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 __RCSID("$FreeBSD$"); 28 29 #include <sys/types.h> 30 #include <sys/stat.h> 31 #include <sys/param.h> 32 33 #include <netinet/in.h> 34 35 #include <errno.h> 36 #include <fcntl.h> 37 #ifdef HAVE_PATHS_H 38 # include <paths.h> 39 #endif 40 #include <pwd.h> 41 #ifdef HAVE_LOGIN_H 42 #include <login.h> 43 #endif 44 #ifdef USE_SHADOW 45 #include <shadow.h> 46 #endif 47 #ifdef HAVE_LIBGEN_H 48 #include <libgen.h> 49 #endif 50 #include <stdarg.h> 51 #include <stdio.h> 52 #include <string.h> 53 #include <unistd.h> 54 55 #include "xmalloc.h" 56 #include "match.h" 57 #include "groupaccess.h" 58 #include "log.h" 59 #include "buffer.h" 60 #include "servconf.h" 61 #include "key.h" 62 #include "hostfile.h" 63 #include "auth.h" 64 #include "auth-options.h" 65 #include "canohost.h" 66 #include "uidswap.h" 67 #include "misc.h" 68 #include "packet.h" 69 #include "loginrec.h" 70 #ifdef GSSAPI 71 #include "ssh-gss.h" 72 #endif 73 #include "authfile.h" 74 #include "monitor_wrap.h" 75 76 /* import */ 77 extern ServerOptions options; 78 extern int use_privsep; 79 extern Buffer loginmsg; 80 extern struct passwd *privsep_pw; 81 82 /* Debugging messages */ 83 Buffer auth_debug; 84 int auth_debug_init; 85 86 /* 87 * Check if the user is allowed to log in via ssh. If user is listed 88 * in DenyUsers or one of user's groups is listed in DenyGroups, false 89 * will be returned. If AllowUsers isn't empty and user isn't listed 90 * there, or if AllowGroups isn't empty and one of user's groups isn't 91 * listed there, false will be returned. 92 * If the user's shell is not executable, false will be returned. 93 * Otherwise true is returned. 94 */ 95 int 96 allowed_user(struct passwd * pw) 97 { 98 struct stat st; 99 const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL; 100 u_int i; 101 #ifdef USE_SHADOW 102 struct spwd *spw = NULL; 103 #endif 104 105 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 106 if (!pw || !pw->pw_name) 107 return 0; 108 109 #ifdef USE_SHADOW 110 if (!options.use_pam) 111 spw = getspnam(pw->pw_name); 112 #ifdef HAS_SHADOW_EXPIRE 113 if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw)) 114 return 0; 115 #endif /* HAS_SHADOW_EXPIRE */ 116 #endif /* USE_SHADOW */ 117 118 /* grab passwd field for locked account check */ 119 passwd = pw->pw_passwd; 120 #ifdef USE_SHADOW 121 if (spw != NULL) 122 #ifdef USE_LIBIAF 123 passwd = get_iaf_password(pw); 124 #else 125 passwd = spw->sp_pwdp; 126 #endif /* USE_LIBIAF */ 127 #endif 128 129 /* check for locked account */ 130 if (!options.use_pam && passwd && *passwd) { 131 int locked = 0; 132 133 #ifdef LOCKED_PASSWD_STRING 134 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0) 135 locked = 1; 136 #endif 137 #ifdef LOCKED_PASSWD_PREFIX 138 if (strncmp(passwd, LOCKED_PASSWD_PREFIX, 139 strlen(LOCKED_PASSWD_PREFIX)) == 0) 140 locked = 1; 141 #endif 142 #ifdef LOCKED_PASSWD_SUBSTR 143 if (strstr(passwd, LOCKED_PASSWD_SUBSTR)) 144 locked = 1; 145 #endif 146 #ifdef USE_LIBIAF 147 free((void *) passwd); 148 #endif /* USE_LIBIAF */ 149 if (locked) { 150 logit("User %.100s not allowed because account is locked", 151 pw->pw_name); 152 return 0; 153 } 154 } 155 156 /* 157 * Deny if shell does not exist or is not executable unless we 158 * are chrooting. 159 */ 160 if (options.chroot_directory == NULL || 161 strcasecmp(options.chroot_directory, "none") == 0) { 162 char *shell = xstrdup((pw->pw_shell[0] == '\0') ? 163 _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ 164 165 if (stat(shell, &st) != 0) { 166 logit("User %.100s not allowed because shell %.100s " 167 "does not exist", pw->pw_name, shell); 168 xfree(shell); 169 return 0; 170 } 171 if (S_ISREG(st.st_mode) == 0 || 172 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 173 logit("User %.100s not allowed because shell %.100s " 174 "is not executable", pw->pw_name, shell); 175 xfree(shell); 176 return 0; 177 } 178 xfree(shell); 179 } 180 181 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 182 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 183 hostname = get_canonical_hostname(options.use_dns); 184 ipaddr = get_remote_ipaddr(); 185 } 186 187 /* Return false if user is listed in DenyUsers */ 188 if (options.num_deny_users > 0) { 189 for (i = 0; i < options.num_deny_users; i++) 190 if (match_user(pw->pw_name, hostname, ipaddr, 191 options.deny_users[i])) { 192 logit("User %.100s from %.100s not allowed " 193 "because listed in DenyUsers", 194 pw->pw_name, hostname); 195 return 0; 196 } 197 } 198 /* Return false if AllowUsers isn't empty and user isn't listed there */ 199 if (options.num_allow_users > 0) { 200 for (i = 0; i < options.num_allow_users; i++) 201 if (match_user(pw->pw_name, hostname, ipaddr, 202 options.allow_users[i])) 203 break; 204 /* i < options.num_allow_users iff we break for loop */ 205 if (i >= options.num_allow_users) { 206 logit("User %.100s from %.100s not allowed because " 207 "not listed in AllowUsers", pw->pw_name, hostname); 208 return 0; 209 } 210 } 211 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 212 /* Get the user's group access list (primary and supplementary) */ 213 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 214 logit("User %.100s from %.100s not allowed because " 215 "not in any group", pw->pw_name, hostname); 216 return 0; 217 } 218 219 /* Return false if one of user's groups is listed in DenyGroups */ 220 if (options.num_deny_groups > 0) 221 if (ga_match(options.deny_groups, 222 options.num_deny_groups)) { 223 ga_free(); 224 logit("User %.100s from %.100s not allowed " 225 "because a group is listed in DenyGroups", 226 pw->pw_name, hostname); 227 return 0; 228 } 229 /* 230 * Return false if AllowGroups isn't empty and one of user's groups 231 * isn't listed there 232 */ 233 if (options.num_allow_groups > 0) 234 if (!ga_match(options.allow_groups, 235 options.num_allow_groups)) { 236 ga_free(); 237 logit("User %.100s from %.100s not allowed " 238 "because none of user's groups are listed " 239 "in AllowGroups", pw->pw_name, hostname); 240 return 0; 241 } 242 ga_free(); 243 } 244 245 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER 246 if (!sys_auth_allowed_user(pw, &loginmsg)) 247 return 0; 248 #endif 249 250 /* We found no reason not to let this user try to log on... */ 251 return 1; 252 } 253 254 void 255 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 256 { 257 void (*authlog) (const char *fmt,...) = verbose; 258 char *authmsg; 259 260 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 261 return; 262 263 /* Raise logging level */ 264 if (authenticated == 1 || 265 !authctxt->valid || 266 authctxt->failures >= options.max_authtries / 2 || 267 strcmp(method, "password") == 0) 268 authlog = logit; 269 270 if (authctxt->postponed) 271 authmsg = "Postponed"; 272 else 273 authmsg = authenticated ? "Accepted" : "Failed"; 274 275 authlog("%s %s for %s%.100s from %.200s port %d%s", 276 authmsg, 277 method, 278 authctxt->valid ? "" : "invalid user ", 279 authctxt->user, 280 get_remote_ipaddr(), 281 get_remote_port(), 282 info); 283 284 #ifdef CUSTOM_FAILED_LOGIN 285 if (authenticated == 0 && !authctxt->postponed && 286 (strcmp(method, "password") == 0 || 287 strncmp(method, "keyboard-interactive", 20) == 0 || 288 strcmp(method, "challenge-response") == 0)) 289 record_failed_login(authctxt->user, 290 get_canonical_hostname(options.use_dns), "ssh"); 291 # ifdef WITH_AIXAUTHENTICATE 292 if (authenticated) 293 sys_auth_record_login(authctxt->user, 294 get_canonical_hostname(options.use_dns), "ssh", &loginmsg); 295 # endif 296 #endif 297 #ifdef SSH_AUDIT_EVENTS 298 if (authenticated == 0 && !authctxt->postponed) 299 audit_event(audit_classify_auth(method)); 300 #endif 301 } 302 303 /* 304 * Check whether root logins are disallowed. 305 */ 306 int 307 auth_root_allowed(char *method) 308 { 309 switch (options.permit_root_login) { 310 case PERMIT_YES: 311 return 1; 312 case PERMIT_NO_PASSWD: 313 if (strcmp(method, "password") != 0) 314 return 1; 315 break; 316 case PERMIT_FORCED_ONLY: 317 if (forced_command) { 318 logit("Root login accepted for forced command."); 319 return 1; 320 } 321 break; 322 } 323 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 324 return 0; 325 } 326 327 328 /* 329 * Given a template and a passwd structure, build a filename 330 * by substituting % tokenised options. Currently, %% becomes '%', 331 * %h becomes the home directory and %u the username. 332 * 333 * This returns a buffer allocated by xmalloc. 334 */ 335 char * 336 expand_authorized_keys(const char *filename, struct passwd *pw) 337 { 338 char *file, ret[MAXPATHLEN]; 339 int i; 340 341 file = percent_expand(filename, "h", pw->pw_dir, 342 "u", pw->pw_name, (char *)NULL); 343 344 /* 345 * Ensure that filename starts anchored. If not, be backward 346 * compatible and prepend the '%h/' 347 */ 348 if (*file == '/') 349 return (file); 350 351 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 352 if (i < 0 || (size_t)i >= sizeof(ret)) 353 fatal("expand_authorized_keys: path too long"); 354 xfree(file); 355 return (xstrdup(ret)); 356 } 357 358 char * 359 authorized_principals_file(struct passwd *pw) 360 { 361 if (options.authorized_principals_file == NULL) 362 return NULL; 363 return expand_authorized_keys(options.authorized_principals_file, pw); 364 } 365 366 /* return ok if key exists in sysfile or userfile */ 367 HostStatus 368 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 369 const char *sysfile, const char *userfile) 370 { 371 char *user_hostfile; 372 struct stat st; 373 HostStatus host_status; 374 struct hostkeys *hostkeys; 375 const struct hostkey_entry *found; 376 377 hostkeys = init_hostkeys(); 378 load_hostkeys(hostkeys, host, sysfile); 379 if (userfile != NULL) { 380 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 381 if (options.strict_modes && 382 (stat(user_hostfile, &st) == 0) && 383 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 384 (st.st_mode & 022) != 0)) { 385 logit("Authentication refused for %.100s: " 386 "bad owner or modes for %.200s", 387 pw->pw_name, user_hostfile); 388 auth_debug_add("Ignored %.200s: bad ownership or modes", 389 user_hostfile); 390 } else { 391 temporarily_use_uid(pw); 392 load_hostkeys(hostkeys, host, user_hostfile); 393 restore_uid(); 394 } 395 xfree(user_hostfile); 396 } 397 host_status = check_key_in_hostkeys(hostkeys, key, &found); 398 if (host_status == HOST_REVOKED) 399 error("WARNING: revoked key for %s attempted authentication", 400 found->host); 401 else if (host_status == HOST_OK) 402 debug("%s: key for %s found at %s:%ld", __func__, 403 found->host, found->file, found->line); 404 else 405 debug("%s: key for host %s not found", __func__, host); 406 407 free_hostkeys(hostkeys); 408 409 return host_status; 410 } 411 412 413 /* 414 * Check a given file for security. This is defined as all components 415 * of the path to the file must be owned by either the owner of 416 * of the file or root and no directories must be group or world writable. 417 * 418 * XXX Should any specific check be done for sym links ? 419 * 420 * Takes an open file descriptor, the file name, a uid and and 421 * error buffer plus max size as arguments. 422 * 423 * Returns 0 on success and -1 on failure 424 */ 425 static int 426 secure_filename(FILE *f, const char *file, struct passwd *pw, 427 char *err, size_t errlen) 428 { 429 uid_t uid = pw->pw_uid; 430 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 431 char *cp; 432 int comparehome = 0; 433 struct stat st; 434 435 if (realpath(file, buf) == NULL) { 436 snprintf(err, errlen, "realpath %s failed: %s", file, 437 strerror(errno)); 438 return -1; 439 } 440 if (realpath(pw->pw_dir, homedir) != NULL) 441 comparehome = 1; 442 443 /* check the open file to avoid races */ 444 if (fstat(fileno(f), &st) < 0 || 445 (st.st_uid != 0 && st.st_uid != uid) || 446 (st.st_mode & 022) != 0) { 447 snprintf(err, errlen, "bad ownership or modes for file %s", 448 buf); 449 return -1; 450 } 451 452 /* for each component of the canonical path, walking upwards */ 453 for (;;) { 454 if ((cp = dirname(buf)) == NULL) { 455 snprintf(err, errlen, "dirname() failed"); 456 return -1; 457 } 458 strlcpy(buf, cp, sizeof(buf)); 459 460 if (stat(buf, &st) < 0 || 461 (st.st_uid != 0 && st.st_uid != uid) || 462 (st.st_mode & 022) != 0) { 463 snprintf(err, errlen, 464 "bad ownership or modes for directory %s", buf); 465 return -1; 466 } 467 468 /* If are past the homedir then we can stop */ 469 if (comparehome && strcmp(homedir, buf) == 0) 470 break; 471 472 /* 473 * dirname should always complete with a "/" path, 474 * but we can be paranoid and check for "." too 475 */ 476 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 477 break; 478 } 479 return 0; 480 } 481 482 static FILE * 483 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 484 int log_missing, char *file_type) 485 { 486 char line[1024]; 487 struct stat st; 488 int fd; 489 FILE *f; 490 491 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 492 if (log_missing || errno != ENOENT) 493 debug("Could not open %s '%s': %s", file_type, file, 494 strerror(errno)); 495 return NULL; 496 } 497 498 if (fstat(fd, &st) < 0) { 499 close(fd); 500 return NULL; 501 } 502 if (!S_ISREG(st.st_mode)) { 503 logit("User %s %s %s is not a regular file", 504 pw->pw_name, file_type, file); 505 close(fd); 506 return NULL; 507 } 508 unset_nonblock(fd); 509 if ((f = fdopen(fd, "r")) == NULL) { 510 close(fd); 511 return NULL; 512 } 513 if (strict_modes && 514 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 515 fclose(f); 516 logit("Authentication refused: %s", line); 517 auth_debug_add("Ignored %s: %s", file_type, line); 518 return NULL; 519 } 520 521 return f; 522 } 523 524 525 FILE * 526 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 527 { 528 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 529 } 530 531 FILE * 532 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 533 { 534 return auth_openfile(file, pw, strict_modes, 0, 535 "authorized principals"); 536 } 537 538 struct passwd * 539 getpwnamallow(const char *user) 540 { 541 #ifdef HAVE_LOGIN_CAP 542 extern login_cap_t *lc; 543 #ifdef BSD_AUTH 544 auth_session_t *as; 545 #endif 546 #endif 547 struct passwd *pw; 548 549 parse_server_match_config(&options, user, 550 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 551 552 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 553 aix_setauthdb(user); 554 #endif 555 556 pw = getpwnam(user); 557 558 #if defined(_AIX) && defined(HAVE_SETAUTHDB) 559 aix_restoreauthdb(); 560 #endif 561 #ifdef HAVE_CYGWIN 562 /* 563 * Windows usernames are case-insensitive. To avoid later problems 564 * when trying to match the username, the user is only allowed to 565 * login if the username is given in the same case as stored in the 566 * user database. 567 */ 568 if (pw != NULL && strcmp(user, pw->pw_name) != 0) { 569 logit("Login name %.100s does not match stored username %.100s", 570 user, pw->pw_name); 571 pw = NULL; 572 } 573 #endif 574 if (pw == NULL) { 575 logit("Invalid user %.100s from %.100s", 576 user, get_remote_ipaddr()); 577 #ifdef CUSTOM_FAILED_LOGIN 578 record_failed_login(user, 579 get_canonical_hostname(options.use_dns), "ssh"); 580 #endif 581 #ifdef SSH_AUDIT_EVENTS 582 audit_event(SSH_INVALID_USER); 583 #endif /* SSH_AUDIT_EVENTS */ 584 return (NULL); 585 } 586 if (!allowed_user(pw)) 587 return (NULL); 588 #ifdef HAVE_LOGIN_CAP 589 if ((lc = login_getpwclass(pw)) == NULL) { 590 debug("unable to get login class: %s", user); 591 return (NULL); 592 } 593 #ifdef BSD_AUTH 594 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 595 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 596 debug("Approval failure for %s", user); 597 pw = NULL; 598 } 599 if (as != NULL) 600 auth_close(as); 601 #endif 602 #endif 603 if (pw != NULL) 604 return (pwcopy(pw)); 605 return (NULL); 606 } 607 608 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 609 int 610 auth_key_is_revoked(Key *key) 611 { 612 char *key_fp; 613 614 if (options.revoked_keys_file == NULL) 615 return 0; 616 617 switch (key_in_file(key, options.revoked_keys_file, 0)) { 618 case 0: 619 /* key not revoked */ 620 return 0; 621 case -1: 622 /* Error opening revoked_keys_file: refuse all keys */ 623 error("Revoked keys file is unreadable: refusing public key " 624 "authentication"); 625 return 1; 626 case 1: 627 /* Key revoked */ 628 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 629 error("WARNING: authentication attempt with a revoked " 630 "%s key %s ", key_type(key), key_fp); 631 xfree(key_fp); 632 return 1; 633 } 634 fatal("key_in_file returned junk"); 635 } 636 637 void 638 auth_debug_add(const char *fmt,...) 639 { 640 char buf[1024]; 641 va_list args; 642 643 if (!auth_debug_init) 644 return; 645 646 va_start(args, fmt); 647 vsnprintf(buf, sizeof(buf), fmt, args); 648 va_end(args); 649 buffer_put_cstring(&auth_debug, buf); 650 } 651 652 void 653 auth_debug_send(void) 654 { 655 char *msg; 656 657 if (!auth_debug_init) 658 return; 659 while (buffer_len(&auth_debug)) { 660 msg = buffer_get_string(&auth_debug, NULL); 661 packet_send_debug("%s", msg); 662 xfree(msg); 663 } 664 } 665 666 void 667 auth_debug_reset(void) 668 { 669 if (auth_debug_init) 670 buffer_clear(&auth_debug); 671 else { 672 buffer_init(&auth_debug); 673 auth_debug_init = 1; 674 } 675 } 676 677 struct passwd * 678 fakepw(void) 679 { 680 static struct passwd fake; 681 682 memset(&fake, 0, sizeof(fake)); 683 fake.pw_name = "NOUSER"; 684 fake.pw_passwd = 685 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 686 fake.pw_gecos = "NOUSER"; 687 fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid; 688 fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid; 689 #ifdef HAVE_PW_CLASS_IN_PASSWD 690 fake.pw_class = ""; 691 #endif 692 fake.pw_dir = "/nonexist"; 693 fake.pw_shell = "/nonexist"; 694 695 return (&fake); 696 } 697