1 /* $OpenBSD: auth.c,v 1.79 2008/07/02 12:03:51 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 40 #include "xmalloc.h" 41 #include "match.h" 42 #include "groupaccess.h" 43 #include "log.h" 44 #include "buffer.h" 45 #include "servconf.h" 46 #include "key.h" 47 #include "hostfile.h" 48 #include "auth.h" 49 #include "auth-options.h" 50 #include "canohost.h" 51 #include "uidswap.h" 52 #include "misc.h" 53 #include "packet.h" 54 #ifdef GSSAPI 55 #include "ssh-gss.h" 56 #endif 57 #include "monitor_wrap.h" 58 59 /* import */ 60 extern ServerOptions options; 61 extern int use_privsep; 62 63 /* Debugging messages */ 64 Buffer auth_debug; 65 int auth_debug_init; 66 67 /* 68 * Check if the user is allowed to log in via ssh. If user is listed 69 * in DenyUsers or one of user's groups is listed in DenyGroups, false 70 * will be returned. If AllowUsers isn't empty and user isn't listed 71 * there, or if AllowGroups isn't empty and one of user's groups isn't 72 * listed there, false will be returned. 73 * If the user's shell is not executable, false will be returned. 74 * Otherwise true is returned. 75 */ 76 int 77 allowed_user(struct passwd * pw) 78 { 79 struct stat st; 80 const char *hostname = NULL, *ipaddr = NULL; 81 char *shell; 82 u_int i; 83 84 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 85 if (!pw || !pw->pw_name) 86 return 0; 87 88 /* 89 * Get the shell from the password data. An empty shell field is 90 * legal, and means /bin/sh. 91 */ 92 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 93 94 /* deny if shell does not exists or is not executable */ 95 if (stat(shell, &st) != 0) { 96 logit("User %.100s not allowed because shell %.100s does not exist", 97 pw->pw_name, shell); 98 return 0; 99 } 100 if (S_ISREG(st.st_mode) == 0 || 101 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 102 logit("User %.100s not allowed because shell %.100s is not executable", 103 pw->pw_name, shell); 104 return 0; 105 } 106 107 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 108 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 109 hostname = get_canonical_hostname(options.use_dns); 110 ipaddr = get_remote_ipaddr(); 111 } 112 113 /* Return false if user is listed in DenyUsers */ 114 if (options.num_deny_users > 0) { 115 for (i = 0; i < options.num_deny_users; i++) 116 if (match_user(pw->pw_name, hostname, ipaddr, 117 options.deny_users[i])) { 118 logit("User %.100s from %.100s not allowed " 119 "because listed in DenyUsers", 120 pw->pw_name, hostname); 121 return 0; 122 } 123 } 124 /* Return false if AllowUsers isn't empty and user isn't listed there */ 125 if (options.num_allow_users > 0) { 126 for (i = 0; i < options.num_allow_users; i++) 127 if (match_user(pw->pw_name, hostname, ipaddr, 128 options.allow_users[i])) 129 break; 130 /* i < options.num_allow_users iff we break for loop */ 131 if (i >= options.num_allow_users) { 132 logit("User %.100s from %.100s not allowed because " 133 "not listed in AllowUsers", pw->pw_name, hostname); 134 return 0; 135 } 136 } 137 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 138 /* Get the user's group access list (primary and supplementary) */ 139 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 140 logit("User %.100s from %.100s not allowed because " 141 "not in any group", pw->pw_name, hostname); 142 return 0; 143 } 144 145 /* Return false if one of user's groups is listed in DenyGroups */ 146 if (options.num_deny_groups > 0) 147 if (ga_match(options.deny_groups, 148 options.num_deny_groups)) { 149 ga_free(); 150 logit("User %.100s from %.100s not allowed " 151 "because a group is listed in DenyGroups", 152 pw->pw_name, hostname); 153 return 0; 154 } 155 /* 156 * Return false if AllowGroups isn't empty and one of user's groups 157 * isn't listed there 158 */ 159 if (options.num_allow_groups > 0) 160 if (!ga_match(options.allow_groups, 161 options.num_allow_groups)) { 162 ga_free(); 163 logit("User %.100s from %.100s not allowed " 164 "because none of user's groups are listed " 165 "in AllowGroups", pw->pw_name, hostname); 166 return 0; 167 } 168 ga_free(); 169 } 170 /* We found no reason not to let this user try to log on... */ 171 return 1; 172 } 173 174 void 175 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 176 { 177 void (*authlog) (const char *fmt,...) = verbose; 178 char *authmsg; 179 180 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 181 return; 182 183 /* Raise logging level */ 184 if (authenticated == 1 || 185 !authctxt->valid || 186 authctxt->failures >= options.max_authtries / 2 || 187 strcmp(method, "password") == 0) 188 authlog = logit; 189 190 if (authctxt->postponed) 191 authmsg = "Postponed"; 192 else 193 authmsg = authenticated ? "Accepted" : "Failed"; 194 195 authlog("%s %s for %s%.100s from %.200s port %d%s", 196 authmsg, 197 method, 198 authctxt->valid ? "" : "invalid user ", 199 authctxt->user, 200 get_remote_ipaddr(), 201 get_remote_port(), 202 info); 203 } 204 205 /* 206 * Check whether root logins are disallowed. 207 */ 208 int 209 auth_root_allowed(char *method) 210 { 211 switch (options.permit_root_login) { 212 case PERMIT_YES: 213 return 1; 214 case PERMIT_NO_PASSWD: 215 if (strcmp(method, "password") != 0) 216 return 1; 217 break; 218 case PERMIT_FORCED_ONLY: 219 if (forced_command) { 220 logit("Root login accepted for forced command."); 221 return 1; 222 } 223 break; 224 } 225 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 226 return 0; 227 } 228 229 230 /* 231 * Given a template and a passwd structure, build a filename 232 * by substituting % tokenised options. Currently, %% becomes '%', 233 * %h becomes the home directory and %u the username. 234 * 235 * This returns a buffer allocated by xmalloc. 236 */ 237 static char * 238 expand_authorized_keys(const char *filename, struct passwd *pw) 239 { 240 char *file, ret[MAXPATHLEN]; 241 int i; 242 243 file = percent_expand(filename, "h", pw->pw_dir, 244 "u", pw->pw_name, (char *)NULL); 245 246 /* 247 * Ensure that filename starts anchored. If not, be backward 248 * compatible and prepend the '%h/' 249 */ 250 if (*file == '/') 251 return (file); 252 253 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 254 if (i < 0 || (size_t)i >= sizeof(ret)) 255 fatal("expand_authorized_keys: path too long"); 256 xfree(file); 257 return (xstrdup(ret)); 258 } 259 260 char * 261 authorized_keys_file(struct passwd *pw) 262 { 263 return expand_authorized_keys(options.authorized_keys_file, pw); 264 } 265 266 char * 267 authorized_keys_file2(struct passwd *pw) 268 { 269 return expand_authorized_keys(options.authorized_keys_file2, pw); 270 } 271 272 /* return ok if key exists in sysfile or userfile */ 273 HostStatus 274 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 275 const char *sysfile, const char *userfile) 276 { 277 Key *found; 278 char *user_hostfile; 279 struct stat st; 280 HostStatus host_status; 281 282 /* Check if we know the host and its host key. */ 283 found = key_new(key->type); 284 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 285 286 if (host_status != HOST_OK && userfile != NULL) { 287 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 288 if (options.strict_modes && 289 (stat(user_hostfile, &st) == 0) && 290 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 291 (st.st_mode & 022) != 0)) { 292 logit("Authentication refused for %.100s: " 293 "bad owner or modes for %.200s", 294 pw->pw_name, user_hostfile); 295 } else { 296 temporarily_use_uid(pw); 297 host_status = check_host_in_hostfile(user_hostfile, 298 host, key, found, NULL); 299 restore_uid(); 300 } 301 xfree(user_hostfile); 302 } 303 key_free(found); 304 305 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 306 "ok" : "not found", host); 307 return host_status; 308 } 309 310 311 /* 312 * Check a given file for security. This is defined as all components 313 * of the path to the file must be owned by either the owner of 314 * of the file or root and no directories must be group or world writable. 315 * 316 * XXX Should any specific check be done for sym links ? 317 * 318 * Takes an open file descriptor, the file name, a uid and and 319 * error buffer plus max size as arguments. 320 * 321 * Returns 0 on success and -1 on failure 322 */ 323 static int 324 secure_filename(FILE *f, const char *file, struct passwd *pw, 325 char *err, size_t errlen) 326 { 327 uid_t uid = pw->pw_uid; 328 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 329 char *cp; 330 int comparehome = 0; 331 struct stat st; 332 333 if (realpath(file, buf) == NULL) { 334 snprintf(err, errlen, "realpath %s failed: %s", file, 335 strerror(errno)); 336 return -1; 337 } 338 if (realpath(pw->pw_dir, homedir) != NULL) 339 comparehome = 1; 340 341 /* check the open file to avoid races */ 342 if (fstat(fileno(f), &st) < 0 || 343 (st.st_uid != 0 && st.st_uid != uid) || 344 (st.st_mode & 022) != 0) { 345 snprintf(err, errlen, "bad ownership or modes for file %s", 346 buf); 347 return -1; 348 } 349 350 /* for each component of the canonical path, walking upwards */ 351 for (;;) { 352 if ((cp = dirname(buf)) == NULL) { 353 snprintf(err, errlen, "dirname() failed"); 354 return -1; 355 } 356 strlcpy(buf, cp, sizeof(buf)); 357 358 debug3("secure_filename: checking '%s'", buf); 359 if (stat(buf, &st) < 0 || 360 (st.st_uid != 0 && st.st_uid != uid) || 361 (st.st_mode & 022) != 0) { 362 snprintf(err, errlen, 363 "bad ownership or modes for directory %s", buf); 364 return -1; 365 } 366 367 /* If are passed the homedir then we can stop */ 368 if (comparehome && strcmp(homedir, buf) == 0) { 369 debug3("secure_filename: terminating check at '%s'", 370 buf); 371 break; 372 } 373 /* 374 * dirname should always complete with a "/" path, 375 * but we can be paranoid and check for "." too 376 */ 377 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 378 break; 379 } 380 return 0; 381 } 382 383 FILE * 384 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 385 { 386 char line[1024]; 387 struct stat st; 388 int fd; 389 FILE *f; 390 391 /* 392 * Open the file containing the authorized keys 393 * Fail quietly if file does not exist 394 */ 395 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) 396 return NULL; 397 398 if (fstat(fd, &st) < 0) { 399 close(fd); 400 return NULL; 401 } 402 if (!S_ISREG(st.st_mode)) { 403 logit("User %s authorized keys %s is not a regular file", 404 pw->pw_name, file); 405 close(fd); 406 return NULL; 407 } 408 unset_nonblock(fd); 409 if ((f = fdopen(fd, "r")) == NULL) { 410 close(fd); 411 return NULL; 412 } 413 if (options.strict_modes && 414 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 415 fclose(f); 416 logit("Authentication refused: %s", line); 417 return NULL; 418 } 419 420 return f; 421 } 422 423 struct passwd * 424 getpwnamallow(const char *user) 425 { 426 extern login_cap_t *lc; 427 auth_session_t *as; 428 struct passwd *pw; 429 430 parse_server_match_config(&options, user, 431 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 432 433 pw = getpwnam(user); 434 if (pw == NULL) { 435 logit("Invalid user %.100s from %.100s", 436 user, get_remote_ipaddr()); 437 return (NULL); 438 } 439 if (!allowed_user(pw)) 440 return (NULL); 441 if ((lc = login_getclass(pw->pw_class)) == NULL) { 442 debug("unable to get login class: %s", user); 443 return (NULL); 444 } 445 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 446 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 447 debug("Approval failure for %s", user); 448 pw = NULL; 449 } 450 if (as != NULL) 451 auth_close(as); 452 if (pw != NULL) 453 return (pwcopy(pw)); 454 return (NULL); 455 } 456 457 void 458 auth_debug_add(const char *fmt,...) 459 { 460 char buf[1024]; 461 va_list args; 462 463 if (!auth_debug_init) 464 return; 465 466 va_start(args, fmt); 467 vsnprintf(buf, sizeof(buf), fmt, args); 468 va_end(args); 469 buffer_put_cstring(&auth_debug, buf); 470 } 471 472 void 473 auth_debug_send(void) 474 { 475 char *msg; 476 477 if (!auth_debug_init) 478 return; 479 while (buffer_len(&auth_debug)) { 480 msg = buffer_get_string(&auth_debug, NULL); 481 packet_send_debug("%s", msg); 482 xfree(msg); 483 } 484 } 485 486 void 487 auth_debug_reset(void) 488 { 489 if (auth_debug_init) 490 buffer_clear(&auth_debug); 491 else { 492 buffer_init(&auth_debug); 493 auth_debug_init = 1; 494 } 495 } 496 497 struct passwd * 498 fakepw(void) 499 { 500 static struct passwd fake; 501 502 memset(&fake, 0, sizeof(fake)); 503 fake.pw_name = "NOUSER"; 504 fake.pw_passwd = 505 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 506 fake.pw_gecos = "NOUSER"; 507 fake.pw_uid = (uid_t)-1; 508 fake.pw_gid = (gid_t)-1; 509 fake.pw_class = ""; 510 fake.pw_dir = "/nonexist"; 511 fake.pw_shell = "/nonexist"; 512 513 return (&fake); 514 } 515