1 /* $OpenBSD: auth.c,v 1.106 2014/07/15 15:54:14 millert 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 <sys/types.h> 27 #include <sys/stat.h> 28 #include <sys/param.h> 29 30 #include <errno.h> 31 #include <fcntl.h> 32 #include <libgen.h> 33 #include <login_cap.h> 34 #include <paths.h> 35 #include <pwd.h> 36 #include <stdarg.h> 37 #include <stdio.h> 38 #include <string.h> 39 #include <unistd.h> 40 41 #include "xmalloc.h" 42 #include "match.h" 43 #include "groupaccess.h" 44 #include "log.h" 45 #include "buffer.h" 46 #include "misc.h" 47 #include "servconf.h" 48 #include "key.h" 49 #include "hostfile.h" 50 #include "auth.h" 51 #include "auth-options.h" 52 #include "canohost.h" 53 #include "uidswap.h" 54 #include "packet.h" 55 #ifdef GSSAPI 56 #include "ssh-gss.h" 57 #endif 58 #include "authfile.h" 59 #include "monitor_wrap.h" 60 #include "krl.h" 61 #include "compat.h" 62 63 /* import */ 64 extern ServerOptions options; 65 extern int use_privsep; 66 67 /* Debugging messages */ 68 Buffer auth_debug; 69 int auth_debug_init; 70 71 /* 72 * Check if the user is allowed to log in via ssh. If user is listed 73 * in DenyUsers or one of user's groups is listed in DenyGroups, false 74 * will be returned. If AllowUsers isn't empty and user isn't listed 75 * there, or if AllowGroups isn't empty and one of user's groups isn't 76 * listed there, false will be returned. 77 * If the user's shell is not executable, false will be returned. 78 * Otherwise true is returned. 79 */ 80 int 81 allowed_user(struct passwd * pw) 82 { 83 struct stat st; 84 const char *hostname = NULL, *ipaddr = NULL; 85 u_int i; 86 87 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 88 if (!pw || !pw->pw_name) 89 return 0; 90 91 /* 92 * Deny if shell does not exist or is not executable unless we 93 * are chrooting. 94 */ 95 if (options.chroot_directory == NULL || 96 strcasecmp(options.chroot_directory, "none") == 0) { 97 char *shell = xstrdup((pw->pw_shell[0] == '\0') ? 98 _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ 99 100 if (stat(shell, &st) != 0) { 101 logit("User %.100s not allowed because shell %.100s " 102 "does not exist", pw->pw_name, shell); 103 free(shell); 104 return 0; 105 } 106 if (S_ISREG(st.st_mode) == 0 || 107 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 108 logit("User %.100s not allowed because shell %.100s " 109 "is not executable", pw->pw_name, shell); 110 free(shell); 111 return 0; 112 } 113 free(shell); 114 } 115 116 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 117 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 118 hostname = get_canonical_hostname(options.use_dns); 119 ipaddr = get_remote_ipaddr(); 120 } 121 122 /* Return false if user is listed in DenyUsers */ 123 if (options.num_deny_users > 0) { 124 for (i = 0; i < options.num_deny_users; i++) 125 if (match_user(pw->pw_name, hostname, ipaddr, 126 options.deny_users[i])) { 127 logit("User %.100s from %.100s not allowed " 128 "because listed in DenyUsers", 129 pw->pw_name, hostname); 130 return 0; 131 } 132 } 133 /* Return false if AllowUsers isn't empty and user isn't listed there */ 134 if (options.num_allow_users > 0) { 135 for (i = 0; i < options.num_allow_users; i++) 136 if (match_user(pw->pw_name, hostname, ipaddr, 137 options.allow_users[i])) 138 break; 139 /* i < options.num_allow_users iff we break for loop */ 140 if (i >= options.num_allow_users) { 141 logit("User %.100s from %.100s not allowed because " 142 "not listed in AllowUsers", pw->pw_name, hostname); 143 return 0; 144 } 145 } 146 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 147 /* Get the user's group access list (primary and supplementary) */ 148 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 149 logit("User %.100s from %.100s not allowed because " 150 "not in any group", pw->pw_name, hostname); 151 return 0; 152 } 153 154 /* Return false if one of user's groups is listed in DenyGroups */ 155 if (options.num_deny_groups > 0) 156 if (ga_match(options.deny_groups, 157 options.num_deny_groups)) { 158 ga_free(); 159 logit("User %.100s from %.100s not allowed " 160 "because a group is listed in DenyGroups", 161 pw->pw_name, hostname); 162 return 0; 163 } 164 /* 165 * Return false if AllowGroups isn't empty and one of user's groups 166 * isn't listed there 167 */ 168 if (options.num_allow_groups > 0) 169 if (!ga_match(options.allow_groups, 170 options.num_allow_groups)) { 171 ga_free(); 172 logit("User %.100s from %.100s not allowed " 173 "because none of user's groups are listed " 174 "in AllowGroups", pw->pw_name, hostname); 175 return 0; 176 } 177 ga_free(); 178 } 179 /* We found no reason not to let this user try to log on... */ 180 return 1; 181 } 182 183 void 184 auth_info(Authctxt *authctxt, const char *fmt, ...) 185 { 186 va_list ap; 187 int i; 188 189 free(authctxt->info); 190 authctxt->info = NULL; 191 192 va_start(ap, fmt); 193 i = vasprintf(&authctxt->info, fmt, ap); 194 va_end(ap); 195 196 if (i < 0 || authctxt->info == NULL) 197 fatal("vasprintf failed"); 198 } 199 200 void 201 auth_log(Authctxt *authctxt, int authenticated, int partial, 202 const char *method, const char *submethod) 203 { 204 void (*authlog) (const char *fmt,...) = verbose; 205 char *authmsg; 206 207 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 208 return; 209 210 /* Raise logging level */ 211 if (authenticated == 1 || 212 !authctxt->valid || 213 authctxt->failures >= options.max_authtries / 2 || 214 strcmp(method, "password") == 0) 215 authlog = logit; 216 217 if (authctxt->postponed) 218 authmsg = "Postponed"; 219 else if (partial) 220 authmsg = "Partial"; 221 else 222 authmsg = authenticated ? "Accepted" : "Failed"; 223 224 authlog("%s %s%s%s for %s%.100s from %.200s port %d %s%s%s", 225 authmsg, 226 method, 227 submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod, 228 authctxt->valid ? "" : "invalid user ", 229 authctxt->user, 230 get_remote_ipaddr(), 231 get_remote_port(), 232 compat20 ? "ssh2" : "ssh1", 233 authctxt->info != NULL ? ": " : "", 234 authctxt->info != NULL ? authctxt->info : ""); 235 free(authctxt->info); 236 authctxt->info = NULL; 237 } 238 239 void 240 auth_maxtries_exceeded(Authctxt *authctxt) 241 { 242 packet_disconnect("Too many authentication failures for " 243 "%s%.100s from %.200s port %d %s", 244 authctxt->valid ? "" : "invalid user ", 245 authctxt->user, 246 get_remote_ipaddr(), 247 get_remote_port(), 248 compat20 ? "ssh2" : "ssh1"); 249 /* NOTREACHED */ 250 } 251 252 /* 253 * Check whether root logins are disallowed. 254 */ 255 int 256 auth_root_allowed(const char *method) 257 { 258 switch (options.permit_root_login) { 259 case PERMIT_YES: 260 return 1; 261 case PERMIT_NO_PASSWD: 262 if (strcmp(method, "password") != 0) 263 return 1; 264 break; 265 case PERMIT_FORCED_ONLY: 266 if (forced_command) { 267 logit("Root login accepted for forced command."); 268 return 1; 269 } 270 break; 271 } 272 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 273 return 0; 274 } 275 276 277 /* 278 * Given a template and a passwd structure, build a filename 279 * by substituting % tokenised options. Currently, %% becomes '%', 280 * %h becomes the home directory and %u the username. 281 * 282 * This returns a buffer allocated by xmalloc. 283 */ 284 char * 285 expand_authorized_keys(const char *filename, struct passwd *pw) 286 { 287 char *file, ret[MAXPATHLEN]; 288 int i; 289 290 file = percent_expand(filename, "h", pw->pw_dir, 291 "u", pw->pw_name, (char *)NULL); 292 293 /* 294 * Ensure that filename starts anchored. If not, be backward 295 * compatible and prepend the '%h/' 296 */ 297 if (*file == '/') 298 return (file); 299 300 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 301 if (i < 0 || (size_t)i >= sizeof(ret)) 302 fatal("expand_authorized_keys: path too long"); 303 free(file); 304 return (xstrdup(ret)); 305 } 306 307 char * 308 authorized_principals_file(struct passwd *pw) 309 { 310 if (options.authorized_principals_file == NULL || 311 strcasecmp(options.authorized_principals_file, "none") == 0) 312 return NULL; 313 return expand_authorized_keys(options.authorized_principals_file, pw); 314 } 315 316 /* return ok if key exists in sysfile or userfile */ 317 HostStatus 318 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 319 const char *sysfile, const char *userfile) 320 { 321 char *user_hostfile; 322 struct stat st; 323 HostStatus host_status; 324 struct hostkeys *hostkeys; 325 const struct hostkey_entry *found; 326 327 hostkeys = init_hostkeys(); 328 load_hostkeys(hostkeys, host, sysfile); 329 if (userfile != NULL) { 330 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 331 if (options.strict_modes && 332 (stat(user_hostfile, &st) == 0) && 333 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 334 (st.st_mode & 022) != 0)) { 335 logit("Authentication refused for %.100s: " 336 "bad owner or modes for %.200s", 337 pw->pw_name, user_hostfile); 338 auth_debug_add("Ignored %.200s: bad ownership or modes", 339 user_hostfile); 340 } else { 341 temporarily_use_uid(pw); 342 load_hostkeys(hostkeys, host, user_hostfile); 343 restore_uid(); 344 } 345 free(user_hostfile); 346 } 347 host_status = check_key_in_hostkeys(hostkeys, key, &found); 348 if (host_status == HOST_REVOKED) 349 error("WARNING: revoked key for %s attempted authentication", 350 found->host); 351 else if (host_status == HOST_OK) 352 debug("%s: key for %s found at %s:%ld", __func__, 353 found->host, found->file, found->line); 354 else 355 debug("%s: key for host %s not found", __func__, host); 356 357 free_hostkeys(hostkeys); 358 359 return host_status; 360 } 361 362 /* 363 * Check a given path for security. This is defined as all components 364 * of the path to the file must be owned by either the owner of 365 * of the file or root and no directories must be group or world writable. 366 * 367 * XXX Should any specific check be done for sym links ? 368 * 369 * Takes a file name, its stat information (preferably from fstat() to 370 * avoid races), the uid of the expected owner, their home directory and an 371 * error buffer plus max size as arguments. 372 * 373 * Returns 0 on success and -1 on failure 374 */ 375 int 376 auth_secure_path(const char *name, struct stat *stp, const char *pw_dir, 377 uid_t uid, char *err, size_t errlen) 378 { 379 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 380 char *cp; 381 int comparehome = 0; 382 struct stat st; 383 384 if (realpath(name, buf) == NULL) { 385 snprintf(err, errlen, "realpath %s failed: %s", name, 386 strerror(errno)); 387 return -1; 388 } 389 if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL) 390 comparehome = 1; 391 392 if (!S_ISREG(stp->st_mode)) { 393 snprintf(err, errlen, "%s is not a regular file", buf); 394 return -1; 395 } 396 if ((stp->st_uid != 0 && stp->st_uid != uid) || 397 (stp->st_mode & 022) != 0) { 398 snprintf(err, errlen, "bad ownership or modes for file %s", 399 buf); 400 return -1; 401 } 402 403 /* for each component of the canonical path, walking upwards */ 404 for (;;) { 405 if ((cp = dirname(buf)) == NULL) { 406 snprintf(err, errlen, "dirname() failed"); 407 return -1; 408 } 409 strlcpy(buf, cp, sizeof(buf)); 410 411 if (stat(buf, &st) < 0 || 412 (st.st_uid != 0 && st.st_uid != uid) || 413 (st.st_mode & 022) != 0) { 414 snprintf(err, errlen, 415 "bad ownership or modes for directory %s", buf); 416 return -1; 417 } 418 419 /* If are past the homedir then we can stop */ 420 if (comparehome && strcmp(homedir, buf) == 0) 421 break; 422 423 /* 424 * dirname should always complete with a "/" path, 425 * but we can be paranoid and check for "." too 426 */ 427 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 428 break; 429 } 430 return 0; 431 } 432 433 /* 434 * Version of secure_path() that accepts an open file descriptor to 435 * avoid races. 436 * 437 * Returns 0 on success and -1 on failure 438 */ 439 static int 440 secure_filename(FILE *f, const char *file, struct passwd *pw, 441 char *err, size_t errlen) 442 { 443 struct stat st; 444 445 /* check the open file to avoid races */ 446 if (fstat(fileno(f), &st) < 0) { 447 snprintf(err, errlen, "cannot stat file %s: %s", 448 file, strerror(errno)); 449 return -1; 450 } 451 return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen); 452 } 453 454 static FILE * 455 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 456 int log_missing, char *file_type) 457 { 458 char line[1024]; 459 struct stat st; 460 int fd; 461 FILE *f; 462 463 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 464 if (log_missing || errno != ENOENT) 465 debug("Could not open %s '%s': %s", file_type, file, 466 strerror(errno)); 467 return NULL; 468 } 469 470 if (fstat(fd, &st) < 0) { 471 close(fd); 472 return NULL; 473 } 474 if (!S_ISREG(st.st_mode)) { 475 logit("User %s %s %s is not a regular file", 476 pw->pw_name, file_type, file); 477 close(fd); 478 return NULL; 479 } 480 unset_nonblock(fd); 481 if ((f = fdopen(fd, "r")) == NULL) { 482 close(fd); 483 return NULL; 484 } 485 if (strict_modes && 486 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 487 fclose(f); 488 logit("Authentication refused: %s", line); 489 auth_debug_add("Ignored %s: %s", file_type, line); 490 return NULL; 491 } 492 493 return f; 494 } 495 496 497 FILE * 498 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 499 { 500 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 501 } 502 503 FILE * 504 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 505 { 506 return auth_openfile(file, pw, strict_modes, 0, 507 "authorized principals"); 508 } 509 510 struct passwd * 511 getpwnamallow(const char *user) 512 { 513 extern login_cap_t *lc; 514 auth_session_t *as; 515 struct passwd *pw; 516 struct connection_info *ci = get_connection_info(1, options.use_dns); 517 518 ci->user = user; 519 parse_server_match_config(&options, ci); 520 521 pw = getpwnam(user); 522 if (pw == NULL) { 523 logit("Invalid user %.100s from %.100s", 524 user, get_remote_ipaddr()); 525 return (NULL); 526 } 527 if (!allowed_user(pw)) 528 return (NULL); 529 if ((lc = login_getclass(pw->pw_class)) == NULL) { 530 debug("unable to get login class: %s", user); 531 return (NULL); 532 } 533 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 534 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 535 debug("Approval failure for %s", user); 536 pw = NULL; 537 } 538 if (as != NULL) 539 auth_close(as); 540 if (pw != NULL) 541 return (pwcopy(pw)); 542 return (NULL); 543 } 544 545 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 546 int 547 auth_key_is_revoked(Key *key) 548 { 549 #ifdef WITH_OPENSSL 550 char *key_fp; 551 552 if (options.revoked_keys_file == NULL) 553 return 0; 554 switch (ssh_krl_file_contains_key(options.revoked_keys_file, key)) { 555 case 0: 556 return 0; /* Not revoked */ 557 case -2: 558 break; /* Not a KRL */ 559 default: 560 goto revoked; 561 } 562 #endif 563 debug3("%s: treating %s as a key list", __func__, 564 options.revoked_keys_file); 565 switch (key_in_file(key, options.revoked_keys_file, 0)) { 566 case 0: 567 /* key not revoked */ 568 return 0; 569 case -1: 570 /* Error opening revoked_keys_file: refuse all keys */ 571 error("Revoked keys file is unreadable: refusing public key " 572 "authentication"); 573 return 1; 574 #ifdef WITH_OPENSSL 575 case 1: 576 revoked: 577 /* Key revoked */ 578 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 579 error("WARNING: authentication attempt with a revoked " 580 "%s key %s ", key_type(key), key_fp); 581 free(key_fp); 582 return 1; 583 #endif 584 } 585 fatal("key_in_file returned junk"); 586 } 587 588 void 589 auth_debug_add(const char *fmt,...) 590 { 591 char buf[1024]; 592 va_list args; 593 594 if (!auth_debug_init) 595 return; 596 597 va_start(args, fmt); 598 vsnprintf(buf, sizeof(buf), fmt, args); 599 va_end(args); 600 buffer_put_cstring(&auth_debug, buf); 601 } 602 603 void 604 auth_debug_send(void) 605 { 606 char *msg; 607 608 if (!auth_debug_init) 609 return; 610 while (buffer_len(&auth_debug)) { 611 msg = buffer_get_string(&auth_debug, NULL); 612 packet_send_debug("%s", msg); 613 free(msg); 614 } 615 } 616 617 void 618 auth_debug_reset(void) 619 { 620 if (auth_debug_init) 621 buffer_clear(&auth_debug); 622 else { 623 buffer_init(&auth_debug); 624 auth_debug_init = 1; 625 } 626 } 627 628 struct passwd * 629 fakepw(void) 630 { 631 static struct passwd fake; 632 633 memset(&fake, 0, sizeof(fake)); 634 fake.pw_name = "NOUSER"; 635 fake.pw_passwd = 636 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 637 fake.pw_gecos = "NOUSER"; 638 fake.pw_uid = (uid_t)-1; 639 fake.pw_gid = (gid_t)-1; 640 fake.pw_class = ""; 641 fake.pw_dir = "/nonexist"; 642 fake.pw_shell = "/nonexist"; 643 644 return (&fake); 645 } 646