1 /* $OpenBSD: auth.c,v 1.87 2010/05/07 11:30:29 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 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 static 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_keys_file(struct passwd *pw) 269 { 270 return expand_authorized_keys(options.authorized_keys_file, pw); 271 } 272 273 char * 274 authorized_keys_file2(struct passwd *pw) 275 { 276 return expand_authorized_keys(options.authorized_keys_file2, pw); 277 } 278 279 char * 280 authorized_principals_file(struct passwd *pw) 281 { 282 if (options.authorized_principals_file == NULL) 283 return NULL; 284 return expand_authorized_keys(options.authorized_principals_file, pw); 285 } 286 287 /* return ok if key exists in sysfile or userfile */ 288 HostStatus 289 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 290 const char *sysfile, const char *userfile) 291 { 292 Key *found; 293 char *user_hostfile; 294 struct stat st; 295 HostStatus host_status; 296 297 /* Check if we know the host and its host key. */ 298 found = key_new(key->type); 299 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 300 301 if (host_status != HOST_OK && userfile != NULL) { 302 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 303 if (options.strict_modes && 304 (stat(user_hostfile, &st) == 0) && 305 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 306 (st.st_mode & 022) != 0)) { 307 logit("Authentication refused for %.100s: " 308 "bad owner or modes for %.200s", 309 pw->pw_name, user_hostfile); 310 } else { 311 temporarily_use_uid(pw); 312 host_status = check_host_in_hostfile(user_hostfile, 313 host, key, found, NULL); 314 restore_uid(); 315 } 316 xfree(user_hostfile); 317 } 318 key_free(found); 319 320 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 321 "ok" : "not found", host); 322 return host_status; 323 } 324 325 326 /* 327 * Check a given file for security. This is defined as all components 328 * of the path to the file must be owned by either the owner of 329 * of the file or root and no directories must be group or world writable. 330 * 331 * XXX Should any specific check be done for sym links ? 332 * 333 * Takes an open file descriptor, the file name, a uid and and 334 * error buffer plus max size as arguments. 335 * 336 * Returns 0 on success and -1 on failure 337 */ 338 static int 339 secure_filename(FILE *f, const char *file, struct passwd *pw, 340 char *err, size_t errlen) 341 { 342 uid_t uid = pw->pw_uid; 343 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 344 char *cp; 345 int comparehome = 0; 346 struct stat st; 347 348 if (realpath(file, buf) == NULL) { 349 snprintf(err, errlen, "realpath %s failed: %s", file, 350 strerror(errno)); 351 return -1; 352 } 353 if (realpath(pw->pw_dir, homedir) != NULL) 354 comparehome = 1; 355 356 /* check the open file to avoid races */ 357 if (fstat(fileno(f), &st) < 0 || 358 (st.st_uid != 0 && st.st_uid != uid) || 359 (st.st_mode & 022) != 0) { 360 snprintf(err, errlen, "bad ownership or modes for file %s", 361 buf); 362 return -1; 363 } 364 365 /* for each component of the canonical path, walking upwards */ 366 for (;;) { 367 if ((cp = dirname(buf)) == NULL) { 368 snprintf(err, errlen, "dirname() failed"); 369 return -1; 370 } 371 strlcpy(buf, cp, sizeof(buf)); 372 373 debug3("secure_filename: checking '%s'", buf); 374 if (stat(buf, &st) < 0 || 375 (st.st_uid != 0 && st.st_uid != uid) || 376 (st.st_mode & 022) != 0) { 377 snprintf(err, errlen, 378 "bad ownership or modes for directory %s", buf); 379 return -1; 380 } 381 382 /* If are past the homedir then we can stop */ 383 if (comparehome && strcmp(homedir, buf) == 0) { 384 debug3("secure_filename: terminating check at '%s'", 385 buf); 386 break; 387 } 388 /* 389 * dirname should always complete with a "/" path, 390 * but we can be paranoid and check for "." too 391 */ 392 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 393 break; 394 } 395 return 0; 396 } 397 398 static FILE * 399 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 400 int log_missing, char *file_type) 401 { 402 char line[1024]; 403 struct stat st; 404 int fd; 405 FILE *f; 406 407 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 408 if (log_missing || errno != ENOENT) 409 debug("Could not open %s '%s': %s", file_type, file, 410 strerror(errno)); 411 return NULL; 412 } 413 414 if (fstat(fd, &st) < 0) { 415 close(fd); 416 return NULL; 417 } 418 if (!S_ISREG(st.st_mode)) { 419 logit("User %s %s %s is not a regular file", 420 pw->pw_name, file_type, file); 421 close(fd); 422 return NULL; 423 } 424 unset_nonblock(fd); 425 if ((f = fdopen(fd, "r")) == NULL) { 426 close(fd); 427 return NULL; 428 } 429 if (options.strict_modes && 430 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 431 fclose(f); 432 logit("Authentication refused: %s", line); 433 return NULL; 434 } 435 436 return f; 437 } 438 439 440 FILE * 441 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 442 { 443 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 444 } 445 446 FILE * 447 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 448 { 449 return auth_openfile(file, pw, strict_modes, 0, 450 "authorized principals"); 451 } 452 453 struct passwd * 454 getpwnamallow(const char *user) 455 { 456 extern login_cap_t *lc; 457 auth_session_t *as; 458 struct passwd *pw; 459 460 parse_server_match_config(&options, user, 461 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 462 463 pw = getpwnam(user); 464 if (pw == NULL) { 465 logit("Invalid user %.100s from %.100s", 466 user, get_remote_ipaddr()); 467 return (NULL); 468 } 469 if (!allowed_user(pw)) 470 return (NULL); 471 if ((lc = login_getclass(pw->pw_class)) == NULL) { 472 debug("unable to get login class: %s", user); 473 return (NULL); 474 } 475 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 476 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 477 debug("Approval failure for %s", user); 478 pw = NULL; 479 } 480 if (as != NULL) 481 auth_close(as); 482 if (pw != NULL) 483 return (pwcopy(pw)); 484 return (NULL); 485 } 486 487 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 488 int 489 auth_key_is_revoked(Key *key) 490 { 491 char *key_fp; 492 493 if (options.revoked_keys_file == NULL) 494 return 0; 495 496 switch (key_in_file(key, options.revoked_keys_file, 0)) { 497 case 0: 498 /* key not revoked */ 499 return 0; 500 case -1: 501 /* Error opening revoked_keys_file: refuse all keys */ 502 error("Revoked keys file is unreadable: refusing public key " 503 "authentication"); 504 return 1; 505 case 1: 506 /* Key revoked */ 507 key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 508 error("WARNING: authentication attempt with a revoked " 509 "%s key %s ", key_type(key), key_fp); 510 xfree(key_fp); 511 return 1; 512 } 513 fatal("key_in_file returned junk"); 514 } 515 516 void 517 auth_debug_add(const char *fmt,...) 518 { 519 char buf[1024]; 520 va_list args; 521 522 if (!auth_debug_init) 523 return; 524 525 va_start(args, fmt); 526 vsnprintf(buf, sizeof(buf), fmt, args); 527 va_end(args); 528 buffer_put_cstring(&auth_debug, buf); 529 } 530 531 void 532 auth_debug_send(void) 533 { 534 char *msg; 535 536 if (!auth_debug_init) 537 return; 538 while (buffer_len(&auth_debug)) { 539 msg = buffer_get_string(&auth_debug, NULL); 540 packet_send_debug("%s", msg); 541 xfree(msg); 542 } 543 } 544 545 void 546 auth_debug_reset(void) 547 { 548 if (auth_debug_init) 549 buffer_clear(&auth_debug); 550 else { 551 buffer_init(&auth_debug); 552 auth_debug_init = 1; 553 } 554 } 555 556 struct passwd * 557 fakepw(void) 558 { 559 static struct passwd fake; 560 561 memset(&fake, 0, sizeof(fake)); 562 fake.pw_name = "NOUSER"; 563 fake.pw_passwd = 564 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 565 fake.pw_gecos = "NOUSER"; 566 fake.pw_uid = (uid_t)-1; 567 fake.pw_gid = (gid_t)-1; 568 fake.pw_class = ""; 569 fake.pw_dir = "/nonexist"; 570 fake.pw_shell = "/nonexist"; 571 572 return (&fake); 573 } 574