1 /* $OpenBSD: auth2-pubkey.c,v 1.34 2013/02/14 21:35:59 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; 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 buffer_put_cstring(&b, authctxt->user); 131 buffer_put_cstring(&b, 132 datafellows & SSH_BUG_PKSERVICE ? 133 "ssh-userauth" : 134 authctxt->service); 135 if (datafellows & SSH_BUG_PKAUTH) { 136 buffer_put_char(&b, have_sig); 137 } else { 138 buffer_put_cstring(&b, "publickey"); 139 buffer_put_char(&b, have_sig); 140 buffer_put_cstring(&b, pkalg); 141 } 142 buffer_put_string(&b, pkblob, blen); 143 #ifdef DEBUG_PK 144 buffer_dump(&b); 145 #endif 146 /* test for correct signature */ 147 authenticated = 0; 148 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 149 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 150 buffer_len(&b))) == 1) 151 authenticated = 1; 152 buffer_free(&b); 153 xfree(sig); 154 } else { 155 debug("test whether pkalg/pkblob are acceptable"); 156 packet_check_eom(); 157 158 /* XXX fake reply and always send PK_OK ? */ 159 /* 160 * XXX this allows testing whether a user is allowed 161 * to login: if you happen to have a valid pubkey this 162 * message is sent. the message is NEVER sent at all 163 * if a user is not allowed to login. is this an 164 * issue? -markus 165 */ 166 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 167 packet_start(SSH2_MSG_USERAUTH_PK_OK); 168 packet_put_string(pkalg, alen); 169 packet_put_string(pkblob, blen); 170 packet_send(); 171 packet_write_wait(); 172 authctxt->postponed = 1; 173 } 174 } 175 if (authenticated != 1) 176 auth_clear_options(); 177 done: 178 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 179 if (key != NULL) 180 key_free(key); 181 xfree(pkalg); 182 xfree(pkblob); 183 return authenticated; 184 } 185 186 static int 187 match_principals_option(const char *principal_list, struct KeyCert *cert) 188 { 189 char *result; 190 u_int i; 191 192 /* XXX percent_expand() sequences for authorized_principals? */ 193 194 for (i = 0; i < cert->nprincipals; i++) { 195 if ((result = match_list(cert->principals[i], 196 principal_list, NULL)) != NULL) { 197 debug3("matched principal from key options \"%.100s\"", 198 result); 199 xfree(result); 200 return 1; 201 } 202 } 203 return 0; 204 } 205 206 static int 207 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert) 208 { 209 FILE *f; 210 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 211 u_long linenum = 0; 212 u_int i; 213 214 temporarily_use_uid(pw); 215 debug("trying authorized principals file %s", file); 216 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 217 restore_uid(); 218 return 0; 219 } 220 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 221 /* Skip leading whitespace. */ 222 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 223 ; 224 /* Skip blank and comment lines. */ 225 if ((ep = strchr(cp, '#')) != NULL) 226 *ep = '\0'; 227 if (!*cp || *cp == '\n') 228 continue; 229 /* Trim trailing whitespace. */ 230 ep = cp + strlen(cp) - 1; 231 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 232 *ep-- = '\0'; 233 /* 234 * If the line has internal whitespace then assume it has 235 * key options. 236 */ 237 line_opts = NULL; 238 if ((ep = strrchr(cp, ' ')) != NULL || 239 (ep = strrchr(cp, '\t')) != NULL) { 240 for (; *ep == ' ' || *ep == '\t'; ep++) 241 ; 242 line_opts = cp; 243 cp = ep; 244 } 245 for (i = 0; i < cert->nprincipals; i++) { 246 if (strcmp(cp, cert->principals[i]) == 0) { 247 debug3("matched principal \"%.100s\" " 248 "from file \"%s\" on line %lu", 249 cert->principals[i], file, linenum); 250 if (auth_parse_options(pw, line_opts, 251 file, linenum) != 1) 252 continue; 253 fclose(f); 254 restore_uid(); 255 return 1; 256 } 257 } 258 } 259 fclose(f); 260 restore_uid(); 261 return 0; 262 } 263 264 /* 265 * Checks whether key is allowed in authorized_keys-format file, 266 * returns 1 if the key is allowed or 0 otherwise. 267 */ 268 static int 269 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw) 270 { 271 char line[SSH_MAX_PUBKEY_BYTES]; 272 const char *reason; 273 int found_key = 0; 274 u_long linenum = 0; 275 Key *found; 276 char *fp; 277 278 found_key = 0; 279 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 280 281 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 282 char *cp, *key_options = NULL; 283 284 auth_clear_options(); 285 286 /* Skip leading whitespace, empty and comment lines. */ 287 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 288 ; 289 if (!*cp || *cp == '\n' || *cp == '#') 290 continue; 291 292 if (key_read(found, &cp) != 1) { 293 /* no key? check if there are options for this key */ 294 int quoted = 0; 295 debug2("user_key_allowed: check options: '%s'", cp); 296 key_options = cp; 297 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 298 if (*cp == '\\' && cp[1] == '"') 299 cp++; /* Skip both */ 300 else if (*cp == '"') 301 quoted = !quoted; 302 } 303 /* Skip remaining whitespace. */ 304 for (; *cp == ' ' || *cp == '\t'; cp++) 305 ; 306 if (key_read(found, &cp) != 1) { 307 debug2("user_key_allowed: advance: '%s'", cp); 308 /* still no key? advance to next line*/ 309 continue; 310 } 311 } 312 if (key_is_cert(key)) { 313 if (!key_equal(found, key->cert->signature_key)) 314 continue; 315 if (auth_parse_options(pw, key_options, file, 316 linenum) != 1) 317 continue; 318 if (!key_is_cert_authority) 319 continue; 320 fp = key_fingerprint(found, SSH_FP_MD5, 321 SSH_FP_HEX); 322 debug("matching CA found: file %s, line %lu, %s %s", 323 file, linenum, key_type(found), fp); 324 /* 325 * If the user has specified a list of principals as 326 * a key option, then prefer that list to matching 327 * their username in the certificate principals list. 328 */ 329 if (authorized_principals != NULL && 330 !match_principals_option(authorized_principals, 331 key->cert)) { 332 reason = "Certificate does not contain an " 333 "authorized principal"; 334 fail_reason: 335 xfree(fp); 336 error("%s", reason); 337 auth_debug_add("%s", reason); 338 continue; 339 } 340 if (key_cert_check_authority(key, 0, 0, 341 authorized_principals == NULL ? pw->pw_name : NULL, 342 &reason) != 0) 343 goto fail_reason; 344 if (auth_cert_options(key, pw) != 0) { 345 xfree(fp); 346 continue; 347 } 348 verbose("Accepted certificate ID \"%s\" " 349 "signed by %s CA %s via %s", key->cert->key_id, 350 key_type(found), fp, file); 351 xfree(fp); 352 found_key = 1; 353 break; 354 } else if (key_equal(found, key)) { 355 if (auth_parse_options(pw, key_options, file, 356 linenum) != 1) 357 continue; 358 if (key_is_cert_authority) 359 continue; 360 found_key = 1; 361 debug("matching key found: file %s, line %lu", 362 file, linenum); 363 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 364 verbose("Found matching %s key: %s", 365 key_type(found), fp); 366 xfree(fp); 367 break; 368 } 369 } 370 key_free(found); 371 if (!found_key) 372 debug2("key not found"); 373 return found_key; 374 } 375 376 /* Authenticate a certificate key against TrustedUserCAKeys */ 377 static int 378 user_cert_trusted_ca(struct passwd *pw, Key *key) 379 { 380 char *ca_fp, *principals_file = NULL; 381 const char *reason; 382 int ret = 0; 383 384 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 385 return 0; 386 387 ca_fp = key_fingerprint(key->cert->signature_key, 388 SSH_FP_MD5, SSH_FP_HEX); 389 390 if (key_in_file(key->cert->signature_key, 391 options.trusted_user_ca_keys, 1) != 1) { 392 debug2("%s: CA %s %s is not listed in %s", __func__, 393 key_type(key->cert->signature_key), ca_fp, 394 options.trusted_user_ca_keys); 395 goto out; 396 } 397 /* 398 * If AuthorizedPrincipals is in use, then compare the certificate 399 * principals against the names in that file rather than matching 400 * against the username. 401 */ 402 if ((principals_file = authorized_principals_file(pw)) != NULL) { 403 if (!match_principals_file(principals_file, pw, key->cert)) { 404 reason = "Certificate does not contain an " 405 "authorized principal"; 406 fail_reason: 407 error("%s", reason); 408 auth_debug_add("%s", reason); 409 goto out; 410 } 411 } 412 if (key_cert_check_authority(key, 0, 1, 413 principals_file == NULL ? pw->pw_name : NULL, &reason) != 0) 414 goto fail_reason; 415 if (auth_cert_options(key, pw) != 0) 416 goto out; 417 418 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", 419 key->cert->key_id, key_type(key->cert->signature_key), ca_fp, 420 options.trusted_user_ca_keys); 421 ret = 1; 422 423 out: 424 if (principals_file != NULL) 425 xfree(principals_file); 426 if (ca_fp != NULL) 427 xfree(ca_fp); 428 return ret; 429 } 430 431 /* 432 * Checks whether key is allowed in file. 433 * returns 1 if the key is allowed or 0 otherwise. 434 */ 435 static int 436 user_key_allowed2(struct passwd *pw, Key *key, char *file) 437 { 438 FILE *f; 439 int found_key = 0; 440 441 /* Temporarily use the user's uid. */ 442 temporarily_use_uid(pw); 443 444 debug("trying public key file %s", file); 445 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 446 found_key = check_authkeys_file(f, file, key, pw); 447 fclose(f); 448 } 449 450 restore_uid(); 451 return found_key; 452 } 453 454 /* 455 * Checks whether key is allowed in output of command. 456 * returns 1 if the key is allowed or 0 otherwise. 457 */ 458 static int 459 user_key_command_allowed2(struct passwd *user_pw, Key *key) 460 { 461 FILE *f; 462 int ok, found_key = 0; 463 struct passwd *pw; 464 struct stat st; 465 int status, devnull, p[2], i; 466 pid_t pid; 467 char *username, errmsg[512]; 468 469 if (options.authorized_keys_command == NULL || 470 options.authorized_keys_command[0] != '/') 471 return 0; 472 473 if (options.authorized_keys_command_user == NULL) { 474 error("No user for AuthorizedKeysCommand specified, skipping"); 475 return 0; 476 } 477 478 username = percent_expand(options.authorized_keys_command_user, 479 "u", user_pw->pw_name, (char *)NULL); 480 pw = getpwnam(username); 481 if (pw == NULL) { 482 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 483 username, strerror(errno)); 484 free(username); 485 return 0; 486 } 487 free(username); 488 489 temporarily_use_uid(pw); 490 491 if (stat(options.authorized_keys_command, &st) < 0) { 492 error("Could not stat AuthorizedKeysCommand \"%s\": %s", 493 options.authorized_keys_command, strerror(errno)); 494 goto out; 495 } 496 if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0, 497 errmsg, sizeof(errmsg)) != 0) { 498 error("Unsafe AuthorizedKeysCommand: %s", errmsg); 499 goto out; 500 } 501 502 if (pipe(p) != 0) { 503 error("%s: pipe: %s", __func__, strerror(errno)); 504 goto out; 505 } 506 507 debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"", 508 options.authorized_keys_command, user_pw->pw_name, pw->pw_name); 509 510 /* 511 * Don't want to call this in the child, where it can fatal() and 512 * run cleanup_exit() code. 513 */ 514 restore_uid(); 515 516 switch ((pid = fork())) { 517 case -1: /* error */ 518 error("%s: fork: %s", __func__, strerror(errno)); 519 close(p[0]); 520 close(p[1]); 521 return 0; 522 case 0: /* child */ 523 for (i = 0; i < NSIG; i++) 524 signal(i, SIG_DFL); 525 526 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { 527 error("%s: open %s: %s", __func__, _PATH_DEVNULL, 528 strerror(errno)); 529 _exit(1); 530 } 531 /* Keep stderr around a while longer to catch errors */ 532 if (dup2(devnull, STDIN_FILENO) == -1 || 533 dup2(p[1], STDOUT_FILENO) == -1) { 534 error("%s: dup2: %s", __func__, strerror(errno)); 535 _exit(1); 536 } 537 closefrom(STDERR_FILENO + 1); 538 539 /* Don't use permanently_set_uid() here to avoid fatal() */ 540 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) { 541 error("setresgid %u: %s", (u_int)pw->pw_gid, 542 strerror(errno)); 543 _exit(1); 544 } 545 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) { 546 error("setresuid %u: %s", (u_int)pw->pw_uid, 547 strerror(errno)); 548 _exit(1); 549 } 550 /* stdin is pointed to /dev/null at this point */ 551 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) { 552 error("%s: dup2: %s", __func__, strerror(errno)); 553 _exit(1); 554 } 555 556 execl(options.authorized_keys_command, 557 options.authorized_keys_command, user_pw->pw_name, NULL); 558 559 error("AuthorizedKeysCommand %s exec failed: %s", 560 options.authorized_keys_command, strerror(errno)); 561 _exit(127); 562 default: /* parent */ 563 break; 564 } 565 566 temporarily_use_uid(pw); 567 568 close(p[1]); 569 if ((f = fdopen(p[0], "r")) == NULL) { 570 error("%s: fdopen: %s", __func__, strerror(errno)); 571 close(p[0]); 572 /* Don't leave zombie child */ 573 kill(pid, SIGTERM); 574 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) 575 ; 576 goto out; 577 } 578 ok = check_authkeys_file(f, options.authorized_keys_command, key, pw); 579 fclose(f); 580 581 while (waitpid(pid, &status, 0) == -1) { 582 if (errno != EINTR) { 583 error("%s: waitpid: %s", __func__, strerror(errno)); 584 goto out; 585 } 586 } 587 if (WIFSIGNALED(status)) { 588 error("AuthorizedKeysCommand %s exited on signal %d", 589 options.authorized_keys_command, WTERMSIG(status)); 590 goto out; 591 } else if (WEXITSTATUS(status) != 0) { 592 error("AuthorizedKeysCommand %s returned status %d", 593 options.authorized_keys_command, WEXITSTATUS(status)); 594 goto out; 595 } 596 found_key = ok; 597 out: 598 restore_uid(); 599 return found_key; 600 } 601 602 /* 603 * Check whether key authenticates and authorises the user. 604 */ 605 int 606 user_key_allowed(struct passwd *pw, Key *key) 607 { 608 u_int success, i; 609 char *file; 610 611 if (auth_key_is_revoked(key)) 612 return 0; 613 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 614 return 0; 615 616 success = user_cert_trusted_ca(pw, key); 617 if (success) 618 return success; 619 620 success = user_key_command_allowed2(pw, key); 621 if (success > 0) 622 return success; 623 624 for (i = 0; !success && i < options.num_authkeys_files; i++) { 625 626 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 627 continue; 628 file = expand_authorized_keys( 629 options.authorized_keys_files[i], pw); 630 631 success = user_key_allowed2(pw, key, file); 632 xfree(file); 633 } 634 635 return success; 636 } 637 638 Authmethod method_pubkey = { 639 "publickey", 640 userauth_pubkey, 641 &options.pubkey_authentication 642 }; 643