1 /* $OpenBSD: auth.c,v 1.125 2018/01/08 15:21:49 markus 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 #include <sys/wait.h> 30 31 #include <errno.h> 32 #include <fcntl.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 /* 199 * Formats any key left in authctxt->auth_method_key for inclusion in 200 * auth_log()'s message. Also includes authxtct->auth_method_info if present. 201 */ 202 static char * 203 format_method_key(Authctxt *authctxt) 204 { 205 const struct sshkey *key = authctxt->auth_method_key; 206 const char *methinfo = authctxt->auth_method_info; 207 char *fp, *ret = NULL; 208 209 if (key == NULL) 210 return NULL; 211 212 if (key_is_cert(key)) { 213 fp = sshkey_fingerprint(key->cert->signature_key, 214 options.fingerprint_hash, SSH_FP_DEFAULT); 215 xasprintf(&ret, "%s ID %s (serial %llu) CA %s %s%s%s", 216 sshkey_type(key), key->cert->key_id, 217 (unsigned long long)key->cert->serial, 218 sshkey_type(key->cert->signature_key), 219 fp == NULL ? "(null)" : fp, 220 methinfo == NULL ? "" : ", ", 221 methinfo == NULL ? "" : methinfo); 222 free(fp); 223 } else { 224 fp = sshkey_fingerprint(key, options.fingerprint_hash, 225 SSH_FP_DEFAULT); 226 xasprintf(&ret, "%s %s%s%s", sshkey_type(key), 227 fp == NULL ? "(null)" : fp, 228 methinfo == NULL ? "" : ", ", 229 methinfo == NULL ? "" : methinfo); 230 free(fp); 231 } 232 return ret; 233 } 234 235 void 236 auth_log(Authctxt *authctxt, int authenticated, int partial, 237 const char *method, const char *submethod) 238 { 239 struct ssh *ssh = active_state; /* XXX */ 240 void (*authlog) (const char *fmt,...) = verbose; 241 const char *authmsg; 242 char *extra = NULL; 243 244 if (use_privsep && !mm_is_monitor() && !authctxt->postponed) 245 return; 246 247 /* Raise logging level */ 248 if (authenticated == 1 || 249 !authctxt->valid || 250 authctxt->failures >= options.max_authtries / 2 || 251 strcmp(method, "password") == 0) 252 authlog = logit; 253 254 if (authctxt->postponed) 255 authmsg = "Postponed"; 256 else if (partial) 257 authmsg = "Partial"; 258 else 259 authmsg = authenticated ? "Accepted" : "Failed"; 260 261 if ((extra = format_method_key(authctxt)) == NULL) { 262 if (authctxt->auth_method_info != NULL) 263 extra = xstrdup(authctxt->auth_method_info); 264 } 265 266 authlog("%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s", 267 authmsg, 268 method, 269 submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod, 270 authctxt->valid ? "" : "invalid user ", 271 authctxt->user, 272 ssh_remote_ipaddr(ssh), 273 ssh_remote_port(ssh), 274 extra != NULL ? ": " : "", 275 extra != NULL ? extra : ""); 276 277 free(extra); 278 } 279 280 void 281 auth_maxtries_exceeded(Authctxt *authctxt) 282 { 283 struct ssh *ssh = active_state; /* XXX */ 284 285 error("maximum authentication attempts exceeded for " 286 "%s%.100s from %.200s port %d ssh2", 287 authctxt->valid ? "" : "invalid user ", 288 authctxt->user, 289 ssh_remote_ipaddr(ssh), 290 ssh_remote_port(ssh)); 291 packet_disconnect("Too many authentication failures"); 292 /* NOTREACHED */ 293 } 294 295 /* 296 * Check whether root logins are disallowed. 297 */ 298 int 299 auth_root_allowed(const char *method) 300 { 301 struct ssh *ssh = active_state; /* XXX */ 302 303 switch (options.permit_root_login) { 304 case PERMIT_YES: 305 return 1; 306 case PERMIT_NO_PASSWD: 307 if (strcmp(method, "publickey") == 0 || 308 strcmp(method, "hostbased") == 0 || 309 strcmp(method, "gssapi-with-mic") == 0) 310 return 1; 311 break; 312 case PERMIT_FORCED_ONLY: 313 if (forced_command) { 314 logit("Root login accepted for forced command."); 315 return 1; 316 } 317 break; 318 } 319 logit("ROOT LOGIN REFUSED FROM %.200s port %d", 320 ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); 321 return 0; 322 } 323 324 325 /* 326 * Given a template and a passwd structure, build a filename 327 * by substituting % tokenised options. Currently, %% becomes '%', 328 * %h becomes the home directory and %u the username. 329 * 330 * This returns a buffer allocated by xmalloc. 331 */ 332 char * 333 expand_authorized_keys(const char *filename, struct passwd *pw) 334 { 335 char *file, ret[PATH_MAX]; 336 int i; 337 338 file = percent_expand(filename, "h", pw->pw_dir, 339 "u", pw->pw_name, (char *)NULL); 340 341 /* 342 * Ensure that filename starts anchored. If not, be backward 343 * compatible and prepend the '%h/' 344 */ 345 if (*file == '/') 346 return (file); 347 348 i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file); 349 if (i < 0 || (size_t)i >= sizeof(ret)) 350 fatal("expand_authorized_keys: path too long"); 351 free(file); 352 return (xstrdup(ret)); 353 } 354 355 char * 356 authorized_principals_file(struct passwd *pw) 357 { 358 if (options.authorized_principals_file == NULL) 359 return NULL; 360 return expand_authorized_keys(options.authorized_principals_file, pw); 361 } 362 363 /* return ok if key exists in sysfile or userfile */ 364 HostStatus 365 check_key_in_hostfiles(struct passwd *pw, struct sshkey *key, const char *host, 366 const char *sysfile, const char *userfile) 367 { 368 char *user_hostfile; 369 struct stat st; 370 HostStatus host_status; 371 struct hostkeys *hostkeys; 372 const struct hostkey_entry *found; 373 374 hostkeys = init_hostkeys(); 375 load_hostkeys(hostkeys, host, sysfile); 376 if (userfile != NULL) { 377 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid); 378 if (options.strict_modes && 379 (stat(user_hostfile, &st) == 0) && 380 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || 381 (st.st_mode & 022) != 0)) { 382 logit("Authentication refused for %.100s: " 383 "bad owner or modes for %.200s", 384 pw->pw_name, user_hostfile); 385 auth_debug_add("Ignored %.200s: bad ownership or modes", 386 user_hostfile); 387 } else { 388 temporarily_use_uid(pw); 389 load_hostkeys(hostkeys, host, user_hostfile); 390 restore_uid(); 391 } 392 free(user_hostfile); 393 } 394 host_status = check_key_in_hostkeys(hostkeys, key, &found); 395 if (host_status == HOST_REVOKED) 396 error("WARNING: revoked key for %s attempted authentication", 397 found->host); 398 else if (host_status == HOST_OK) 399 debug("%s: key for %s found at %s:%ld", __func__, 400 found->host, found->file, found->line); 401 else 402 debug("%s: key for host %s not found", __func__, host); 403 404 free_hostkeys(hostkeys); 405 406 return host_status; 407 } 408 409 static FILE * 410 auth_openfile(const char *file, struct passwd *pw, int strict_modes, 411 int log_missing, char *file_type) 412 { 413 char line[1024]; 414 struct stat st; 415 int fd; 416 FILE *f; 417 418 if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { 419 if (log_missing || errno != ENOENT) 420 debug("Could not open %s '%s': %s", file_type, file, 421 strerror(errno)); 422 return NULL; 423 } 424 425 if (fstat(fd, &st) < 0) { 426 close(fd); 427 return NULL; 428 } 429 if (!S_ISREG(st.st_mode)) { 430 logit("User %s %s %s is not a regular file", 431 pw->pw_name, file_type, file); 432 close(fd); 433 return NULL; 434 } 435 unset_nonblock(fd); 436 if ((f = fdopen(fd, "r")) == NULL) { 437 close(fd); 438 return NULL; 439 } 440 if (strict_modes && 441 safe_path_fd(fileno(f), file, pw, line, sizeof(line)) != 0) { 442 fclose(f); 443 logit("Authentication refused: %s", line); 444 auth_debug_add("Ignored %s: %s", file_type, line); 445 return NULL; 446 } 447 448 return f; 449 } 450 451 452 FILE * 453 auth_openkeyfile(const char *file, struct passwd *pw, int strict_modes) 454 { 455 return auth_openfile(file, pw, strict_modes, 1, "authorized keys"); 456 } 457 458 FILE * 459 auth_openprincipals(const char *file, struct passwd *pw, int strict_modes) 460 { 461 return auth_openfile(file, pw, strict_modes, 0, 462 "authorized principals"); 463 } 464 465 struct passwd * 466 getpwnamallow(const char *user) 467 { 468 struct ssh *ssh = active_state; /* XXX */ 469 extern login_cap_t *lc; 470 auth_session_t *as; 471 struct passwd *pw; 472 struct connection_info *ci = get_connection_info(1, options.use_dns); 473 474 ci->user = user; 475 parse_server_match_config(&options, ci); 476 log_change_level(options.log_level); 477 process_permitopen(ssh, &options); 478 479 pw = getpwnam(user); 480 if (pw == NULL) { 481 logit("Invalid user %.100s from %.100s port %d", 482 user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh)); 483 return (NULL); 484 } 485 if (!allowed_user(pw)) 486 return (NULL); 487 if ((lc = login_getclass(pw->pw_class)) == NULL) { 488 debug("unable to get login class: %s", user); 489 return (NULL); 490 } 491 if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 || 492 auth_approval(as, lc, pw->pw_name, "ssh") <= 0) { 493 debug("Approval failure for %s", user); 494 pw = NULL; 495 } 496 if (as != NULL) 497 auth_close(as); 498 if (pw != NULL) 499 return (pwcopy(pw)); 500 return (NULL); 501 } 502 503 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */ 504 int 505 auth_key_is_revoked(struct sshkey *key) 506 { 507 char *fp = NULL; 508 int r; 509 510 if (options.revoked_keys_file == NULL) 511 return 0; 512 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 513 SSH_FP_DEFAULT)) == NULL) { 514 r = SSH_ERR_ALLOC_FAIL; 515 error("%s: fingerprint key: %s", __func__, ssh_err(r)); 516 goto out; 517 } 518 519 r = sshkey_check_revoked(key, options.revoked_keys_file); 520 switch (r) { 521 case 0: 522 break; /* not revoked */ 523 case SSH_ERR_KEY_REVOKED: 524 error("Authentication key %s %s revoked by file %s", 525 sshkey_type(key), fp, options.revoked_keys_file); 526 goto out; 527 default: 528 error("Error checking authentication key %s %s in " 529 "revoked keys file %s: %s", sshkey_type(key), fp, 530 options.revoked_keys_file, ssh_err(r)); 531 goto out; 532 } 533 534 /* Success */ 535 r = 0; 536 537 out: 538 free(fp); 539 return r == 0 ? 0 : 1; 540 } 541 542 void 543 auth_debug_add(const char *fmt,...) 544 { 545 char buf[1024]; 546 va_list args; 547 548 if (!auth_debug_init) 549 return; 550 551 va_start(args, fmt); 552 vsnprintf(buf, sizeof(buf), fmt, args); 553 va_end(args); 554 buffer_put_cstring(&auth_debug, buf); 555 } 556 557 void 558 auth_debug_send(void) 559 { 560 char *msg; 561 562 if (!auth_debug_init) 563 return; 564 while (buffer_len(&auth_debug)) { 565 msg = buffer_get_string(&auth_debug, NULL); 566 packet_send_debug("%s", msg); 567 free(msg); 568 } 569 } 570 571 void 572 auth_debug_reset(void) 573 { 574 if (auth_debug_init) 575 buffer_clear(&auth_debug); 576 else { 577 buffer_init(&auth_debug); 578 auth_debug_init = 1; 579 } 580 } 581 582 struct passwd * 583 fakepw(void) 584 { 585 static struct passwd fake; 586 587 memset(&fake, 0, sizeof(fake)); 588 fake.pw_name = "NOUSER"; 589 fake.pw_passwd = 590 "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK"; 591 fake.pw_gecos = "NOUSER"; 592 fake.pw_uid = (uid_t)-1; 593 fake.pw_gid = (gid_t)-1; 594 fake.pw_class = ""; 595 fake.pw_dir = "/nonexist"; 596 fake.pw_shell = "/nonexist"; 597 598 return (&fake); 599 } 600 601 /* 602 * Returns the remote DNS hostname as a string. The returned string must not 603 * be freed. NB. this will usually trigger a DNS query the first time it is 604 * called. 605 * This function does additional checks on the hostname to mitigate some 606 * attacks on legacy rhosts-style authentication. 607 * XXX is RhostsRSAAuthentication vulnerable to these? 608 * XXX Can we remove these checks? (or if not, remove RhostsRSAAuthentication?) 609 */ 610 611 static char * 612 remote_hostname(struct ssh *ssh) 613 { 614 struct sockaddr_storage from; 615 socklen_t fromlen; 616 struct addrinfo hints, *ai, *aitop; 617 char name[NI_MAXHOST], ntop2[NI_MAXHOST]; 618 const char *ntop = ssh_remote_ipaddr(ssh); 619 620 /* Get IP address of client. */ 621 fromlen = sizeof(from); 622 memset(&from, 0, sizeof(from)); 623 if (getpeername(ssh_packet_get_connection_in(ssh), 624 (struct sockaddr *)&from, &fromlen) < 0) { 625 debug("getpeername failed: %.100s", strerror(errno)); 626 return strdup(ntop); 627 } 628 629 debug3("Trying to reverse map address %.100s.", ntop); 630 /* Map the IP address to a host name. */ 631 if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name), 632 NULL, 0, NI_NAMEREQD) != 0) { 633 /* Host name not found. Use ip address. */ 634 return strdup(ntop); 635 } 636 637 /* 638 * if reverse lookup result looks like a numeric hostname, 639 * someone is trying to trick us by PTR record like following: 640 * 1.1.1.10.in-addr.arpa. IN PTR 2.3.4.5 641 */ 642 memset(&hints, 0, sizeof(hints)); 643 hints.ai_socktype = SOCK_DGRAM; /*dummy*/ 644 hints.ai_flags = AI_NUMERICHOST; 645 if (getaddrinfo(name, NULL, &hints, &ai) == 0) { 646 logit("Nasty PTR record \"%s\" is set up for %s, ignoring", 647 name, ntop); 648 freeaddrinfo(ai); 649 return strdup(ntop); 650 } 651 652 /* Names are stored in lowercase. */ 653 lowercase(name); 654 655 /* 656 * Map it back to an IP address and check that the given 657 * address actually is an address of this host. This is 658 * necessary because anyone with access to a name server can 659 * define arbitrary names for an IP address. Mapping from 660 * name to IP address can be trusted better (but can still be 661 * fooled if the intruder has access to the name server of 662 * the domain). 663 */ 664 memset(&hints, 0, sizeof(hints)); 665 hints.ai_family = from.ss_family; 666 hints.ai_socktype = SOCK_STREAM; 667 if (getaddrinfo(name, NULL, &hints, &aitop) != 0) { 668 logit("reverse mapping checking getaddrinfo for %.700s " 669 "[%s] failed.", name, ntop); 670 return strdup(ntop); 671 } 672 /* Look for the address from the list of addresses. */ 673 for (ai = aitop; ai; ai = ai->ai_next) { 674 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2, 675 sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 && 676 (strcmp(ntop, ntop2) == 0)) 677 break; 678 } 679 freeaddrinfo(aitop); 680 /* If we reached the end of the list, the address was not there. */ 681 if (ai == NULL) { 682 /* Address not found for the host name. */ 683 logit("Address %.100s maps to %.600s, but this does not " 684 "map back to the address.", ntop, name); 685 return strdup(ntop); 686 } 687 return strdup(name); 688 } 689 690 /* 691 * Return the canonical name of the host in the other side of the current 692 * connection. The host name is cached, so it is efficient to call this 693 * several times. 694 */ 695 696 const char * 697 auth_get_canonical_hostname(struct ssh *ssh, int use_dns) 698 { 699 static char *dnsname; 700 701 if (!use_dns) 702 return ssh_remote_ipaddr(ssh); 703 else if (dnsname != NULL) 704 return dnsname; 705 else { 706 dnsname = remote_hostname(ssh); 707 return dnsname; 708 } 709 } 710 711 /* 712 * Runs command in a subprocess wuth a minimal environment. 713 * Returns pid on success, 0 on failure. 714 * The child stdout and stderr maybe captured, left attached or sent to 715 * /dev/null depending on the contents of flags. 716 * "tag" is prepended to log messages. 717 * NB. "command" is only used for logging; the actual command executed is 718 * av[0]. 719 */ 720 pid_t 721 subprocess(const char *tag, struct passwd *pw, const char *command, 722 int ac, char **av, FILE **child, u_int flags) 723 { 724 FILE *f = NULL; 725 struct stat st; 726 int fd, devnull, p[2], i; 727 pid_t pid; 728 char *cp, errmsg[512]; 729 u_int envsize; 730 char **child_env; 731 732 if (child != NULL) 733 *child = NULL; 734 735 debug3("%s: %s command \"%s\" running as %s (flags 0x%x)", __func__, 736 tag, command, pw->pw_name, flags); 737 738 /* Check consistency */ 739 if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 && 740 (flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) { 741 error("%s: inconsistent flags", __func__); 742 return 0; 743 } 744 if (((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) != (child == NULL)) { 745 error("%s: inconsistent flags/output", __func__); 746 return 0; 747 } 748 749 /* 750 * If executing an explicit binary, then verify the it exists 751 * and appears safe-ish to execute 752 */ 753 if (*av[0] != '/') { 754 error("%s path is not absolute", tag); 755 return 0; 756 } 757 temporarily_use_uid(pw); 758 if (stat(av[0], &st) < 0) { 759 error("Could not stat %s \"%s\": %s", tag, 760 av[0], strerror(errno)); 761 restore_uid(); 762 return 0; 763 } 764 if (safe_path(av[0], &st, NULL, 0, errmsg, sizeof(errmsg)) != 0) { 765 error("Unsafe %s \"%s\": %s", tag, av[0], errmsg); 766 restore_uid(); 767 return 0; 768 } 769 /* Prepare to keep the child's stdout if requested */ 770 if (pipe(p) != 0) { 771 error("%s: pipe: %s", tag, strerror(errno)); 772 restore_uid(); 773 return 0; 774 } 775 restore_uid(); 776 777 switch ((pid = fork())) { 778 case -1: /* error */ 779 error("%s: fork: %s", tag, strerror(errno)); 780 close(p[0]); 781 close(p[1]); 782 return 0; 783 case 0: /* child */ 784 /* Prepare a minimal environment for the child. */ 785 envsize = 5; 786 child_env = xcalloc(sizeof(*child_env), envsize); 787 child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH); 788 child_set_env(&child_env, &envsize, "USER", pw->pw_name); 789 child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name); 790 child_set_env(&child_env, &envsize, "HOME", pw->pw_dir); 791 if ((cp = getenv("LANG")) != NULL) 792 child_set_env(&child_env, &envsize, "LANG", cp); 793 794 for (i = 0; i < NSIG; i++) 795 signal(i, SIG_DFL); 796 797 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { 798 error("%s: open %s: %s", tag, _PATH_DEVNULL, 799 strerror(errno)); 800 _exit(1); 801 } 802 if (dup2(devnull, STDIN_FILENO) == -1) { 803 error("%s: dup2: %s", tag, strerror(errno)); 804 _exit(1); 805 } 806 807 /* Set up stdout as requested; leave stderr in place for now. */ 808 fd = -1; 809 if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) != 0) 810 fd = p[1]; 811 else if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0) 812 fd = devnull; 813 if (fd != -1 && dup2(fd, STDOUT_FILENO) == -1) { 814 error("%s: dup2: %s", tag, strerror(errno)); 815 _exit(1); 816 } 817 closefrom(STDERR_FILENO + 1); 818 819 /* Don't use permanently_set_uid() here to avoid fatal() */ 820 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) { 821 error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid, 822 strerror(errno)); 823 _exit(1); 824 } 825 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) { 826 error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid, 827 strerror(errno)); 828 _exit(1); 829 } 830 /* stdin is pointed to /dev/null at this point */ 831 if ((flags & SSH_SUBPROCESS_STDOUT_DISCARD) != 0 && 832 dup2(STDIN_FILENO, STDERR_FILENO) == -1) { 833 error("%s: dup2: %s", tag, strerror(errno)); 834 _exit(1); 835 } 836 837 execve(av[0], av, child_env); 838 error("%s exec \"%s\": %s", tag, command, strerror(errno)); 839 _exit(127); 840 default: /* parent */ 841 break; 842 } 843 844 close(p[1]); 845 if ((flags & SSH_SUBPROCESS_STDOUT_CAPTURE) == 0) 846 close(p[0]); 847 else if ((f = fdopen(p[0], "r")) == NULL) { 848 error("%s: fdopen: %s", tag, strerror(errno)); 849 close(p[0]); 850 /* Don't leave zombie child */ 851 kill(pid, SIGTERM); 852 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) 853 ; 854 return 0; 855 } 856 /* Success */ 857 debug3("%s: %s pid %ld", __func__, tag, (long)pid); 858 if (child != NULL) 859 *child = f; 860 return pid; 861 } 862