_string(pkblob, blen); 176 packet_send(); 177 packet_write_wait(); 178 authctxt->postponed = 1; 179 } 180 } 181 if (authenticated != 1) 182 auth_clear_options(); 183 done: 184 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 185 if (key != NULL) 186 key_free(key); 187 free(pkalg); 188 free(pkblob); 189 return authenticated; 190 } 191 192 void 193 pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...) 194 { 195 char *fp, *extra; 196 va_list ap; 197 int i; 198 199 extra = NULL; 200 if (fmt != NULL) { 201 va_start(ap, fmt); 202 i = vasprintf(&extra, fmt, ap); 203 va_end(ap); 204 if (i < 0 || extra == NULL) 205 fatal("%s: vasprintf failed", __func__); 206 } 207 208 if (key_is_cert(key)) { 209 fp = key_fingerprint(key->cert->signature_key, 210 SSH_FP_MD5, SSH_FP_HEX); 211 auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s", 212 key_type(key), key->cert->key_id, 213 (unsigned long long)key->cert->serial, 214 key_type(key->cert->signature_key), fp, 215 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 216 free(fp); 217 } else { 218 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 219 auth_info(authctxt, "%s %s%s%s", key_type(key), fp, 220 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 221 free(fp); 222 } 223 free(extra); 224 } 225 226 static int 227 match_principals_option(const char *principal_list, struct KeyCert *cert) 228 { 229 char *result; 230 u_int i; 231 232 /* XXX percent_expand() sequences for authorized_principals? */ 233 234 for (i = 0; i < cert->nprincipals; i++) { 235 if ((result = match_list(cert->principals[i], 236 principal_list, NULL)) != NULL) { 237 debug3("matched principal from key options \"%.100s\"", 238 result); 239 free(result); 240 return 1; 241 } 242 } 243 return 0; 244 } 245 246 static int 247 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert) 248 { 249 FILE *f; 250 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 251 u_long linenum = 0; 252 u_int i; 253 254 temporarily_use_uid(pw); 255 debug("trying authorized principals file %s", file); 256 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 257 restore_uid(); 258 return 0; 259 } 260 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 261 /* Skip leading whitespace. */ 262 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 263 ; 264 /* Skip blank and comment lines. */ 265 if ((ep = strchr(cp, '#')) != NULL) 266 *ep = '\0'; 267 if (!*cp || *cp == '\n') 268 continue; 269 /* Trim trailing whitespace. */ 270 ep = cp + strlen(cp) - 1; 271 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 272 *ep-- = '\0'; 273 /* 274 * If the line has internal whitespace then assume it has 275 * key options. 276 */ 277 line_opts = NULL; 278 if ((ep = strrchr(cp, ' ')) != NULL || 279 (ep = strrchr(cp, '\t')) != NULL) { 280 for (; *ep == ' ' || *ep == '\t'; ep++) 281 ; 282 line_opts = cp; 283 cp = ep; 284 } 285 for (i = 0; i < cert->nprincipals; i++) { 286 if (strcmp(cp, cert->principals[i]) == 0) { 287 debug3("matched principal \"%.100s\" " 288 "from file \"%s\" on line %lu", 289 cert->principals[i], file, linenum); 290 if (auth_parse_options(pw, line_opts, 291 file, linenum) != 1) 292 continue; 293 fclose(f); 294 restore_uid(); 295 return 1; 296 } 297 } 298 } 299 fclose(f); 300 restore_uid(); 301 return 0; 302 } 303 304 /* 305 * Checks whether key is allowed in authorized_keys-format file, 306 * returns 1 if the key is allowed or 0 otherwise. 307 */ 308 static int 309 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw) 310 { 311 char line[SSH_MAX_PUBKEY_BYTES]; 312 const char *reason; 313 int found_key = 0; 314 u_long linenum = 0; 315 Key *found; 316 char *fp; 317 318 found_key = 0; 319 320 found = NULL; 321 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 322 char *cp, *key_options = NULL; 323 if (found != NULL) 324 key_free(found); 325 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 326 auth_clear_options(); 327 328 /* Skip leading whitespace, empty and comment lines. */ 329 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 330 ; 331 if (!*cp || *cp == '\n' || *cp == '#') 332 continue; 333 334 if (key_read(found, &cp) != 1) { 335 /* no key? check if there are options for this key */ 336 int quoted = 0; 337 debug2("user_key_allowed: check options: '%s'", cp); 338 key_options = cp; 339 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 340 if (*cp == '\\' && cp[1] == '"') 341 cp++; /* Skip both */ 342 else if (*cp == '"') 343 quoted = !quoted; 344 } 345 /* Skip remaining whitespace. */ 346 for (; *cp == ' ' || *cp == '\t'; cp++) 347 ; 348 if (key_read(found, &cp) != 1) { 349 debug2("user_key_allowed: advance: '%s'", cp); 350 /* still no key? advance to next line*/ 351 continue; 352 } 353 } 354 if (key_is_cert(key)) { 355 if (!key_equal(found, key->cert->signature_key)) 356 continue; 357 if (auth_parse_options(pw, key_options, file, 358 linenum) != 1) 359 continue; 360 if (!key_is_cert_authority) 361 continue; 362 fp = key_fingerprint(found, SSH_FP_MD5, 363 SSH_FP_HEX); 364 debug("matching CA found: file %s, line %lu, %s %s", 365 file, linenum, key_type(found), fp); 366 /* 367 * If the user has specified a list of principals as 368 * a key option, then prefer that list to matching 369 * their username in the certificate principals list. 370 */ 371 if (authorized_principals != NULL && 372 !match_principals_option(authorized_principals, 373 key->cert)) { 374 reason = "Certificate does not contain an " 375 "authorized principal"; 376 fail_reason: 377 free(fp); 378 error("%s", reason); 379 auth_debug_add("%s", reason); 380 continue; 381 } 382 if (key_cert_check_authority(key, 0, 0, 383 authorized_principals == NULL ? pw->pw_name : NULL, 384 &reason) != 0) 385 goto fail_reason; 386 if (auth_cert_options(key, pw) != 0) { 387 free(fp); 388 continue; 389 } 390 verbose("Accepted certificate ID \"%s\" " 391 "signed by %s CA %s via %s", key->cert->key_id, 392 key_type(found), fp, file); 393 free(fp); 394 found_key = 1; 395 break; 396 } else if (key_equal(found, key)) { 397 if (auth_parse_options(pw, key_options, file, 398 linenum) != 1) 399 continue; 400 if (key_is_cert_authority) 401 continue; 402 found_key = 1; 403 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 404 debug("matching key found: file %s, line %lu %s %s", 405 file, linenum, key_type(found), fp); 406 free(fp); 407 break; 408 } 409 } 410 if (found != NULL) 411 key_free(found); 412 if (!found_key) 413 debug2("key not found"); 414 return found_key; 415 } 416 417 /* Authenticate a certificate key against TrustedUserCAKeys */ 418 static int 419 user_cert_trusted_ca(struct passwd *pw, Key *key) 420 { 421 char *ca_fp, *principals_file = NULL; 422 const char *reason; 423 int ret = 0; 424 425 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 426 return 0; 427 428 ca_fp = key_fingerprint(key->cert->signature_key, 429 SSH_FP_MD5, SSH_FP_HEX); 430 431 if (key_in_file(key->cert->signature_key, 432 options.trusted_user_ca_keys, 1) != 1) { 433 debug2("%s: CA %s %s is not listed in %s", __func__, 434 key_type(key->cert->signature_key), ca_fp, 435 options.trusted_user_ca_keys); 436 goto out; 437 } 438 /* 439 * If AuthorizedPrincipals is in use, then compare the certificate 440 * principals against the names in that file rather than matching 441 * against the username. 442 */ 443 if ((principals_file = authorized_principals_file(pw)) != NULL) { 444 if (!match_principals_file(principals_file, pw, key->cert)) { 445 reason = "Certificate does not contain an " 446 "authorized principal"; 447 fail_reason: 448 error("%s", reason); 449 auth_debug_add("%s", reason); 450 goto out; 451 } 452 } 453 if (key_cert_check_authority(key, 0, 1, 454 principals_file == NULL ? pw->pw_name : NULL, &reason) != 0) 455 goto fail_reason; 456 if (auth_cert_options(key, pw) != 0) 457 goto out; 458 459 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", 460 key->cert->key_id, key_type(key->cert->signature_key), ca_fp, 461 options.trusted_user_ca_keys); 462 ret = 1; 463 464 out: 465 free(principals_file); 466 free(ca_fp); 467 return ret; 468 } 469 470 /* 471 * Checks whether key is allowed in file. 472 * returns 1 if the key is allowed or 0 otherwise. 473 */ 474 static int 475 user_key_allowed2(struct passwd *pw, Key *key, char *file) 476 { 477 FILE *f; 478 int found_key = 0; 479 480 /* Temporarily use the user's uid. */ 481 temporarily_use_uid(pw); 482 483 debug("trying public key file %s", file); 484 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 485 found_key = check_authkeys_file(f, file, key, pw); 486 fclose(f); 487 } 488 489 restore_uid(); 490 return found_key; 491 } 492 493 /* 494 * Checks whether key is allowed in output of command. 495 * returns 1 if the key is allowed or 0 otherwise. 496 */ 497 static int 498 user_key_command_allowed2(struct passwd *user_pw, Key *key) 499 { 500 FILE *f; 501 int ok, found_key = 0; 502 struct passwd *pw; 503 struct stat st; 504 int status, devnull, p[2], i; 505 pid_t pid; 506 char *username, errmsg[512]; 507 508 if (options.authorized_keys_command == NULL || 509 options.authorized_keys_command[0] != '/') 510 return 0; 511 512 if (options.authorized_keys_command_user == NULL) { 513 error("No user for AuthorizedKeysCommand specified, skipping"); 514 return 0; 515 } 516 517 username = percent_expand(options.authorized_keys_command_user, 518 "u", user_pw->pw_name, (char *)NULL); 519 pw = getpwnam(username); 520 if (pw == NULL) { 521 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 522 username, strerror(errno)); 523 free(username); 524 return 0; 525 } 526 free(username); 527 528 temporarily_use_uid(pw); 529 530 if (stat(options.authorized_keys_command, &st) < 0) { 531 error("Could not stat AuthorizedKeysCommand \"%s\": %s", 532 options.authorized_keys_command, strerror(errno)); 533 goto out; 534 } 535 if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0, 536 errmsg, sizeof(errmsg)) != 0) { 537 error("Unsafe AuthorizedKeysCommand: %s", errmsg); 538 goto out; 539 } 540 541 if (pipe(p) != 0) { 542 error("%s: pipe: %s", __func__, strerror(errno)); 543 goto out; 544 } 545 546 debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"", 547 options.authorized_keys_command, user_pw->pw_name, pw->pw_name); 548 549 /* 550 * Don't want to call this in the child, where it can fatal() and 551 * run cleanup_exit() code. 552 */ 553 restore_uid(); 554 555 switch ((pid = fork())) { 556 case -1: /* error */ 557 error("%s: fork: %s", __func__, strerror(errno)); 558 close(p[0]); 559 close(p[1]); 560 return 0; 561 case 0: /* child */ 562 for (i = 0; i < NSIG; i++) 563 signal(i, SIG_DFL); 564 565 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { 566 error("%s: open %s: %s", __func__, _PATH_DEVNULL, 567 strerror(errno)); 568 _exit(1); 569 } 570 /* Keep stderr around a while longer to catch errors */ 571 if (dup2(devnull, STDIN_FILENO) == -1 || 572 dup2(p[1], STDOUT_FILENO) == -1) { 573 error("%s: dup2: %s", __func__, strerror(errno)); 574 _exit(1); 575 } 576 closefrom(STDERR_FILENO + 1); 577 578 /* Don't use permanently_set_uid() here to avoid fatal() */ 579 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) { 580 error("setresgid %u: %s", (u_int)pw->pw_gid, 581 strerror(errno)); 582 _exit(1); 583 } 584 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) { 585 error("setresuid %u: %s", (u_int)pw->pw_uid, 586 strerror(errno)); 587 _exit(1); 588 } 589 /* stdin is pointed to /dev/null at this point */ 590 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) { 591 error("%s: dup2: %s", __func__, strerror(errno)); 592 _exit(1); 593 } 594 595 execl(options.authorized_keys_command, 596 options.authorized_keys_command, user_pw->pw_name, NULL); 597 598 error("AuthorizedKeysCommand %s exec failed: %s", 599 options.authorized_keys_command, strerror(errno)); 600 _exit(127); 601 default: /* parent */ 602 break; 603 } 604 605 temporarily_use_uid(pw); 606 607 close(p[1]); 608 if ((f = fdopen(p[0], "r")) == NULL) { 609 error("%s: fdopen: %s", __func__, strerror(errno)); 610 close(p[0]); 611 /* Don't leave zombie child */ 612 kill(pid, SIGTERM); 613 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) 614 ; 615 goto out; 616 } 617 ok = check_authkeys_file(f, options.authorized_keys_command, key, pw); 618 fclose(f); 619 620 while (waitpid(pid, &status, 0) == -1) { 621 if (errno != EINTR) { 622 error("%s: waitpid: %s", __func__, strerror(errno)); 623 goto out; 624 } 625 } 626 if (WIFSIGNALED(status)) { 627 error("AuthorizedKeysCommand %s exited on signal %d", 628 options.authorized_keys_command, WTERMSIG(status)); 629 goto out; 630 } else if (WEXITSTATUS(status) != 0) { 631 error("AuthorizedKeysCommand %s returned status %d", 632 options.authorized_keys_command, WEXITSTATUS(status)); 633 goto out; 634 } 635 found_key = ok; 636 out: 637 restore_uid(); 638 return found_key; 639 } 640 641 /* 642 * Check whether key authenticates and authorises the user. 643 */ 644 int 645 user_key_allowed(struct passwd *pw, Key *key) 646 { 647 u_int success, i; 648 char *file; 649 650 if (auth_key_is_revoked(key)) 651 return 0; 652 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 653 return 0; 654 655 success = user_cert_trusted_ca(pw, key); 656 if (success) 657 return success; 658 659 success = user_key_command_allowed2(pw, key); 660 if (success > 0) 661 return success; 662 663 for (i = 0; !success && i < options.num_authkeys_files; i++) { 664 665 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 666 continue; 667 file = expand_authorized_keys( 668 options.authorized_keys_files[i], pw); 669 670 success = user_key_allowed2(pw, key, file); 671 free(file); 672 } 673 674 return success; 675 } 676 677 Authmethod method_pubkey = { 678 "publickey", 679 userauth_pubkey, 680 &options.pubkey_authentication 681 }; 682