1 /* $OpenBSD: auth.c,v 1.119 2016/12/15 21:29:05 dtucker 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/socket.h> 29 30 #include <errno.h> 31 #include <fcntl.h> 32 #include <libgen.h> 33 #include <login_cap.h> 34 #include <paths.h> 35 #include <pwd.h> 36 #include <stdarg.h> 37 #include <stdio.h> 38 #include <string.h> 39 #include <unistd.h> 40 #include <limits.h> 41 #include <netdb.h> 42 43 #include "xmalloc.h" 44 #include "match.h" 45 #include "groupaccess.h" 46 #include "log.h" 47 #include "buffer.h" 48 #include "misc.h" 49 #include "servconf.h" 50 #include "key.h" 51 #include "hostfile.h" 52 #include "auth.h" 53 #include "auth-options.h" 54 #include "canohost.h" 55 #include "uidswap.h" 56 #include "packet.h" 57 #ifdef GSSAPI 58 #include "ssh-gss.h" 59 #endif 60 #include "authfile.h" 61 #include "monitor_wrap.h" 62 #include "authfile.h" 63 #include "ssherr.h" 64 #include "compat.h" 65 66 /* import */ 67 extern ServerOptions options; 68 extern int use_privsep; 69 70 /* Debugging messages */ 71 Buffer auth_debug; 72 int auth_debug_init; 73 74 /* 75 * Check if the user is allowed to log in via ssh. If user is listed 76 * in DenyUsers or one of user's groups is listed in DenyGroups, false 77 * will be returned. If AllowUsers isn't empty and user isn't listed 78 * there, or if AllowGroups isn't empty and one of user's groups isn't 79 * listed there, false will be returned. 80 * If the user's shell is not executable, false will be returned. 81 * Otherwise true is returned. 82 */ 83 int 84 allowed_user(struct passwd * pw) 85 { 86 struct ssh *ssh = active_state; /* XXX */ 87 struct stat st; 88 const char *hostname = NULL, *ipaddr = NULL; 89 int r; 90 u_int i; 91 92 /* Shouldn't be called if pw is NULL, but better safe than sorry... */ 93 if (!pw || !pw->pw_name) 94 return 0; 95 96 /* 97 * Deny if shell does not exist or is not executable unless we 98 * are chrooting. 99 */ 100 if (options.chroot_directory == NULL || 101 strcasecmp(options.chroot_directory, "none") == 0) { 102 char *shell = xstrdup((pw->pw_shell[0] == '\0') ? 103 _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */ 104 105 if (stat(shell, &st) != 0) { 106 logit("User %.100s not allowed because shell %.100s " 107 "does not exist", pw->pw_name, shell); 108 free(shell); 109 return 0; 110 } 111 if (S_ISREG(st.st_mode) == 0 || 112 (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) { 113 logit("User %.100s not allowed because shell %.100s " 114 "is not executable", pw->pw_name, shell); 115 free(shell); 116 return 0; 117 } 118 free(shell); 119 } 120 121 if (options.num_deny_users > 0 || options.num_allow_users > 0 || 122 options.num_deny_groups > 0 || options.num_allow_groups > 0) { 123 hostname = auth_get_canonical_hostname(ssh, options.use_dns); 124 ipaddr = ssh_remote_ipaddr(ssh); 125 } 126 127 /* Return false if user is listed in DenyUsers */ 128 if (options.num_deny_users > 0) { 129 for (i = 0; i < options.num_deny_users; i++) { 130 r = match_user(pw->pw_name, hostname, ipaddr, 131 options.deny_users[i]); 132 if (r < 0) { 133 fatal("Invalid DenyUsers pattern \"%.100s\"", 134 options.deny_users[i]); 135 } else if (r != 0) { 136 logit("User %.100s from %.100s not allowed " 137 "because listed in DenyUsers", 138 pw->pw_name, hostname); 139 return 0; 140 } 141 } 142 } 143 /* Return false if AllowUsers isn't empty and user isn't listed there */ 144 if (options.num_allow_users > 0) { 145 for (i = 0; i < options.num_allow_users; i++) { 146 r = match_user(pw->pw_name, hostname, ipaddr, 147 options.allow_users[i]); 148 if (r < 0) { 149 fatal("Invalid AllowUsers pattern \"%.100s\"", 150 options.allow_users[i]); 151 } else if (r == 1) 152 break; 153 } 154 /* i < options.num_allow_users iff we break for loop */ 155 if (i >= options.num_allow_users) { 156 logit("User %.100s from %.100s not allowed because " 157 "not listed in AllowUsers", pw->pw_name, hostname); 158 return 0; 159 } 160 } 161 if (options.num_deny_groups > 0 || options.num_allow_groups > 0) { 162 /* Get the user's group access list (primary and supplementary) */ 163 if (ga_init(pw->pw_name, pw->pw_gid) == 0) { 164 logit("User %.100s from %.100s not allowed because " 165 "not in any group", pw->pw_name, hostname); 166 return 0; 167 } 168 169 /* Return false if one of user's groups is listed in DenyGroups */ 170 if (options.num_deny_groups > 0) 171 if (ga_match(options.deny_groups, 172 options.num_deny_groups)) { 173 ga_free(); 174 logit("User %.100s from %.100s not allowed " 175 "because a group is listed in DenyGroups", 176 pw->pw_name, hostname); 177 return 0; 178 } 179 /* 180 * Return false if AllowGroups isn't empty and one of user's groups 181 * isn't listed there 182 */ 183 if (options.num_allow_groups > 0) 184 if (!ga_match(options.allow_groups, 185 options.num_allow_groups)) { 186 ga_free(); 187 logit("User %.100s from %.100s not allowed " 188 "because none of user's groups are listed " 189 "in AllowGroups", pw->pw_name, hostname); 190 return 0; 191 } 192 ga_free(); 193 } 194 /* We found no reason not to let this user try to log on... */ 195 return 1; 196 } 197 198 void 199 auth_info(Authctxt *authctxt, const char *fmt, ...) 200 { 201 va_list ap; 202 int i; 203 204 free(authctxt->info); 205 authctxt->info = NULL; 206 207 va_start(ap, fmt); 208 i = vasprintf(&authctxt->info, fmt, ap); 209 va_end(ap); 210 211 if (i < 0 || authctxt->info == NULL) 212 fatal("vasprintf failed"); 213 } 214 215 void 216 auth_log(Authctxt *authctxt, int authenticated, int partial, 217 const char *method, const char *submethod) 218 { 219 struct ssh *ssh = active_state; /* XXX */ 220 void (*authlog) (const char *fmt,...) = verbose; 221 char *authmsg; 222 223 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 224 return; 225 226 /* Raise logging level */ 227 if (authenticated == 1 || 228 !authctxt->valid || 229 authctxt->failures >= options.max_authtries / 2 || 230 strcmp(method, "password") == 0) 231 authlog = logit; 232 233 if (authctxt->postponed) 234 authmsg = "Postponed"; 235 else if (partial) 236 authmsg = "Partial"; 237 else 238 authmsg = authenticated ? "Accepted" : "Failed"; 239 240 authlog("%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s", 241 authmsg, 242 method, 243 submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod, 244 authctxt->valid ? "" : "invalid user ", 245 authctxt->user, 246 ssh_remote_ipaddr(ssh), 247 ssh_remote_port(ssh), 248 authctxt->info != NULL ? ": " : "", 249 authctxt->info != NULL ? authctxt->info : ""); 250 free(authctxt->info); 251 authctxt->info = NULL; 252 } 253 254 void 255 auth_maxtries_exceeded(Authctxt *authctxt) 256 { 257 struct ssh *ssh = active_state; /* XXX */ 258 259 error("maximum authentication attempts exceeded for " 260 "%s%.100s from %.200s port %d ssh2", 261 authctxt->valid ? "" : "invalid user ", 262 authctxt->user, 263 ssh_remote_ipaddr(ssh), 264 ssh_remote_port(ssh)); 265 packet_disconnect("Too many authentication failures"); 266 /* NOTREACHED */ 267 } 268 269 /* 270 * Check whether root logins are disallowed. 271 */ 272 int 273 auth_root_allowed(const char *method) 274 { 275 struct ssh *ssh = active_state; /* XXX */ 276 277 switch (options.permit_root_login) { 278 case PERMIT_YES: 279 return 1; 280 case PERMIT_NO_PASSWD: 281 if (strcmp(method, "publickey") == 0 || 282 strcmp(method, "hostbased") == 0 || 283 strcmp(method, "gssapi-with-mic") == 0) 284 return 1; 285 break; 286 case PERMIT_FORCED_ONLY: 287 if (forced_command) { 288 logit("Root login accepted for forced command."); 289 return 1; 290 } 291 break; 292 } 293 logit("ROOT LOGIN REFUSED FROM %.200s port %d", 294 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); 295 return 0; 296 } 297 298 299 /* 300 * Given a template and a passwd structure, build a filename 301 * by substituting % tokenised options. Currently, %% becomes '%', 302 * %h becomes the home directory and %u the username. 303 * 304 * This returns a buffer allocated by xmalloc. 305 */ 306 char * 307 expand_authorized_keys(const char *filename, struct passwd *pw) 308 { 309 char *file, ret[PATH_MAX]; 310 int i; 311 312 file = percent_expand(filename, "h", pw->pw_dir, 313 "u", pw->pw_name, (char *)NULL); 314 315 /* 316 * Ensure that filename starts anchored. If not, be backward 317 * compatible and prepend the '%h/' 318 */ 319 if (*file == '/') 320 return (file); 321 322 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 323 if (i < 0 || (size_t)i >= sizeof(ret)) 324 fatal("expand_authorized_keys: path too long"); 325 free(file); 326 return (xstrdup(ret)); 327 } 328 329 char * 330 authorized_principals_file(struct passwd *pw) 331 { 332 if (options.authorized_principals_file == NULL) 333 return NULL; 334 return expand_authorized_keys(options.authorized_principals_file, pw); 335 } 336 337 /* return ok if key exists in sysfile or userfile */ 338 HostStatus 339 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host, 340 const char *sysfile, const char *userfile) 341 { 342 char *user_hostfile; 343 struct stat st; 344 HostStatus host_status; 345 struct hostkeys *hostkeys; 346 const struct hostkey_entry *found; 347 348 hostkeys = init_hostkeys(); 349 load_hostkeys(hostkeys, host, sysfile); 350 if (userfile != NULL) { 351 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 352 if (options.strict_modes && 353 (stat(user_hostfile, &st) == 0) && 354 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 355 (st.st_mode & 022) != 0)) { 356 logit("Authentication refused for %.100s: " 357 "bad owner or modes for %.200s", 358 pw->pw_name, user_hostfile); 359 auth_debug_add("Ignored %.200s: bad ownership or modes", 360 user_hostfile); 361 } else { 362 temporarily_use_uid(pw); 363 load_hostkeys(hostkeys, host, user_hostfile); 364 restore_uid(); 365 } 366 free(user_hostfile); 367 } 368 host_status = check_key_in_hostkeys(hostkeys, key, &found); 369 if (host_status == HOST_REVOKED) 370 error("WARNING: revoked key for %s attempted authentication", 371 found->host); 372 else if (host_status == HOST_OK) 373 debug("%s: key for %s found at %s:%ld", __func__, 374 found->host, found->file, found->line); 375 else 376 debug("%s: key for host %s not found", __func__, host); 377 378 free_hostkeys(hostkeys); 379 380 return host_status; 381 } 382 383 /* 384 * Check a given path for security. This is defined as all components 385 * of the path to the file must be owned by either the owner of 386 * of the file or root and no directories must be group or world writable. 387 * 388 * XXX Should any specific check be done for sym links ? 389 * 390 * Takes a file name, its stat information (preferably from fstat() to 391 * avoid races), the uid of the expected owner, their home directory and an 392 * error buffer plus max size as arguments. 393 * 394 * Returns 0 on success and -1 on failure 395 */ 396 int 397 auth_secure_path(const char *name, struct stat *stp, const char *pw_dir, 398 uid_t uid, char *err, size_t errlen) 399 { 400 char buf[PATH_MAX], homedir[PATH_MAX]; 401 char *cp; 402 int comparehome = 0; 403 struct stat st; 404 405 if (realpath(name, buf) == NULL) { 406 snprintf(err, errlen, "realpath %s failed: %s", name, 407 strerror(errno)); 408 return -1; 409 } 410 if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL) 411 comparehome = 1; 412 413 if (!S_ISREG(stp->st_mode)) { 414 snprintf(err, errlen, "%s is not a regular file", buf); 415 return -1; 416 } 417 if ((stp->st_uid != 0 && stp->st_uid != uid) || 418 (stp->st_mode & 022) != 0) { 419 snprintf(err, errlen, "bad ownership or modes for file %s", 420 buf); 421 return -1; 422 } 423 424 /* for each component of the canonical path, walking upwards */ 425 for (;;) { 426 if ((cp = dirname(buf)) == NULL) { 427 snprintf(err, errlen, "dirname() failed"); 428 return -1; 429 } 430 strlcpy(buf, cp, sizeof(buf)); 431 432 if (stat(buf, &st) < 0 || 433 (st.st_uid != 0 && st.st_uid != uid) || 434 (st.st_mode & 022) != 0) { 435 snprintf(err, errlen, 436 "bad ownership or modes for directory %s", buf); 437 return -1; 438 } 439 440 /* If are past the homedir then we can stop */ 441 if (comparehome && strcmp(homedir, buf) == 0) 442 break; 443 444 /* 445 * dirname should always complete with a "/" path, 446 * but we can be paranoid and check for "." too 447 */ 448 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0)) 449 break; 450 } 451 return 0; 452 } 453 454 /* 455 * Version of secure_path() that accepts an open file descriptor to 456 * avoid races. 457 * 458 * Returns 0 on success and -1 on failure 459 */ 460 static int 461 secure_filename(FILE *f, const char *file, struct passwd *pw, 462 char *err, size_t errlen) 463 { 464 struct stat st; 465 466 /* check the open file to avoid races */ 467 if (fstat(fileno(f), &st) < 0) { 468 snprintf(err, errlen, "cannot stat file %s: %s", 469 file, strerror(errno)); 470 return -1; 471 } 472 return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen); 473 } 474 475 static FILE * 476 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 477 int log_missing, char *file_type) 478 { 479 char line[1024]; 480 struct stat st; 481 int fd; 482 FILE *f; 483 484 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 485 if (log_missing || errno != ENOENT) 486 debug("Could not open %s '%s': %s", file_type, file, 487 strerror(errno)); 488 return NULL; 489 } 490 491 if (fstat(fd, &st) < 0) { 492 close(fd); 493 return NULL; 494 } 495 if (!S_ISREG(st.st_mode)) { 496 logit("User %s %s %s is not a regular file", 497 pw->pw_name, file_type, file); 498 close(fd); 499 return NULL; 500 } 501 unset_nonblock(fd); 502 if ((f = fdopen(fd, "r")) == NULL) { 503 close(fd); 504 return NULL; 505 } 506 if (strict_modes && 507 secure_filename(f, file, pw, line, sizeof(line)) != 0) { 508 fclose(f); 509 logit("Authentication refused: %s", line); 510 auth_debug_add("Ignored %s: %s", file_type, line); 511 return NULL; 512 } 513 514 return f; 515 } 516 517 518 FILE * 519 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 520 { 521 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 522 } 523 524 FILE * 525 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 526 { 527 return auth_openfile(file, pw, strict_modes, 0, 528 "authorized principals"); 529 } 530 531 struct passwd * 532 getpwnamallow(const char *user) 533 { 534 struct ssh *ssh = active_state; /* XXX */ 535 extern login_cap_t *lc; 536 auth_session_t *as; 537 struct passwd *pw; 538 struct connection_info *ci = get_connection_info(1, options.use_dns); 539 540 ci->user = user; 541 parse_server_match_config(&options, ci); 542 543 pw = getpwnam(user); 544 if (pw == NULL) { 545 logit("Invalid user %.100s from %.100s port %d", 546 user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); 547 return (NULL); 548 } 549 if (!allowed_user(pw)) 550 return (NULL); 551 if ((lc = login_getclass(pw->pw_class)) == NULL) { 552 debug("unable to get login class: %s", user); 553 return (NULL); 554 } 555 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 556 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 557 debug("Approval failure for %s", user); 558 pw = NULL; 559 } 560 if (as != NULL) 561 auth_close(as); 562 if (pw != NULL) 563 return (pwcopy(pw)); 564 return (NULL); 565 } 566 567 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 568 int 569 auth_key_is_revoked(Key *key) 570 { 571 char *fp = NULL; 572 int r; 573 574 if (options.revoked_keys_file == NULL) 575 return 0; 576 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 577 SSH_FP_DEFAULT)) == NULL) { 578 r = SSH_ERR_ALLOC_FAIL; 579 error("%s: fingerprint key: %s", __func__, ssh_err(r)); 580 goto out; 581 } 582 583 r = sshkey_check_revoked(key, options.revoked_keys_file); 584 switch (r) { 585 case 0: 586 break; /* not revoked */ 587 case SSH_ERR_KEY_REVOKED: 588 error("Authentication key %s %s revoked by file %s", 589 sshkey_type(key), fp, options.revoked_keys_file); 590 goto out; 591 default: 592 error("Error checking authentication key %s %s in " 593 "revoked keys file %s: %s", sshkey_type(key), fp, 594 options.revoked_keys_file, ssh_err(r)); 595 goto out; 596 } 597 598 /* Success */ 599 r = 0; 600 601 out: 602 free(fp); 603 return r == 0 ? 0 : 1; 604 } 605 606 void 607 auth_debug_add(const char *fmt,...) 608 { 609 char buf[1024]; 610 va_list args; 611 612 if (!auth_debug_init) 613 return; 614 615 va_start(args, fmt); 616 vsnprintf(buf, sizeof(buf), fmt, args); 617 va_end(args); 618 buffer_put_cstring(&auth_debug, buf); 619 } 620 621 void 622 auth_debug_send(void) 623 { 624 char *msg; 625 626 if (!auth_debug_init) 627 return; 628 while (buffer_len(&auth_debug)) { 629 msg = buffer_get_string(&auth_debug, NULL); 630 packet_send_debug("%s", msg); 631 free(msg); 632 } 633 } 634 635 void 636 auth_debug_reset(void) 637 { 638 if (auth_debug_init) 639 buffer_clear(&auth_debug); 640 else { 641 buffer_init(&auth_debug); 642 auth_debug_init = 1; 643 } 644 } 645 646 struct passwd * 647 fakepw(void) 648 { 649 static struct passwd fake; 650 651 memset(&fake, 0, sizeof(fake)); 652 fake.pw_name = "NOUSER"; 653 fake.pw_passwd = 654 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 655 fake.pw_gecos = "NOUSER"; 656 fake.pw_uid = (uid_t)-1; 657 fake.pw_gid = (gid_t)-1; 658 fake.pw_class = ""; 659 fake.pw_dir = "/nonexist"; 660 fake.pw_shell = "/nonexist"; 661 662 return (&fake); 663 } 664 665 /* 666 * Returns the remote DNS hostname as a string. The returned string must not 667 * be freed. NB. this will usually trigger a DNS query the first time it is 668 * called. 669 * This function does additional checks on the hostname to mitigate some 670 * attacks on legacy rhosts-style authentication. 671 * XXX is RhostsRSAAuthentication vulnerable to these? 672 * XXX Can we remove these checks? (or if not, remove RhostsRSAAuthentication?) 673 */ 674 675 static char * 676 remote_hostname(struct ssh *ssh) 677 { 678 struct sockaddr_storage from; 679 socklen_t fromlen; 680 struct addrinfo hints, *ai, *aitop; 681 char name[NI_MAXHOST], ntop2[NI_MAXHOST]; 682 const char *ntop = ssh_remote_ipaddr(ssh); 683 684 /* Get IP address of client. */ 685 fromlen = sizeof(from); 686 memset(&from, 0, sizeof(from)); 687 if (getpeername(ssh_packet_get_connection_in(ssh), 688 (struct sockaddr *)&from, &fromlen) < 0) { 689 debug("getpeername failed: %.100s", strerror(errno)); 690 return strdup(ntop); 691 } 692 693 debug3("Trying to reverse map address %.100s.", ntop); 694 /* Map the IP address to a host name. */ 695 if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name), 696 NULL, 0, NI_NAMEREQD) != 0) { 697 /* Host name not found. Use ip address. */ 698 return strdup(ntop); 699 } 700 701 /* 702 * if reverse lookup result looks like a numeric hostname, 703 * someone is trying to trick us by PTR record like following: 704 * 1.1.1.10.in-addr.arpa. IN PTR 2.3.4.5 705 */ 706 memset(&hints, 0, sizeof(hints)); 707 hints.ai_socktype = SOCK_DGRAM; /*dummy*/ 708 hints.ai_flags = AI_NUMERICHOST; 709 if (getaddrinfo(name, NULL, &hints, &ai) == 0) { 710 logit("Nasty PTR record \"%s\" is set up for %s, ignoring", 711 name, ntop); 712 freeaddrinfo(ai); 713 return strdup(ntop); 714 } 715 716 /* Names are stored in lowercase. */ 717 lowercase(name); 718 719 /* 720 * Map it back to an IP address and check that the given 721 * address actually is an address of this host. This is 722 * necessary because anyone with access to a name server can 723 * define arbitrary names for an IP address. Mapping from 724 * name to IP address can be trusted better (but can still be 725 * fooled if the intruder has access to the name server of 726 * the domain). 727 */ 728 memset(&hints, 0, sizeof(hints)); 729 hints.ai_family = from.ss_family; 730 hints.ai_socktype = SOCK_STREAM; 731 if (getaddrinfo(name, NULL, &hints, &aitop) != 0) { 732 logit("reverse mapping checking getaddrinfo for %.700s " 733 "[%s] failed.", name, ntop); 734 return strdup(ntop); 735 } 736 /* Look for the address from the list of addresses. */ 737 for (ai = aitop; ai; ai = ai->ai_next) { 738 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2, 739 sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 && 740 (strcmp(ntop, ntop2) == 0)) 741 break; 742 } 743 freeaddrinfo(aitop); 744 /* If we reached the end of the list, the address was not there. */ 745 if (ai == NULL) { 746 /* Address not found for the host name. */ 747 logit("Address %.100s maps to %.600s, but this does not " 748 "map back to the address.", ntop, name); 749 return strdup(ntop); 750 } 751 return strdup(name); 752 } 753 754 /* 755 * Return the canonical name of the host in the other side of the current 756 * connection. The host name is cached, so it is efficient to call this 757 * several times. 758 */ 759 760 const char * 761 auth_get_canonical_hostname(struct ssh *ssh, int use_dns) 762 { 763 static char *dnsname; 764 765 if (!use_dns) 766 return ssh_remote_ipaddr(ssh); 767 else if (dnsname != NULL) 768 return dnsname; 769 else { 770 dnsname = remote_hostname(ssh); 771 return dnsname; 772 } 773 } 774