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 1.51 2003/11/21 11:57:02 djm 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 logit("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 logit("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.use_dns); 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 logit("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 logit("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 logit("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 logit("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 logit("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 void 157 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 158 { 159 void (*authlog) (const char *fmt,...) = verbose; 160 char *authmsg; 161 162 /* Raise logging level */ 163 if (authenticated == 1 || 164 !authctxt->valid || 165 authctxt->failures >= AUTH_FAIL_LOG || 166 strcmp(method, "password") == 0) 167 authlog = logit; 168 169 if (authctxt->postponed) 170 authmsg = "Postponed"; 171 else 172 authmsg = authenticated ? "Accepted" : "Failed"; 173 174 authlog("%s %s for %s%.100s from %.200s port %d%s", 175 authmsg, 176 method, 177 authctxt->valid ? "" : "illegal user ", 178 authctxt->user, 179 get_remote_ipaddr(), 180 get_remote_port(), 181 info); 182 } 183 184 /* 185 * Check whether root logins are disallowed. 186 */ 187 int 188 auth_root_allowed(char *method) 189 { 190 switch (options.permit_root_login) { 191 case PERMIT_YES: 192 return 1; 193 break; 194 case PERMIT_NO_PASSWD: 195 if (strcmp(method, "password") != 0) 196 return 1; 197 break; 198 case PERMIT_FORCED_ONLY: 199 if (forced_command) { 200 logit("Root login accepted for forced command."); 201 return 1; 202 } 203 break; 204 } 205 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 206 return 0; 207 } 208 209 210 /* 211 * Given a template and a passwd structure, build a filename 212 * by substituting % tokenised options. Currently, %% becomes '%', 213 * %h becomes the home directory and %u the username. 214 * 215 * This returns a buffer allocated by xmalloc. 216 */ 217 char * 218 expand_filename(const char *filename, struct passwd *pw) 219 { 220 Buffer buffer; 221 char *file; 222 const char *cp; 223 224 /* 225 * Build the filename string in the buffer by making the appropriate 226 * substitutions to the given file name. 227 */ 228 buffer_init(&buffer); 229 for (cp = filename; *cp; cp++) { 230 if (cp[0] == '%' && cp[1] == '%') { 231 buffer_append(&buffer, "%", 1); 232 cp++; 233 continue; 234 } 235 if (cp[0] == '%' && cp[1] == 'h') { 236 buffer_append(&buffer, pw->pw_dir, strlen(pw->pw_dir)); 237 cp++; 238 continue; 239 } 240 if (cp[0] == '%' && cp[1] == 'u') { 241 buffer_append(&buffer, pw->pw_name, 242 strlen(pw->pw_name)); 243 cp++; 244 continue; 245 } 246 buffer_append(&buffer, cp, 1); 247 } 248 buffer_append(&buffer, "\0", 1); 249 250 /* 251 * Ensure that filename starts anchored. If not, be backward 252 * compatible and prepend the '%h/' 253 */ 254 file = xmalloc(MAXPATHLEN); 255 cp = buffer_ptr(&buffer); 256 if (*cp != '/') 257 snprintf(file, MAXPATHLEN, "%s/%s", pw->pw_dir, cp); 258 else 259 strlcpy(file, cp, MAXPATHLEN); 260 261 buffer_free(&buffer); 262 return file; 263 } 264 265 char * 266 authorized_keys_file(struct passwd *pw) 267 { 268 return expand_filename(options.authorized_keys_file, pw); 269 } 270 271 char * 272 authorized_keys_file2(struct passwd *pw) 273 { 274 return expand_filename(options.authorized_keys_file2, pw); 275 } 276 277 /* return ok if key exists in sysfile or userfile */ 278 HostStatus 279 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 280 const char *sysfile, const char *userfile) 281 { 282 Key *found; 283 char *user_hostfile; 284 struct stat st; 285 HostStatus host_status; 286 287 /* Check if we know the host and its host key. */ 288 found = key_new(key->type); 289 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 290 291 if (host_status != HOST_OK && userfile != NULL) { 292 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 293 if (options.strict_modes && 294 (stat(user_hostfile, &st) == 0) && 295 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 296 (st.st_mode & 022) != 0)) { 297 logit("Authentication refused for %.100s: " 298 "bad owner or modes for %.200s", 299 pw->pw_name, user_hostfile); 300 } else { 301 temporarily_use_uid(pw); 302 host_status = check_host_in_hostfile(user_hostfile, 303 host, key, found, NULL); 304 restore_uid(); 305 } 306 xfree(user_hostfile); 307 } 308 key_free(found); 309 310 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 311 "ok" : "not found", host); 312 return host_status; 313 } 314 315 316 /* 317 * Check a given file for security. This is defined as all components 318 * of the path to the file must be owned by either the owner of 319 * of the file or root and no directories must be group or world writable. 320 * 321 * XXX Should any specific check be done for sym links ? 322 * 323 * Takes an open file descriptor, the file name, a uid and and 324 * error buffer plus max size as arguments. 325 * 326 * Returns 0 on success and -1 on failure 327 */ 328 int 329 secure_filename(FILE *f, const char *file, struct passwd *pw, 330 char *err, size_t errlen) 331 { 332 uid_t uid = pw->pw_uid; 333 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 334 char *cp; 335 int comparehome = 0; 336 struct stat st; 337 338 if (realpath(file, buf) == NULL) { 339 snprintf(err, errlen, "realpath %s failed: %s", file, 340 strerror(errno)); 341 return -1; 342 } 343 if (realpath(pw->pw_dir, homedir) != NULL) 344 comparehome = 1; 345 346 /* check the open file to avoid races */ 347 if (fstat(fileno(f), &st) < 0 || 348 (st.st_uid != 0 && st.st_uid != uid) || 349 (st.st_mode & 022) != 0) { 350 snprintf(err, errlen, "bad ownership or modes for file %s", 351 buf); 352 return -1; 353 } 354 355 /* for each component of the canonical path, walking upwards */ 356 for (;;) { 357 if ((cp = dirname(buf)) == NULL) { 358 snprintf(err, errlen, "dirname() failed"); 359 return -1; 360 } 361 strlcpy(buf, cp, sizeof(buf)); 362 363 debug3("secure_filename: checking '%s'", buf); 364 if (stat(buf, &st) < 0 || 365 (st.st_uid != 0 && st.st_uid != uid) || 366 (st.st_mode & 022) != 0) { 367 snprintf(err, errlen, 368 "bad ownership or modes for directory %s", buf); 369 return -1; 370 } 371 372 /* If are passed the homedir then we can stop */ 373 if (comparehome && strcmp(homedir, buf) == 0) { 374 debug3("secure_filename: terminating check at '%s'", 375 buf); 376 break; 377 } 378 /* 379 * dirname should always complete with a "/" path, 380 * but we can be paranoid and check for "." too 381 */ 382 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 383 break; 384 } 385 return 0; 386 } 387 388 struct passwd * 389 getpwnamallow(const char *user) 390 { 391 #ifdef HAVE_LOGIN_CAP 392 extern login_cap_t *lc; 393 #ifdef BSD_AUTH 394 auth_session_t *as; 395 #endif 396 #endif 397 struct passwd *pw; 398 399 pw = getpwnam(user); 400 if (pw == NULL) { 401 logit("Illegal user %.100s from %.100s", 402 user, get_remote_ipaddr()); 403 return (NULL); 404 } 405 if (!allowed_user(pw)) 406 return (NULL); 407 #ifdef HAVE_LOGIN_CAP 408 if ((lc = login_getclass(pw->pw_class)) == NULL) { 409 debug("unable to get login class: %s", user); 410 return (NULL); 411 } 412 #ifdef BSD_AUTH 413 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 414 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 415 debug("Approval failure for %s", user); 416 pw = NULL; 417 } 418 if (as != NULL) 419 auth_close(as); 420 #endif 421 #endif 422 if (pw != NULL) 423 return (pwcopy(pw)); 424 return (NULL); 425 } 426 427 void 428 auth_debug_add(const char *fmt,...) 429 { 430 char buf[1024]; 431 va_list args; 432 433 if (!auth_debug_init) 434 return; 435 436 va_start(args, fmt); 437 vsnprintf(buf, sizeof(buf), fmt, args); 438 va_end(args); 439 buffer_put_cstring(&auth_debug, buf); 440 } 441 442 void 443 auth_debug_send(void) 444 { 445 char *msg; 446 447 if (!auth_debug_init) 448 return; 449 while (buffer_len(&auth_debug)) { 450 msg = buffer_get_string(&auth_debug, NULL); 451 packet_send_debug("%s", msg); 452 xfree(msg); 453 } 454 } 455 456 void 457 auth_debug_reset(void) 458 { 459 if (auth_debug_init) 460 buffer_clear(&auth_debug); 461 else { 462 buffer_init(&auth_debug); 463 auth_debug_init = 1; 464 } 465 } 466 467 struct passwd * 468 fakepw(void) 469 { 470 static struct passwd fake; 471 472 memset(&fake, 0, sizeof(fake)); 473 fake.pw_name = "NOUSER"; 474 fake.pw_passwd = 475 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 476 fake.pw_gecos = "NOUSER"; 477 fake.pw_uid = -1; 478 fake.pw_gid = -1; 479 fake.pw_class = ""; 480 fake.pw_dir = "/nonexist"; 481 fake.pw_shell = "/nonexist"; 482 483 return (&fake); 484 } 485