1 /* $OpenBSD: auth.c,v 1.96 2012/05/13 01:42:32 dtucker 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 61 /* import */ 62 extern ServerOptions options; 63 extern int use_privsep; 64 65 /* Debugging messages */ 66 Buffer auth_debug; 67 int auth_debug_init; 68 69 /* 70 * Check if the user is allowed to log in via ssh. If user is listed 71 * in DenyUsers or one of user's groups is listed in DenyGroups, false 72 * will be returned. If AllowUsers isn't empty and user isn't listed 73 * there, or if AllowGroups isn't empty and one of user's groups isn't 74 * listed there, false will be returned. 75 * If the user's shell is not executable, false will be returned. 76 * Otherwise true is returned. 77 */ 78 int 79 allowed_user(struct passwd * pw) 80 { 81 struct stat st; 82 const char *hostname = NULL, *ipaddr = NULL; 83 u_int i; 84 85 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 86 if (!pw || !pw->pw_name) 87 return 0; 88 89 /* 90 * Deny if shell does not exist or is not executable unless we 91 * are chrooting. 92 */ 93 if (options.chroot_directory == NULL || 94 strcasecmp(options.chroot_directory, "none") == 0) { 95 char *shell = xstrdup((pw->pw_shell[0] == '\0') ? 96 _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ 97 98 if (stat(shell, &st) != 0) { 99 logit("User %.100s not allowed because shell %.100s " 100 "does not exist", pw->pw_name, shell); 101 xfree(shell); 102 return 0; 103 } 104 if (S_ISREG(st.st_mode) == 0 || 105 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 106 logit("User %.100s not allowed because shell %.100s " 107 "is not executable", pw->pw_name, shell); 108 xfree(shell); 109 return 0; 110 } 111 xfree(shell); 112 } 113 114 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 115 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 116 hostname = get_canonical_hostname(options.use_dns); 117 ipaddr = get_remote_ipaddr(); 118 } 119 120 /* Return false if user is listed in DenyUsers */ 121 if (options.num_deny_users > 0) { 122 for (i = 0; i < options.num_deny_users; i++) 123 if (match_user(pw->pw_name, hostname, ipaddr, 124 options.deny_users[i])) { 125 logit("User %.100s from %.100s not allowed " 126 "because listed in DenyUsers", 127 pw->pw_name, hostname); 128 return 0; 129 } 130 } 131 /* Return false if AllowUsers isn't empty and user isn't listed there */ 132 if (options.num_allow_users > 0) { 133 for (i = 0; i < options.num_allow_users; i++) 134 if (match_user(pw->pw_name, hostname, ipaddr, 135 options.allow_users[i])) 136 break; 137 /* i < options.num_allow_users iff we break for loop */ 138 if (i >= options.num_allow_users) { 139 logit("User %.100s from %.100s not allowed because " 140 "not listed in AllowUsers", pw->pw_name, hostname); 141 return 0; 142 } 143 } 144 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 145 /* Get the user's group access list (primary and supplementary) */ 146 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 147 logit("User %.100s from %.100s not allowed because " 148 "not in any group", pw->pw_name, hostname); 149 return 0; 150 } 151 152 /* Return false if one of user's groups is listed in DenyGroups */ 153 if (options.num_deny_groups > 0) 154 if (ga_match(options.deny_groups, 155 options.num_deny_groups)) { 156 ga_free(); 157 logit("User %.100s from %.100s not allowed " 158 "because a group is listed in DenyGroups", 159 pw->pw_name, hostname); 160 return 0; 161 } 162 /* 163 * Return false if AllowGroups isn't empty and one of user's groups 164 * isn't listed there 165 */ 166 if (options.num_allow_groups > 0) 167 if (!ga_match(options.allow_groups, 168 options.num_allow_groups)) { 169 ga_free(); 170 logit("User %.100s from %.100s not allowed " 171 "because none of user's groups are listed " 172 "in AllowGroups", pw->pw_name, hostname); 173 return 0; 174 } 175 ga_free(); 176 } 177 /* We found no reason not to let this user try to log on... */ 178 return 1; 179 } 180 181 void 182 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 183 { 184 void (*authlog) (const char *fmt,...) = verbose; 185 char *authmsg; 186 187 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 188 return; 189 190 /* Raise logging level */ 191 if (authenticated == 1 || 192 !authctxt->valid || 193 authctxt->failures >= options.max_authtries / 2 || 194 strcmp(method, "password") == 0) 195 authlog = logit; 196 197 if (authctxt->postponed) 198 authmsg = "Postponed"; 199 else 200 authmsg = authenticated ? "Accepted" : "Failed"; 201 202 authlog("%s %s for %s%.100s from %.200s port %d%s", 203 authmsg, 204 method, 205 authctxt->valid ? "" : "invalid user ", 206 authctxt->user, 207 get_remote_ipaddr(), 208 get_remote_port(), 209 info); 210 } 211 212 /* 213 * Check whether root logins are disallowed. 214 */ 215 int 216 auth_root_allowed(char *method) 217 { 218 switch (options.permit_root_login) { 219 case PERMIT_YES: 220 return 1; 221 case PERMIT_NO_PASSWD: 222 if (strcmp(method, "password") != 0) 223 return 1; 224 break; 225 case PERMIT_FORCED_ONLY: 226 if (forced_command) { 227 logit("Root login accepted for forced command."); 228 return 1; 229 } 230 break; 231 } 232 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 233 return 0; 234 } 235 236 237 /* 238 * Given a template and a passwd structure, build a filename 239 * by substituting % tokenised options. Currently, %% becomes '%', 240 * %h becomes the home directory and %u the username. 241 * 242 * This returns a buffer allocated by xmalloc. 243 */ 244 char * 245 expand_authorized_keys(const char *filename, struct passwd *pw) 246 { 247 char *file, ret[MAXPATHLEN]; 248 int i; 249 250 file = percent_expand(filename, "h", pw->pw_dir, 251 "u", pw->pw_name, (char *)NULL); 252 253 /* 254 * Ensure that filename starts anchored. If not, be backward 255 * compatible and prepend the '%h/' 256 */ 257 if (*file == '/') 258 return (file); 259 260 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 261 if (i < 0 || (size_t)i >= sizeof(ret)) 262 fatal("expand_authorized_keys: path too long"); 263 xfree(file); 264 return (xstrdup(ret)); 265 } 266 267 char * 268 authorized_principals_file(struct passwd *pw) 269 { 270 if (options.authorized_principals_file == NULL || 271 strcasecmp(options.authorized_principals_file, "none") == 0) 272 return NULL; 273 return expand_authorized_keys(options.authorized_principals_file, pw); 274 } 275 276 /* return ok if key exists in sysfile or userfile */ 277 HostStatus 278 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 279 const char *sysfile, const char *userfile) 280 { 281 char *user_hostfile; 282 struct stat st; 283 HostStatus host_status; 284 struct hostkeys *hostkeys; 285 const struct hostkey_entry *found; 286 287 hostkeys = init_hostkeys(); 288 load_hostkeys(hostkeys, host, sysfile); 289 if (userfile != NULL) { 290 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 291 if (options.strict_modes && 292 (stat(user_hostfile, &st) == 0) && 293 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 294 (st.st_mode & 022) != 0)) { 295 logit("Authentication refused for %.100s: " 296 "bad owner or modes for %.200s", 297 pw->pw_name, user_hostfile); 298 auth_debug_add("Ignored %.200s: bad ownership or modes", 299 user_hostfile); 300 } else { 301 temporarily_use_uid(pw); 302 load_hostkeys(hostkeys, host, user_hostfile); 303 restore_uid(); 304 } 305 xfree(user_hostfile); 306 } 307 host_status = check_key_in_hostkeys(hostkeys, key, &found); 308 if (host_status == HOST_REVOKED) 309 error("WARNING: revoked key for %s attempted authentication", 310 found->host); 311 else if (host_status == HOST_OK) 312 debug("%s: key for %s found at %s:%ld", __func__, 313 found->host, found->file, found->line); 314 else 315 debug("%s: key for host %s not found", __func__, host); 316 317 free_hostkeys(hostkeys); 318 319 return host_status; 320 } 321 322 323 /* 324 * Check a given file for security. This is defined as all components 325 * of the path to the file must be owned by either the owner of 326 * of the file or root and no directories must be group or world writable. 327 * 328 * XXX Should any specific check be done for sym links ? 329 * 330 * Takes an open file descriptor, the file name, a uid and and 331 * error buffer plus max size as arguments. 332 * 333 * Returns 0 on success and -1 on failure 334 */ 335 static int 336 secure_filename(FILE *f, const char *file, struct passwd *pw, 337 char *err, size_t errlen) 338 { 339 uid_t uid = pw->pw_uid; 340 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 341 char *cp; 342 int comparehome = 0; 343 struct stat st; 344 345 if (realpath(file, buf) == NULL) { 346 snprintf(err, errlen, "realpath %s failed: %s", file, 347 strerror(errno)); 348 return -1; 349 } 350 if (realpath(pw->pw_dir, homedir) != NULL) 351 comparehome = 1; 352 353 /* check the open file to avoid races */ 354 if (fstat(fileno(f), &st) < 0 || 355 (st.st_uid != 0 && st.st_uid != uid) || 356 (st.st_mode & 022) != 0) { 357 snprintf(err, errlen, "bad ownership or modes for file %s", 358 buf); 359 return -1; 360 } 361 362 /* for each component of the canonical path, walking upwards */ 363 for (;;) { 364 if ((cp = dirname(buf)) == NULL) { 365 snprintf(err, errlen, "dirname() failed"); 366 return -1; 367 } 368 strlcpy(buf, cp, sizeof(buf)); 369 370 if (stat(buf, &st) < 0 || 371 (st.st_uid != 0 && st.st_uid != uid) || 372 (st.st_mode & 022) != 0) { 373 snprintf(err, errlen, 374 "bad ownership or modes for directory %s", buf); 375 return -1; 376 } 377 378 /* If are past the homedir then we can stop */ 379 if (comparehome && strcmp(homedir, buf) == 0) 380 break; 381 382 /* 383 * dirname should always complete with a "/" path, 384 * but we can be paranoid and check for "." too 385 */ 386 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 387 break; 388 } 389 return 0; 390 } 391 392 static FILE * 393 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 394 int log_missing, char *file_type) 395 { 396 char line[1024]; 397 struct stat st; 398 int fd; 399 FILE *f; 400 401 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 402 if (log_missing || errno != ENOENT) 403 debug("Could not open %s '%s': %s", file_type, file, 404 strerror(errno)); 405 return NULL; 406 } 407 408 if (fstat(fd, &st) < 0) { 409 close(fd); 410 return NULL; 411 } 412 if (!S_ISREG(st.st_mode)) { 413 logit("User %s %s %s is not a regular file", 414 pw->pw_name, file_type, file); 415 close(fd); 416 return NULL; 417 } 418 unset_nonblock(fd); 419 if ((f = fdopen(fd, "r")) == NULL) { 420 close(fd); 421 return NULL; 422 } 423 if (strict_modes && 424 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 425 fclose(f); 426 logit("Authentication refused: %s", line); 427 auth_debug_add("Ignored %s: %s", file_type, line); 428 return NULL; 429 } 430 431 return f; 432 } 433 434 435 FILE * 436 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 437 { 438 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 439 } 440 441 FILE * 442 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 443 { 444 return auth_openfile(file, pw, strict_modes, 0, 445 "authorized principals"); 446 } 447 448 struct passwd * 449 getpwnamallow(const char *user) 450 { 451 extern login_cap_t *lc; 452 auth_session_t *as; 453 struct passwd *pw; 454 struct connection_info *ci = get_connection_info(1, options.use_dns); 455 456 ci->user = user; 457 parse_server_match_config(&options, ci); 458 459 pw = getpwnam(user); 460 if (pw == NULL) { 461 logit("Invalid user %.100s from %.100s", 462 user, get_remote_ipaddr()); 463 return (NULL); 464 } 465 if (!allowed_user(pw)) 466 return (NULL); 467 if ((lc = login_getclass(pw->pw_class)) == NULL) { 468 debug("unable to get login class: %s", user); 469 return (NULL); 470 } 471 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 472 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 473 debug("Approval failure for %s", user); 474 pw = NULL; 475 } 476 if (as != NULL) 477 auth_close(as); 478 if (pw != NULL) 479 return (pwcopy(pw)); 480 return (NULL); 481 } 482 483 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 484 int 485 auth_key_is_revoked(Key *key) 486 { 487 char *key_fp; 488 489 if (options.revoked_keys_file == NULL) 490 return 0; 491 492 switch (key_in_file(key, options.revoked_keys_file, 0)) { 493 case 0: 494 /* key not revoked */ 495 return 0; 496 case -1: 497 /* Error opening revoked_keys_file: refuse all keys */ 498 error("Revoked keys file is unreadable: refusing public key " 499 "authentication"); 500 return 1; 501 case 1: 502 /* Key revoked */ 503 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 504 error("WARNING: authentication attempt with a revoked " 505 "%s key %s ", key_type(key), key_fp); 506 xfree(key_fp); 507 return 1; 508 } 509 fatal("key_in_file returned junk"); 510 } 511 512 void 513 auth_debug_add(const char *fmt,...) 514 { 515 char buf[1024]; 516 va_list args; 517 518 if (!auth_debug_init) 519 return; 520 521 va_start(args, fmt); 522 vsnprintf(buf, sizeof(buf), fmt, args); 523 va_end(args); 524 buffer_put_cstring(&auth_debug, buf); 525 } 526 527 void 528 auth_debug_send(void) 529 { 530 char *msg; 531 532 if (!auth_debug_init) 533 return; 534 while (buffer_len(&auth_debug)) { 535 msg = buffer_get_string(&auth_debug, NULL); 536 packet_send_debug("%s", msg); 537 xfree(msg); 538 } 539 } 540 541 void 542 auth_debug_reset(void) 543 { 544 if (auth_debug_init) 545 buffer_clear(&auth_debug); 546 else { 547 buffer_init(&auth_debug); 548 auth_debug_init = 1; 549 } 550 } 551 552 struct passwd * 553 fakepw(void) 554 { 555 static struct passwd fake; 556 557 memset(&fake, 0, sizeof(fake)); 558 fake.pw_name = "NOUSER"; 559 fake.pw_passwd = 560 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 561 fake.pw_gecos = "NOUSER"; 562 fake.pw_uid = (uid_t)-1; 563 fake.pw_gid = (gid_t)-1; 564 fake.pw_class = ""; 565 fake.pw_dir = "/nonexist"; 566 fake.pw_shell = "/nonexist"; 567 568 return (&fake); 569 } 570