1 /* $OpenBSD: auth2.c,v 1.132 2014/07/15 15:54:14 millert 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/uio.h> 31 32 #include <fcntl.h> 33 #include <pwd.h> 34 #include <stdarg.h> 35 #include <string.h> 36 #include <unistd.h> 37 38 #include "atomicio.h" 39 #include "xmalloc.h" 40 #include "ssh2.h" 41 #include "packet.h" 42 #include "log.h" 43 #include "buffer.h" 44 #include "misc.h" 45 #include "servconf.h" 46 #include "compat.h" 47 #include "key.h" 48 #include "hostfile.h" 49 #include "auth.h" 50 #include "dispatch.h" 51 #include "pathnames.h" 52 #include "buffer.h" 53 #include "canohost.h" 54 55 #ifdef GSSAPI 56 #include "ssh-gss.h" 57 #endif 58 #include "monitor_wrap.h" 59 60 /* import */ 61 extern ServerOptions options; 62 extern u_char *session_id2; 63 extern u_int session_id2_len; 64 extern Buffer loginmsg; 65 66 /* methods */ 67 68 extern Authmethod method_none; 69 extern Authmethod method_pubkey; 70 extern Authmethod method_passwd; 71 extern Authmethod method_kbdint; 72 extern Authmethod method_hostbased; 73 #ifdef GSSAPI 74 extern Authmethod method_gssapi; 75 #endif 76 77 static int log_flag = 0; 78 79 80 Authmethod *authmethods[] = { 81 &method_none, 82 &method_pubkey, 83 #ifdef GSSAPI 84 &method_gssapi, 85 #endif 86 &method_passwd, 87 &method_kbdint, 88 &method_hostbased, 89 NULL 90 }; 91 92 /* protocol */ 93 94 static void input_service_request(int, u_int32_t, void *); 95 static void input_userauth_request(int, u_int32_t, void *); 96 97 /* helper */ 98 static Authmethod *authmethod_lookup(Authctxt *, const char *); 99 static char *authmethods_get(Authctxt *authctxt); 100 101 #define MATCH_NONE 0 /* method or submethod mismatch */ 102 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 103 #define MATCH_BOTH 2 /* method and submethod match */ 104 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 105 static int list_starts_with(const char *, const char *, const char *); 106 107 char * 108 auth2_read_banner(void) 109 { 110 struct stat st; 111 char *banner = NULL; 112 size_t len, n; 113 int fd; 114 115 if ((fd = open(options.banner, O_RDONLY)) == -1) 116 return (NULL); 117 if (fstat(fd, &st) == -1) { 118 close(fd); 119 return (NULL); 120 } 121 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 122 close(fd); 123 return (NULL); 124 } 125 126 len = (size_t)st.st_size; /* truncate */ 127 banner = xmalloc(len + 1); 128 n = atomicio(read, fd, banner, len); 129 close(fd); 130 131 if (n != len) { 132 free(banner); 133 return (NULL); 134 } 135 banner[n] = '\0'; 136 137 return (banner); 138 } 139 140 void 141 userauth_send_banner(const char *msg) 142 { 143 if (datafellows & SSH_BUG_BANNER) 144 return; 145 146 packet_start(SSH2_MSG_USERAUTH_BANNER); 147 packet_put_cstring(msg); 148 packet_put_cstring(""); /* language, unused */ 149 packet_send(); 150 debug("%s: sent", __func__); 151 } 152 153 static void 154 userauth_banner(void) 155 { 156 char *banner = NULL; 157 158 if (options.banner == NULL || 159 strcasecmp(options.banner, "none") == 0 || 160 (datafellows & SSH_BUG_BANNER) != 0) 161 return; 162 163 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 164 goto done; 165 userauth_send_banner(banner); 166 167 done: 168 free(banner); 169 } 170 171 /* 172 * loop until authctxt->success == TRUE 173 */ 174 void 175 do_authentication2(Authctxt *authctxt) 176 { 177 dispatch_init(&dispatch_protocol_error); 178 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 179 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 180 } 181 182 /*ARGSUSED*/ 183 static void 184 input_service_request(int type, u_int32_t seq, void *ctxt) 185 { 186 Authctxt *authctxt = ctxt; 187 u_int len; 188 int acceptit = 0; 189 char *service = packet_get_cstring(&len); 190 packet_check_eom(); 191 192 if (authctxt == NULL) 193 fatal("input_service_request: no authctxt"); 194 195 if (strcmp(service, "ssh-userauth") == 0) { 196 if (!authctxt->success) { 197 acceptit = 1; 198 /* now we can handle user-auth requests */ 199 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 200 } 201 } 202 /* XXX all other service requests are denied */ 203 204 if (acceptit) { 205 packet_start(SSH2_MSG_SERVICE_ACCEPT); 206 packet_put_cstring(service); 207 packet_send(); 208 packet_write_wait(); 209 } else { 210 debug("bad service request %s", service); 211 packet_disconnect("bad service request %s", service); 212 } 213 free(service); 214 } 215 216 /*ARGSUSED*/ 217 static void 218 input_userauth_request(int type, u_int32_t seq, void *ctxt) 219 { 220 Authctxt *authctxt = ctxt; 221 Authmethod *m = NULL; 222 char *user, *service, *method, *style = NULL; 223 int authenticated = 0; 224 #ifdef HAVE_LOGIN_CAP 225 login_cap_t *lc; 226 const char *from_host, *from_ip; 227 228 from_host = get_canonical_hostname(options.use_dns); 229 from_ip = get_remote_ipaddr(); 230 #endif 231 232 if (authctxt == NULL) 233 fatal("input_userauth_request: no authctxt"); 234 235 user = packet_get_cstring(NULL); 236 service = packet_get_cstring(NULL); 237 method = packet_get_cstring(NULL); 238 debug("userauth-request for user %s service %s method %s", user, service, method); 239 if (!log_flag) { 240 logit("SSH: Server;Ltype: Authname;Remote: %s-%d;Name: %s", 241 get_remote_ipaddr(), get_remote_port(), user); 242 log_flag = 1; 243 } 244 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 245 246 if ((style = strchr(user, ':')) != NULL) 247 *style++ = 0; 248 249 if (authctxt->attempt++ == 0) { 250 /* setup auth context */ 251 authctxt->pw = PRIVSEP(getpwnamallow(user)); 252 authctxt->user = xstrdup(user); 253 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 254 authctxt->valid = 1; 255 debug2("input_userauth_request: setting up authctxt for %s", user); 256 } else { 257 logit("input_userauth_request: invalid user %s", user); 258 authctxt->pw = fakepw(); 259 #ifdef SSH_AUDIT_EVENTS 260 PRIVSEP(audit_event(SSH_INVALID_USER)); 261 #endif 262 } 263 #ifdef USE_PAM 264 if (options.use_pam) 265 PRIVSEP(start_pam(authctxt)); 266 #endif 267 setproctitle("%s%s", authctxt->valid ? user : "unknown", 268 use_privsep ? " [net]" : ""); 269 authctxt->service = xstrdup(service); 270 authctxt->style = style ? xstrdup(style) : NULL; 271 if (use_privsep) 272 mm_inform_authserv(service, style); 273 userauth_banner(); 274 if (auth2_setup_methods_lists(authctxt) != 0) 275 packet_disconnect("no authentication methods enabled"); 276 } else if (strcmp(user, authctxt->user) != 0 || 277 strcmp(service, authctxt->service) != 0) { 278 packet_disconnect("Change of username or service not allowed: " 279 "(%s,%s) -> (%s,%s)", 280 authctxt->user, authctxt->service, user, service); 281 } 282 283 #ifdef HAVE_LOGIN_CAP 284 if (authctxt->pw != NULL) { 285 lc = login_getpwclass(authctxt->pw); 286 if (lc == NULL) 287 lc = login_getclassbyname(NULL, authctxt->pw); 288 if (!auth_hostok(lc, from_host, from_ip)) { 289 logit("Denied connection for %.200s from %.200s [%.200s].", 290 authctxt->pw->pw_name, from_host, from_ip); 291 packet_disconnect("Sorry, you are not allowed to connect."); 292 } 293 if (!auth_timeok(lc, time(NULL))) { 294 logit("LOGIN %.200s REFUSED (TIME) FROM %.200s", 295 authctxt->pw->pw_name, from_host); 296 packet_disconnect("Logins not available right now."); 297 } 298 login_close(lc); 299 lc = NULL; 300 } 301 #endif /* HAVE_LOGIN_CAP */ 302 303 /* reset state */ 304 auth2_challenge_stop(authctxt); 305 306 #ifdef GSSAPI 307 /* XXX move to auth2_gssapi_stop() */ 308 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 309 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 310 #endif 311 312 authctxt->postponed = 0; 313 authctxt->server_caused_failure = 0; 314 315 /* try to authenticate user */ 316 m = authmethod_lookup(authctxt, method); 317 if (m != NULL && authctxt->failures < options.max_authtries) { 318 debug2("input_userauth_request: try method %s", method); 319 authenticated = m->userauth(authctxt); 320 } 321 userauth_finish(authctxt, authenticated, method, NULL); 322 323 free(service); 324 free(user); 325 free(method); 326 } 327 328 void 329 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 330 const char *submethod) 331 { 332 char *methods; 333 int partial = 0; 334 335 if (!authctxt->valid && authenticated) 336 fatal("INTERNAL ERROR: authenticated invalid user %s", 337 authctxt->user); 338 if (authenticated && authctxt->postponed) 339 fatal("INTERNAL ERROR: authenticated and postponed"); 340 341 /* Special handling for root */ 342 if (authenticated && authctxt->pw->pw_uid == 0 && 343 !auth_root_allowed(method)) { 344 authenticated = 0; 345 #ifdef SSH_AUDIT_EVENTS 346 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 347 #endif 348 } 349 350 if (authenticated && options.num_auth_methods != 0) { 351 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 352 authenticated = 0; 353 partial = 1; 354 } 355 } 356 357 /* Log before sending the reply */ 358 auth_log(authctxt, authenticated, partial, method, submethod); 359 360 if (authctxt->postponed) 361 return; 362 363 #ifdef USE_PAM 364 if (options.use_pam && authenticated) { 365 if (!PRIVSEP(do_pam_account())) { 366 /* if PAM returned a message, send it to the user */ 367 if (buffer_len(&loginmsg) > 0) { 368 buffer_append(&loginmsg, "\0", 1); 369 userauth_send_banner(buffer_ptr(&loginmsg)); 370 packet_write_wait(); 371 } 372 fatal("Access denied for user %s by PAM account " 373 "configuration", authctxt->user); 374 } 375 } 376 #endif 377 378 #ifdef _UNICOS 379 if (authenticated && cray_access_denied(authctxt->user)) { 380 authenticated = 0; 381 fatal("Access denied for user %s.", authctxt->user); 382 } 383 #endif /* _UNICOS */ 384 385 if (authenticated == 1) { 386 /* turn off userauth */ 387 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 388 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 389 packet_send(); 390 packet_write_wait(); 391 /* now we can break out */ 392 authctxt->success = 1; 393 } else { 394 395 /* Allow initial try of "none" auth without failure penalty */ 396 if (!authctxt->server_caused_failure && 397 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 398 authctxt->failures++; 399 if (authctxt->failures >= options.max_authtries) { 400 #ifdef SSH_AUDIT_EVENTS 401 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 402 #endif 403 auth_maxtries_exceeded(authctxt); 404 } 405 methods = authmethods_get(authctxt); 406 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 407 partial, methods); 408 packet_start(SSH2_MSG_USERAUTH_FAILURE); 409 packet_put_cstring(methods); 410 packet_put_char(partial); 411 packet_send(); 412 packet_write_wait(); 413 free(methods); 414 } 415 } 416 417 /* 418 * Checks whether method is allowed by at least one AuthenticationMethods 419 * methods list. Returns 1 if allowed, or no methods lists configured. 420 * 0 otherwise. 421 */ 422 int 423 auth2_method_allowed(Authctxt *authctxt, const char *method, 424 const char *submethod) 425 { 426 u_int i; 427 428 /* 429 * NB. authctxt->num_auth_methods might be zero as a result of 430 * auth2_setup_methods_lists(), so check the configuration. 431 */ 432 if (options.num_auth_methods == 0) 433 return 1; 434 for (i = 0; i < authctxt->num_auth_methods; i++) { 435 if (list_starts_with(authctxt->auth_methods[i], method, 436 submethod) != MATCH_NONE) 437 return 1; 438 } 439 return 0; 440 } 441 442 static char * 443 authmethods_get(Authctxt *authctxt) 444 { 445 Buffer b; 446 char *list; 447 u_int i; 448 449 buffer_init(&b); 450 for (i = 0; authmethods[i] != NULL; i++) { 451 if (strcmp(authmethods[i]->name, "none") == 0) 452 continue; 453 if (authmethods[i]->enabled == NULL || 454 *(authmethods[i]->enabled) == 0) 455 continue; 456 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 457 NULL)) 458 continue; 459 if (buffer_len(&b) > 0) 460 buffer_append(&b, ",", 1); 461 buffer_append(&b, authmethods[i]->name, 462 strlen(authmethods[i]->name)); 463 } 464 buffer_append(&b, "\0", 1); 465 list = xstrdup(buffer_ptr(&b)); 466 buffer_free(&b); 467 return list; 468 } 469 470 static Authmethod * 471 authmethod_lookup(Authctxt *authctxt, const char *name) 472 { 473 int i; 474 475 if (name != NULL) 476 for (i = 0; authmethods[i] != NULL; i++) 477 if (authmethods[i]->enabled != NULL && 478 *(authmethods[i]->enabled) != 0 && 479 strcmp(name, authmethods[i]->name) == 0 && 480 auth2_method_allowed(authctxt, 481 authmethods[i]->name, NULL)) 482 return authmethods[i]; 483 debug2("Unrecognized authentication method name: %s", 484 name ? name : "NULL"); 485 return NULL; 486 } 487 488 /* 489 * Check a comma-separated list of methods for validity. Is need_enable is 490 * non-zero, then also require that the methods are enabled. 491 * Returns 0 on success or -1 if the methods list is invalid. 492 */ 493 int 494 auth2_methods_valid(const char *_methods, int need_enable) 495 { 496 char *methods, *omethods, *method, *p; 497 u_int i, found; 498 int ret = -1; 499 500 if (*_methods == '\0') { 501 error("empty authentication method list"); 502 return -1; 503 } 504 omethods = methods = xstrdup(_methods); 505 while ((method = strsep(&methods, ",")) != NULL) { 506 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 507 if ((p = strchr(method, ':')) != NULL) 508 *p = '\0'; 509 if (strcmp(method, authmethods[i]->name) != 0) 510 continue; 511 if (need_enable) { 512 if (authmethods[i]->enabled == NULL || 513 *(authmethods[i]->enabled) == 0) { 514 error("Disabled method \"%s\" in " 515 "AuthenticationMethods list \"%s\"", 516 method, _methods); 517 goto out; 518 } 519 } 520 found = 1; 521 break; 522 } 523 if (!found) { 524 error("Unknown authentication method \"%s\" in list", 525 method); 526 goto out; 527 } 528 } 529 ret = 0; 530 out: 531 free(omethods); 532 return ret; 533 } 534 535 /* 536 * Prune the AuthenticationMethods supplied in the configuration, removing 537 * any methods lists that include disabled methods. Note that this might 538 * leave authctxt->num_auth_methods == 0, even when multiple required auth 539 * has been requested. For this reason, all tests for whether multiple is 540 * enabled should consult options.num_auth_methods directly. 541 */ 542 int 543 auth2_setup_methods_lists(Authctxt *authctxt) 544 { 545 u_int i; 546 547 if (options.num_auth_methods == 0) 548 return 0; 549 debug3("%s: checking methods", __func__); 550 authctxt->auth_methods = xcalloc(options.num_auth_methods, 551 sizeof(*authctxt->auth_methods)); 552 authctxt->num_auth_methods = 0; 553 for (i = 0; i < options.num_auth_methods; i++) { 554 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 555 logit("Authentication methods list \"%s\" contains " 556 "disabled method, skipping", 557 options.auth_methods[i]); 558 continue; 559 } 560 debug("authentication methods list %d: %s", 561 authctxt->num_auth_methods, options.auth_methods[i]); 562 authctxt->auth_methods[authctxt->num_auth_methods++] = 563 xstrdup(options.auth_methods[i]); 564 } 565 if (authctxt->num_auth_methods == 0) { 566 error("No AuthenticationMethods left after eliminating " 567 "disabled methods"); 568 return -1; 569 } 570 return 0; 571 } 572 573 static int 574 list_starts_with(const char *methods, const char *method, 575 const char *submethod) 576 { 577 size_t l = strlen(method); 578 int match; 579 const char *p; 580 581 if (strncmp(methods, method, l) != 0) 582 return MATCH_NONE; 583 p = methods + l; 584 match = MATCH_METHOD; 585 if (*p == ':') { 586 if (!submethod) 587 return MATCH_PARTIAL; 588 l = strlen(submethod); 589 p += 1; 590 if (strncmp(submethod, p, l)) 591 return MATCH_NONE; 592 p += l; 593 match = MATCH_BOTH; 594 } 595 if (*p != ',' && *p != '\0') 596 return MATCH_NONE; 597 return match; 598 } 599 600 /* 601 * Remove method from the start of a comma-separated list of methods. 602 * Returns 0 if the list of methods did not start with that method or 1 603 * if it did. 604 */ 605 static int 606 remove_method(char **methods, const char *method, const char *submethod) 607 { 608 char *omethods = *methods, *p; 609 size_t l = strlen(method); 610 int match; 611 612 match = list_starts_with(omethods, method, submethod); 613 if (match != MATCH_METHOD && match != MATCH_BOTH) 614 return 0; 615 p = omethods + l; 616 if (submethod && match == MATCH_BOTH) 617 p += 1 + strlen(submethod); /* include colon */ 618 if (*p == ',') 619 p++; 620 *methods = xstrdup(p); 621 free(omethods); 622 return 1; 623 } 624 625 /* 626 * Called after successful authentication. Will remove the successful method 627 * from the start of each list in which it occurs. If it was the last method 628 * in any list, then authentication is deemed successful. 629 * Returns 1 if the method completed any authentication list or 0 otherwise. 630 */ 631 int 632 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 633 const char *submethod) 634 { 635 u_int i, found = 0; 636 637 debug3("%s: updating methods list after \"%s\"", __func__, method); 638 for (i = 0; i < authctxt->num_auth_methods; i++) { 639 if (!remove_method(&(authctxt->auth_methods[i]), method, 640 submethod)) 641 continue; 642 found = 1; 643 if (*authctxt->auth_methods[i] == '\0') { 644 debug2("authentication methods list %d complete", i); 645 return 1; 646 } 647 debug3("authentication methods list %d remaining: \"%s\"", 648 i, authctxt->auth_methods[i]); 649 } 650 /* This should not happen, but would be bad if it did */ 651 if (!found) 652 fatal("%s: method not in AuthenticationMethods", __func__); 653 return 0; 654 } 655 656 657