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