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 #ifdef ANDROID 447 /* needed to allow root login on android */ 448 if (getuid() != 0) 449 #endif 450 { 451 snprintf(err, errlen, "bad ownership or modes for file %s", 452 buf); 453 return -1; 454 } 455 } 456 457 /* for each component of the canonical path, walking upwards */ 458 for (;;) { 459 if ((cp = dirname(buf)) == NULL) { 460 snprintf(err, errlen, "dirname() failed"); 461 return -1; 462 } 463 strlcpy(buf, cp, sizeof(buf)); 464 465 #ifndef ANDROID 466 /* /data is owned by system user, which causes this check to fail */ 467 if (stat(buf, &st) < 0 || 468 (st.st_uid != 0 && st.st_uid != uid) || 469 (st.st_mode & 022) != 0) { 470 snprintf(err, errlen, 471 "bad ownership or modes for directory %s", buf); 472 return -1; 473 } 474 #endif 475 /* If are past the homedir then we can stop */ 476 if (comparehome && strcmp(homedir, buf) == 0) 477 break; 478 479 /* 480 * dirname should always complete with a "/" path, 481 * but we can be paranoid and check for "." too 482 */ 483 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 484 break; 485 } 486 return 0; 487 } 488 489 static FILE * 490 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 491 int log_missing, char *file_type) 492 { 493 char line[1024]; 494 struct stat st; 495 int fd; 496 FILE *f; 497 498 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 499 if (log_missing || errno != ENOENT) 500 debug("Could not open %s '%s': %s", file_type, file, 501 strerror(errno)); 502 return NULL; 503 } 504 505 if (fstat(fd, &st) < 0) { 506 close(fd); 507 return NULL; 508 } 509 if (!S_ISREG(st.st_mode)) { 510 logit("User %s %s %s is not a regular file", 511 pw->pw_name, file_type, file); 512 close(fd); 513 return NULL; 514 } 515 unset_nonblock(fd); 516 if ((f = fdopen(fd, "r")) == NULL) { 517 close(fd); 518 return NULL; 519 } 520 if (strict_modes && 521 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 522 fclose(f); 523 logit("Authentication refused: %s", line); 524 auth_debug_add("Ignored %s: %s", file_type, line); 525 return NULL; 526 } 527 528 return f; 529 } 530 531 532 FILE * 533 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 534 { 535 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 536 } 537 538 FILE * 539 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 540 { 541 return auth_openfile(file, pw, strict_modes, 0, 542 "authorized principals"); 543 } 544 545 struct passwd * 546 getpwnamallow(const char *user) 547 { 548 #ifdef HAVE_LOGIN_CAP 549 extern login_cap_t *lc; 550 #ifdef BSD_AUTH 551 auth_session_t *as; 552 #endif 553 #endif 554 struct passwd *pw; 555 556 parse_server_match_config(&options, user, 557 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 558 559 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 560 aix_setauthdb(user); 561 #endif 562 563 pw = getpwnam(user); 564 565 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 566 aix_restoreauthdb(); 567 #endif 568 #ifdef HAVE_CYGWIN 569 /* 570 * Windows usernames are case-insensitive. To avoid later problems 571 * when trying to match the username, the user is only allowed to 572 * login if the username is given in the same case as stored in the 573 * user database. 574 */ 575 if (pw != NULL && strcmp(user, pw->pw_name) != 0) { 576 logit("Login name %.100s does not match stored username %.100s", 577 user, pw->pw_name); 578 pw = NULL; 579 } 580 #endif 581 if (pw == NULL) { 582 logit("Invalid user %.100s from %.100s", 583 user, get_remote_ipaddr()); 584 #ifdef CUSTOM_FAILED_LOGIN 585 record_failed_login(user, 586 get_canonical_hostname(options.use_dns), "ssh"); 587 #endif 588 #ifdef SSH_AUDIT_EVENTS 589 audit_event(SSH_INVALID_USER); 590 #endif /* SSH_AUDIT_EVENTS */ 591 return (NULL); 592 } 593 if (!allowed_user(pw)) 594 return (NULL); 595 #ifdef HAVE_LOGIN_CAP 596 if ((lc = login_getclass(pw->pw_class)) == NULL) { 597 debug("unable to get login class: %s", user); 598 return (NULL); 599 } 600 #ifdef BSD_AUTH 601 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 602 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 603 debug("Approval failure for %s", user); 604 pw = NULL; 605 } 606 if (as != NULL) 607 auth_close(as); 608 #endif 609 #endif 610 if (pw != NULL) 611 return (pwcopy(pw)); 612 return (NULL); 613 } 614 615 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 616 int 617 auth_key_is_revoked(Key *key) 618 { 619 char *key_fp; 620 621 if (options.revoked_keys_file == NULL) 622 return 0; 623 624 switch (key_in_file(key, options.revoked_keys_file, 0)) { 625 case 0: 626 /* key not revoked */ 627 return 0; 628 case -1: 629 /* Error opening revoked_keys_file: refuse all keys */ 630 error("Revoked keys file is unreadable: refusing public key " 631 "authentication"); 632 return 1; 633 case 1: 634 /* Key revoked */ 635 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 636 error("WARNING: authentication attempt with a revoked " 637 "%s key %s ", key_type(key), key_fp); 638 xfree(key_fp); 639 return 1; 640 } 641 fatal("key_in_file returned junk"); 642 } 643 644 void 645 auth_debug_add(const char *fmt,...) 646 { 647 char buf[1024]; 648 va_list args; 649 650 if (!auth_debug_init) 651 return; 652 653 va_start(args, fmt); 654 vsnprintf(buf, sizeof(buf), fmt, args); 655 va_end(args); 656 buffer_put_cstring(&auth_debug, buf); 657 } 658 659 void 660 auth_debug_send(void) 661 { 662 char *msg; 663 664 if (!auth_debug_init) 665 return; 666 while (buffer_len(&auth_debug)) { 667 msg = buffer_get_string(&auth_debug, NULL); 668 packet_send_debug("%s", msg); 669 xfree(msg); 670 } 671 } 672 673 void 674 auth_debug_reset(void) 675 { 676 if (auth_debug_init) 677 buffer_clear(&auth_debug); 678 else { 679 buffer_init(&auth_debug); 680 auth_debug_init = 1; 681 } 682 } 683 684 struct passwd * 685 fakepw(void) 686 { 687 static struct passwd fake; 688 689 memset(&fake, 0, sizeof(fake)); 690 fake.pw_name = "NOUSER"; 691 fake.pw_passwd = 692 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 693 #ifdef HAVE_PW_GECOS_IN_PASSWD 694 fake.pw_gecos = "NOUSER"; 695 #endif 696 fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid; 697 fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid; 698 #ifdef HAVE_PW_CLASS_IN_PASSWD 699 fake.pw_class = ""; 700 #endif 701 fake.pw_dir = "/nonexist"; 702 fake.pw_shell = "/nonexist"; 703 704 return (&fake); 705 } 706
