1 /* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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 Authctxt *authctxt = ctxt; 218 Authmethod *m = NULL; 219 char *user, *service, *method, *style = NULL; 220 int authenticated = 0; 221 #ifdef HAVE_LOGIN_CAP 222 struct ssh *ssh = active_state; /* XXX */ 223 login_cap_t *lc; 224 const char *from_host, *from_ip; 225 #endif 226 if (authctxt == NULL) 227 fatal("input_userauth_request: no authctxt"); 228 229 user = packet_get_cstring(NULL); 230 service = packet_get_cstring(NULL); 231 method = packet_get_cstring(NULL); 232 debug("userauth-request for user %s service %s method %s", user, service, method); 233 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 234 235 if ((style = strchr(user, ':')) != NULL) 236 *style++ = 0; 237 238 if (authctxt->attempt++ == 0) { 239 /* setup auth context */ 240 authctxt->pw = PRIVSEP(getpwnamallow(user)); 241 authctxt->user = xstrdup(user); 242 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 243 authctxt->valid = 1; 244 debug2("input_userauth_request: setting up authctxt for %s", user); 245 } else { 246 logit("input_userauth_request: invalid user %s", user); 247 authctxt->pw = fakepw(); 248 #ifdef SSH_AUDIT_EVENTS 249 PRIVSEP(audit_event(SSH_INVALID_USER)); 250 #endif 251 } 252 #ifdef USE_PAM 253 if (options.use_pam) 254 PRIVSEP(start_pam(authctxt)); 255 #endif 256 setproctitle("%s%s", authctxt->valid ? user : "unknown", 257 use_privsep ? " [net]" : ""); 258 authctxt->service = xstrdup(service); 259 authctxt->style = style ? xstrdup(style) : NULL; 260 if (use_privsep) 261 mm_inform_authserv(service, style); 262 userauth_banner(); 263 if (auth2_setup_methods_lists(authctxt) != 0) 264 packet_disconnect("no authentication methods enabled"); 265 } else if (strcmp(user, authctxt->user) != 0 || 266 strcmp(service, authctxt->service) != 0) { 267 packet_disconnect("Change of username or service not allowed: " 268 "(%s,%s) -> (%s,%s)", 269 authctxt->user, authctxt->service, user, service); 270 } 271 272 #ifdef HAVE_LOGIN_CAP 273 if (authctxt->pw != NULL && 274 (lc = login_getpwclass(authctxt->pw)) != NULL) { 275 logit("user %s login class %s", authctxt->pw->pw_name, 276 authctxt->pw->pw_class); 277 from_host = auth_get_canonical_hostname(ssh, options.use_dns); 278 from_ip = ssh_remote_ipaddr(ssh); 279 if (!auth_hostok(lc, from_host, from_ip)) { 280 logit("Denied connection for %.200s from %.200s [%.200s].", 281 authctxt->pw->pw_name, from_host, from_ip); 282 packet_disconnect("Sorry, you are not allowed to connect."); 283 } 284 if (!auth_timeok(lc, time(NULL))) { 285 logit("LOGIN %.200s REFUSED (TIME) FROM %.200s", 286 authctxt->pw->pw_name, from_host); 287 packet_disconnect("Logins not available right now."); 288 } 289 login_close(lc); 290 } 291 #endif /* HAVE_LOGIN_CAP */ 292 293 /* reset state */ 294 auth2_challenge_stop(authctxt); 295 296 #ifdef GSSAPI 297 /* XXX move to auth2_gssapi_stop() */ 298 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 299 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 300 #endif 301 302 authctxt->postponed = 0; 303 authctxt->server_caused_failure = 0; 304 305 /* try to authenticate user */ 306 m = authmethod_lookup(authctxt, method); 307 if (m != NULL && authctxt->failures < options.max_authtries) { 308 debug2("input_userauth_request: try method %s", method); 309 authenticated = m->userauth(authctxt); 310 } 311 userauth_finish(authctxt, authenticated, method, NULL); 312 313 free(service); 314 free(user); 315 free(method); 316 return 0; 317 } 318 319 void 320 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 321 const char *submethod) 322 { 323 char *methods; 324 int partial = 0; 325 326 if (!authctxt->valid && authenticated) 327 fatal("INTERNAL ERROR: authenticated invalid user %s", 328 authctxt->user); 329 if (authenticated && authctxt->postponed) 330 fatal("INTERNAL ERROR: authenticated and postponed"); 331 332 /* Special handling for root */ 333 if (authenticated && authctxt->pw->pw_uid == 0 && 334 !auth_root_allowed(method)) { 335 authenticated = 0; 336 #ifdef SSH_AUDIT_EVENTS 337 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 338 #endif 339 } 340 341 if (authenticated && options.num_auth_methods != 0) { 342 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 343 authenticated = 0; 344 partial = 1; 345 } 346 } 347 348 /* Log before sending the reply */ 349 auth_log(authctxt, authenticated, partial, method, submethod); 350 351 if (authctxt->postponed) 352 return; 353 354 #ifdef USE_PAM 355 if (options.use_pam && authenticated) { 356 if (!PRIVSEP(do_pam_account())) { 357 /* if PAM returned a message, send it to the user */ 358 if (buffer_len(&loginmsg) > 0) { 359 buffer_append(&loginmsg, "\0", 1); 360 userauth_send_banner(buffer_ptr(&loginmsg)); 361 packet_write_wait(); 362 } 363 fatal("Access denied for user %s by PAM account " 364 "configuration", authctxt->user); 365 } 366 } 367 #endif 368 369 #ifdef _UNICOS 370 if (authenticated && cray_access_denied(authctxt->user)) { 371 authenticated = 0; 372 fatal("Access denied for user %s.", authctxt->user); 373 } 374 #endif /* _UNICOS */ 375 376 if (authenticated == 1) { 377 /* turn off userauth */ 378 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 379 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 380 packet_send(); 381 packet_write_wait(); 382 /* now we can break out */ 383 authctxt->success = 1; 384 } else { 385 386 /* Allow initial try of "none" auth without failure penalty */ 387 if (!partial && !authctxt->server_caused_failure && 388 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) { 389 authctxt->failures++; 390 BLACKLIST_NOTIFY(BLACKLIST_AUTH_FAIL, "ssh"); 391 } 392 if (authctxt->failures >= options.max_authtries) { 393 #ifdef SSH_AUDIT_EVENTS 394 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 395 #endif 396 auth_maxtries_exceeded(authctxt); 397 } 398 methods = authmethods_get(authctxt); 399 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 400 partial, methods); 401 packet_start(SSH2_MSG_USERAUTH_FAILURE); 402 packet_put_cstring(methods); 403 packet_put_char(partial); 404 packet_send(); 405 packet_write_wait(); 406 free(methods); 407 } 408 } 409 410 /* 411 * Checks whether method is allowed by at least one AuthenticationMethods 412 * methods list. Returns 1 if allowed, or no methods lists configured. 413 * 0 otherwise. 414 */ 415 int 416 auth2_method_allowed(Authctxt *authctxt, const char *method, 417 const char *submethod) 418 { 419 u_int i; 420 421 /* 422 * NB. authctxt->num_auth_methods might be zero as a result of 423 * auth2_setup_methods_lists(), so check the configuration. 424 */ 425 if (options.num_auth_methods == 0) 426 return 1; 427 for (i = 0; i < authctxt->num_auth_methods; i++) { 428 if (list_starts_with(authctxt->auth_methods[i], method, 429 submethod) != MATCH_NONE) 430 return 1; 431 } 432 return 0; 433 } 434 435 static char * 436 authmethods_get(Authctxt *authctxt) 437 { 438 Buffer b; 439 char *list; 440 u_int i; 441 442 buffer_init(&b); 443 for (i = 0; authmethods[i] != NULL; i++) { 444 if (strcmp(authmethods[i]->name, "none") == 0) 445 continue; 446 if (authmethods[i]->enabled == NULL || 447 *(authmethods[i]->enabled) == 0) 448 continue; 449 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 450 NULL)) 451 continue; 452 if (buffer_len(&b) > 0) 453 buffer_append(&b, ",", 1); 454 buffer_append(&b, authmethods[i]->name, 455 strlen(authmethods[i]->name)); 456 } 457 if ((list = sshbuf_dup_string(&b)) == NULL) 458 fatal("%s: sshbuf_dup_string failed", __func__); 459 buffer_free(&b); 460 return list; 461 } 462 463 static Authmethod * 464 authmethod_lookup(Authctxt *authctxt, const char *name) 465 { 466 int i; 467 468 if (name != NULL) 469 for (i = 0; authmethods[i] != NULL; i++) 470 if (authmethods[i]->enabled != NULL && 471 *(authmethods[i]->enabled) != 0 && 472 strcmp(name, authmethods[i]->name) == 0 && 473 auth2_method_allowed(authctxt, 474 authmethods[i]->name, NULL)) 475 return authmethods[i]; 476 debug2("Unrecognized authentication method name: %s", 477 name ? name : "NULL"); 478 return NULL; 479 } 480 481 /* 482 * Check a comma-separated list of methods for validity. Is need_enable is 483 * non-zero, then also require that the methods are enabled. 484 * Returns 0 on success or -1 if the methods list is invalid. 485 */ 486 int 487 auth2_methods_valid(const char *_methods, int need_enable) 488 { 489 char *methods, *omethods, *method, *p; 490 u_int i, found; 491 int ret = -1; 492 493 if (*_methods == '\0') { 494 error("empty authentication method list"); 495 return -1; 496 } 497 omethods = methods = xstrdup(_methods); 498 while ((method = strsep(&methods, ",")) != NULL) { 499 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 500 if ((p = strchr(method, ':')) != NULL) 501 *p = '\0'; 502 if (strcmp(method, authmethods[i]->name) != 0) 503 continue; 504 if (need_enable) { 505 if (authmethods[i]->enabled == NULL || 506 *(authmethods[i]->enabled) == 0) { 507 error("Disabled method \"%s\" in " 508 "AuthenticationMethods list \"%s\"", 509 method, _methods); 510 goto out; 511 } 512 } 513 found = 1; 514 break; 515 } 516 if (!found) { 517 error("Unknown authentication method \"%s\" in list", 518 method); 519 goto out; 520 } 521 } 522 ret = 0; 523 out: 524 free(omethods); 525 return ret; 526 } 527 528 /* 529 * Prune the AuthenticationMethods supplied in the configuration, removing 530 * any methods lists that include disabled methods. Note that this might 531 * leave authctxt->num_auth_methods == 0, even when multiple required auth 532 * has been requested. For this reason, all tests for whether multiple is 533 * enabled should consult options.num_auth_methods directly. 534 */ 535 int 536 auth2_setup_methods_lists(Authctxt *authctxt) 537 { 538 u_int i; 539 540 if (options.num_auth_methods == 0) 541 return 0; 542 debug3("%s: checking methods", __func__); 543 authctxt->auth_methods = xcalloc(options.num_auth_methods, 544 sizeof(*authctxt->auth_methods)); 545 authctxt->num_auth_methods = 0; 546 for (i = 0; i < options.num_auth_methods; i++) { 547 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 548 logit("Authentication methods list \"%s\" contains " 549 "disabled method, skipping", 550 options.auth_methods[i]); 551 continue; 552 } 553 debug("authentication methods list %d: %s", 554 authctxt->num_auth_methods, options.auth_methods[i]); 555 authctxt->auth_methods[authctxt->num_auth_methods++] = 556 xstrdup(options.auth_methods[i]); 557 } 558 if (authctxt->num_auth_methods == 0) { 559 error("No AuthenticationMethods left after eliminating " 560 "disabled methods"); 561 return -1; 562 } 563 return 0; 564 } 565 566 static int 567 list_starts_with(const char *methods, const char *method, 568 const char *submethod) 569 { 570 size_t l = strlen(method); 571 int match; 572 const char *p; 573 574 if (strncmp(methods, method, l) != 0) 575 return MATCH_NONE; 576 p = methods + l; 577 match = MATCH_METHOD; 578 if (*p == ':') { 579 if (!submethod) 580 return MATCH_PARTIAL; 581 l = strlen(submethod); 582 p += 1; 583 if (strncmp(submethod, p, l)) 584 return MATCH_NONE; 585 p += l; 586 match = MATCH_BOTH; 587 } 588 if (*p != ',' && *p != '\0') 589 return MATCH_NONE; 590 return match; 591 } 592 593 /* 594 * Remove method from the start of a comma-separated list of methods. 595 * Returns 0 if the list of methods did not start with that method or 1 596 * if it did. 597 */ 598 static int 599 remove_method(char **methods, const char *method, const char *submethod) 600 { 601 char *omethods = *methods, *p; 602 size_t l = strlen(method); 603 int match; 604 605 match = list_starts_with(omethods, method, submethod); 606 if (match != MATCH_METHOD && match != MATCH_BOTH) 607 return 0; 608 p = omethods + l; 609 if (submethod && match == MATCH_BOTH) 610 p += 1 + strlen(submethod); /* include colon */ 611 if (*p == ',') 612 p++; 613 *methods = xstrdup(p); 614 free(omethods); 615 return 1; 616 } 617 618 /* 619 * Called after successful authentication. Will remove the successful method 620 * from the start of each list in which it occurs. If it was the last method 621 * in any list, then authentication is deemed successful. 622 * Returns 1 if the method completed any authentication list or 0 otherwise. 623 */ 624 int 625 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 626 const char *submethod) 627 { 628 u_int i, found = 0; 629 630 debug3("%s: updating methods list after \"%s\"", __func__, method); 631 for (i = 0; i < authctxt->num_auth_methods; i++) { 632 if (!remove_method(&(authctxt->auth_methods[i]), method, 633 submethod)) 634 continue; 635 found = 1; 636 if (*authctxt->auth_methods[i] == '\0') { 637 debug2("authentication methods list %d complete", i); 638 return 1; 639 } 640 debug3("authentication methods list %d remaining: \"%s\"", 641 i, authctxt->auth_methods[i]); 642 } 643 /* This should not happen, but would be bad if it did */ 644 if (!found) 645 fatal("%s: method not in AuthenticationMethods", __func__); 646 return 0; 647 } 648 649 650