1 /* $OpenBSD: auth.c,v 1.75 2006/08/03 03:34:41 deraadt 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 #ifdef HAVE_PATHS_H 37 # include <paths.h> 38 #endif 39 #include <pwd.h> 40 #ifdef HAVE_LOGIN_H 41 #include <login.h> 42 #endif 43 #ifdef USE_SHADOW 44 #include <shadow.h> 45 #endif 46 #ifdef HAVE_LIBGEN_H 47 #include <libgen.h> 48 #endif 49 #include <stdarg.h> 50 #include <stdio.h> 51 #include <string.h> 52 53 #include "xmalloc.h" 54 #include "match.h" 55 #include "groupaccess.h" 56 #include "log.h" 57 #include "buffer.h" 58 #include "servconf.h" 59 #include "key.h" 60 #include "hostfile.h" 61 #include "auth.h" 62 #include "auth-options.h" 63 #include "canohost.h" 64 #include "uidswap.h" 65 #include "misc.h" 66 #include "packet.h" 67 #include "loginrec.h" 68 #ifdef GSSAPI 69 #include "ssh-gss.h" 70 #endif 71 #include "monitor_wrap.h" 72 73 /* import */ 74 extern ServerOptions options; 75 extern int use_privsep; 76 extern Buffer loginmsg; 77 extern struct passwd *privsep_pw; 78 79 /* Debugging messages */ 80 Buffer auth_debug; 81 int auth_debug_init; 82 83 /* 84 * Check if the user is allowed to log in via ssh. If user is listed 85 * in DenyUsers or one of user's groups is listed in DenyGroups, false 86 * will be returned. If AllowUsers isn't empty and user isn't listed 87 * there, or if AllowGroups isn't empty and one of user's groups isn't 88 * listed there, false will be returned. 89 * If the user's shell is not executable, false will be returned. 90 * Otherwise true is returned. 91 */ 92 int 93 allowed_user(struct passwd * pw) 94 { 95 struct stat st; 96 const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL; 97 char *shell; 98 u_int i; 99 #ifdef USE_SHADOW 100 struct spwd *spw = NULL; 101 #endif 102 103 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 104 if (!pw || !pw->pw_name) 105 return 0; 106 107 #ifdef USE_SHADOW 108 if (!options.use_pam) 109 spw = getspnam(pw->pw_name); 110 #ifdef HAS_SHADOW_EXPIRE 111 if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw)) 112 return 0; 113 #endif /* HAS_SHADOW_EXPIRE */ 114 #endif /* USE_SHADOW */ 115 116 /* grab passwd field for locked account check */ 117 #ifdef USE_SHADOW 118 if (spw != NULL) 119 #if defined(HAVE_LIBIAF) && !defined(BROKEN_LIBIAF) 120 passwd = get_iaf_password(pw); 121 #else 122 passwd = spw->sp_pwdp; 123 #endif /* HAVE_LIBIAF && !BROKEN_LIBIAF */ 124 #else 125 passwd = pw->pw_passwd; 126 #endif 127 128 /* check for locked account */ 129 if (!options.use_pam && passwd && *passwd) { 130 int locked = 0; 131 132 #ifdef LOCKED_PASSWD_STRING 133 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0) 134 locked = 1; 135 #endif 136 #ifdef LOCKED_PASSWD_PREFIX 137 if (strncmp(passwd, LOCKED_PASSWD_PREFIX, 138 strlen(LOCKED_PASSWD_PREFIX)) == 0) 139 locked = 1; 140 #endif 141 #ifdef LOCKED_PASSWD_SUBSTR 142 if (strstr(passwd, LOCKED_PASSWD_SUBSTR)) 143 locked = 1; 144 #endif 145 #if defined(HAVE_LIBIAF) && !defined(BROKEN_LIBIAF) 146 free(passwd); 147 #endif /* HAVE_LIBIAF && !BROKEN_LIBIAF */ 148 if (locked) { 149 logit("User %.100s not allowed because account is locked", 150 pw->pw_name); 151 return 0; 152 } 153 } 154 155 /* 156 * Get the shell from the password data. An empty shell field is 157 * legal, and means /bin/sh. 158 */ 159 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 160 161 /* deny if shell does not exists or is not executable */ 162 if (stat(shell, &st) != 0) { 163 logit("User %.100s not allowed because shell %.100s does not exist", 164 pw->pw_name, shell); 165 return 0; 166 } 167 if (S_ISREG(st.st_mode) == 0 || 168 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 169 logit("User %.100s not allowed because shell %.100s is not executable", 170 pw->pw_name, shell); 171 return 0; 172 } 173 174 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 175 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 176 hostname = get_canonical_hostname(options.use_dns); 177 ipaddr = get_remote_ipaddr(); 178 } 179 180 /* Return false if user is listed in DenyUsers */ 181 if (options.num_deny_users > 0) { 182 for (i = 0; i < options.num_deny_users; i++) 183 if (match_user(pw->pw_name, hostname, ipaddr, 184 options.deny_users[i])) { 185 logit("User %.100s from %.100s not allowed " 186 "because listed in DenyUsers", 187 pw->pw_name, hostname); 188 return 0; 189 } 190 } 191 /* Return false if AllowUsers isn't empty and user isn't listed there */ 192 if (options.num_allow_users > 0) { 193 for (i = 0; i < options.num_allow_users; i++) 194 if (match_user(pw->pw_name, hostname, ipaddr, 195 options.allow_users[i])) 196 break; 197 /* i < options.num_allow_users iff we break for loop */ 198 if (i >= options.num_allow_users) { 199 logit("User %.100s from %.100s not allowed because " 200 "not listed in AllowUsers", pw->pw_name, hostname); 201 return 0; 202 } 203 } 204 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 205 /* Get the user's group access list (primary and supplementary) */ 206 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 207 logit("User %.100s from %.100s not allowed because " 208 "not in any group", pw->pw_name, hostname); 209 return 0; 210 } 211 212 /* Return false if one of user's groups is listed in DenyGroups */ 213 if (options.num_deny_groups > 0) 214 if (ga_match(options.deny_groups, 215 options.num_deny_groups)) { 216 ga_free(); 217 logit("User %.100s from %.100s not allowed " 218 "because a group is listed in DenyGroups", 219 pw->pw_name, hostname); 220 return 0; 221 } 222 /* 223 * Return false if AllowGroups isn't empty and one of user's groups 224 * isn't listed there 225 */ 226 if (options.num_allow_groups > 0) 227 if (!ga_match(options.allow_groups, 228 options.num_allow_groups)) { 229 ga_free(); 230 logit("User %.100s from %.100s not allowed " 231 "because none of user's groups are listed " 232 "in AllowGroups", pw->pw_name, hostname); 233 return 0; 234 } 235 ga_free(); 236 } 237 238 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER 239 if (!sys_auth_allowed_user(pw, &loginmsg)) 240 return 0; 241 #endif 242 243 /* We found no reason not to let this user try to log on... */ 244 return 1; 245 } 246 247 void 248 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 249 { 250 void (*authlog) (const char *fmt,...) = verbose; 251 char *authmsg; 252 253 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 254 return; 255 256 /* Raise logging level */ 257 if (authenticated == 1 || 258 !authctxt->valid || 259 authctxt->failures >= options.max_authtries / 2 || 260 strcmp(method, "password") == 0) 261 authlog = logit; 262 263 if (authctxt->postponed) 264 authmsg = "Postponed"; 265 else 266 authmsg = authenticated ? "Accepted" : "Failed"; 267 268 authlog("%s %s for %s%.100s from %.200s port %d%s", 269 authmsg, 270 method, 271 authctxt->valid ? "" : "invalid user ", 272 authctxt->user, 273 get_remote_ipaddr(), 274 get_remote_port(), 275 info); 276 277 #ifdef CUSTOM_FAILED_LOGIN 278 if (authenticated == 0 && !authctxt->postponed && 279 (strcmp(method, "password") == 0 || 280 strncmp(method, "keyboard-interactive", 20) == 0 || 281 strcmp(method, "challenge-response") == 0)) 282 record_failed_login(authctxt->user, 283 get_canonical_hostname(options.use_dns), "ssh"); 284 # ifdef WITH_AIXAUTHENTICATE 285 if (authenticated) 286 sys_auth_record_login(authctxt->user, 287 get_canonical_hostname(options.use_dns), "ssh", &loginmsg); 288 # endif 289 #endif 290 #ifdef SSH_AUDIT_EVENTS 291 if (authenticated == 0 && !authctxt->postponed) 292 audit_event(audit_classify_auth(method)); 293 #endif 294 } 295 296 /* 297 * Check whether root logins are disallowed. 298 */ 299 int 300 auth_root_allowed(char *method) 301 { 302 switch (options.permit_root_login) { 303 case PERMIT_YES: 304 return 1; 305 case PERMIT_NO_PASSWD: 306 if (strcmp(method, "password") != 0) 307 return 1; 308 break; 309 case PERMIT_FORCED_ONLY: 310 if (forced_command) { 311 logit("Root login accepted for forced command."); 312 return 1; 313 } 314 break; 315 } 316 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 317 return 0; 318 } 319 320 321 /* 322 * Given a template and a passwd structure, build a filename 323 * by substituting % tokenised options. Currently, %% becomes '%', 324 * %h becomes the home directory and %u the username. 325 * 326 * This returns a buffer allocated by xmalloc. 327 */ 328 static char * 329 expand_authorized_keys(const char *filename, struct passwd *pw) 330 { 331 char *file, ret[MAXPATHLEN]; 332 int i; 333 334 file = percent_expand(filename, "h", pw->pw_dir, 335 "u", pw->pw_name, (char *)NULL); 336 337 /* 338 * Ensure that filename starts anchored. If not, be backward 339 * compatible and prepend the '%h/' 340 */ 341 if (*file == '/') 342 return (file); 343 344 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 345 if (i < 0 || (size_t)i >= sizeof(ret)) 346 fatal("expand_authorized_keys: path too long"); 347 xfree(file); 348 return (xstrdup(ret)); 349 } 350 351 char * 352 authorized_keys_file(struct passwd *pw) 353 { 354 return expand_authorized_keys(options.authorized_keys_file, pw); 355 } 356 357 char * 358 authorized_keys_file2(struct passwd *pw) 359 { 360 return expand_authorized_keys(options.authorized_keys_file2, pw); 361 } 362 363 /* return ok if key exists in sysfile or userfile */ 364 HostStatus 365 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 366 const char *sysfile, const char *userfile) 367 { 368 Key *found; 369 char *user_hostfile; 370 struct stat st; 371 HostStatus host_status; 372 373 /* Check if we know the host and its host key. */ 374 found = key_new(key->type); 375 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 376 377 if (host_status != HOST_OK && userfile != NULL) { 378 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 379 if (options.strict_modes && 380 (stat(user_hostfile, &st) == 0) && 381 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 382 (st.st_mode & 022) != 0)) { 383 logit("Authentication refused for %.100s: " 384 "bad owner or modes for %.200s", 385 pw->pw_name, user_hostfile); 386 } else { 387 temporarily_use_uid(pw); 388 host_status = check_host_in_hostfile(user_hostfile, 389 host, key, found, NULL); 390 restore_uid(); 391 } 392 xfree(user_hostfile); 393 } 394 key_free(found); 395 396 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 397 "ok" : "not found", host); 398 return host_status; 399 } 400 401 402 /* 403 * Check a given file for security. This is defined as all components 404 * of the path to the file must be owned by either the owner of 405 * of the file or root and no directories must be group or world writable. 406 * 407 * XXX Should any specific check be done for sym links ? 408 * 409 * Takes an open file descriptor, the file name, a uid and and 410 * error buffer plus max size as arguments. 411 * 412 * Returns 0 on success and -1 on failure 413 */ 414 int 415 secure_filename(FILE *f, const char *file, struct passwd *pw, 416 char *err, size_t errlen) 417 { 418 uid_t uid = pw->pw_uid; 419 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 420 char *cp; 421 int comparehome = 0; 422 struct stat st; 423 424 if (realpath(file, buf) == NULL) { 425 snprintf(err, errlen, "realpath %s failed: %s", file, 426 strerror(errno)); 427 return -1; 428 } 429 if (realpath(pw->pw_dir, homedir) != NULL) 430 comparehome = 1; 431 432 /* check the open file to avoid races */ 433 if (fstat(fileno(f), &st) < 0 || 434 (st.st_uid != 0 && st.st_uid != uid) || 435 (st.st_mode & 022) != 0) { 436 snprintf(err, errlen, "bad ownership or modes for file %s", 437 buf); 438 return -1; 439 } 440 441 /* for each component of the canonical path, walking upwards */ 442 for (;;) { 443 if ((cp = dirname(buf)) == NULL) { 444 snprintf(err, errlen, "dirname() failed"); 445 return -1; 446 } 447 strlcpy(buf, cp, sizeof(buf)); 448 449 debug3("secure_filename: checking '%s'", buf); 450 if (stat(buf, &st) < 0 || 451 (st.st_uid != 0 && st.st_uid != uid) || 452 (st.st_mode & 022) != 0) { 453 snprintf(err, errlen, 454 "bad ownership or modes for directory %s", buf); 455 return -1; 456 } 457 458 /* If are passed the homedir then we can stop */ 459 if (comparehome && strcmp(homedir, buf) == 0) { 460 debug3("secure_filename: terminating check at '%s'", 461 buf); 462 break; 463 } 464 /* 465 * dirname should always complete with a "/" path, 466 * but we can be paranoid and check for "." too 467 */ 468 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 469 break; 470 } 471 return 0; 472 } 473 474 struct passwd * 475 getpwnamallow(const char *user) 476 { 477 #ifdef HAVE_LOGIN_CAP 478 extern login_cap_t *lc; 479 #ifdef BSD_AUTH 480 auth_session_t *as; 481 #endif 482 #endif 483 struct passwd *pw; 484 485 parse_server_match_config(&options, user, 486 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 487 488 pw = getpwnam(user); 489 if (pw == NULL) { 490 logit("Invalid user %.100s from %.100s", 491 user, get_remote_ipaddr()); 492 #ifdef CUSTOM_FAILED_LOGIN 493 record_failed_login(user, 494 get_canonical_hostname(options.use_dns), "ssh"); 495 #endif 496 #ifdef SSH_AUDIT_EVENTS 497 audit_event(SSH_INVALID_USER); 498 #endif /* SSH_AUDIT_EVENTS */ 499 return (NULL); 500 } 501 if (!allowed_user(pw)) 502 return (NULL); 503 #ifdef HAVE_LOGIN_CAP 504 if ((lc = login_getpwclass(pw)) == NULL) { 505 debug("unable to get login class: %s", user); 506 return (NULL); 507 } 508 #ifdef BSD_AUTH 509 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 510 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 511 debug("Approval failure for %s", user); 512 pw = NULL; 513 } 514 if (as != NULL) 515 auth_close(as); 516 #endif 517 #endif 518 if (pw != NULL) 519 return (pwcopy(pw)); 520 return (NULL); 521 } 522 523 void 524 auth_debug_add(const char *fmt,...) 525 { 526 char buf[1024]; 527 va_list args; 528 529 if (!auth_debug_init) 530 return; 531 532 va_start(args, fmt); 533 vsnprintf(buf, sizeof(buf), fmt, args); 534 va_end(args); 535 buffer_put_cstring(&auth_debug, buf); 536 } 537 538 void 539 auth_debug_send(void) 540 { 541 char *msg; 542 543 if (!auth_debug_init) 544 return; 545 while (buffer_len(&auth_debug)) { 546 msg = buffer_get_string(&auth_debug, NULL); 547 packet_send_debug("%s", msg); 548 xfree(msg); 549 } 550 } 551 552 void 553 auth_debug_reset(void) 554 { 555 if (auth_debug_init) 556 buffer_clear(&auth_debug); 557 else { 558 buffer_init(&auth_debug); 559 auth_debug_init = 1; 560 } 561 } 562 563 struct passwd * 564 fakepw(void) 565 { 566 static struct passwd fake; 567 568 memset(&fake, 0, sizeof(fake)); 569 fake.pw_name = "NOUSER"; 570 fake.pw_passwd = 571 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 572 fake.pw_gecos = "NOUSER"; 573 fake.pw_uid = privsep_pw->pw_uid; 574 fake.pw_gid = privsep_pw->pw_gid; 575 #ifdef HAVE_PW_CLASS_IN_PASSWD 576 fake.pw_class = ""; 577 #endif 578 fake.pw_dir = "/nonexist"; 579 fake.pw_shell = "/nonexist"; 580 581 return (&fake); 582 } 583