1 /* $OpenBSD: auth2.c,v 1.137 2017/02/03 23:05:57 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 __RCSID("$FreeBSD$"); 28 29 #include <sys/types.h> 30 #include <sys/stat.h> 31 #include <sys/uio.h> 32 33 #include <fcntl.h> 34 #include <pwd.h> 35 #include <stdarg.h> 36 #include <string.h> 37 #include <unistd.h> 38 39 #include "atomicio.h" 40 #include "xmalloc.h" 41 #include "ssh2.h" 42 #include "packet.h" 43 #include "log.h" 44 #include "buffer.h" 45 #include "misc.h" 46 #include "servconf.h" 47 #include "compat.h" 48 #include "key.h" 49 #include "hostfile.h" 50 #include "auth.h" 51 #include "dispatch.h" 52 #include "pathnames.h" 53 #include "buffer.h" 54 #include "blacklist_client.h" 55 56 #ifdef GSSAPI 57 #include "ssh-gss.h" 58 #endif 59 #include "monitor_wrap.h" 60 61 /* import */ 62 extern ServerOptions options; 63 extern u_char *session_id2; 64 extern u_int session_id2_len; 65 extern Buffer loginmsg; 66 67 /* methods */ 68 69 extern Authmethod method_none; 70 extern Authmethod method_pubkey; 71 extern Authmethod method_passwd; 72 extern Authmethod method_kbdint; 73 extern Authmethod method_hostbased; 74 #ifdef GSSAPI 75 extern Authmethod method_gssapi; 76 #endif 77 78 Authmethod *authmethods[] = { 79 &method_none, 80 &method_pubkey, 81 #ifdef GSSAPI 82 &method_gssapi, 83 #endif 84 &method_passwd, 85 &method_kbdint, 86 &method_hostbased, 87 NULL 88 }; 89 90 /* protocol */ 91 92 static int input_service_request(int, u_int32_t, void *); 93 static int input_userauth_request(int, u_int32_t, void *); 94 95 /* helper */ 96 static Authmethod *authmethod_lookup(Authctxt *, const char *); 97 static char *authmethods_get(Authctxt *authctxt); 98 99 #define MATCH_NONE 0 /* method or submethod mismatch */ 100 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 101 #define MATCH_BOTH 2 /* method and submethod match */ 102 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 103 static int list_starts_with(const char *, const char *, const char *); 104 105 char * 106 auth2_read_banner(void) 107 { 108 struct stat st; 109 char *banner = NULL; 110 size_t len, n; 111 int fd; 112 113 if ((fd = open(options.banner, O_RDONLY)) == -1) 114 return (NULL); 115 if (fstat(fd, &st) == -1) { 116 close(fd); 117 return (NULL); 118 } 119 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 120 close(fd); 121 return (NULL); 122 } 123 124 len = (size_t)st.st_size; /* truncate */ 125 banner = xmalloc(len + 1); 126 n = atomicio(read, fd, banner, len); 127 close(fd); 128 129 if (n != len) { 130 free(banner); 131 return (NULL); 132 } 133 banner[n] = '\0'; 134 135 return (banner); 136 } 137 138 void 139 userauth_send_banner(const char *msg) 140 { 141 if (datafellows & SSH_BUG_BANNER) 142 return; 143 144 packet_start(SSH2_MSG_USERAUTH_BANNER); 145 packet_put_cstring(msg); 146 packet_put_cstring(""); /* language, unused */ 147 packet_send(); 148 debug("%s: sent", __func__); 149 } 150 151 static void 152 userauth_banner(void) 153 { 154 char *banner = NULL; 155 156 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0) 157 return; 158 159 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 160 goto done; 161 userauth_send_banner(banner); 162 163 done: 164 free(banner); 165 } 166 167 /* 168 * loop until authctxt->success == TRUE 169 */ 170 void 171 do_authentication2(Authctxt *authctxt) 172 { 173 dispatch_init(&dispatch_protocol_error); 174 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 175 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 176 } 177 178 /*ARGSUSED*/ 179 static int 180 input_service_request(int type, u_int32_t seq, void *ctxt) 181 { 182 Authctxt *authctxt = ctxt; 183 u_int len; 184 int acceptit = 0; 185 char *service = packet_get_cstring(&len); 186 packet_check_eom(); 187 188 if (authctxt == NULL) 189 fatal("input_service_request: no authctxt"); 190 191 if (strcmp(service, "ssh-userauth") == 0) { 192 if (!authctxt->success) { 193 acceptit = 1; 194 /* now we can handle user-auth requests */ 195 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 196 } 197 } 198 /* XXX all other service requests are denied */ 199 200 if (acceptit) { 201 packet_start(SSH2_MSG_SERVICE_ACCEPT); 202 packet_put_cstring(service); 203 packet_send(); 204 packet_write_wait(); 205 } else { 206 debug("bad service request %s", service); 207 packet_disconnect("bad service request %s", service); 208 } 209 free(service); 210 return 0; 211 } 212 213 /*ARGSUSED*/ 214 static int 215 input_userauth_request(int type, u_int32_t seq, void *ctxt) 216 { 217 struct ssh *ssh = active_state; /* XXX */ 218 Authctxt *authctxt = ctxt; 219 Authmethod *m = NULL; 220 char *user, *service, *method, *style = NULL; 221 int authenticated = 0; 222 #ifdef HAVE_LOGIN_CAP 223 login_cap_t *lc; 224 const char *from_host, *from_ip; 225 #endif 226 227 if (authctxt == NULL) 228 fatal("input_userauth_request: no authctxt"); 229 230 user = packet_get_cstring(NULL); 231 service = packet_get_cstring(NULL); 232 method = packet_get_cstring(NULL); 233 debug("userauth-request for user %s service %s method %s", user, service, method); 234 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 235 236 if ((style = strchr(user, ':')) != NULL) 237 *style++ = 0; 238 239 if (authctxt->attempt++ == 0) { 240 /* setup auth context */ 241 authctxt->pw = PRIVSEP(getpwnamallow(user)); 242 authctxt->user = xstrdup(user); 243 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 244 authctxt->valid = 1; 245 debug2("%s: setting up authctxt for %s", 246 __func__, user); 247 } else { 248 /* Invalid user, fake password information */ 249 authctxt->pw = fakepw(); 250 #ifdef SSH_AUDIT_EVENTS 251 PRIVSEP(audit_event(SSH_INVALID_USER)); 252 #endif 253 } 254 #ifdef USE_PAM 255 if (options.use_pam) 256 PRIVSEP(start_pam(authctxt)); 257 #endif 258 ssh_packet_set_log_preamble(ssh, "%suser %s", 259 authctxt->valid ? "authenticating " : "invalid ", user); 260 setproctitle("%s%s", authctxt->valid ? user : "unknown", 261 use_privsep ? " [net]" : ""); 262 authctxt->service = xstrdup(service); 263 authctxt->style = style ? xstrdup(style) : NULL; 264 if (use_privsep) 265 mm_inform_authserv(service, style); 266 userauth_banner(); 267 if (auth2_setup_methods_lists(authctxt) != 0) 268 packet_disconnect("no authentication methods enabled"); 269 } else if (strcmp(user, authctxt->user) != 0 || 270 strcmp(service, authctxt->service) != 0) { 271 packet_disconnect("Change of username or service not allowed: " 272 "(%s,%s) -> (%s,%s)", 273 authctxt->user, authctxt->service, user, service); 274 } 275 276 #ifdef HAVE_LOGIN_CAP 277 if (authctxt->pw != NULL && 278 (lc = login_getpwclass(authctxt->pw)) != NULL) { 279 logit("user %s login class %s", authctxt->pw->pw_name, 280 authctxt->pw->pw_class); 281 from_host = auth_get_canonical_hostname(ssh, options.use_dns); 282 from_ip = ssh_remote_ipaddr(ssh); 283 if (!auth_hostok(lc, from_host, from_ip)) { 284 logit("Denied connection for %.200s from %.200s [%.200s].", 285 authctxt->pw->pw_name, from_host, from_ip); 286 packet_disconnect("Sorry, you are not allowed to connect."); 287 } 288 if (!auth_timeok(lc, time(NULL))) { 289 logit("LOGIN %.200s REFUSED (TIME) FROM %.200s", 290 authctxt->pw->pw_name, from_host); 291 packet_disconnect("Logins not available right now."); 292 } 293 login_close(lc); 294 } 295 #endif /* HAVE_LOGIN_CAP */ 296 297 /* reset state */ 298 auth2_challenge_stop(authctxt); 299 300 #ifdef GSSAPI 301 /* XXX move to auth2_gssapi_stop() */ 302 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 303 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 304 #endif 305 306 authctxt->postponed = 0; 307 authctxt->server_caused_failure = 0; 308 309 /* try to authenticate user */ 310 m = authmethod_lookup(authctxt, method); 311 if (m != NULL && authctxt->failures < options.max_authtries) { 312 debug2("input_userauth_request: try method %s", method); 313 authenticated = m->userauth(authctxt); 314 } 315 userauth_finish(authctxt, authenticated, method, NULL); 316 317 free(service); 318 free(user); 319 free(method); 320 return 0; 321 } 322 323 void 324 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 325 const char *submethod) 326 { 327 struct ssh *ssh = active_state; /* XXX */ 328 char *methods; 329 int partial = 0; 330 331 if (!authctxt->valid && authenticated) 332 fatal("INTERNAL ERROR: authenticated invalid user %s", 333 authctxt->user); 334 if (authenticated && authctxt->postponed) 335 fatal("INTERNAL ERROR: authenticated and postponed"); 336 337 /* Special handling for root */ 338 if (authenticated && authctxt->pw->pw_uid == 0 && 339 !auth_root_allowed(method)) { 340 authenticated = 0; 341 #ifdef SSH_AUDIT_EVENTS 342 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 343 #endif 344 } 345 346 if (authenticated && options.num_auth_methods != 0) { 347 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 348 authenticated = 0; 349 partial = 1; 350 } 351 } 352 353 /* Log before sending the reply */ 354 auth_log(authctxt, authenticated, partial, method, submethod); 355 356 if (authctxt->postponed) 357 return; 358 359 #ifdef USE_PAM 360 if (options.use_pam && authenticated) { 361 if (!PRIVSEP(do_pam_account())) { 362 /* if PAM returned a message, send it to the user */ 363 if (buffer_len(&loginmsg) > 0) { 364 buffer_append(&loginmsg, "\0", 1); 365 userauth_send_banner(buffer_ptr(&loginmsg)); 366 packet_write_wait(); 367 } 368 fatal("Access denied for user %s by PAM account " 369 "configuration", authctxt->user); 370 } 371 } 372 #endif 373 374 #ifdef _UNICOS 375 if (authenticated && cray_access_denied(authctxt->user)) { 376 authenticated = 0; 377 fatal("Access denied for user %s.", authctxt->user); 378 } 379 #endif /* _UNICOS */ 380 381 if (authenticated == 1) { 382 /* turn off userauth */ 383 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 384 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 385 packet_send(); 386 packet_write_wait(); 387 /* now we can break out */ 388 authctxt->success = 1; 389 ssh_packet_set_log_preamble(ssh, "user %s", authctxt->user); 390 } else { 391 392 /* Allow initial try of "none" auth without failure penalty */ 393 if (!partial && !authctxt->server_caused_failure && 394 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) { 395 authctxt->failures++; 396 BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL, "ssh"); 397 } 398 if (authctxt->failures >= options.max_authtries) { 399 #ifdef SSH_AUDIT_EVENTS 400 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 401 #endif 402 auth_maxtries_exceeded(authctxt); 403 } 404 methods = authmethods_get(authctxt); 405 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 406 partial, methods); 407 packet_start(SSH2_MSG_USERAUTH_FAILURE); 408 packet_put_cstring(methods); 409 packet_put_char(partial); 410 packet_send(); 411 packet_write_wait(); 412 free(methods); 413 } 414 } 415 416 /* 417 * Checks whether method is allowed by at least one AuthenticationMethods 418 * methods list. Returns 1 if allowed, or no methods lists configured. 419 * 0 otherwise. 420 */ 421 int 422 auth2_method_allowed(Authctxt *authctxt, const char *method, 423 const char *submethod) 424 { 425 u_int i; 426 427 /* 428 * NB. authctxt->num_auth_methods might be zero as a result of 429 * auth2_setup_methods_lists(), so check the configuration. 430 */ 431 if (options.num_auth_methods == 0) 432 return 1; 433 for (i = 0; i < authctxt->num_auth_methods; i++) { 434 if (list_starts_with(authctxt->auth_methods[i], method, 435 submethod) != MATCH_NONE) 436 return 1; 437 } 438 return 0; 439 } 440 441 static char * 442 authmethods_get(Authctxt *authctxt) 443 { 444 Buffer b; 445 char *list; 446 u_int i; 447 448 buffer_init(&b); 449 for (i = 0; authmethods[i] != NULL; i++) { 450 if (strcmp(authmethods[i]->name, "none") == 0) 451 continue; 452 if (authmethods[i]->enabled == NULL || 453 *(authmethods[i]->enabled) == 0) 454 continue; 455 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 456 NULL)) 457 continue; 458 if (buffer_len(&b) > 0) 459 buffer_append(&b, ",", 1); 460 buffer_append(&b, authmethods[i]->name, 461 strlen(authmethods[i]->name)); 462 } 463 if ((list = sshbuf_dup_string(&b)) == NULL) 464 fatal("%s: sshbuf_dup_string failed", __func__); 465 buffer_free(&b); 466 return list; 467 } 468 469 static Authmethod * 470 authmethod_lookup(Authctxt *authctxt, const char *name) 471 { 472 int i; 473 474 if (name != NULL) 475 for (i = 0; authmethods[i] != NULL; i++) 476 if (authmethods[i]->enabled != NULL && 477 *(authmethods[i]->enabled) != 0 && 478 strcmp(name, authmethods[i]->name) == 0 && 479 auth2_method_allowed(authctxt, 480 authmethods[i]->name, NULL)) 481 return authmethods[i]; 482 debug2("Unrecognized authentication method name: %s", 483 name ? name : "NULL"); 484 return NULL; 485 } 486 487 /* 488 * Check a comma-separated list of methods for validity. Is need_enable is 489 * non-zero, then also require that the methods are enabled. 490 * Returns 0 on success or -1 if the methods list is invalid. 491 */ 492 int 493 auth2_methods_valid(const char *_methods, int need_enable) 494 { 495 char *methods, *omethods, *method, *p; 496 u_int i, found; 497 int ret = -1; 498 499 if (*_methods == '\0') { 500 error("empty authentication method list"); 501 return -1; 502 } 503 omethods = methods = xstrdup(_methods); 504 while ((method = strsep(&methods, ",")) != NULL) { 505 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 506 if ((p = strchr(method, ':')) != NULL) 507 *p = '\0'; 508 if (strcmp(method, authmethods[i]->name) != 0) 509 continue; 510 if (need_enable) { 511 if (authmethods[i]->enabled == NULL || 512 *(authmethods[i]->enabled) == 0) { 513 error("Disabled method \"%s\" in " 514 "AuthenticationMethods list \"%s\"", 515 method, _methods); 516 goto out; 517 } 518 } 519 found = 1; 520 break; 521 } 522 if (!found) { 523 error("Unknown authentication method \"%s\" in list", 524 method); 525 goto out; 526 } 527 } 528 ret = 0; 529 out: 530 free(omethods); 531 return ret; 532 } 533 534 /* 535 * Prune the AuthenticationMethods supplied in the configuration, removing 536 * any methods lists that include disabled methods. Note that this might 537 * leave authctxt->num_auth_methods == 0, even when multiple required auth 538 * has been requested. For this reason, all tests for whether multiple is 539 * enabled should consult options.num_auth_methods directly. 540 */ 541 int 542 auth2_setup_methods_lists(Authctxt *authctxt) 543 { 544 u_int i; 545 546 if (options.num_auth_methods == 0) 547 return 0; 548 debug3("%s: checking methods", __func__); 549 authctxt->auth_methods = xcalloc(options.num_auth_methods, 550 sizeof(*authctxt->auth_methods)); 551 authctxt->num_auth_methods = 0; 552 for (i = 0; i < options.num_auth_methods; i++) { 553 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 554 logit("Authentication methods list \"%s\" contains " 555 "disabled method, skipping", 556 options.auth_methods[i]); 557 continue; 558 } 559 debug("authentication methods list %d: %s", 560 authctxt->num_auth_methods, options.auth_methods[i]); 561 authctxt->auth_methods[authctxt->num_auth_methods++] = 562 xstrdup(options.auth_methods[i]); 563 } 564 if (authctxt->num_auth_methods == 0) { 565 error("No AuthenticationMethods left after eliminating " 566 "disabled methods"); 567 return -1; 568 } 569 return 0; 570 } 571 572 static int 573 list_starts_with(const char *methods, const char *method, 574 const char *submethod) 575 { 576 size_t l = strlen(method); 577 int match; 578 const char *p; 579 580 if (strncmp(methods, method, l) != 0) 581 return MATCH_NONE; 582 p = methods + l; 583 match = MATCH_METHOD; 584 if (*p == ':') { 585 if (!submethod) 586 return MATCH_PARTIAL; 587 l = strlen(submethod); 588 p += 1; 589 if (strncmp(submethod, p, l)) 590 return MATCH_NONE; 591 p += l; 592 match = MATCH_BOTH; 593 } 594 if (*p != ',' && *p != '\0') 595 return MATCH_NONE; 596 return match; 597 } 598 599 /* 600 * Remove method from the start of a comma-separated list of methods. 601 * Returns 0 if the list of methods did not start with that method or 1 602 * if it did. 603 */ 604 static int 605 remove_method(char **methods, const char *method, const char *submethod) 606 { 607 char *omethods = *methods, *p; 608 size_t l = strlen(method); 609 int match; 610 611 match = list_starts_with(omethods, method, submethod); 612 if (match != MATCH_METHOD && match != MATCH_BOTH) 613 return 0; 614 p = omethods + l; 615 if (submethod && match == MATCH_BOTH) 616 p += 1 + strlen(submethod); /* include colon */ 617 if (*p == ',') 618 p++; 619 *methods = xstrdup(p); 620 free(omethods); 621 return 1; 622 } 623 624 /* 625 * Called after successful authentication. Will remove the successful method 626 * from the start of each list in which it occurs. If it was the last method 627 * in any list, then authentication is deemed successful. 628 * Returns 1 if the method completed any authentication list or 0 otherwise. 629 */ 630 int 631 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 632 const char *submethod) 633 { 634 u_int i, found = 0; 635 636 debug3("%s: updating methods list after \"%s\"", __func__, method); 637 for (i = 0; i < authctxt->num_auth_methods; i++) { 638 if (!remove_method(&(authctxt->auth_methods[i]), method, 639 submethod)) 640 continue; 641 found = 1; 642 if (*authctxt->auth_methods[i] == '\0') { 643 debug2("authentication methods list %d complete", i); 644 return 1; 645 } 646 debug3("authentication methods list %d remaining: \"%s\"", 647 i, authctxt->auth_methods[i]); 648 } 649 /* This should not happen, but would be bad if it did */ 650 if (!found) 651 fatal("%s: method not in AuthenticationMethods", __func__); 652 return 0; 653 } 654 655 656