1 /* 2 * Copyright (c) 2000 Markus Friedl. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 25 #include "includes.h" 26 RCSID("$OpenBSD: auth.c,v 1.56 2004/07/28 09:40:29 markus Exp $"); 27 RCSID("$FreeBSD$"); 28 29 #ifdef HAVE_LOGIN_H 30 #include <login.h> 31 #endif 32 #ifdef USE_SHADOW 33 #include <shadow.h> 34 #endif 35 36 #ifdef HAVE_LIBGEN_H 37 #include <libgen.h> 38 #endif 39 40 #include "xmalloc.h" 41 #include "match.h" 42 #include "groupaccess.h" 43 #include "log.h" 44 #include "servconf.h" 45 #include "auth.h" 46 #include "auth-options.h" 47 #include "canohost.h" 48 #include "buffer.h" 49 #include "bufaux.h" 50 #include "uidswap.h" 51 #include "misc.h" 52 #include "bufaux.h" 53 #include "packet.h" 54 55 /* import */ 56 extern ServerOptions options; 57 extern Buffer loginmsg; 58 59 /* Debugging messages */ 60 Buffer auth_debug; 61 int auth_debug_init; 62 63 /* 64 * Check if the user is allowed to log in via ssh. If user is listed 65 * in DenyUsers or one of user's groups is listed in DenyGroups, false 66 * will be returned. If AllowUsers isn't empty and user isn't listed 67 * there, or if AllowGroups isn't empty and one of user's groups isn't 68 * listed there, false will be returned. 69 * If the user's shell is not executable, false will be returned. 70 * Otherwise true is returned. 71 */ 72 int 73 allowed_user(struct passwd * pw) 74 { 75 struct stat st; 76 const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL; 77 char *shell; 78 int i; 79 #ifdef USE_SHADOW 80 struct spwd *spw = NULL; 81 #endif 82 83 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 84 if (!pw || !pw->pw_name) 85 return 0; 86 87 #ifdef USE_SHADOW 88 if (!options.use_pam) 89 spw = getspnam(pw->pw_name); 90 #ifdef HAS_SHADOW_EXPIRE 91 if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw)) 92 return 0; 93 #endif /* HAS_SHADOW_EXPIRE */ 94 #endif /* USE_SHADOW */ 95 96 /* grab passwd field for locked account check */ 97 #ifdef USE_SHADOW 98 if (spw != NULL) 99 passwd = spw->sp_pwdp; 100 #else 101 passwd = pw->pw_passwd; 102 #endif 103 104 /* check for locked account */ 105 if (!options.use_pam && passwd && *passwd) { 106 int locked = 0; 107 108 #ifdef LOCKED_PASSWD_STRING 109 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0) 110 locked = 1; 111 #endif 112 #ifdef LOCKED_PASSWD_PREFIX 113 if (strncmp(passwd, LOCKED_PASSWD_PREFIX, 114 strlen(LOCKED_PASSWD_PREFIX)) == 0) 115 locked = 1; 116 #endif 117 #ifdef LOCKED_PASSWD_SUBSTR 118 if (strstr(passwd, LOCKED_PASSWD_SUBSTR)) 119 locked = 1; 120 #endif 121 if (locked) { 122 logit("User %.100s not allowed because account is locked", 123 pw->pw_name); 124 return 0; 125 } 126 } 127 128 /* 129 * Get the shell from the password data. An empty shell field is 130 * legal, and means /bin/sh. 131 */ 132 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 133 134 /* deny if shell does not exists or is not executable */ 135 if (stat(shell, &st) != 0) { 136 logit("User %.100s not allowed because shell %.100s does not exist", 137 pw->pw_name, shell); 138 return 0; 139 } 140 if (S_ISREG(st.st_mode) == 0 || 141 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 142 logit("User %.100s not allowed because shell %.100s is not executable", 143 pw->pw_name, shell); 144 return 0; 145 } 146 147 if (options.num_deny_users > 0 || options.num_allow_users > 0) { 148 hostname = get_canonical_hostname(options.use_dns); 149 ipaddr = get_remote_ipaddr(); 150 } 151 152 /* Return false if user is listed in DenyUsers */ 153 if (options.num_deny_users > 0) { 154 for (i = 0; i < options.num_deny_users; i++) 155 if (match_user(pw->pw_name, hostname, ipaddr, 156 options.deny_users[i])) { 157 logit("User %.100s not allowed because listed in DenyUsers", 158 pw->pw_name); 159 return 0; 160 } 161 } 162 /* Return false if AllowUsers isn't empty and user isn't listed there */ 163 if (options.num_allow_users > 0) { 164 for (i = 0; i < options.num_allow_users; i++) 165 if (match_user(pw->pw_name, hostname, ipaddr, 166 options.allow_users[i])) 167 break; 168 /* i < options.num_allow_users iff we break for loop */ 169 if (i >= options.num_allow_users) { 170 logit("User %.100s not allowed because not listed in AllowUsers", 171 pw->pw_name); 172 return 0; 173 } 174 } 175 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 176 /* Get the user's group access list (primary and supplementary) */ 177 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 178 logit("User %.100s not allowed because not in any group", 179 pw->pw_name); 180 return 0; 181 } 182 183 /* Return false if one of user's groups is listed in DenyGroups */ 184 if (options.num_deny_groups > 0) 185 if (ga_match(options.deny_groups, 186 options.num_deny_groups)) { 187 ga_free(); 188 logit("User %.100s not allowed because a group is listed in DenyGroups", 189 pw->pw_name); 190 return 0; 191 } 192 /* 193 * Return false if AllowGroups isn't empty and one of user's groups 194 * isn't listed there 195 */ 196 if (options.num_allow_groups > 0) 197 if (!ga_match(options.allow_groups, 198 options.num_allow_groups)) { 199 ga_free(); 200 logit("User %.100s not allowed because none of user's groups are listed in AllowGroups", 201 pw->pw_name); 202 return 0; 203 } 204 ga_free(); 205 } 206 207 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER 208 if (!sys_auth_allowed_user(pw)) 209 return 0; 210 #endif 211 212 /* We found no reason not to let this user try to log on... */ 213 return 1; 214 } 215 216 void 217 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 218 { 219 void (*authlog) (const char *fmt,...) = verbose; 220 char *authmsg; 221 222 /* Raise logging level */ 223 if (authenticated == 1 || 224 !authctxt->valid || 225 authctxt->failures >= options.max_authtries / 2 || 226 strcmp(method, "password") == 0) 227 authlog = logit; 228 229 if (authctxt->postponed) 230 authmsg = "Postponed"; 231 else 232 authmsg = authenticated ? "Accepted" : "Failed"; 233 234 authlog("%s %s for %s%.100s from %.200s port %d%s", 235 authmsg, 236 method, 237 authctxt->valid ? "" : "invalid user ", 238 authctxt->user, 239 get_remote_ipaddr(), 240 get_remote_port(), 241 info); 242 243 #ifdef CUSTOM_FAILED_LOGIN 244 if (authenticated == 0 && strcmp(method, "password") == 0) 245 record_failed_login(authctxt->user, "ssh"); 246 #endif 247 } 248 249 /* 250 * Check whether root logins are disallowed. 251 */ 252 int 253 auth_root_allowed(char *method) 254 { 255 switch (options.permit_root_login) { 256 case PERMIT_YES: 257 return 1; 258 break; 259 case PERMIT_NO_PASSWD: 260 if (strcmp(method, "password") != 0) 261 return 1; 262 break; 263 case PERMIT_FORCED_ONLY: 264 if (forced_command) { 265 logit("Root login accepted for forced command."); 266 return 1; 267 } 268 break; 269 } 270 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 271 return 0; 272 } 273 274 275 /* 276 * Given a template and a passwd structure, build a filename 277 * by substituting % tokenised options. Currently, %% becomes '%', 278 * %h becomes the home directory and %u the username. 279 * 280 * This returns a buffer allocated by xmalloc. 281 */ 282 char * 283 expand_filename(const char *filename, struct passwd *pw) 284 { 285 Buffer buffer; 286 char *file; 287 const char *cp; 288 289 /* 290 * Build the filename string in the buffer by making the appropriate 291 * substitutions to the given file name. 292 */ 293 buffer_init(&buffer); 294 for (cp = filename; *cp; cp++) { 295 if (cp[0] == '%' && cp[1] == '%') { 296 buffer_append(&buffer, "%", 1); 297 cp++; 298 continue; 299 } 300 if (cp[0] == '%' && cp[1] == 'h') { 301 buffer_append(&buffer, pw->pw_dir, strlen(pw->pw_dir)); 302 cp++; 303 continue; 304 } 305 if (cp[0] == '%' && cp[1] == 'u') { 306 buffer_append(&buffer, pw->pw_name, 307 strlen(pw->pw_name)); 308 cp++; 309 continue; 310 } 311 buffer_append(&buffer, cp, 1); 312 } 313 buffer_append(&buffer, "\0", 1); 314 315 /* 316 * Ensure that filename starts anchored. If not, be backward 317 * compatible and prepend the '%h/' 318 */ 319 file = xmalloc(MAXPATHLEN); 320 cp = buffer_ptr(&buffer); 321 if (*cp != '/') 322 snprintf(file, MAXPATHLEN, "%s/%s", pw->pw_dir, cp); 323 else 324 strlcpy(file, cp, MAXPATHLEN); 325 326 buffer_free(&buffer); 327 return file; 328 } 329 330 char * 331 authorized_keys_file(struct passwd *pw) 332 { 333 return expand_filename(options.authorized_keys_file, pw); 334 } 335 336 char * 337 authorized_keys_file2(struct passwd *pw) 338 { 339 return expand_filename(options.authorized_keys_file2, pw); 340 } 341 342 /* return ok if key exists in sysfile or userfile */ 343 HostStatus 344 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 345 const char *sysfile, const char *userfile) 346 { 347 Key *found; 348 char *user_hostfile; 349 struct stat st; 350 HostStatus host_status; 351 352 /* Check if we know the host and its host key. */ 353 found = key_new(key->type); 354 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 355 356 if (host_status != HOST_OK && userfile != NULL) { 357 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 358 if (options.strict_modes && 359 (stat(user_hostfile, &st) == 0) && 360 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 361 (st.st_mode & 022) != 0)) { 362 logit("Authentication refused for %.100s: " 363 "bad owner or modes for %.200s", 364 pw->pw_name, user_hostfile); 365 } else { 366 temporarily_use_uid(pw); 367 host_status = check_host_in_hostfile(user_hostfile, 368 host, key, found, NULL); 369 restore_uid(); 370 } 371 xfree(user_hostfile); 372 } 373 key_free(found); 374 375 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 376 "ok" : "not found", host); 377 return host_status; 378 } 379 380 381 /* 382 * Check a given file for security. This is defined as all components 383 * of the path to the file must be owned by either the owner of 384 * of the file or root and no directories must be group or world writable. 385 * 386 * XXX Should any specific check be done for sym links ? 387 * 388 * Takes an open file descriptor, the file name, a uid and and 389 * error buffer plus max size as arguments. 390 * 391 * Returns 0 on success and -1 on failure 392 */ 393 int 394 secure_filename(FILE *f, const char *file, struct passwd *pw, 395 char *err, size_t errlen) 396 { 397 uid_t uid = pw->pw_uid; 398 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 399 char *cp; 400 int comparehome = 0; 401 struct stat st; 402 403 if (realpath(file, buf) == NULL) { 404 snprintf(err, errlen, "realpath %s failed: %s", file, 405 strerror(errno)); 406 return -1; 407 } 408 if (realpath(pw->pw_dir, homedir) != NULL) 409 comparehome = 1; 410 411 /* check the open file to avoid races */ 412 if (fstat(fileno(f), &st) < 0 || 413 (st.st_uid != 0 && st.st_uid != uid) || 414 (st.st_mode & 022) != 0) { 415 snprintf(err, errlen, "bad ownership or modes for file %s", 416 buf); 417 return -1; 418 } 419 420 /* for each component of the canonical path, walking upwards */ 421 for (;;) { 422 if ((cp = dirname(buf)) == NULL) { 423 snprintf(err, errlen, "dirname() failed"); 424 return -1; 425 } 426 strlcpy(buf, cp, sizeof(buf)); 427 428 debug3("secure_filename: checking '%s'", buf); 429 if (stat(buf, &st) < 0 || 430 (st.st_uid != 0 && st.st_uid != uid) || 431 (st.st_mode & 022) != 0) { 432 snprintf(err, errlen, 433 "bad ownership or modes for directory %s", buf); 434 return -1; 435 } 436 437 /* If are passed the homedir then we can stop */ 438 if (comparehome && strcmp(homedir, buf) == 0) { 439 debug3("secure_filename: terminating check at '%s'", 440 buf); 441 break; 442 } 443 /* 444 * dirname should always complete with a "/" path, 445 * but we can be paranoid and check for "." too 446 */ 447 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 448 break; 449 } 450 return 0; 451 } 452 453 struct passwd * 454 getpwnamallow(const char *user) 455 { 456 #ifdef HAVE_LOGIN_CAP 457 extern login_cap_t *lc; 458 #ifdef BSD_AUTH 459 auth_session_t *as; 460 #endif 461 #endif 462 struct passwd *pw; 463 464 pw = getpwnam(user); 465 if (pw == NULL) { 466 logit("Invalid user %.100s from %.100s", 467 user, get_remote_ipaddr()); 468 #ifdef CUSTOM_FAILED_LOGIN 469 record_failed_login(user, "ssh"); 470 #endif 471 return (NULL); 472 } 473 if (!allowed_user(pw)) 474 return (NULL); 475 #ifdef HAVE_LOGIN_CAP 476 if ((lc = login_getpwclass(pw)) == NULL) { 477 debug("unable to get login class: %s", user); 478 return (NULL); 479 } 480 #ifdef BSD_AUTH 481 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 482 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 483 debug("Approval failure for %s", user); 484 pw = NULL; 485 } 486 if (as != NULL) 487 auth_close(as); 488 #endif 489 #endif 490 if (pw != NULL) 491 return (pwcopy(pw)); 492 return (NULL); 493 } 494 495 void 496 auth_debug_add(const char *fmt,...) 497 { 498 char buf[1024]; 499 va_list args; 500 501 if (!auth_debug_init) 502 return; 503 504 va_start(args, fmt); 505 vsnprintf(buf, sizeof(buf), fmt, args); 506 va_end(args); 507 buffer_put_cstring(&auth_debug, buf); 508 } 509 510 void 511 auth_debug_send(void) 512 { 513 char *msg; 514 515 if (!auth_debug_init) 516 return; 517 while (buffer_len(&auth_debug)) { 518 msg = buffer_get_string(&auth_debug, NULL); 519 packet_send_debug("%s", msg); 520 xfree(msg); 521 } 522 } 523 524 void 525 auth_debug_reset(void) 526 { 527 if (auth_debug_init) 528 buffer_clear(&auth_debug); 529 else { 530 buffer_init(&auth_debug); 531 auth_debug_init = 1; 532 } 533 } 534 535 struct passwd * 536 fakepw(void) 537 { 538 static struct passwd fake; 539 540 memset(&fake, 0, sizeof(fake)); 541 fake.pw_name = "NOUSER"; 542 fake.pw_passwd = 543 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 544 fake.pw_gecos = "NOUSER"; 545 fake.pw_uid = (uid_t)-1; 546 fake.pw_gid = (gid_t)-1; 547 #ifdef HAVE_PW_CLASS_IN_PASSWD 548 fake.pw_class = ""; 549 #endif 550 fake.pw_dir = "/nonexist"; 551 fake.pw_shell = "/nonexist"; 552 553 return (&fake); 554 } 555