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 <sys/types.h> 27 #include <sys/stat.h> 28 #include <sys/param.h> 29 30 #include <errno.h> 31 #include <libgen.h> 32 #include <paths.h> 33 #include <pwd.h> 34 #include <stdarg.h> 35 #include <stdio.h> 36 #include <string.h> 37 38 #include "xmalloc.h" 39 #include "match.h" 40 #include "groupaccess.h" 41 #include "log.h" 42 #include "buffer.h" 43 #include "servconf.h" 44 #include "key.h" 45 #include "hostfile.h" 46 #include "auth.h" 47 #include "auth-options.h" 48 #include "canohost.h" 49 #include "uidswap.h" 50 #include "misc.h" 51 #include "packet.h" 52 #ifdef GSSAPI 53 #include "ssh-gss.h" 54 #endif 55 #include "monitor_wrap.h" 56 57 /* import */ 58 extern ServerOptions options; 59 extern int use_privsep; 60 61 /* Debugging messages */ 62 Buffer auth_debug; 63 int auth_debug_init; 64 65 /* 66 * Check if the user is allowed to log in via ssh. If user is listed 67 * in DenyUsers or one of user's groups is listed in DenyGroups, false 68 * will be returned. If AllowUsers isn't empty and user isn't listed 69 * there, or if AllowGroups isn't empty and one of user's groups isn't 70 * listed there, false will be returned. 71 * If the user's shell is not executable, false will be returned. 72 * Otherwise true is returned. 73 */ 74 int 75 allowed_user(struct passwd * pw) 76 { 77 struct stat st; 78 const char *hostname = NULL, *ipaddr = NULL; 79 char *shell; 80 u_int i; 81 82 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 83 if (!pw || !pw->pw_name) 84 return 0; 85 86 /* 87 * Get the shell from the password data. An empty shell field is 88 * legal, and means /bin/sh. 89 */ 90 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 91 92 /* deny if shell does not exists or is not executable */ 93 if (stat(shell, &st) != 0) { 94 logit("User %.100s not allowed because shell %.100s does not exist", 95 pw->pw_name, shell); 96 return 0; 97 } 98 if (S_ISREG(st.st_mode) == 0 || 99 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 100 logit("User %.100s not allowed because shell %.100s is not executable", 101 pw->pw_name, shell); 102 return 0; 103 } 104 105 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 106 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 107 hostname = get_canonical_hostname(options.use_dns); 108 ipaddr = get_remote_ipaddr(); 109 } 110 111 /* Return false if user is listed in DenyUsers */ 112 if (options.num_deny_users > 0) { 113 for (i = 0; i < options.num_deny_users; i++) 114 if (match_user(pw->pw_name, hostname, ipaddr, 115 options.deny_users[i])) { 116 logit("User %.100s from %.100s not allowed " 117 "because listed in DenyUsers", 118 pw->pw_name, hostname); 119 return 0; 120 } 121 } 122 /* Return false if AllowUsers isn't empty and user isn't listed there */ 123 if (options.num_allow_users > 0) { 124 for (i = 0; i < options.num_allow_users; i++) 125 if (match_user(pw->pw_name, hostname, ipaddr, 126 options.allow_users[i])) 127 break; 128 /* i < options.num_allow_users iff we break for loop */ 129 if (i >= options.num_allow_users) { 130 logit("User %.100s from %.100s not allowed because " 131 "not listed in AllowUsers", pw->pw_name, hostname); 132 return 0; 133 } 134 } 135 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 136 /* Get the user's group access list (primary and supplementary) */ 137 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 138 logit("User %.100s from %.100s not allowed because " 139 "not in any group", pw->pw_name, hostname); 140 return 0; 141 } 142 143 /* Return false if one of user's groups is listed in DenyGroups */ 144 if (options.num_deny_groups > 0) 145 if (ga_match(options.deny_groups, 146 options.num_deny_groups)) { 147 ga_free(); 148 logit("User %.100s from %.100s not allowed " 149 "because a group is listed in DenyGroups", 150 pw->pw_name, hostname); 151 return 0; 152 } 153 /* 154 * Return false if AllowGroups isn't empty and one of user's groups 155 * isn't listed there 156 */ 157 if (options.num_allow_groups > 0) 158 if (!ga_match(options.allow_groups, 159 options.num_allow_groups)) { 160 ga_free(); 161 logit("User %.100s from %.100s not allowed " 162 "because none of user's groups are listed " 163 "in AllowGroups", pw->pw_name, hostname); 164 return 0; 165 } 166 ga_free(); 167 } 168 /* We found no reason not to let this user try to log on... */ 169 return 1; 170 } 171 172 void 173 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 174 { 175 void (*authlog) (const char *fmt,...) = verbose; 176 char *authmsg; 177 178 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 179 return; 180 181 /* Raise logging level */ 182 if (authenticated == 1 || 183 !authctxt->valid || 184 authctxt->failures >= options.max_authtries / 2 || 185 strcmp(method, "password") == 0) 186 authlog = logit; 187 188 if (authctxt->postponed) 189 authmsg = "Postponed"; 190 else 191 authmsg = authenticated ? "Accepted" : "Failed"; 192 193 authlog("%s %s for %s%.100s from %.200s port %d%s", 194 authmsg, 195 method, 196 authctxt->valid ? "" : "invalid user ", 197 authctxt->user, 198 get_remote_ipaddr(), 199 get_remote_port(), 200 info); 201 } 202 203 /* 204 * Check whether root logins are disallowed. 205 */ 206 int 207 auth_root_allowed(char *method) 208 { 209 switch (options.permit_root_login) { 210 case PERMIT_YES: 211 return 1; 212 case PERMIT_NO_PASSWD: 213 if (strcmp(method, "password") != 0) 214 return 1; 215 break; 216 case PERMIT_FORCED_ONLY: 217 if (forced_command) { 218 logit("Root login accepted for forced command."); 219 return 1; 220 } 221 break; 222 } 223 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 224 return 0; 225 } 226 227 228 /* 229 * Given a template and a passwd structure, build a filename 230 * by substituting % tokenised options. Currently, %% becomes '%', 231 * %h becomes the home directory and %u the username. 232 * 233 * This returns a buffer allocated by xmalloc. 234 */ 235 static char * 236 expand_authorized_keys(const char *filename, struct passwd *pw) 237 { 238 char *file, ret[MAXPATHLEN]; 239 int i; 240 241 file = percent_expand(filename, "h", pw->pw_dir, 242 "u", pw->pw_name, (char *)NULL); 243 244 /* 245 * Ensure that filename starts anchored. If not, be backward 246 * compatible and prepend the '%h/' 247 */ 248 if (*file == '/') 249 return (file); 250 251 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 252 if (i < 0 || (size_t)i >= sizeof(ret)) 253 fatal("expand_authorized_keys: path too long"); 254 xfree(file); 255 return (xstrdup(ret)); 256 } 257 258 char * 259 authorized_keys_file(struct passwd *pw) 260 { 261 return expand_authorized_keys(options.authorized_keys_file, pw); 262 } 263 264 char * 265 authorized_keys_file2(struct passwd *pw) 266 { 267 return expand_authorized_keys(options.authorized_keys_file2, pw); 268 } 269 270 /* return ok if key exists in sysfile or userfile */ 271 HostStatus 272 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 273 const char *sysfile, const char *userfile) 274 { 275 Key *found; 276 char *user_hostfile; 277 struct stat st; 278 HostStatus host_status; 279 280 /* Check if we know the host and its host key. */ 281 found = key_new(key->type); 282 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 283 284 if (host_status != HOST_OK && userfile != NULL) { 285 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 286 if (options.strict_modes && 287 (stat(user_hostfile, &st) == 0) && 288 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 289 (st.st_mode & 022) != 0)) { 290 logit("Authentication refused for %.100s: " 291 "bad owner or modes for %.200s", 292 pw->pw_name, user_hostfile); 293 } else { 294 temporarily_use_uid(pw); 295 host_status = check_host_in_hostfile(user_hostfile, 296 host, key, found, NULL); 297 restore_uid(); 298 } 299 xfree(user_hostfile); 300 } 301 key_free(found); 302 303 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 304 "ok" : "not found", host); 305 return host_status; 306 } 307 308 309 /* 310 * Check a given file for security. This is defined as all components 311 * of the path to the file must be owned by either the owner of 312 * of the file or root and no directories must be group or world writable. 313 * 314 * XXX Should any specific check be done for sym links ? 315 * 316 * Takes an open file descriptor, the file name, a uid and and 317 * error buffer plus max size as arguments. 318 * 319 * Returns 0 on success and -1 on failure 320 */ 321 int 322 secure_filename(FILE *f, const char *file, struct passwd *pw, 323 char *err, size_t errlen) 324 { 325 uid_t uid = pw->pw_uid; 326 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 327 char *cp; 328 int comparehome = 0; 329 struct stat st; 330 331 if (realpath(file, buf) == NULL) { 332 snprintf(err, errlen, "realpath %s failed: %s", file, 333 strerror(errno)); 334 return -1; 335 } 336 if (realpath(pw->pw_dir, homedir) != NULL) 337 comparehome = 1; 338 339 /* check the open file to avoid races */ 340 if (fstat(fileno(f), &st) < 0 || 341 (st.st_uid != 0 && st.st_uid != uid) || 342 (st.st_mode & 022) != 0) { 343 snprintf(err, errlen, "bad ownership or modes for file %s", 344 buf); 345 return -1; 346 } 347 348 /* for each component of the canonical path, walking upwards */ 349 for (;;) { 350 if ((cp = dirname(buf)) == NULL) { 351 snprintf(err, errlen, "dirname() failed"); 352 return -1; 353 } 354 strlcpy(buf, cp, sizeof(buf)); 355 356 debug3("secure_filename: checking '%s'", buf); 357 if (stat(buf, &st) < 0 || 358 (st.st_uid != 0 && st.st_uid != uid) || 359 (st.st_mode & 022) != 0) { 360 snprintf(err, errlen, 361 "bad ownership or modes for directory %s", buf); 362 return -1; 363 } 364 365 /* If are passed the homedir then we can stop */ 366 if (comparehome && strcmp(homedir, buf) == 0) { 367 debug3("secure_filename: terminating check at '%s'", 368 buf); 369 break; 370 } 371 /* 372 * dirname should always complete with a "/" path, 373 * but we can be paranoid and check for "." too 374 */ 375 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 376 break; 377 } 378 return 0; 379 } 380 381 struct passwd * 382 getpwnamallow(const char *user) 383 { 384 #ifdef HAVE_LOGIN_CAP 385 extern login_cap_t *lc; 386 #ifdef BSD_AUTH 387 auth_session_t *as; 388 #endif 389 #endif 390 struct passwd *pw; 391 392 parse_server_match_config(&options, user, 393 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 394 395 pw = getpwnam(user); 396 if (pw == NULL) { 397 logit("Invalid user %.100s from %.100s", 398 user, get_remote_ipaddr()); 399 return (NULL); 400 } 401 if (!allowed_user(pw)) 402 return (NULL); 403 #ifdef HAVE_LOGIN_CAP 404 if ((lc = login_getclass(pw->pw_class)) == NULL) { 405 debug("unable to get login class: %s", user); 406 return (NULL); 407 } 408 #ifdef BSD_AUTH 409 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 410 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 411 debug("Approval failure for %s", user); 412 pw = NULL; 413 } 414 if (as != NULL) 415 auth_close(as); 416 #endif 417 #endif 418 if (pw != NULL) 419 return (pwcopy(pw)); 420 return (NULL); 421 } 422 423 void 424 auth_debug_add(const char *fmt,...) 425 { 426 char buf[1024]; 427 va_list args; 428 429 if (!auth_debug_init) 430 return; 431 432 va_start(args, fmt); 433 vsnprintf(buf, sizeof(buf), fmt, args); 434 va_end(args); 435 buffer_put_cstring(&auth_debug, buf); 436 } 437 438 void 439 auth_debug_send(void) 440 { 441 char *msg; 442 443 if (!auth_debug_init) 444 return; 445 while (buffer_len(&auth_debug)) { 446 msg = buffer_get_string(&auth_debug, NULL); 447 packet_send_debug("%s", msg); 448 xfree(msg); 449 } 450 } 451 452 void 453 auth_debug_reset(void) 454 { 455 if (auth_debug_init) 456 buffer_clear(&auth_debug); 457 else { 458 buffer_init(&auth_debug); 459 auth_debug_init = 1; 460 } 461 } 462 463 struct passwd * 464 fakepw(void) 465 { 466 static struct passwd fake; 467 468 memset(&fake, 0, sizeof(fake)); 469 fake.pw_name = "NOUSER"; 470 fake.pw_passwd = 471 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 472 fake.pw_gecos = "NOUSER"; 473 fake.pw_uid = (uid_t)-1; 474 fake.pw_gid = (gid_t)-1; 475 fake.pw_class = ""; 476 fake.pw_dir = "/nonexist"; 477 fake.pw_shell = "/nonexist"; 478 479 return (&fake); 480 } 481