1 /* $NetBSD: auth2.c,v 1.8 2013/11/08 19:18:24 christos Exp $ */ 2 /* $OpenBSD: auth2.c,v 1.126 2012/12/02 20:34:09 djm Exp $ */ 3 /* 4 * Copyright (c) 2000 Markus Friedl. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27 #include "includes.h" 28 __RCSID("$NetBSD: auth2.c,v 1.8 2013/11/08 19:18:24 christos Exp $"); 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 "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 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 KRB5 75 extern Authmethod method_kerberos; 76 #endif 77 #ifdef GSSAPI 78 extern Authmethod method_gssapi; 79 #endif 80 #ifdef JPAKE 81 extern Authmethod method_jpake; 82 #endif 83 84 static int log_flag = 0; 85 86 Authmethod *authmethods[] = { 87 &method_none, 88 &method_pubkey, 89 #ifdef GSSAPI 90 &method_gssapi, 91 #endif 92 #ifdef JPAKE 93 &method_jpake, 94 #endif 95 &method_passwd, 96 &method_kbdint, 97 &method_hostbased, 98 #ifdef KRB5 99 &method_kerberos, 100 #endif 101 NULL 102 }; 103 104 /* protocol */ 105 106 static void input_service_request(int, u_int32_t, void *); 107 static void input_userauth_request(int, u_int32_t, void *); 108 109 /* helper */ 110 static Authmethod *authmethod_lookup(Authctxt *, const char *); 111 static char *authmethods_get(Authctxt *authctxt); 112 113 #define MATCH_NONE 0 /* method or submethod mismatch */ 114 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 115 #define MATCH_BOTH 2 /* method and submethod match */ 116 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 117 static int list_starts_with(const char *, const char *, const char *); 118 119 char * 120 auth2_read_banner(void) 121 { 122 struct stat st; 123 char *banner = NULL; 124 size_t len, n; 125 int fd; 126 127 if ((fd = open(options.banner, O_RDONLY)) == -1) 128 return (NULL); 129 if (fstat(fd, &st) == -1) { 130 close(fd); 131 return (NULL); 132 } 133 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 134 close(fd); 135 return (NULL); 136 } 137 138 len = (size_t)st.st_size; /* truncate */ 139 banner = xmalloc(len + 1); 140 n = atomicio(read, fd, banner, len); 141 close(fd); 142 143 if (n != len) { 144 free(banner); 145 return (NULL); 146 } 147 banner[n] = '\0'; 148 149 return (banner); 150 } 151 152 static void 153 userauth_send_banner(const char *msg) 154 { 155 if (datafellows & SSH_BUG_BANNER) 156 return; 157 158 packet_start(SSH2_MSG_USERAUTH_BANNER); 159 packet_put_cstring(msg); 160 packet_put_cstring(""); /* language, unused */ 161 packet_send(); 162 debug("%s: sent", __func__); 163 } 164 165 static void 166 userauth_banner(void) 167 { 168 char *banner = NULL; 169 170 if (options.banner == NULL || 171 strcasecmp(options.banner, "none") == 0 || 172 (datafellows & SSH_BUG_BANNER) != 0) 173 return; 174 175 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 176 goto done; 177 178 userauth_send_banner(banner); 179 done: 180 free(banner); 181 } 182 183 /* 184 * loop until authctxt->success == TRUE 185 */ 186 void 187 do_authentication2(Authctxt *authctxt) 188 { 189 dispatch_init(&dispatch_protocol_error); 190 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 191 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 192 } 193 194 /*ARGSUSED*/ 195 static void 196 input_service_request(int type, u_int32_t seq, void *ctxt) 197 { 198 Authctxt *authctxt = ctxt; 199 u_int len; 200 int acceptit = 0; 201 char *service = packet_get_cstring(&len); 202 packet_check_eom(); 203 204 if (authctxt == NULL) 205 fatal("input_service_request: no authctxt"); 206 207 if (strcmp(service, "ssh-userauth") == 0) { 208 if (!authctxt->success) { 209 acceptit = 1; 210 /* now we can handle user-auth requests */ 211 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 212 } 213 } 214 /* XXX all other service requests are denied */ 215 216 if (acceptit) { 217 packet_start(SSH2_MSG_SERVICE_ACCEPT); 218 packet_put_cstring(service); 219 packet_send(); 220 packet_write_wait(); 221 } else { 222 debug("bad service request %s", service); 223 packet_disconnect("bad service request %s", service); 224 } 225 free(service); 226 } 227 228 /*ARGSUSED*/ 229 static void 230 input_userauth_request(int type, u_int32_t seq, void *ctxt) 231 { 232 Authctxt *authctxt = ctxt; 233 Authmethod *m = NULL; 234 char *user, *service, *method, *style = NULL; 235 int authenticated = 0; 236 237 if (authctxt == NULL) 238 fatal("input_userauth_request: no authctxt"); 239 240 user = packet_get_cstring(NULL); 241 service = packet_get_cstring(NULL); 242 method = packet_get_cstring(NULL); 243 debug("userauth-request for user %s service %s method %s", user, service, method); 244 if (!log_flag) { 245 logit("SSH: Server;Ltype: Authname;Remote: %s-%d;Name: %s", 246 get_remote_ipaddr(), get_remote_port(), user); 247 log_flag = 1; 248 } 249 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 250 251 if ((style = strchr(user, ':')) != NULL) 252 *style++ = 0; 253 254 if (authctxt->attempt++ == 0) { 255 /* setup auth context */ 256 authctxt->pw = PRIVSEP(getpwnamallow(user)); 257 authctxt->user = xstrdup(user); 258 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 259 authctxt->valid = 1; 260 debug2("input_userauth_request: setting up authctxt for %s", user); 261 } else { 262 logit("input_userauth_request: invalid user %s", user); 263 authctxt->pw = fakepw(); 264 } 265 #ifdef USE_PAM 266 if (options.use_pam) 267 PRIVSEP(start_pam(authctxt)); 268 #endif 269 setproctitle("%s%s", authctxt->valid ? user : "unknown", 270 use_privsep ? " [net]" : ""); 271 authctxt->service = xstrdup(service); 272 authctxt->style = style ? xstrdup(style) : NULL; 273 if (use_privsep) 274 mm_inform_authserv(service, style); 275 userauth_banner(); 276 if (auth2_setup_methods_lists(authctxt) != 0) 277 packet_disconnect("no authentication methods enabled"); 278 } else if (strcmp(user, authctxt->user) != 0 || 279 strcmp(service, authctxt->service) != 0) { 280 packet_disconnect("Change of username or service not allowed: " 281 "(%s,%s) -> (%s,%s)", 282 authctxt->user, authctxt->service, user, service); 283 } 284 /* reset state */ 285 auth2_challenge_stop(authctxt); 286 #ifdef JPAKE 287 auth2_jpake_stop(authctxt); 288 #endif 289 290 #ifdef GSSAPI 291 /* XXX move to auth2_gssapi_stop() */ 292 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 293 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 294 #endif 295 296 authctxt->postponed = 0; 297 authctxt->server_caused_failure = 0; 298 299 /* try to authenticate user */ 300 m = authmethod_lookup(authctxt, method); 301 if (m != NULL && authctxt->failures < options.max_authtries) { 302 debug2("input_userauth_request: try method %s", method); 303 authenticated = m->userauth(authctxt); 304 } 305 userauth_finish(authctxt, authenticated, method, NULL); 306 307 free(service); 308 free(user); 309 free(method); 310 } 311 312 void 313 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 314 const char *submethod) 315 { 316 char *methods; 317 int partial = 0; 318 319 if (!authctxt->valid && authenticated) 320 fatal("INTERNAL ERROR: authenticated invalid user %s", 321 authctxt->user); 322 if (authenticated && authctxt->postponed) 323 fatal("INTERNAL ERROR: authenticated and postponed"); 324 325 /* Special handling for root */ 326 if (authenticated && authctxt->pw->pw_uid == 0 && 327 !auth_root_allowed(method)) { 328 authenticated = 0; 329 #ifdef SSH_AUDIT_EVENTS 330 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 331 #endif 332 } 333 334 #ifdef USE_PAM 335 if (options.use_pam && authenticated) { 336 if (!PRIVSEP(do_pam_account())) { 337 /* if PAM returned a message, send it to the user */ 338 if (buffer_len(&loginmsg) > 0) { 339 buffer_append(&loginmsg, "\0", 1); 340 userauth_send_banner(buffer_ptr(&loginmsg)); 341 packet_write_wait(); 342 } 343 fatal("Access denied for user %s by PAM account " 344 "configuration", authctxt->user); 345 } 346 } 347 #endif 348 349 if (authenticated && options.num_auth_methods != 0) { 350 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 351 authenticated = 0; 352 partial = 1; 353 } 354 } 355 356 /* Log before sending the reply */ 357 auth_log(authctxt, authenticated, partial, method, submethod); 358 359 if (authctxt->postponed) 360 return; 361 362 if (authenticated == 1) { 363 /* turn off userauth */ 364 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 365 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 366 packet_send(); 367 packet_write_wait(); 368 /* now we can break out */ 369 authctxt->success = 1; 370 } else { 371 /* Allow initial try of "none" auth without failure penalty */ 372 if (!authctxt->server_caused_failure && 373 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 374 authctxt->failures++; 375 if (authctxt->failures >= options.max_authtries) { 376 packet_disconnect(AUTH_FAIL_MSG, authctxt->user); 377 #ifdef SSH_AUDIT_EVENTS 378 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 379 #endif 380 } 381 methods = authmethods_get(authctxt); 382 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 383 partial, methods); 384 packet_start(SSH2_MSG_USERAUTH_FAILURE); 385 packet_put_cstring(methods); 386 packet_put_char(partial); 387 packet_send(); 388 packet_write_wait(); 389 free(methods); 390 } 391 } 392 393 /* 394 * Checks whether method is allowed by at least one AuthenticationMethods 395 * methods list. Returns 1 if allowed, or no methods lists configured. 396 * 0 otherwise. 397 */ 398 int 399 auth2_method_allowed(Authctxt *authctxt, const char *method, 400 const char *submethod) 401 { 402 u_int i; 403 404 /* 405 * NB. authctxt->num_auth_methods might be zero as a result of 406 * auth2_setup_methods_lists(), so check the configuration. 407 */ 408 if (options.num_auth_methods == 0) 409 return 1; 410 for (i = 0; i < authctxt->num_auth_methods; i++) { 411 if (list_starts_with(authctxt->auth_methods[i], method, 412 submethod) != MATCH_NONE) 413 return 1; 414 } 415 return 0; 416 } 417 418 static char * 419 authmethods_get(Authctxt *authctxt) 420 { 421 Buffer b; 422 char *list; 423 u_int i; 424 425 buffer_init(&b); 426 for (i = 0; authmethods[i] != NULL; i++) { 427 if (strcmp(authmethods[i]->name, "none") == 0) 428 continue; 429 if (authmethods[i]->enabled == NULL || 430 *(authmethods[i]->enabled) == 0) 431 continue; 432 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 433 NULL)) 434 continue; 435 if (buffer_len(&b) > 0) 436 buffer_append(&b, ",", 1); 437 buffer_append(&b, authmethods[i]->name, 438 strlen(authmethods[i]->name)); 439 } 440 buffer_append(&b, "\0", 1); 441 list = xstrdup(buffer_ptr(&b)); 442 buffer_free(&b); 443 return list; 444 } 445 446 static Authmethod * 447 authmethod_lookup(Authctxt *authctxt, const char *name) 448 { 449 int i; 450 451 if (name != NULL) 452 for (i = 0; authmethods[i] != NULL; i++) 453 if (authmethods[i]->enabled != NULL && 454 *(authmethods[i]->enabled) != 0 && 455 strcmp(name, authmethods[i]->name) == 0 && 456 auth2_method_allowed(authctxt, 457 authmethods[i]->name, NULL)) 458 return authmethods[i]; 459 debug2("Unrecognized authentication method name: %s", 460 name ? name : "NULL"); 461 return NULL; 462 } 463 464 /* 465 * Check a comma-separated list of methods for validity. Is need_enable is 466 * non-zero, then also require that the methods are enabled. 467 * Returns 0 on success or -1 if the methods list is invalid. 468 */ 469 int 470 auth2_methods_valid(const char *_methods, int need_enable) 471 { 472 char *methods, *omethods, *method, *p; 473 u_int i, found; 474 int ret = -1; 475 476 if (*_methods == '\0') { 477 error("empty authentication method list"); 478 return -1; 479 } 480 omethods = methods = xstrdup(_methods); 481 while ((method = strsep(&methods, ",")) != NULL) { 482 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 483 if ((p = strchr(method, ':')) != NULL) 484 *p = '\0'; 485 if (strcmp(method, authmethods[i]->name) != 0) 486 continue; 487 if (need_enable) { 488 if (authmethods[i]->enabled == NULL || 489 *(authmethods[i]->enabled) == 0) { 490 error("Disabled method \"%s\" in " 491 "AuthenticationMethods list \"%s\"", 492 method, _methods); 493 goto out; 494 } 495 } 496 found = 1; 497 break; 498 } 499 if (!found) { 500 error("Unknown authentication method \"%s\" in list", 501 method); 502 goto out; 503 } 504 } 505 ret = 0; 506 out: 507 free(omethods); 508 return ret; 509 } 510 511 /* 512 * Prune the AuthenticationMethods supplied in the configuration, removing 513 * any methods lists that include disabled methods. Note that this might 514 * leave authctxt->num_auth_methods == 0, even when multiple required auth 515 * has been requested. For this reason, all tests for whether multiple is 516 * enabled should consult options.num_auth_methods directly. 517 */ 518 int 519 auth2_setup_methods_lists(Authctxt *authctxt) 520 { 521 u_int i; 522 523 if (options.num_auth_methods == 0) 524 return 0; 525 debug3("%s: checking methods", __func__); 526 authctxt->auth_methods = xcalloc(options.num_auth_methods, 527 sizeof(*authctxt->auth_methods)); 528 authctxt->num_auth_methods = 0; 529 for (i = 0; i < options.num_auth_methods; i++) { 530 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 531 logit("Authentication methods list \"%s\" contains " 532 "disabled method, skipping", 533 options.auth_methods[i]); 534 continue; 535 } 536 debug("authentication methods list %d: %s", 537 authctxt->num_auth_methods, options.auth_methods[i]); 538 authctxt->auth_methods[authctxt->num_auth_methods++] = 539 xstrdup(options.auth_methods[i]); 540 } 541 if (authctxt->num_auth_methods == 0) { 542 error("No AuthenticationMethods left after eliminating " 543 "disabled methods"); 544 return -1; 545 } 546 return 0; 547 } 548 549 static int 550 list_starts_with(const char *methods, const char *method, 551 const char *submethod) 552 { 553 size_t l = strlen(method); 554 int match; 555 const char *p; 556 557 if (strncmp(methods, method, l) != 0) 558 return MATCH_NONE; 559 p = methods + l; 560 match = MATCH_METHOD; 561 if (*p == ':') { 562 if (!submethod) 563 return MATCH_PARTIAL; 564 l = strlen(submethod); 565 p += 1; 566 if (strncmp(submethod, p, l)) 567 return MATCH_NONE; 568 p += l; 569 match = MATCH_BOTH; 570 } 571 if (*p != ',' && *p != '\0') 572 return MATCH_NONE; 573 return match; 574 } 575 576 /* 577 * Remove method from the start of a comma-separated list of methods. 578 * Returns 0 if the list of methods did not start with that method or 1 579 * if it did. 580 */ 581 static int 582 remove_method(char **methods, const char *method, const char *submethod) 583 { 584 char *omethods = *methods, *p; 585 size_t l = strlen(method); 586 int match; 587 588 match = list_starts_with(omethods, method, submethod); 589 if (match != MATCH_METHOD && match != MATCH_BOTH) 590 return 0; 591 p = omethods + l; 592 if (submethod && match == MATCH_BOTH) 593 p += 1 + strlen(submethod); /* include colon */ 594 if (*p == ',') 595 p++; 596 *methods = xstrdup(p); 597 free(omethods); 598 return 1; 599 } 600 601 /* 602 * Called after successful authentication. Will remove the successful method 603 * from the start of each list in which it occurs. If it was the last method 604 * in any list, then authentication is deemed successful. 605 * Returns 1 if the method completed any authentication list or 0 otherwise. 606 */ 607 int 608 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 609 const char *submethod) 610 { 611 u_int i, found = 0; 612 613 debug3("%s: updating methods list after \"%s\"", __func__, method); 614 for (i = 0; i < authctxt->num_auth_methods; i++) { 615 if (!remove_method(&(authctxt->auth_methods[i]), method, 616 submethod)) 617 continue; 618 found = 1; 619 if (*authctxt->auth_methods[i] == '\0') { 620 debug2("authentication methods list %d complete", i); 621 return 1; 622 } 623 debug3("authentication methods list %d remaining: \"%s\"", 624 i, authctxt->auth_methods[i]); 625 } 626 /* This should not happen, but would be bad if it did */ 627 if (!found) 628 fatal("%s: method not in AuthenticationMethods", __func__); 629 return 0; 630 } 631 632 633