1 /* $OpenBSD: auth.c,v 1.103 2013/05/19 02:42:42 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 <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 "servconf.h" 47 #include "key.h" 48 #include "hostfile.h" 49 #include "auth.h" 50 #include "auth-options.h" 51 #include "canohost.h" 52 #include "uidswap.h" 53 #include "misc.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 /* 240 * Check whether root logins are disallowed. 241 */ 242 int 243 auth_root_allowed(const char *method) 244 { 245 switch (options.permit_root_login) { 246 case PERMIT_YES: 247 return 1; 248 case PERMIT_NO_PASSWD: 249 if (strcmp(method, "password") != 0) 250 return 1; 251 break; 252 case PERMIT_FORCED_ONLY: 253 if (forced_command) { 254 logit("Root login accepted for forced command."); 255 return 1; 256 } 257 break; 258 } 259 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 260 return 0; 261 } 262 263 264 /* 265 * Given a template and a passwd structure, build a filename 266 * by substituting % tokenised options. Currently, %% becomes '%', 267 * %h becomes the home directory and %u the username. 268 * 269 * This returns a buffer allocated by xmalloc. 270 */ 271 char * 272 expand_authorized_keys(const char *filename, struct passwd *pw) 273 { 274 char *file, ret[MAXPATHLEN]; 275 int i; 276 277 file = percent_expand(filename, "h", pw->pw_dir, 278 "u", pw->pw_name, (char *)NULL); 279 280 /* 281 * Ensure that filename starts anchored. If not, be backward 282 * compatible and prepend the '%h/' 283 */ 284 if (*file == '/') 285 return (file); 286 287 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 288 if (i < 0 || (size_t)i >= sizeof(ret)) 289 fatal("expand_authorized_keys: path too long"); 290 free(file); 291 return (xstrdup(ret)); 292 } 293 294 char * 295 authorized_principals_file(struct passwd *pw) 296 { 297 if (options.authorized_principals_file == NULL || 298 strcasecmp(options.authorized_principals_file, "none") == 0) 299 return NULL; 300 return expand_authorized_keys(options.authorized_principals_file, pw); 301 } 302 303 /* return ok if key exists in sysfile or userfile */ 304 HostStatus 305 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 306 const char *sysfile, const char *userfile) 307 { 308 char *user_hostfile; 309 struct stat st; 310 HostStatus host_status; 311 struct hostkeys *hostkeys; 312 const struct hostkey_entry *found; 313 314 hostkeys = init_hostkeys(); 315 load_hostkeys(hostkeys, host, sysfile); 316 if (userfile != NULL) { 317 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 318 if (options.strict_modes && 319 (stat(user_hostfile, &st) == 0) && 320 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 321 (st.st_mode & 022) != 0)) { 322 logit("Authentication refused for %.100s: " 323 "bad owner or modes for %.200s", 324 pw->pw_name, user_hostfile); 325 auth_debug_add("Ignored %.200s: bad ownership or modes", 326 user_hostfile); 327 } else { 328 temporarily_use_uid(pw); 329 load_hostkeys(hostkeys, host, user_hostfile); 330 restore_uid(); 331 } 332 free(user_hostfile); 333 } 334 host_status = check_key_in_hostkeys(hostkeys, key, &found); 335 if (host_status == HOST_REVOKED) 336 error("WARNING: revoked key for %s attempted authentication", 337 found->host); 338 else if (host_status == HOST_OK) 339 debug("%s: key for %s found at %s:%ld", __func__, 340 found->host, found->file, found->line); 341 else 342 debug("%s: key for host %s not found", __func__, host); 343 344 free_hostkeys(hostkeys); 345 346 return host_status; 347 } 348 349 /* 350 * Check a given path for security. This is defined as all components 351 * of the path to the file must be owned by either the owner of 352 * of the file or root and no directories must be group or world writable. 353 * 354 * XXX Should any specific check be done for sym links ? 355 * 356 * Takes a file name, its stat information (preferably from fstat() to 357 * avoid races), the uid of the expected owner, their home directory and an 358 * error buffer plus max size as arguments. 359 * 360 * Returns 0 on success and -1 on failure 361 */ 362 int 363 auth_secure_path(const char *name, struct stat *stp, const char *pw_dir, 364 uid_t uid, char *err, size_t errlen) 365 { 366 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 367 char *cp; 368 int comparehome = 0; 369 struct stat st; 370 371 if (realpath(name, buf) == NULL) { 372 snprintf(err, errlen, "realpath %s failed: %s", name, 373 strerror(errno)); 374 return -1; 375 } 376 if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL) 377 comparehome = 1; 378 379 if (!S_ISREG(stp->st_mode)) { 380 snprintf(err, errlen, "%s is not a regular file", buf); 381 return -1; 382 } 383 if ((stp->st_uid != 0 && stp->st_uid != uid) || 384 (stp->st_mode & 022) != 0) { 385 snprintf(err, errlen, "bad ownership or modes for file %s", 386 buf); 387 return -1; 388 } 389 390 /* for each component of the canonical path, walking upwards */ 391 for (;;) { 392 if ((cp = dirname(buf)) == NULL) { 393 snprintf(err, errlen, "dirname() failed"); 394 return -1; 395 } 396 strlcpy(buf, cp, sizeof(buf)); 397 398 if (stat(buf, &st) < 0 || 399 (st.st_uid != 0 && st.st_uid != uid) || 400 (st.st_mode & 022) != 0) { 401 snprintf(err, errlen, 402 "bad ownership or modes for directory %s", buf); 403 return -1; 404 } 405 406 /* If are past the homedir then we can stop */ 407 if (comparehome && strcmp(homedir, buf) == 0) 408 break; 409 410 /* 411 * dirname should always complete with a "/" path, 412 * but we can be paranoid and check for "." too 413 */ 414 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 415 break; 416 } 417 return 0; 418 } 419 420 /* 421 * Version of secure_path() that accepts an open file descriptor to 422 * avoid races. 423 * 424 * Returns 0 on success and -1 on failure 425 */ 426 static int 427 secure_filename(FILE *f, const char *file, struct passwd *pw, 428 char *err, size_t errlen) 429 { 430 struct stat st; 431 432 /* check the open file to avoid races */ 433 if (fstat(fileno(f), &st) < 0) { 434 snprintf(err, errlen, "cannot stat file %s: %s", 435 file, strerror(errno)); 436 return -1; 437 } 438 return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen); 439 } 440 441 static FILE * 442 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 443 int log_missing, char *file_type) 444 { 445 char line[1024]; 446 struct stat st; 447 int fd; 448 FILE *f; 449 450 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 451 if (log_missing || errno != ENOENT) 452 debug("Could not open %s '%s': %s", file_type, file, 453 strerror(errno)); 454 return NULL; 455 } 456 457 if (fstat(fd, &st) < 0) { 458 close(fd); 459 return NULL; 460 } 461 if (!S_ISREG(st.st_mode)) { 462 logit("User %s %s %s is not a regular file", 463 pw->pw_name, file_type, file); 464 close(fd); 465 return NULL; 466 } 467 unset_nonblock(fd); 468 if ((f = fdopen(fd, "r")) == NULL) { 469 close(fd); 470 return NULL; 471 } 472 if (strict_modes && 473 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 474 fclose(f); 475 logit("Authentication refused: %s", line); 476 auth_debug_add("Ignored %s: %s", file_type, line); 477 return NULL; 478 } 479 480 return f; 481 } 482 483 484 FILE * 485 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 486 { 487 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 488 } 489 490 FILE * 491 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 492 { 493 return auth_openfile(file, pw, strict_modes, 0, 494 "authorized principals"); 495 } 496 497 struct passwd * 498 getpwnamallow(const char *user) 499 { 500 extern login_cap_t *lc; 501 auth_session_t *as; 502 struct passwd *pw; 503 struct connection_info *ci = get_connection_info(1, options.use_dns); 504 505 ci->user = user; 506 parse_server_match_config(&options, ci); 507 508 pw = getpwnam(user); 509 if (pw == NULL) { 510 logit("Invalid user %.100s from %.100s", 511 user, get_remote_ipaddr()); 512 return (NULL); 513 } 514 if (!allowed_user(pw)) 515 return (NULL); 516 if ((lc = login_getclass(pw->pw_class)) == NULL) { 517 debug("unable to get login class: %s", user); 518 return (NULL); 519 } 520 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 521 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 522 debug("Approval failure for %s", user); 523 pw = NULL; 524 } 525 if (as != NULL) 526 auth_close(as); 527 if (pw != NULL) 528 return (pwcopy(pw)); 529 return (NULL); 530 } 531 532 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 533 int 534 auth_key_is_revoked(Key *key) 535 { 536 char *key_fp; 537 538 if (options.revoked_keys_file == NULL) 539 return 0; 540 switch (ssh_krl_file_contains_key(options.revoked_keys_file, key)) { 541 case 0: 542 return 0; /* Not revoked */ 543 case -2: 544 break; /* Not a KRL */ 545 default: 546 goto revoked; 547 } 548 debug3("%s: treating %s as a key list", __func__, 549 options.revoked_keys_file); 550 switch (key_in_file(key, options.revoked_keys_file, 0)) { 551 case 0: 552 /* key not revoked */ 553 return 0; 554 case -1: 555 /* Error opening revoked_keys_file: refuse all keys */ 556 error("Revoked keys file is unreadable: refusing public key " 557 "authentication"); 558 return 1; 559 case 1: 560 revoked: 561 /* Key revoked */ 562 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 563 error("WARNING: authentication attempt with a revoked " 564 "%s key %s ", key_type(key), key_fp); 565 free(key_fp); 566 return 1; 567 } 568 fatal("key_in_file returned junk"); 569 } 570 571 void 572 auth_debug_add(const char *fmt,...) 573 { 574 char buf[1024]; 575 va_list args; 576 577 if (!auth_debug_init) 578 return; 579 580 va_start(args, fmt); 581 vsnprintf(buf, sizeof(buf), fmt, args); 582 va_end(args); 583 buffer_put_cstring(&auth_debug, buf); 584 } 585 586 void 587 auth_debug_send(void) 588 { 589 char *msg; 590 591 if (!auth_debug_init) 592 return; 593 while (buffer_len(&auth_debug)) { 594 msg = buffer_get_string(&auth_debug, NULL); 595 packet_send_debug("%s", msg); 596 free(msg); 597 } 598 } 599 600 void 601 auth_debug_reset(void) 602 { 603 if (auth_debug_init) 604 buffer_clear(&auth_debug); 605 else { 606 buffer_init(&auth_debug); 607 auth_debug_init = 1; 608 } 609 } 610 611 struct passwd * 612 fakepw(void) 613 { 614 static struct passwd fake; 615 616 memset(&fake, 0, sizeof(fake)); 617 fake.pw_name = "NOUSER"; 618 fake.pw_passwd = 619 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 620 fake.pw_gecos = "NOUSER"; 621 fake.pw_uid = (uid_t)-1; 622 fake.pw_gid = (gid_t)-1; 623 fake.pw_class = ""; 624 fake.pw_dir = "/nonexist"; 625 fake.pw_shell = "/nonexist"; 626 627 return (&fake); 628 } 629