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 1.46 2002/11/04 10:07:53 markus Exp $"); 27 28 #include <libgen.h> 29 30 #include "xmalloc.h" 31 #include "match.h" 32 #include "groupaccess.h" 33 #include "log.h" 34 #include "servconf.h" 35 #include "auth.h" 36 #include "auth-options.h" 37 #include "canohost.h" 38 #include "buffer.h" 39 #include "bufaux.h" 40 #include "uidswap.h" 41 #include "tildexpand.h" 42 #include "misc.h" 43 #include "bufaux.h" 44 #include "packet.h" 45 46 /* import */ 47 extern ServerOptions options; 48 49 /* Debugging messages */ 50 Buffer auth_debug; 51 int auth_debug_init; 52 53 /* 54 * Check if the user is allowed to log in via ssh. If user is listed 55 * in DenyUsers or one of user's groups is listed in DenyGroups, false 56 * will be returned. If AllowUsers isn't empty and user isn't listed 57 * there, or if AllowGroups isn't empty and one of user's groups isn't 58 * listed there, false will be returned. 59 * If the user's shell is not executable, false will be returned. 60 * Otherwise true is returned. 61 */ 62 int 63 allowed_user(struct passwd * pw) 64 { 65 struct stat st; 66 const char *hostname = NULL, *ipaddr = NULL; 67 char *shell; 68 int i; 69 70 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 71 if (!pw || !pw->pw_name) 72 return 0; 73 74 /* 75 * Get the shell from the password data. An empty shell field is 76 * legal, and means /bin/sh. 77 */ 78 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 79 80 /* deny if shell does not exists or is not executable */ 81 if (stat(shell, &st) != 0) { 82 log("User %.100s not allowed because shell %.100s does not exist", 83 pw->pw_name, shell); 84 return 0; 85 } 86 if (S_ISREG(st.st_mode) == 0 || 87 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 88 log("User %.100s not allowed because shell %.100s is not executable", 89 pw->pw_name, shell); 90 return 0; 91 } 92 93 if (options.num_deny_users > 0 || options.num_allow_users > 0) { 94 hostname = get_canonical_hostname(options.verify_reverse_mapping); 95 ipaddr = get_remote_ipaddr(); 96 } 97 98 /* Return false if user is listed in DenyUsers */ 99 if (options.num_deny_users > 0) { 100 for (i = 0; i < options.num_deny_users; i++) 101 if (match_user(pw->pw_name, hostname, ipaddr, 102 options.deny_users[i])) { 103 log("User %.100s not allowed because listed in DenyUsers", 104 pw->pw_name); 105 return 0; 106 } 107 } 108 /* Return false if AllowUsers isn't empty and user isn't listed there */ 109 if (options.num_allow_users > 0) { 110 for (i = 0; i < options.num_allow_users; i++) 111 if (match_user(pw->pw_name, hostname, ipaddr, 112 options.allow_users[i])) 113 break; 114 /* i < options.num_allow_users iff we break for loop */ 115 if (i >= options.num_allow_users) { 116 log("User %.100s not allowed because not listed in AllowUsers", 117 pw->pw_name); 118 return 0; 119 } 120 } 121 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 122 /* Get the user's group access list (primary and supplementary) */ 123 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 124 log("User %.100s not allowed because not in any group", 125 pw->pw_name); 126 return 0; 127 } 128 129 /* Return false if one of user's groups is listed in DenyGroups */ 130 if (options.num_deny_groups > 0) 131 if (ga_match(options.deny_groups, 132 options.num_deny_groups)) { 133 ga_free(); 134 log("User %.100s not allowed because a group is listed in DenyGroups", 135 pw->pw_name); 136 return 0; 137 } 138 /* 139 * Return false if AllowGroups isn't empty and one of user's groups 140 * isn't listed there 141 */ 142 if (options.num_allow_groups > 0) 143 if (!ga_match(options.allow_groups, 144 options.num_allow_groups)) { 145 ga_free(); 146 log("User %.100s not allowed because none of user's groups are listed in AllowGroups", 147 pw->pw_name); 148 return 0; 149 } 150 ga_free(); 151 } 152 /* We found no reason not to let this user try to log on... */ 153 return 1; 154 } 155 156 Authctxt * 157 authctxt_new(void) 158 { 159 Authctxt *authctxt = xmalloc(sizeof(*authctxt)); 160 memset(authctxt, 0, sizeof(*authctxt)); 161 return authctxt; 162 } 163 164 void 165 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 166 { 167 void (*authlog) (const char *fmt,...) = verbose; 168 char *authmsg; 169 170 /* Raise logging level */ 171 if (authenticated == 1 || 172 !authctxt->valid || 173 authctxt->failures >= AUTH_FAIL_LOG || 174 strcmp(method, "password") == 0) 175 authlog = log; 176 177 if (authctxt->postponed) 178 authmsg = "Postponed"; 179 else 180 authmsg = authenticated ? "Accepted" : "Failed"; 181 182 authlog("%s %s for %s%.100s from %.200s port %d%s", 183 authmsg, 184 method, 185 authctxt->valid ? "" : "illegal user ", 186 authctxt->user, 187 get_remote_ipaddr(), 188 get_remote_port(), 189 info); 190 } 191 192 /* 193 * Check whether root logins are disallowed. 194 */ 195 int 196 auth_root_allowed(char *method) 197 { 198 switch (options.permit_root_login) { 199 case PERMIT_YES: 200 return 1; 201 break; 202 case PERMIT_NO_PASSWD: 203 if (strcmp(method, "password") != 0) 204 return 1; 205 break; 206 case PERMIT_FORCED_ONLY: 207 if (forced_command) { 208 log("Root login accepted for forced command."); 209 return 1; 210 } 211 break; 212 } 213 log("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 214 return 0; 215 } 216 217 218 /* 219 * Given a template and a passwd structure, build a filename 220 * by substituting % tokenised options. Currently, %% becomes '%', 221 * %h becomes the home directory and %u the username. 222 * 223 * This returns a buffer allocated by xmalloc. 224 */ 225 char * 226 expand_filename(const char *filename, struct passwd *pw) 227 { 228 Buffer buffer; 229 char *file; 230 const char *cp; 231 232 /* 233 * Build the filename string in the buffer by making the appropriate 234 * substitutions to the given file name. 235 */ 236 buffer_init(&buffer); 237 for (cp = filename; *cp; cp++) { 238 if (cp[0] == '%' && cp[1] == '%') { 239 buffer_append(&buffer, "%", 1); 240 cp++; 241 continue; 242 } 243 if (cp[0] == '%' && cp[1] == 'h') { 244 buffer_append(&buffer, pw->pw_dir, strlen(pw->pw_dir)); 245 cp++; 246 continue; 247 } 248 if (cp[0] == '%' && cp[1] == 'u') { 249 buffer_append(&buffer, pw->pw_name, 250 strlen(pw->pw_name)); 251 cp++; 252 continue; 253 } 254 buffer_append(&buffer, cp, 1); 255 } 256 buffer_append(&buffer, "\0", 1); 257 258 /* 259 * Ensure that filename starts anchored. If not, be backward 260 * compatible and prepend the '%h/' 261 */ 262 file = xmalloc(MAXPATHLEN); 263 cp = buffer_ptr(&buffer); 264 if (*cp != '/') 265 snprintf(file, MAXPATHLEN, "%s/%s", pw->pw_dir, cp); 266 else 267 strlcpy(file, cp, MAXPATHLEN); 268 269 buffer_free(&buffer); 270 return file; 271 } 272 273 char * 274 authorized_keys_file(struct passwd *pw) 275 { 276 return expand_filename(options.authorized_keys_file, pw); 277 } 278 279 char * 280 authorized_keys_file2(struct passwd *pw) 281 { 282 return expand_filename(options.authorized_keys_file2, pw); 283 } 284 285 /* return ok if key exists in sysfile or userfile */ 286 HostStatus 287 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 288 const char *sysfile, const char *userfile) 289 { 290 Key *found; 291 char *user_hostfile; 292 struct stat st; 293 HostStatus host_status; 294 295 /* Check if we know the host and its host key. */ 296 found = key_new(key->type); 297 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 298 299 if (host_status != HOST_OK && userfile != NULL) { 300 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 301 if (options.strict_modes && 302 (stat(user_hostfile, &st) == 0) && 303 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 304 (st.st_mode & 022) != 0)) { 305 log("Authentication refused for %.100s: " 306 "bad owner or modes for %.200s", 307 pw->pw_name, user_hostfile); 308 } else { 309 temporarily_use_uid(pw); 310 host_status = check_host_in_hostfile(user_hostfile, 311 host, key, found, NULL); 312 restore_uid(); 313 } 314 xfree(user_hostfile); 315 } 316 key_free(found); 317 318 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 319 "ok" : "not found", host); 320 return host_status; 321 } 322 323 324 /* 325 * Check a given file for security. This is defined as all components 326 * of the path to the file must be owned by either the owner of 327 * of the file or root and no directories must be group or world writable. 328 * 329 * XXX Should any specific check be done for sym links ? 330 * 331 * Takes an open file descriptor, the file name, a uid and and 332 * error buffer plus max size as arguments. 333 * 334 * Returns 0 on success and -1 on failure 335 */ 336 int 337 secure_filename(FILE *f, const char *file, struct passwd *pw, 338 char *err, size_t errlen) 339 { 340 uid_t uid = pw->pw_uid; 341 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 342 char *cp; 343 int comparehome = 0; 344 struct stat st; 345 346 if (realpath(file, buf) == NULL) { 347 snprintf(err, errlen, "realpath %s failed: %s", file, 348 strerror(errno)); 349 return -1; 350 } 351 if (realpath(pw->pw_dir, homedir) != NULL) 352 comparehome = 1; 353 354 /* check the open file to avoid races */ 355 if (fstat(fileno(f), &st) < 0 || 356 (st.st_uid != 0 && st.st_uid != uid) || 357 (st.st_mode & 022) != 0) { 358 snprintf(err, errlen, "bad ownership or modes for file %s", 359 buf); 360 return -1; 361 } 362 363 /* for each component of the canonical path, walking upwards */ 364 for (;;) { 365 if ((cp = dirname(buf)) == NULL) { 366 snprintf(err, errlen, "dirname() failed"); 367 return -1; 368 } 369 strlcpy(buf, cp, sizeof(buf)); 370 371 debug3("secure_filename: checking '%s'", buf); 372 if (stat(buf, &st) < 0 || 373 (st.st_uid != 0 && st.st_uid != uid) || 374 (st.st_mode & 022) != 0) { 375 snprintf(err, errlen, 376 "bad ownership or modes for directory %s", buf); 377 return -1; 378 } 379 380 /* If are passed the homedir then we can stop */ 381 if (comparehome && strcmp(homedir, buf) == 0) { 382 debug3("secure_filename: terminating check at '%s'", 383 buf); 384 break; 385 } 386 /* 387 * dirname should always complete with a "/" path, 388 * but we can be paranoid and check for "." too 389 */ 390 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 391 break; 392 } 393 return 0; 394 } 395 396 struct passwd * 397 getpwnamallow(const char *user) 398 { 399 #ifdef HAVE_LOGIN_CAP 400 extern login_cap_t *lc; 401 #ifdef BSD_AUTH 402 auth_session_t *as; 403 #endif 404 #endif 405 struct passwd *pw; 406 407 pw = getpwnam(user); 408 if (pw == NULL) { 409 log("Illegal user %.100s from %.100s", 410 user, get_remote_ipaddr()); 411 return (NULL); 412 } 413 if (!allowed_user(pw)) 414 return (NULL); 415 #ifdef HAVE_LOGIN_CAP 416 if ((lc = login_getclass(pw->pw_class)) == NULL) { 417 debug("unable to get login class: %s", user); 418 return (NULL); 419 } 420 #ifdef BSD_AUTH 421 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 422 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 423 debug("Approval failure for %s", user); 424 pw = NULL; 425 } 426 if (as != NULL) 427 auth_close(as); 428 #endif 429 #endif 430 if (pw != NULL) 431 return (pwcopy(pw)); 432 return (NULL); 433 } 434 435 void 436 auth_debug_add(const char *fmt,...) 437 { 438 char buf[1024]; 439 va_list args; 440 441 if (!auth_debug_init) 442 return; 443 444 va_start(args, fmt); 445 vsnprintf(buf, sizeof(buf), fmt, args); 446 va_end(args); 447 buffer_put_cstring(&auth_debug, buf); 448 } 449 450 void 451 auth_debug_send(void) 452 { 453 char *msg; 454 455 if (!auth_debug_init) 456 return; 457 while (buffer_len(&auth_debug)) { 458 msg = buffer_get_string(&auth_debug, NULL); 459 packet_send_debug("%s", msg); 460 xfree(msg); 461 } 462 } 463 464 void 465 auth_debug_reset(void) 466 { 467 if (auth_debug_init) 468 buffer_clear(&auth_debug); 469 else { 470 buffer_init(&auth_debug); 471 auth_debug_init = 1; 472 } 473 } 474