1 /* $OpenBSD: auth.c,v 1.94 2011/05/23 03:33:38 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/param.h> 31 32 #include <netinet/in.h> 33 34 #include <errno.h> 35 #include <fcntl.h> 36 #ifdef HAVE_PATHS_H 37 # include <paths.h> 38 #endif 39 #include <pwd.h> 40 #ifdef HAVE_LOGIN_H 41 #include <login.h> 42 #endif 43 #ifdef USE_SHADOW 44 #include <shadow.h> 45 #endif 46 #ifdef HAVE_LIBGEN_H 47 #include <libgen.h> 48 #endif 49 #include <stdarg.h> 50 #include <stdio.h> 51 #include <string.h> 52 #include <unistd.h> 53 54 #include "xmalloc.h" 55 #include "match.h" 56 #include "groupaccess.h" 57 #include "log.h" 58 #include "buffer.h" 59 #include "servconf.h" 60 #include "key.h" 61 #include "hostfile.h" 62 #include "auth.h" 63 #include "auth-options.h" 64 #include "canohost.h" 65 #include "uidswap.h" 66 #include "misc.h" 67 #include "packet.h" 68 #include "loginrec.h" 69 #ifdef GSSAPI 70 #include "ssh-gss.h" 71 #endif 72 #include "authfile.h" 73 #include "monitor_wrap.h" 74 75 /* import */ 76 extern ServerOptions options; 77 extern int use_privsep; 78 extern Buffer loginmsg; 79 extern struct passwd *privsep_pw; 80 81 /* Debugging messages */ 82 Buffer auth_debug; 83 int auth_debug_init; 84 85 /* 86 * Check if the user is allowed to log in via ssh. If user is listed 87 * in DenyUsers or one of user's groups is listed in DenyGroups, false 88 * will be returned. If AllowUsers isn't empty and user isn't listed 89 * there, or if AllowGroups isn't empty and one of user's groups isn't 90 * listed there, false will be returned. 91 * If the user's shell is not executable, false will be returned. 92 * Otherwise true is returned. 93 */ 94 int 95 allowed_user(struct passwd * pw) 96 { 97 struct stat st; 98 const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL; 99 u_int i; 100 #ifdef USE_SHADOW 101 struct spwd *spw = NULL; 102 #endif 103 104 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 105 if (!pw || !pw->pw_name) 106 return 0; 107 108 #ifdef USE_SHADOW 109 if (!options.use_pam) 110 spw = getspnam(pw->pw_name); 111 #ifdef HAS_SHADOW_EXPIRE 112 if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw)) 113 return 0; 114 #endif /* HAS_SHADOW_EXPIRE */ 115 #endif /* USE_SHADOW */ 116 117 /* grab passwd field for locked account check */ 118 passwd = pw->pw_passwd; 119 #ifdef USE_SHADOW 120 if (spw != NULL) 121 #ifdef USE_LIBIAF 122 passwd = get_iaf_password(pw); 123 #else 124 passwd = spw->sp_pwdp; 125 #endif /* USE_LIBIAF */ 126 #endif 127 128 /* check for locked account */ 129 if (!options.use_pam && passwd && *passwd) { 130 int locked = 0; 131 132 #ifdef LOCKED_PASSWD_STRING 133 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0) 134 locked = 1; 135 #endif 136 #ifdef LOCKED_PASSWD_PREFIX 137 if (strncmp(passwd, LOCKED_PASSWD_PREFIX, 138 strlen(LOCKED_PASSWD_PREFIX)) == 0) 139 locked = 1; 140 #endif 141 #ifdef LOCKED_PASSWD_SUBSTR 142 if (strstr(passwd, LOCKED_PASSWD_SUBSTR)) 143 locked = 1; 144 #endif 145 #ifdef USE_LIBIAF 146 free((void *) passwd); 147 #endif /* USE_LIBIAF */ 148 if (locked) { 149 logit("User %.100s not allowed because account is locked", 150 pw->pw_name); 151 return 0; 152 } 153 } 154 155 /* 156 * Deny if shell does not exist or is not executable unless we 157 * are chrooting. 158 */ 159 if (options.chroot_directory == NULL || 160 strcasecmp(options.chroot_directory, "none") == 0) { 161 char *shell = xstrdup((pw->pw_shell[0] == '\0') ? 162 _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ 163 164 if (stat(shell, &st) != 0) { 165 logit("User %.100s not allowed because shell %.100s " 166 "does not exist", pw->pw_name, shell); 167 xfree(shell); 168 return 0; 169 } 170 if (S_ISREG(st.st_mode) == 0 || 171 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 172 logit("User %.100s not allowed because shell %.100s " 173 "is not executable", pw->pw_name, shell); 174 xfree(shell); 175 return 0; 176 } 177 xfree(shell); 178 } 179 180 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 181 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 182 hostname = get_canonical_hostname(options.use_dns); 183 ipaddr = get_remote_ipaddr(); 184 } 185 186 /* Return false if user is listed in DenyUsers */ 187 if (options.num_deny_users > 0) { 188 for (i = 0; i < options.num_deny_users; i++) 189 if (match_user(pw->pw_name, hostname, ipaddr, 190 options.deny_users[i])) { 191 logit("User %.100s from %.100s not allowed " 192 "because listed in DenyUsers", 193 pw->pw_name, hostname); 194 return 0; 195 } 196 } 197 /* Return false if AllowUsers isn't empty and user isn't listed there */ 198 if (options.num_allow_users > 0) { 199 for (i = 0; i < options.num_allow_users; i++) 200 if (match_user(pw->pw_name, hostname, ipaddr, 201 options.allow_users[i])) 202 break; 203 /* i < options.num_allow_users iff we break for loop */ 204 if (i >= options.num_allow_users) { 205 logit("User %.100s from %.100s not allowed because " 206 "not listed in AllowUsers", pw->pw_name, hostname); 207 return 0; 208 } 209 } 210 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 211 /* Get the user's group access list (primary and supplementary) */ 212 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 213 logit("User %.100s from %.100s not allowed because " 214 "not in any group", pw->pw_name, hostname); 215 return 0; 216 } 217 218 /* Return false if one of user's groups is listed in DenyGroups */ 219 if (options.num_deny_groups > 0) 220 if (ga_match(options.deny_groups, 221 options.num_deny_groups)) { 222 ga_free(); 223 logit("User %.100s from %.100s not allowed " 224 "because a group is listed in DenyGroups", 225 pw->pw_name, hostname); 226 return 0; 227 } 228 /* 229 * Return false if AllowGroups isn't empty and one of user's groups 230 * isn't listed there 231 */ 232 if (options.num_allow_groups > 0) 233 if (!ga_match(options.allow_groups, 234 options.num_allow_groups)) { 235 ga_free(); 236 logit("User %.100s from %.100s not allowed " 237 "because none of user's groups are listed " 238 "in AllowGroups", pw->pw_name, hostname); 239 return 0; 240 } 241 ga_free(); 242 } 243 244 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER 245 if (!sys_auth_allowed_user(pw, &loginmsg)) 246 return 0; 247 #endif 248 249 /* We found no reason not to let this user try to log on... */ 250 return 1; 251 } 252 253 void 254 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 255 { 256 void (*authlog) (const char *fmt,...) = verbose; 257 char *authmsg; 258 259 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 260 return; 261 262 /* Raise logging level */ 263 if (authenticated == 1 || 264 !authctxt->valid || 265 authctxt->failures >= options.max_authtries / 2 || 266 strcmp(method, "password") == 0) 267 authlog = logit; 268 269 if (authctxt->postponed) 270 authmsg = "Postponed"; 271 else 272 authmsg = authenticated ? "Accepted" : "Failed"; 273 274 authlog("%s %s for %s%.100s from %.200s port %d%s", 275 authmsg, 276 method, 277 authctxt->valid ? "" : "invalid user ", 278 authctxt->user, 279 get_remote_ipaddr(), 280 get_remote_port(), 281 info); 282 283 #ifdef CUSTOM_FAILED_LOGIN 284 if (authenticated == 0 && !authctxt->postponed && 285 (strcmp(method, "password") == 0 || 286 strncmp(method, "keyboard-interactive", 20) == 0 || 287 strcmp(method, "challenge-response") == 0)) 288 record_failed_login(authctxt->user, 289 get_canonical_hostname(options.use_dns), "ssh"); 290 # ifdef WITH_AIXAUTHENTICATE 291 if (authenticated) 292 sys_auth_record_login(authctxt->user, 293 get_canonical_hostname(options.use_dns), "ssh", &loginmsg); 294 # endif 295 #endif 296 #ifdef SSH_AUDIT_EVENTS 297 if (authenticated == 0 && !authctxt->postponed) 298 audit_event(audit_classify_auth(method)); 299 #endif 300 } 301 302 /* 303 * Check whether root logins are disallowed. 304 */ 305 int 306 auth_root_allowed(char *method) 307 { 308 switch (options.permit_root_login) { 309 case PERMIT_YES: 310 return 1; 311 case PERMIT_NO_PASSWD: 312 if (strcmp(method, "password") != 0) 313 return 1; 314 break; 315 case PERMIT_FORCED_ONLY: 316 if (forced_command) { 317 logit("Root login accepted for forced command."); 318 return 1; 319 } 320 break; 321 } 322 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 323 return 0; 324 } 325 326 327 /* 328 * Given a template and a passwd structure, build a filename 329 * by substituting % tokenised options. Currently, %% becomes '%', 330 * %h becomes the home directory and %u the username. 331 * 332 * This returns a buffer allocated by xmalloc. 333 */ 334 char * 335 expand_authorized_keys(const char *filename, struct passwd *pw) 336 { 337 char *file, ret[MAXPATHLEN]; 338 int i; 339 340 file = percent_expand(filename, "h", pw->pw_dir, 341 "u", pw->pw_name, (char *)NULL); 342 343 /* 344 * Ensure that filename starts anchored. If not, be backward 345 * compatible and prepend the '%h/' 346 */ 347 if (*file == '/') 348 return (file); 349 350 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 351 if (i < 0 || (size_t)i >= sizeof(ret)) 352 fatal("expand_authorized_keys: path too long"); 353 xfree(file); 354 return (xstrdup(ret)); 355 } 356 357 char * 358 authorized_principals_file(struct passwd *pw) 359 { 360 if (options.authorized_principals_file == NULL) 361 return NULL; 362 return expand_authorized_keys(options.authorized_principals_file, pw); 363 } 364 365 /* return ok if key exists in sysfile or userfile */ 366 HostStatus 367 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 368 const char *sysfile, const char *userfile) 369 { 370 char *user_hostfile; 371 struct stat st; 372 HostStatus host_status; 373 struct hostkeys *hostkeys; 374 const struct hostkey_entry *found; 375 376 hostkeys = init_hostkeys(); 377 load_hostkeys(hostkeys, host, sysfile); 378 if (userfile != NULL) { 379 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 380 if (options.strict_modes && 381 (stat(user_hostfile, &st) == 0) && 382 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 383 (st.st_mode & 022) != 0)) { 384 logit("Authentication refused for %.100s: " 385 "bad owner or modes for %.200s", 386 pw->pw_name, user_hostfile); 387 auth_debug_add("Ignored %.200s: bad ownership or modes", 388 user_hostfile); 389 } else { 390 temporarily_use_uid(pw); 391 load_hostkeys(hostkeys, host, user_hostfile); 392 restore_uid(); 393 } 394 xfree(user_hostfile); 395 } 396 host_status = check_key_in_hostkeys(hostkeys, key, &found); 397 if (host_status == HOST_REVOKED) 398 error("WARNING: revoked key for %s attempted authentication", 399 found->host); 400 else if (host_status == HOST_OK) 401 debug("%s: key for %s found at %s:%ld", __func__, 402 found->host, found->file, found->line); 403 else 404 debug("%s: key for host %s not found", __func__, host); 405 406 free_hostkeys(hostkeys); 407 408 return host_status; 409 } 410 411 412 /* 413 * Check a given file for security. This is defined as all components 414 * of the path to the file must be owned by either the owner of 415 * of the file or root and no directories must be group or world writable. 416 * 417 * XXX Should any specific check be done for sym links ? 418 * 419 * Takes an open file descriptor, the file name, a uid and and 420 * error buffer plus max size as arguments. 421 * 422 * Returns 0 on success and -1 on failure 423 */ 424 static int 425 secure_filename(FILE *f, const char *file, struct passwd *pw, 426 char *err, size_t errlen) 427 { 428 uid_t uid = pw->pw_uid; 429 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 430 char *cp; 431 int comparehome = 0; 432 struct stat st; 433 434 if (realpath(file, buf) == NULL) { 435 snprintf(err, errlen, "realpath %s failed: %s", file, 436 strerror(errno)); 437 return -1; 438 } 439 if (realpath(pw->pw_dir, homedir) != NULL) 440 comparehome = 1; 441 442 /* check the open file to avoid races */ 443 if (fstat(fileno(f), &st) < 0 || 444 (st.st_uid != 0 && st.st_uid != uid) || 445 (st.st_mode & 022) != 0) { 446 snprintf(err, errlen, "bad ownership or modes for file %s", 447 buf); 448 return -1; 449 } 450 451 /* for each component of the canonical path, walking upwards */ 452 for (;;) { 453 if ((cp = dirname(buf)) == NULL) { 454 snprintf(err, errlen, "dirname() failed"); 455 return -1; 456 } 457 strlcpy(buf, cp, sizeof(buf)); 458 459 if (stat(buf, &st) < 0 || 460 (st.st_uid != 0 && st.st_uid != uid) || 461 (st.st_mode & 022) != 0) { 462 snprintf(err, errlen, 463 "bad ownership or modes for directory %s", buf); 464 return -1; 465 } 466 467 /* If are past the homedir then we can stop */ 468 if (comparehome && strcmp(homedir, buf) == 0) 469 break; 470 471 /* 472 * dirname should always complete with a "/" path, 473 * but we can be paranoid and check for "." too 474 */ 475 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 476 break; 477 } 478 return 0; 479 } 480 481 static FILE * 482 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 483 int log_missing, char *file_type) 484 { 485 char line[1024]; 486 struct stat st; 487 int fd; 488 FILE *f; 489 490 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 491 if (log_missing || errno != ENOENT) 492 debug("Could not open %s '%s': %s", file_type, file, 493 strerror(errno)); 494 return NULL; 495 } 496 497 if (fstat(fd, &st) < 0) { 498 close(fd); 499 return NULL; 500 } 501 if (!S_ISREG(st.st_mode)) { 502 logit("User %s %s %s is not a regular file", 503 pw->pw_name, file_type, file); 504 close(fd); 505 return NULL; 506 } 507 unset_nonblock(fd); 508 if ((f = fdopen(fd, "r")) == NULL) { 509 close(fd); 510 return NULL; 511 } 512 if (strict_modes && 513 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 514 fclose(f); 515 logit("Authentication refused: %s", line); 516 auth_debug_add("Ignored %s: %s", file_type, line); 517 return NULL; 518 } 519 520 return f; 521 } 522 523 524 FILE * 525 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 526 { 527 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 528 } 529 530 FILE * 531 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 532 { 533 return auth_openfile(file, pw, strict_modes, 0, 534 "authorized principals"); 535 } 536 537 struct passwd * 538 getpwnamallow(const char *user) 539 { 540 #ifdef HAVE_LOGIN_CAP 541 extern login_cap_t *lc; 542 #ifdef BSD_AUTH 543 auth_session_t *as; 544 #endif 545 #endif 546 struct passwd *pw; 547 548 parse_server_match_config(&options, user, 549 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 550 551 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 552 aix_setauthdb(user); 553 #endif 554 555 pw = getpwnam(user); 556 557 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 558 aix_restoreauthdb(); 559 #endif 560 #ifdef HAVE_CYGWIN 561 /* 562 * Windows usernames are case-insensitive. To avoid later problems 563 * when trying to match the username, the user is only allowed to 564 * login if the username is given in the same case as stored in the 565 * user database. 566 */ 567 if (pw != NULL && strcmp(user, pw->pw_name) != 0) { 568 logit("Login name %.100s does not match stored username %.100s", 569 user, pw->pw_name); 570 pw = NULL; 571 } 572 #endif 573 if (pw == NULL) { 574 logit("Invalid user %.100s from %.100s", 575 user, get_remote_ipaddr()); 576 #ifdef CUSTOM_FAILED_LOGIN 577 record_failed_login(user, 578 get_canonical_hostname(options.use_dns), "ssh"); 579 #endif 580 #ifdef SSH_AUDIT_EVENTS 581 audit_event(SSH_INVALID_USER); 582 #endif /* SSH_AUDIT_EVENTS */ 583 return (NULL); 584 } 585 if (!allowed_user(pw)) 586 return (NULL); 587 #ifdef HAVE_LOGIN_CAP 588 if ((lc = login_getclass(pw->pw_class)) == NULL) { 589 debug("unable to get login class: %s", user); 590 return (NULL); 591 } 592 #ifdef BSD_AUTH 593 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 594 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 595 debug("Approval failure for %s", user); 596 pw = NULL; 597 } 598 if (as != NULL) 599 auth_close(as); 600 #endif 601 #endif 602 if (pw != NULL) 603 return (pwcopy(pw)); 604 return (NULL); 605 } 606 607 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 608 int 609 auth_key_is_revoked(Key *key) 610 { 611 char *key_fp; 612 613 if (options.revoked_keys_file == NULL) 614 return 0; 615 616 switch (key_in_file(key, options.revoked_keys_file, 0)) { 617 case 0: 618 /* key not revoked */ 619 return 0; 620 case -1: 621 /* Error opening revoked_keys_file: refuse all keys */ 622 error("Revoked keys file is unreadable: refusing public key " 623 "authentication"); 624 return 1; 625 case 1: 626 /* Key revoked */ 627 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 628 error("WARNING: authentication attempt with a revoked " 629 "%s key %s ", key_type(key), key_fp); 630 xfree(key_fp); 631 return 1; 632 } 633 fatal("key_in_file returned junk"); 634 } 635 636 void 637 auth_debug_add(const char *fmt,...) 638 { 639 char buf[1024]; 640 va_list args; 641 642 if (!auth_debug_init) 643 return; 644 645 va_start(args, fmt); 646 vsnprintf(buf, sizeof(buf), fmt, args); 647 va_end(args); 648 buffer_put_cstring(&auth_debug, buf); 649 } 650 651 void 652 auth_debug_send(void) 653 { 654 char *msg; 655 656 if (!auth_debug_init) 657 return; 658 while (buffer_len(&auth_debug)) { 659 msg = buffer_get_string(&auth_debug, NULL); 660 packet_send_debug("%s", msg); 661 xfree(msg); 662 } 663 } 664 665 void 666 auth_debug_reset(void) 667 { 668 if (auth_debug_init) 669 buffer_clear(&auth_debug); 670 else { 671 buffer_init(&auth_debug); 672 auth_debug_init = 1; 673 } 674 } 675 676 struct passwd * 677 fakepw(void) 678 { 679 static struct passwd fake; 680 681 memset(&fake, 0, sizeof(fake)); 682 fake.pw_name = "NOUSER"; 683 fake.pw_passwd = 684 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 685 fake.pw_gecos = "NOUSER"; 686 fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid; 687 fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid; 688 #ifdef HAVE_PW_CLASS_IN_PASSWD 689 fake.pw_class = ""; 690 #endif 691 fake.pw_dir = "/nonexist"; 692 fake.pw_shell = "/nonexist"; 693 694 return (&fake); 695 } 696