1 /* $OpenBSD: auth2-pubkey.c,v 1.55 2016/01/27 00:53:12 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 "includes.h" 27 28 #include <sys/types.h> 29 #include <sys/stat.h> 30 #include <sys/wait.h> 31 32 #include <errno.h> 33 #include <fcntl.h> 34 #ifdef HAVE_PATHS_H 35 # include <paths.h> 36 #endif 37 #include <pwd.h> 38 #include <signal.h> 39 #include <stdio.h> 40 #include <stdarg.h> 41 #include <string.h> 42 #include <time.h> 43 #include <unistd.h> 44 #include <limits.h> 45 46 #include "xmalloc.h" 47 #include "ssh.h" 48 #include "ssh2.h" 49 #include "packet.h" 50 #include "buffer.h" 51 #include "log.h" 52 #include "misc.h" 53 #include "servconf.h" 54 #include "compat.h" 55 #include "key.h" 56 #include "hostfile.h" 57 #include "auth.h" 58 #include "pathnames.h" 59 #include "uidswap.h" 60 #include "auth-options.h" 61 #include "canohost.h" 62 #ifdef GSSAPI 63 #include "ssh-gss.h" 64 #endif 65 #include "monitor_wrap.h" 66 #include "authfile.h" 67 #include "match.h" 68 #include "ssherr.h" 69 #include "channels.h" /* XXX for session.h */ 70 #include "session.h" /* XXX for child_set_env(); refactor? */ 71 72 /* import */ 73 extern ServerOptions options; 74 extern u_char *session_id2; 75 extern u_int session_id2_len; 76 77 static int 78 userauth_pubkey(Authctxt *authctxt) 79 { 80 Buffer b; 81 Key *key = NULL; 82 char *pkalg, *userstyle, *fp = NULL; 83 u_char *pkblob, *sig; 84 u_int alen, blen, slen; 85 int have_sig, pktype; 86 int authenticated = 0; 87 88 if (!authctxt->valid) { 89 debug2("%s: disabled because of invalid user", __func__); 90 return 0; 91 } 92 have_sig = packet_get_char(); 93 if (datafellows & SSH_BUG_PKAUTH) { 94 debug2("%s: SSH_BUG_PKAUTH", __func__); 95 /* no explicit pkalg given */ 96 pkblob = packet_get_string(&blen); 97 buffer_init(&b); 98 buffer_append(&b, pkblob, blen); 99 /* so we have to extract the pkalg from the pkblob */ 100 pkalg = buffer_get_string(&b, &alen); 101 buffer_free(&b); 102 } else { 103 pkalg = packet_get_string(&alen); 104 pkblob = packet_get_string(&blen); 105 } 106 pktype = key_type_from_name(pkalg); 107 if (pktype == KEY_UNSPEC) { 108 /* this is perfectly legal */ 109 logit("%s: unsupported public key algorithm: %s", 110 __func__, pkalg); 111 goto done; 112 } 113 key = key_from_blob(pkblob, blen); 114 if (key == NULL) { 115 error("%s: cannot decode key: %s", __func__, pkalg); 116 goto done; 117 } 118 if (key->type != pktype) { 119 error("%s: type mismatch for decoded key " 120 "(received %d, expected %d)", __func__, key->type, pktype); 121 goto done; 122 } 123 if (key_type_plain(key->type) == KEY_RSA && 124 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 125 logit("Refusing RSA key because client uses unsafe " 126 "signature scheme"); 127 goto done; 128 } 129 fp = sshkey_fingerprint(key, options.fingerprint_hash, SSH_FP_DEFAULT); 130 if (auth2_userkey_already_used(authctxt, key)) { 131 logit("refusing previously-used %s key", key_type(key)); 132 goto done; 133 } 134 if (match_pattern_list(sshkey_ssh_name(key), 135 options.pubkey_key_types, 0) != 1) { 136 logit("%s: key type %s not in PubkeyAcceptedKeyTypes", 137 __func__, sshkey_ssh_name(key)); 138 goto done; 139 } 140 141 if (have_sig) { 142 debug3("%s: have signature for %s %s", 143 __func__, sshkey_type(key), fp); 144 sig = packet_get_string(&slen); 145 packet_check_eom(); 146 buffer_init(&b); 147 if (datafellows & SSH_OLD_SESSIONID) { 148 buffer_append(&b, session_id2, session_id2_len); 149 } else { 150 buffer_put_string(&b, session_id2, session_id2_len); 151 } 152 /* reconstruct packet */ 153 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 154 xasprintf(&userstyle, "%s%s%s", authctxt->user, 155 authctxt->style ? ":" : "", 156 authctxt->style ? authctxt->style : ""); 157 buffer_put_cstring(&b, userstyle); 158 free(userstyle); 159 buffer_put_cstring(&b, 160 datafellows & SSH_BUG_PKSERVICE ? 161 "ssh-userauth" : 162 authctxt->service); 163 if (datafellows & SSH_BUG_PKAUTH) { 164 buffer_put_char(&b, have_sig); 165 } else { 166 buffer_put_cstring(&b, "publickey"); 167 buffer_put_char(&b, have_sig); 168 buffer_put_cstring(&b, pkalg); 169 } 170 buffer_put_string(&b, pkblob, blen); 171 #ifdef DEBUG_PK 172 buffer_dump(&b); 173 #endif 174 pubkey_auth_info(authctxt, key, NULL); 175 176 /* test for correct signature */ 177 authenticated = 0; 178 if (PRIVSEP(user_key_allowed(authctxt->pw, key, 1)) && 179 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 180 buffer_len(&b))) == 1) { 181 authenticated = 1; 182 /* Record the successful key to prevent reuse */ 183 auth2_record_userkey(authctxt, key); 184 key = NULL; /* Don't free below */ 185 } 186 buffer_free(&b); 187 free(sig); 188 } else { 189 debug("%s: test whether pkalg/pkblob are acceptable for %s %s", 190 __func__, sshkey_type(key), fp); 191 packet_check_eom(); 192 193 /* XXX fake reply and always send PK_OK ? */ 194 /* 195 * XXX this allows testing whether a user is allowed 196 * to login: if you happen to have a valid pubkey this 197 * message is sent. the message is NEVER sent at all 198 * if a user is not allowed to login. is this an 199 * issue? -markus 200 */ 201 if (PRIVSEP(user_key_allowed(authctxt->pw, key, 0))) { 202 packet_start(SSH2_MSG_USERAUTH_PK_OK); 203 packet_put_string(pkalg, alen); 204 packet_put_string(pkblob, blen); 205 packet_send(); 206 packet_write_wait(); 207 authctxt->postponed = 1; 208 } 209 } 210 if (authenticated != 1) 211 auth_clear_options(); 212 done: 213 debug2("%s: authenticated %d pkalg %s", __func__, authenticated, pkalg); 214 if (key != NULL) 215 key_free(key); 216 free(pkalg); 217 free(pkblob); 218 free(fp); 219 return authenticated; 220 } 221 222 void 223 pubkey_auth_info(Authctxt *authctxt, const Key *key, const char *fmt, ...) 224 { 225 char *fp, *extra; 226 va_list ap; 227 int i; 228 229 extra = NULL; 230 if (fmt != NULL) { 231 va_start(ap, fmt); 232 i = vasprintf(&extra, fmt, ap); 233 va_end(ap); 234 if (i < 0 || extra == NULL) 235 fatal("%s: vasprintf failed", __func__); 236 } 237 238 if (key_is_cert(key)) { 239 fp = sshkey_fingerprint(key->cert->signature_key, 240 options.fingerprint_hash, SSH_FP_DEFAULT); 241 auth_info(authctxt, "%s ID %s (serial %llu) CA %s %s%s%s", 242 key_type(key), key->cert->key_id, 243 (unsigned long long)key->cert->serial, 244 key_type(key->cert->signature_key), 245 fp == NULL ? "(null)" : fp, 246 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 247 free(fp); 248 } else { 249 fp = sshkey_fingerprint(key, options.fingerprint_hash, 250 SSH_FP_DEFAULT); 251 auth_info(authctxt, "%s %s%s%s", key_type(key), 252 fp == NULL ? "(null)" : fp, 253 extra == NULL ? "" : ", ", extra == NULL ? "" : extra); 254 free(fp); 255 } 256 free(extra); 257 } 258 259 /* 260 * Splits 's' into an argument vector. Handles quoted string and basic 261 * escape characters (\\, \", \'). Caller must free the argument vector 262 * and its members. 263 */ 264 static int 265 split_argv(const char *s, int *argcp, char ***argvp) 266 { 267 int r = SSH_ERR_INTERNAL_ERROR; 268 int argc = 0, quote, i, j; 269 char *arg, **argv = xcalloc(1, sizeof(*argv)); 270 271 *argvp = NULL; 272 *argcp = 0; 273 274 for (i = 0; s[i] != '\0'; i++) { 275 /* Skip leading whitespace */ 276 if (s[i] == ' ' || s[i] == '\t') 277 continue; 278 279 /* Start of a token */ 280 quote = 0; 281 if (s[i] == '\\' && 282 (s[i + 1] == '\'' || s[i + 1] == '\"' || s[i + 1] == '\\')) 283 i++; 284 else if (s[i] == '\'' || s[i] == '"') 285 quote = s[i++]; 286 287 argv = xreallocarray(argv, (argc + 2), sizeof(*argv)); 288 arg = argv[argc++] = xcalloc(1, strlen(s + i) + 1); 289 argv[argc] = NULL; 290 291 /* Copy the token in, removing escapes */ 292 for (j = 0; s[i] != '\0'; i++) { 293 if (s[i] == '\\') { 294 if (s[i + 1] == '\'' || 295 s[i + 1] == '\"' || 296 s[i + 1] == '\\') { 297 i++; /* Skip '\' */ 298 arg[j++] = s[i]; 299 } else { 300 /* Unrecognised escape */ 301 arg[j++] = s[i]; 302 } 303 } else if (quote == 0 && (s[i] == ' ' || s[i] == '\t')) 304 break; /* done */ 305 else if (quote != 0 && s[i] == quote) 306 break; /* done */ 307 else 308 arg[j++] = s[i]; 309 } 310 if (s[i] == '\0') { 311 if (quote != 0) { 312 /* Ran out of string looking for close quote */ 313 r = SSH_ERR_INVALID_FORMAT; 314 goto out; 315 } 316 break; 317 } 318 } 319 /* Success */ 320 *argcp = argc; 321 *argvp = argv; 322 argc = 0; 323 argv = NULL; 324 r = 0; 325 out: 326 if (argc != 0 && argv != NULL) { 327 for (i = 0; i < argc; i++) 328 free(argv[i]); 329 free(argv); 330 } 331 return r; 332 } 333 334 /* 335 * Reassemble an argument vector into a string, quoting and escaping as 336 * necessary. Caller must free returned string. 337 */ 338 static char * 339 assemble_argv(int argc, char **argv) 340 { 341 int i, j, ws, r; 342 char c, *ret; 343 struct sshbuf *buf, *arg; 344 345 if ((buf = sshbuf_new()) == NULL || (arg = sshbuf_new()) == NULL) 346 fatal("%s: sshbuf_new failed", __func__); 347 348 for (i = 0; i < argc; i++) { 349 ws = 0; 350 sshbuf_reset(arg); 351 for (j = 0; argv[i][j] != '\0'; j++) { 352 r = 0; 353 c = argv[i][j]; 354 switch (c) { 355 case ' ': 356 case '\t': 357 ws = 1; 358 r = sshbuf_put_u8(arg, c); 359 break; 360 case '\\': 361 case '\'': 362 case '"': 363 if ((r = sshbuf_put_u8(arg, '\\')) != 0) 364 break; 365 /* FALLTHROUGH */ 366 default: 367 r = sshbuf_put_u8(arg, c); 368 break; 369 } 370 if (r != 0) 371 fatal("%s: sshbuf_put_u8: %s", 372 __func__, ssh_err(r)); 373 } 374 if ((i != 0 && (r = sshbuf_put_u8(buf, ' ')) != 0) || 375 (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0) || 376 (r = sshbuf_putb(buf, arg)) != 0 || 377 (ws != 0 && (r = sshbuf_put_u8(buf, '"')) != 0)) 378 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 379 } 380 if ((ret = malloc(sshbuf_len(buf) + 1)) == NULL) 381 fatal("%s: malloc failed", __func__); 382 memcpy(ret, sshbuf_ptr(buf), sshbuf_len(buf)); 383 ret[sshbuf_len(buf)] = '\0'; 384 sshbuf_free(buf); 385 sshbuf_free(arg); 386 return ret; 387 } 388 389 /* 390 * Runs command in a subprocess. Returns pid on success and a FILE* to the 391 * subprocess' stdout or 0 on failure. 392 * NB. "command" is only used for logging. 393 */ 394 static pid_t 395 subprocess(const char *tag, struct passwd *pw, const char *command, 396 int ac, char **av, FILE **child) 397 { 398 FILE *f; 399 struct stat st; 400 int devnull, p[2], i; 401 pid_t pid; 402 char *cp, errmsg[512]; 403 u_int envsize; 404 char **child_env; 405 406 *child = NULL; 407 408 debug3("%s: %s command \"%s\" running as %s", __func__, 409 tag, command, pw->pw_name); 410 411 /* Verify the path exists and is safe-ish to execute */ 412 if (*av[0] != '/') { 413 error("%s path is not absolute", tag); 414 return 0; 415 } 416 temporarily_use_uid(pw); 417 if (stat(av[0], &st) < 0) { 418 error("Could not stat %s \"%s\": %s", tag, 419 av[0], strerror(errno)); 420 restore_uid(); 421 return 0; 422 } 423 if (auth_secure_path(av[0], &st, NULL, 0, 424 errmsg, sizeof(errmsg)) != 0) { 425 error("Unsafe %s \"%s\": %s", tag, av[0], errmsg); 426 restore_uid(); 427 return 0; 428 } 429 430 /* 431 * Run the command; stderr is left in place, stdout is the 432 * authorized_keys output. 433 */ 434 if (pipe(p) != 0) { 435 error("%s: pipe: %s", tag, strerror(errno)); 436 restore_uid(); 437 return 0; 438 } 439 440 /* 441 * Don't want to call this in the child, where it can fatal() and 442 * run cleanup_exit() code. 443 */ 444 restore_uid(); 445 446 switch ((pid = fork())) { 447 case -1: /* error */ 448 error("%s: fork: %s", tag, strerror(errno)); 449 close(p[0]); 450 close(p[1]); 451 return 0; 452 case 0: /* child */ 453 /* Prepare a minimal environment for the child. */ 454 envsize = 5; 455 child_env = xcalloc(sizeof(*child_env), envsize); 456 child_set_env(&child_env, &envsize, "PATH", _PATH_STDPATH); 457 child_set_env(&child_env, &envsize, "USER", pw->pw_name); 458 child_set_env(&child_env, &envsize, "LOGNAME", pw->pw_name); 459 child_set_env(&child_env, &envsize, "HOME", pw->pw_dir); 460 if ((cp = getenv("LANG")) != NULL) 461 child_set_env(&child_env, &envsize, "LANG", cp); 462 463 for (i = 0; i < NSIG; i++) 464 signal(i, SIG_DFL); 465 466 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) { 467 error("%s: open %s: %s", tag, _PATH_DEVNULL, 468 strerror(errno)); 469 _exit(1); 470 } 471 /* Keep stderr around a while longer to catch errors */ 472 if (dup2(devnull, STDIN_FILENO) == -1 || 473 dup2(p[1], STDOUT_FILENO) == -1) { 474 error("%s: dup2: %s", tag, strerror(errno)); 475 _exit(1); 476 } 477 closefrom(STDERR_FILENO + 1); 478 479 /* Don't use permanently_set_uid() here to avoid fatal() */ 480 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) { 481 error("%s: setresgid %u: %s", tag, (u_int)pw->pw_gid, 482 strerror(errno)); 483 _exit(1); 484 } 485 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) { 486 error("%s: setresuid %u: %s", tag, (u_int)pw->pw_uid, 487 strerror(errno)); 488 _exit(1); 489 } 490 /* stdin is pointed to /dev/null at this point */ 491 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) { 492 error("%s: dup2: %s", tag, strerror(errno)); 493 _exit(1); 494 } 495 496 execve(av[0], av, child_env); 497 error("%s exec \"%s\": %s", tag, command, strerror(errno)); 498 _exit(127); 499 default: /* parent */ 500 break; 501 } 502 503 close(p[1]); 504 if ((f = fdopen(p[0], "r")) == NULL) { 505 error("%s: fdopen: %s", tag, strerror(errno)); 506 close(p[0]); 507 /* Don't leave zombie child */ 508 kill(pid, SIGTERM); 509 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR) 510 ; 511 return 0; 512 } 513 /* Success */ 514 debug3("%s: %s pid %ld", __func__, tag, (long)pid); 515 *child = f; 516 return pid; 517 } 518 519 /* Returns 0 if pid exited cleanly, non-zero otherwise */ 520 static int 521 exited_cleanly(pid_t pid, const char *tag, const char *cmd) 522 { 523 int status; 524 525 while (waitpid(pid, &status, 0) == -1) { 526 if (errno != EINTR) { 527 error("%s: waitpid: %s", tag, strerror(errno)); 528 return -1; 529 } 530 } 531 if (WIFSIGNALED(status)) { 532 error("%s %s exited on signal %d", tag, cmd, WTERMSIG(status)); 533 return -1; 534 } else if (WEXITSTATUS(status) != 0) { 535 error("%s %s failed, status %d", tag, cmd, WEXITSTATUS(status)); 536 return -1; 537 } 538 return 0; 539 } 540 541 static int 542 match_principals_option(const char *principal_list, struct sshkey_cert *cert) 543 { 544 char *result; 545 u_int i; 546 547 /* XXX percent_expand() sequences for authorized_principals? */ 548 549 for (i = 0; i < cert->nprincipals; i++) { 550 if ((result = match_list(cert->principals[i], 551 principal_list, NULL)) != NULL) { 552 debug3("matched principal from key options \"%.100s\"", 553 result); 554 free(result); 555 return 1; 556 } 557 } 558 return 0; 559 } 560 561 static int 562 process_principals(FILE *f, char *file, struct passwd *pw, 563 struct sshkey_cert *cert) 564 { 565 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 566 u_long linenum = 0; 567 u_int i; 568 569 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 570 /* Skip leading whitespace. */ 571 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 572 ; 573 /* Skip blank and comment lines. */ 574 if ((ep = strchr(cp, '#')) != NULL) 575 *ep = '\0'; 576 if (!*cp || *cp == '\n') 577 continue; 578 /* Trim trailing whitespace. */ 579 ep = cp + strlen(cp) - 1; 580 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 581 *ep-- = '\0'; 582 /* 583 * If the line has internal whitespace then assume it has 584 * key options. 585 */ 586 line_opts = NULL; 587 if ((ep = strrchr(cp, ' ')) != NULL || 588 (ep = strrchr(cp, '\t')) != NULL) { 589 for (; *ep == ' ' || *ep == '\t'; ep++) 590 ; 591 line_opts = cp; 592 cp = ep; 593 } 594 for (i = 0; i < cert->nprincipals; i++) { 595 if (strcmp(cp, cert->principals[i]) == 0) { 596 debug3("%s:%lu: matched principal \"%.100s\"", 597 file == NULL ? "(command)" : file, 598 linenum, cert->principals[i]); 599 if (auth_parse_options(pw, line_opts, 600 file, linenum) != 1) 601 continue; 602 return 1; 603 } 604 } 605 } 606 return 0; 607 } 608 609 static int 610 match_principals_file(char *file, struct passwd *pw, struct sshkey_cert *cert) 611 { 612 FILE *f; 613 int success; 614 615 temporarily_use_uid(pw); 616 debug("trying authorized principals file %s", file); 617 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 618 restore_uid(); 619 return 0; 620 } 621 success = process_principals(f, file, pw, cert); 622 fclose(f); 623 restore_uid(); 624 return success; 625 } 626 627 /* 628 * Checks whether principal is allowed in output of command. 629 * returns 1 if the principal is allowed or 0 otherwise. 630 */ 631 static int 632 match_principals_command(struct passwd *user_pw, struct sshkey_cert *cert) 633 { 634 FILE *f = NULL; 635 int ok, found_principal = 0; 636 struct passwd *pw; 637 int i, ac = 0, uid_swapped = 0; 638 pid_t pid; 639 char *tmp, *username = NULL, *command = NULL, **av = NULL; 640 void (*osigchld)(int); 641 642 if (options.authorized_principals_command == NULL) 643 return 0; 644 if (options.authorized_principals_command_user == NULL) { 645 error("No user for AuthorizedPrincipalsCommand specified, " 646 "skipping"); 647 return 0; 648 } 649 650 /* 651 * NB. all returns later this function should go via "out" to 652 * ensure the original SIGCHLD handler is restored properly. 653 */ 654 osigchld = signal(SIGCHLD, SIG_DFL); 655 656 /* Prepare and verify the user for the command */ 657 username = percent_expand(options.authorized_principals_command_user, 658 "u", user_pw->pw_name, (char *)NULL); 659 pw = getpwnam(username); 660 if (pw == NULL) { 661 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s", 662 username, strerror(errno)); 663 goto out; 664 } 665 666 /* Turn the command into an argument vector */ 667 if (split_argv(options.authorized_principals_command, &ac, &av) != 0) { 668 error("AuthorizedPrincipalsCommand \"%s\" contains " 669 "invalid quotes", command); 670 goto out; 671 } 672 if (ac == 0) { 673 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments", 674 command); 675 goto out; 676 } 677 for (i = 1; i < ac; i++) { 678 tmp = percent_expand(av[i], 679 "u", user_pw->pw_name, 680 "h", user_pw->pw_dir, 681 (char *)NULL); 682 if (tmp == NULL) 683 fatal("%s: percent_expand failed", __func__); 684 free(av[i]); 685 av[i] = tmp; 686 } 687 /* Prepare a printable command for logs, etc. */ 688 command = assemble_argv(ac, av); 689 690 if ((pid = subprocess("AuthorizedPrincipalsCommand", pw, command, 691 ac, av, &f)) == 0) 692 goto out; 693 694 uid_swapped = 1; 695 temporarily_use_uid(pw); 696 697 ok = process_principals(f, NULL, pw, cert); 698 699 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command) != 0) 700 goto out; 701 702 /* Read completed successfully */ 703 found_principal = ok; 704 out: 705 if (f != NULL) 706 fclose(f); 707 signal(SIGCHLD, osigchld); 708 for (i = 0; i < ac; i++) 709 free(av[i]); 710 free(av); 711 if (uid_swapped) 712 restore_uid(); 713 free(command); 714 free(username); 715 return found_principal; 716 } 717 /* 718 * Checks whether key is allowed in authorized_keys-format file, 719 * returns 1 if the key is allowed or 0 otherwise. 720 */ 721 static int 722 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw) 723 { 724 char line[SSH_MAX_PUBKEY_BYTES]; 725 const char *reason; 726 int found_key = 0; 727 u_long linenum = 0; 728 Key *found; 729 char *fp; 730 731 found_key = 0; 732 733 found = NULL; 734 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 735 char *cp, *key_options = NULL; 736 if (found != NULL) 737 key_free(found); 738 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 739 auth_clear_options(); 740 741 /* Skip leading whitespace, empty and comment lines. */ 742 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 743 ; 744 if (!*cp || *cp == '\n' || *cp == '#') 745 continue; 746 747 if (key_read(found, &cp) != 1) { 748 /* no key? check if there are options for this key */ 749 int quoted = 0; 750 debug2("user_key_allowed: check options: '%s'", cp); 751 key_options = cp; 752 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 753 if (*cp == '\\' && cp[1] == '"') 754 cp++; /* Skip both */ 755 else if (*cp == '"') 756 quoted = !quoted; 757 } 758 /* Skip remaining whitespace. */ 759 for (; *cp == ' ' || *cp == '\t'; cp++) 760 ; 761 if (key_read(found, &cp) != 1) { 762 debug2("user_key_allowed: advance: '%s'", cp); 763 /* still no key? advance to next line*/ 764 continue; 765 } 766 } 767 if (key_is_cert(key)) { 768 if (!key_equal(found, key->cert->signature_key)) 769 continue; 770 if (auth_parse_options(pw, key_options, file, 771 linenum) != 1) 772 continue; 773 if (!key_is_cert_authority) 774 continue; 775 if ((fp = sshkey_fingerprint(found, 776 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 777 continue; 778 debug("matching CA found: file %s, line %lu, %s %s", 779 file, linenum, key_type(found), fp); 780 /* 781 * If the user has specified a list of principals as 782 * a key option, then prefer that list to matching 783 * their username in the certificate principals list. 784 */ 785 if (authorized_principals != NULL && 786 !match_principals_option(authorized_principals, 787 key->cert)) { 788 reason = "Certificate does not contain an " 789 "authorized principal"; 790 fail_reason: 791 free(fp); 792 error("%s", reason); 793 auth_debug_add("%s", reason); 794 continue; 795 } 796 if (key_cert_check_authority(key, 0, 0, 797 authorized_principals == NULL ? pw->pw_name : NULL, 798 &reason) != 0) 799 goto fail_reason; 800 if (auth_cert_options(key, pw) != 0) { 801 free(fp); 802 continue; 803 } 804 verbose("Accepted certificate ID \"%s\" (serial %llu) " 805 "signed by %s CA %s via %s", key->cert->key_id, 806 (unsigned long long)key->cert->serial, 807 key_type(found), fp, file); 808 free(fp); 809 found_key = 1; 810 break; 811 } else if (key_equal(found, key)) { 812 if (auth_parse_options(pw, key_options, file, 813 linenum) != 1) 814 continue; 815 if (key_is_cert_authority) 816 continue; 817 if ((fp = sshkey_fingerprint(found, 818 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 819 continue; 820 debug("matching key found: file %s, line %lu %s %s", 821 file, linenum, key_type(found), fp); 822 free(fp); 823 found_key = 1; 824 break; 825 } 826 } 827 if (found != NULL) 828 key_free(found); 829 if (!found_key) 830 debug2("key not found"); 831 return found_key; 832 } 833 834 /* Authenticate a certificate key against TrustedUserCAKeys */ 835 static int 836 user_cert_trusted_ca(struct passwd *pw, Key *key) 837 { 838 char *ca_fp, *principals_file = NULL; 839 const char *reason; 840 int ret = 0, found_principal = 0, use_authorized_principals; 841 842 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 843 return 0; 844 845 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key, 846 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 847 return 0; 848 849 if (sshkey_in_file(key->cert->signature_key, 850 options.trusted_user_ca_keys, 1, 0) != 0) { 851 debug2("%s: CA %s %s is not listed in %s", __func__, 852 key_type(key->cert->signature_key), ca_fp, 853 options.trusted_user_ca_keys); 854 goto out; 855 } 856 /* 857 * If AuthorizedPrincipals is in use, then compare the certificate 858 * principals against the names in that file rather than matching 859 * against the username. 860 */ 861 if ((principals_file = authorized_principals_file(pw)) != NULL) { 862 if (match_principals_file(principals_file, pw, key->cert)) 863 found_principal = 1; 864 } 865 /* Try querying command if specified */ 866 if (!found_principal && match_principals_command(pw, key->cert)) 867 found_principal = 1; 868 /* If principals file or command is specified, then require a match */ 869 use_authorized_principals = principals_file != NULL || 870 options.authorized_principals_command != NULL; 871 if (!found_principal && use_authorized_principals) { 872 reason = "Certificate does not contain an authorized principal"; 873 fail_reason: 874 error("%s", reason); 875 auth_debug_add("%s", reason); 876 goto out; 877 } 878 if (key_cert_check_authority(key, 0, 1, 879 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0) 880 goto fail_reason; 881 if (auth_cert_options(key, pw) != 0) 882 goto out; 883 884 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by " 885 "%s CA %s via %s", key->cert->key_id, 886 (unsigned long long)key->cert->serial, 887 key_type(key->cert->signature_key), ca_fp, 888 options.trusted_user_ca_keys); 889 ret = 1; 890 891 out: 892 free(principals_file); 893 free(ca_fp); 894 return ret; 895 } 896 897 /* 898 * Checks whether key is allowed in file. 899 * returns 1 if the key is allowed or 0 otherwise. 900 */ 901 static int 902 user_key_allowed2(struct passwd *pw, Key *key, char *file) 903 { 904 FILE *f; 905 int found_key = 0; 906 907 /* Temporarily use the user's uid. */ 908 temporarily_use_uid(pw); 909 910 debug("trying public key file %s", file); 911 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) { 912 found_key = check_authkeys_file(f, file, key, pw); 913 fclose(f); 914 } 915 916 restore_uid(); 917 return found_key; 918 } 919 920 /* 921 * Checks whether key is allowed in output of command. 922 * returns 1 if the key is allowed or 0 otherwise. 923 */ 924 static int 925 user_key_command_allowed2(struct passwd *user_pw, Key *key) 926 { 927 FILE *f = NULL; 928 int r, ok, found_key = 0; 929 struct passwd *pw; 930 int i, uid_swapped = 0, ac = 0; 931 pid_t pid; 932 char *username = NULL, *key_fp = NULL, *keytext = NULL; 933 char *tmp, *command = NULL, **av = NULL; 934 void (*osigchld)(int); 935 936 if (options.authorized_keys_command == NULL) 937 return 0; 938 if (options.authorized_keys_command_user == NULL) { 939 error("No user for AuthorizedKeysCommand specified, skipping"); 940 return 0; 941 } 942 943 /* 944 * NB. all returns later this function should go via "out" to 945 * ensure the original SIGCHLD handler is restored properly. 946 */ 947 osigchld = signal(SIGCHLD, SIG_DFL); 948 949 /* Prepare and verify the user for the command */ 950 username = percent_expand(options.authorized_keys_command_user, 951 "u", user_pw->pw_name, (char *)NULL); 952 pw = getpwnam(username); 953 if (pw == NULL) { 954 error("AuthorizedKeysCommandUser \"%s\" not found: %s", 955 username, strerror(errno)); 956 goto out; 957 } 958 959 /* Prepare AuthorizedKeysCommand */ 960 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash, 961 SSH_FP_DEFAULT)) == NULL) { 962 error("%s: sshkey_fingerprint failed", __func__); 963 goto out; 964 } 965 if ((r = sshkey_to_base64(key, &keytext)) != 0) { 966 error("%s: sshkey_to_base64 failed: %s", __func__, ssh_err(r)); 967 goto out; 968 } 969 970 /* Turn the command into an argument vector */ 971 if (split_argv(options.authorized_keys_command, &ac, &av) != 0) { 972 error("AuthorizedKeysCommand \"%s\" contains invalid quotes", 973 command); 974 goto out; 975 } 976 if (ac == 0) { 977 error("AuthorizedKeysCommand \"%s\" yielded no arguments", 978 command); 979 goto out; 980 } 981 for (i = 1; i < ac; i++) { 982 tmp = percent_expand(av[i], 983 "u", user_pw->pw_name, 984 "h", user_pw->pw_dir, 985 "t", sshkey_ssh_name(key), 986 "f", key_fp, 987 "k", keytext, 988 (char *)NULL); 989 if (tmp == NULL) 990 fatal("%s: percent_expand failed", __func__); 991 free(av[i]); 992 av[i] = tmp; 993 } 994 /* Prepare a printable command for logs, etc. */ 995 command = assemble_argv(ac, av); 996 997 /* 998 * If AuthorizedKeysCommand was run without arguments 999 * then fall back to the old behaviour of passing the 1000 * target username as a single argument. 1001 */ 1002 if (ac == 1) { 1003 av = xreallocarray(av, ac + 2, sizeof(*av)); 1004 av[1] = xstrdup(user_pw->pw_name); 1005 av[2] = NULL; 1006 /* Fix up command too, since it is used in log messages */ 1007 free(command); 1008 xasprintf(&command, "%s %s", av[0], av[1]); 1009 } 1010 1011 if ((pid = subprocess("AuthorizedKeysCommand", pw, command, 1012 ac, av, &f)) == 0) 1013 goto out; 1014 1015 uid_swapped = 1; 1016 temporarily_use_uid(pw); 1017 1018 ok = check_authkeys_file(f, options.authorized_keys_command, key, pw); 1019 1020 if (exited_cleanly(pid, "AuthorizedKeysCommand", command) != 0) 1021 goto out; 1022 1023 /* Read completed successfully */ 1024 found_key = ok; 1025 out: 1026 if (f != NULL) 1027 fclose(f); 1028 signal(SIGCHLD, osigchld); 1029 for (i = 0; i < ac; i++) 1030 free(av[i]); 1031 free(av); 1032 if (uid_swapped) 1033 restore_uid(); 1034 free(command); 1035 free(username); 1036 free(key_fp); 1037 free(keytext); 1038 return found_key; 1039 } 1040 1041 /* 1042 * Check whether key authenticates and authorises the user. 1043 */ 1044 int 1045 user_key_allowed(struct passwd *pw, Key *key, int auth_attempt) 1046 { 1047 u_int success, i; 1048 char *file; 1049 1050 if (auth_key_is_revoked(key)) 1051 return 0; 1052 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 1053 return 0; 1054 1055 success = user_cert_trusted_ca(pw, key); 1056 if (success) 1057 return success; 1058 1059 success = user_key_command_allowed2(pw, key); 1060 if (success > 0) 1061 return success; 1062 1063 for (i = 0; !success && i < options.num_authkeys_files; i++) { 1064 1065 if (strcasecmp(options.authorized_keys_files[i], "none") == 0) 1066 continue; 1067 file = expand_authorized_keys( 1068 options.authorized_keys_files[i], pw); 1069 1070 success = user_key_allowed2(pw, key, file); 1071 free(file); 1072 } 1073 1074 return success; 1075 } 1076 1077 /* Records a public key in the list of previously-successful keys */ 1078 void 1079 auth2_record_userkey(Authctxt *authctxt, struct sshkey *key) 1080 { 1081 struct sshkey **tmp; 1082 1083 if (authctxt->nprev_userkeys >= INT_MAX || 1084 (tmp = reallocarray(authctxt->prev_userkeys, 1085 authctxt->nprev_userkeys + 1, sizeof(*tmp))) == NULL) 1086 fatal("%s: reallocarray failed", __func__); 1087 authctxt->prev_userkeys = tmp; 1088 authctxt->prev_userkeys[authctxt->nprev_userkeys] = key; 1089 authctxt->nprev_userkeys++; 1090 } 1091 1092 /* Checks whether a key has already been used successfully for authentication */ 1093 int 1094 auth2_userkey_already_used(Authctxt *authctxt, struct sshkey *key) 1095 { 1096 u_int i; 1097 1098 for (i = 0; i < authctxt->nprev_userkeys; i++) { 1099 if (sshkey_equal_public(key, authctxt->prev_userkeys[i])) { 1100 return 1; 1101 } 1102 } 1103 return 0; 1104 } 1105 1106 Authmethod method_pubkey = { 1107 "publickey", 1108 userauth_pubkey, 1109 &options.pubkey_authentication 1110 }; 1111