1 /* $OpenBSD: auth.c,v 1.78 2007/09/21 08:15:29 djm 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 <login_cap.h> 33 #include <paths.h> 34 #include <pwd.h> 35 #include <stdarg.h> 36 #include <stdio.h> 37 #include <string.h> 38 39 #include "xmalloc.h" 40 #include "match.h" 41 #include "groupaccess.h" 42 #include "log.h" 43 #include "buffer.h" 44 #include "servconf.h" 45 #include "key.h" 46 #include "hostfile.h" 47 #include "auth.h" 48 #include "auth-options.h" 49 #include "canohost.h" 50 #include "uidswap.h" 51 #include "misc.h" 52 #include "packet.h" 53 #ifdef GSSAPI 54 #include "ssh-gss.h" 55 #endif 56 #include "monitor_wrap.h" 57 58 /* import */ 59 extern ServerOptions options; 60 extern int use_privsep; 61 62 /* Debugging messages */ 63 Buffer auth_debug; 64 int auth_debug_init; 65 66 /* 67 * Check if the user is allowed to log in via ssh. If user is listed 68 * in DenyUsers or one of user's groups is listed in DenyGroups, false 69 * will be returned. If AllowUsers isn't empty and user isn't listed 70 * there, or if AllowGroups isn't empty and one of user's groups isn't 71 * listed there, false will be returned. 72 * If the user's shell is not executable, false will be returned. 73 * Otherwise true is returned. 74 */ 75 int 76 allowed_user(struct passwd * pw) 77 { 78 struct stat st; 79 const char *hostname = NULL, *ipaddr = NULL; 80 char *shell; 81 u_int i; 82 83 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 84 if (!pw || !pw->pw_name) 85 return 0; 86 87 /* 88 * Get the shell from the password data. An empty shell field is 89 * legal, and means /bin/sh. 90 */ 91 shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell; 92 93 /* deny if shell does not exists or is not executable */ 94 if (stat(shell, &st) != 0) { 95 logit("User %.100s not allowed because shell %.100s does not exist", 96 pw->pw_name, shell); 97 return 0; 98 } 99 if (S_ISREG(st.st_mode) == 0 || 100 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 101 logit("User %.100s not allowed because shell %.100s is not executable", 102 pw->pw_name, shell); 103 return 0; 104 } 105 106 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 107 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 108 hostname = get_canonical_hostname(options.use_dns); 109 ipaddr = get_remote_ipaddr(); 110 } 111 112 /* Return false if user is listed in DenyUsers */ 113 if (options.num_deny_users > 0) { 114 for (i = 0; i < options.num_deny_users; i++) 115 if (match_user(pw->pw_name, hostname, ipaddr, 116 options.deny_users[i])) { 117 logit("User %.100s from %.100s not allowed " 118 "because listed in DenyUsers", 119 pw->pw_name, hostname); 120 return 0; 121 } 122 } 123 /* Return false if AllowUsers isn't empty and user isn't listed there */ 124 if (options.num_allow_users > 0) { 125 for (i = 0; i < options.num_allow_users; i++) 126 if (match_user(pw->pw_name, hostname, ipaddr, 127 options.allow_users[i])) 128 break; 129 /* i < options.num_allow_users iff we break for loop */ 130 if (i >= options.num_allow_users) { 131 logit("User %.100s from %.100s not allowed because " 132 "not listed in AllowUsers", pw->pw_name, hostname); 133 return 0; 134 } 135 } 136 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 137 /* Get the user's group access list (primary and supplementary) */ 138 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 139 logit("User %.100s from %.100s not allowed because " 140 "not in any group", pw->pw_name, hostname); 141 return 0; 142 } 143 144 /* Return false if one of user's groups is listed in DenyGroups */ 145 if (options.num_deny_groups > 0) 146 if (ga_match(options.deny_groups, 147 options.num_deny_groups)) { 148 ga_free(); 149 logit("User %.100s from %.100s not allowed " 150 "because a group is listed in DenyGroups", 151 pw->pw_name, hostname); 152 return 0; 153 } 154 /* 155 * Return false if AllowGroups isn't empty and one of user's groups 156 * isn't listed there 157 */ 158 if (options.num_allow_groups > 0) 159 if (!ga_match(options.allow_groups, 160 options.num_allow_groups)) { 161 ga_free(); 162 logit("User %.100s from %.100s not allowed " 163 "because none of user's groups are listed " 164 "in AllowGroups", pw->pw_name, hostname); 165 return 0; 166 } 167 ga_free(); 168 } 169 /* We found no reason not to let this user try to log on... */ 170 return 1; 171 } 172 173 void 174 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info) 175 { 176 void (*authlog) (const char *fmt,...) = verbose; 177 char *authmsg; 178 179 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 180 return; 181 182 /* Raise logging level */ 183 if (authenticated == 1 || 184 !authctxt->valid || 185 authctxt->failures >= options.max_authtries / 2 || 186 strcmp(method, "password") == 0) 187 authlog = logit; 188 189 if (authctxt->postponed) 190 authmsg = "Postponed"; 191 else 192 authmsg = authenticated ? "Accepted" : "Failed"; 193 194 authlog("%s %s for %s%.100s from %.200s port %d%s", 195 authmsg, 196 method, 197 authctxt->valid ? "" : "invalid user ", 198 authctxt->user, 199 get_remote_ipaddr(), 200 get_remote_port(), 201 info); 202 } 203 204 /* 205 * Check whether root logins are disallowed. 206 */ 207 int 208 auth_root_allowed(char *method) 209 { 210 switch (options.permit_root_login) { 211 case PERMIT_YES: 212 return 1; 213 case PERMIT_NO_PASSWD: 214 if (strcmp(method, "password") != 0) 215 return 1; 216 break; 217 case PERMIT_FORCED_ONLY: 218 if (forced_command) { 219 logit("Root login accepted for forced command."); 220 return 1; 221 } 222 break; 223 } 224 logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr()); 225 return 0; 226 } 227 228 229 /* 230 * Given a template and a passwd structure, build a filename 231 * by substituting % tokenised options. Currently, %% becomes '%', 232 * %h becomes the home directory and %u the username. 233 * 234 * This returns a buffer allocated by xmalloc. 235 */ 236 static char * 237 expand_authorized_keys(const char *filename, struct passwd *pw) 238 { 239 char *file, ret[MAXPATHLEN]; 240 int i; 241 242 file = percent_expand(filename, "h", pw->pw_dir, 243 "u", pw->pw_name, (char *)NULL); 244 245 /* 246 * Ensure that filename starts anchored. If not, be backward 247 * compatible and prepend the '%h/' 248 */ 249 if (*file == '/') 250 return (file); 251 252 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 253 if (i < 0 || (size_t)i >= sizeof(ret)) 254 fatal("expand_authorized_keys: path too long"); 255 xfree(file); 256 return (xstrdup(ret)); 257 } 258 259 char * 260 authorized_keys_file(struct passwd *pw) 261 { 262 return expand_authorized_keys(options.authorized_keys_file, pw); 263 } 264 265 char * 266 authorized_keys_file2(struct passwd *pw) 267 { 268 return expand_authorized_keys(options.authorized_keys_file2, pw); 269 } 270 271 /* return ok if key exists in sysfile or userfile */ 272 HostStatus 273 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 274 const char *sysfile, const char *userfile) 275 { 276 Key *found; 277 char *user_hostfile; 278 struct stat st; 279 HostStatus host_status; 280 281 /* Check if we know the host and its host key. */ 282 found = key_new(key->type); 283 host_status = check_host_in_hostfile(sysfile, host, key, found, NULL); 284 285 if (host_status != HOST_OK && userfile != NULL) { 286 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 287 if (options.strict_modes && 288 (stat(user_hostfile, &st) == 0) && 289 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 290 (st.st_mode & 022) != 0)) { 291 logit("Authentication refused for %.100s: " 292 "bad owner or modes for %.200s", 293 pw->pw_name, user_hostfile); 294 } else { 295 temporarily_use_uid(pw); 296 host_status = check_host_in_hostfile(user_hostfile, 297 host, key, found, NULL); 298 restore_uid(); 299 } 300 xfree(user_hostfile); 301 } 302 key_free(found); 303 304 debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ? 305 "ok" : "not found", host); 306 return host_status; 307 } 308 309 310 /* 311 * Check a given file for security. This is defined as all components 312 * of the path to the file must be owned by either the owner of 313 * of the file or root and no directories must be group or world writable. 314 * 315 * XXX Should any specific check be done for sym links ? 316 * 317 * Takes an open file descriptor, the file name, a uid and and 318 * error buffer plus max size as arguments. 319 * 320 * Returns 0 on success and -1 on failure 321 */ 322 int 323 secure_filename(FILE *f, const char *file, struct passwd *pw, 324 char *err, size_t errlen) 325 { 326 uid_t uid = pw->pw_uid; 327 char buf[MAXPATHLEN], homedir[MAXPATHLEN]; 328 char *cp; 329 int comparehome = 0; 330 struct stat st; 331 332 if (realpath(file, buf) == NULL) { 333 snprintf(err, errlen, "realpath %s failed: %s", file, 334 strerror(errno)); 335 return -1; 336 } 337 if (realpath(pw->pw_dir, homedir) != NULL) 338 comparehome = 1; 339 340 /* check the open file to avoid races */ 341 if (fstat(fileno(f), &st) < 0 || 342 (st.st_uid != 0 && st.st_uid != uid) || 343 (st.st_mode & 022) != 0) { 344 snprintf(err, errlen, "bad ownership or modes for file %s", 345 buf); 346 return -1; 347 } 348 349 /* for each component of the canonical path, walking upwards */ 350 for (;;) { 351 if ((cp = dirname(buf)) == NULL) { 352 snprintf(err, errlen, "dirname() failed"); 353 return -1; 354 } 355 strlcpy(buf, cp, sizeof(buf)); 356 357 debug3("secure_filename: checking '%s'", buf); 358 if (stat(buf, &st) < 0 || 359 (st.st_uid != 0 && st.st_uid != uid) || 360 (st.st_mode & 022) != 0) { 361 snprintf(err, errlen, 362 "bad ownership or modes for directory %s", buf); 363 return -1; 364 } 365 366 /* If are passed the homedir then we can stop */ 367 if (comparehome && strcmp(homedir, buf) == 0) { 368 debug3("secure_filename: terminating check at '%s'", 369 buf); 370 break; 371 } 372 /* 373 * dirname should always complete with a "/" path, 374 * but we can be paranoid and check for "." too 375 */ 376 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 377 break; 378 } 379 return 0; 380 } 381 382 struct passwd * 383 getpwnamallow(const char *user) 384 { 385 extern login_cap_t *lc; 386 auth_session_t *as; 387 struct passwd *pw; 388 389 parse_server_match_config(&options, user, 390 get_canonical_hostname(options.use_dns), get_remote_ipaddr()); 391 392 pw = getpwnam(user); 393 if (pw == NULL) { 394 logit("Invalid user %.100s from %.100s", 395 user, get_remote_ipaddr()); 396 return (NULL); 397 } 398 if (!allowed_user(pw)) 399 return (NULL); 400 if ((lc = login_getclass(pw->pw_class)) == NULL) { 401 debug("unable to get login class: %s", user); 402 return (NULL); 403 } 404 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 405 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 406 debug("Approval failure for %s", user); 407 pw = NULL; 408 } 409 if (as != NULL) 410 auth_close(as); 411 if (pw != NULL) 412 return (pwcopy(pw)); 413 return (NULL); 414 } 415 416 void 417 auth_debug_add(const char *fmt,...) 418 { 419 char buf[1024]; 420 va_list args; 421 422 if (!auth_debug_init) 423 return; 424 425 va_start(args, fmt); 426 vsnprintf(buf, sizeof(buf), fmt, args); 427 va_end(args); 428 buffer_put_cstring(&auth_debug, buf); 429 } 430 431 void 432 auth_debug_send(void) 433 { 434 char *msg; 435 436 if (!auth_debug_init) 437 return; 438 while (buffer_len(&auth_debug)) { 439 msg = buffer_get_string(&auth_debug, NULL); 440 packet_send_debug("%s", msg); 441 xfree(msg); 442 } 443 } 444 445 void 446 auth_debug_reset(void) 447 { 448 if (auth_debug_init) 449 buffer_clear(&auth_debug); 450 else { 451 buffer_init(&auth_debug); 452 auth_debug_init = 1; 453 } 454 } 455 456 struct passwd * 457 fakepw(void) 458 { 459 static struct passwd fake; 460 461 memset(&fake, 0, sizeof(fake)); 462 fake.pw_name = "NOUSER"; 463 fake.pw_passwd = 464 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 465 fake.pw_gecos = "NOUSER"; 466 fake.pw_uid = (uid_t)-1; 467 fake.pw_gid = (gid_t)-1; 468 fake.pw_class = ""; 469 fake.pw_dir = "/nonexist"; 470 fake.pw_shell = "/nonexist"; 471 472 return (&fake); 473 } 474