1 /* $NetBSD: auth2.c,v 1.11 2015/04/03 23:58:19 christos Exp $ */ 2 /* $OpenBSD: auth2.c,v 1.135 2015/01/19 20:07:45 markus 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 1.11 2015/04/03 23:58:19 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 "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 "canohost.h" 55 #include "pfilter.h" 56 57 #ifdef GSSAPI 58 #include "ssh-gss.h" 59 #endif 60 61 #include "monitor_wrap.h" 62 63 /* import */ 64 extern ServerOptions options; 65 extern u_char *session_id2; 66 extern u_int session_id2_len; 67 extern Buffer loginmsg; 68 69 /* methods */ 70 71 extern Authmethod method_none; 72 extern Authmethod method_pubkey; 73 extern Authmethod method_passwd; 74 extern Authmethod method_kbdint; 75 extern Authmethod method_hostbased; 76 #ifdef KRB5 77 extern Authmethod method_kerberos; 78 #endif 79 #ifdef GSSAPI 80 extern Authmethod method_gssapi; 81 #endif 82 83 static int log_flag = 0; 84 85 Authmethod *authmethods[] = { 86 &method_none, 87 &method_pubkey, 88 #ifdef GSSAPI 89 &method_gssapi, 90 #endif 91 &method_passwd, 92 &method_kbdint, 93 &method_hostbased, 94 #ifdef KRB5 95 &method_kerberos, 96 #endif 97 NULL 98 }; 99 100 /* protocol */ 101 102 static int input_service_request(int, u_int32_t, void *); 103 static int input_userauth_request(int, u_int32_t, void *); 104 105 /* helper */ 106 static Authmethod *authmethod_lookup(Authctxt *, const char *); 107 static char *authmethods_get(Authctxt *authctxt); 108 109 #define MATCH_NONE 0 /* method or submethod mismatch */ 110 #define MATCH_METHOD 1 /* method matches (no submethod specified) */ 111 #define MATCH_BOTH 2 /* method and submethod match */ 112 #define MATCH_PARTIAL 3 /* method matches, submethod can't be checked */ 113 static int list_starts_with(const char *, const char *, const char *); 114 115 char * 116 auth2_read_banner(void) 117 { 118 struct stat st; 119 char *banner = NULL; 120 size_t len, n; 121 int fd; 122 123 if ((fd = open(options.banner, O_RDONLY)) == -1) 124 return (NULL); 125 if (fstat(fd, &st) == -1) { 126 close(fd); 127 return (NULL); 128 } 129 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 130 close(fd); 131 return (NULL); 132 } 133 134 len = (size_t)st.st_size; /* truncate */ 135 banner = xmalloc(len + 1); 136 n = atomicio(read, fd, banner, len); 137 close(fd); 138 139 if (n != len) { 140 free(banner); 141 return (NULL); 142 } 143 banner[n] = '\0'; 144 145 return (banner); 146 } 147 148 static void 149 userauth_send_banner(const char *msg) 150 { 151 if (datafellows & SSH_BUG_BANNER) 152 return; 153 154 packet_start(SSH2_MSG_USERAUTH_BANNER); 155 packet_put_cstring(msg); 156 packet_put_cstring(""); /* language, unused */ 157 packet_send(); 158 debug("%s: sent", __func__); 159 } 160 161 static void 162 userauth_banner(void) 163 { 164 char *banner = NULL; 165 166 if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0) 167 return; 168 169 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 170 goto done; 171 172 userauth_send_banner(banner); 173 done: 174 free(banner); 175 } 176 177 /* 178 * loop until authctxt->success == TRUE 179 */ 180 void 181 do_authentication2(Authctxt *authctxt) 182 { 183 dispatch_init(&dispatch_protocol_error); 184 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 185 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 186 } 187 188 /*ARGSUSED*/ 189 static int 190 input_service_request(int type, u_int32_t seq, void *ctxt) 191 { 192 Authctxt *authctxt = ctxt; 193 u_int len; 194 int acceptit = 0; 195 char *service = packet_get_cstring(&len); 196 packet_check_eom(); 197 198 if (authctxt == NULL) 199 fatal("input_service_request: no authctxt"); 200 201 if (strcmp(service, "ssh-userauth") == 0) { 202 if (!authctxt->success) { 203 acceptit = 1; 204 /* now we can handle user-auth requests */ 205 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 206 } 207 } 208 /* XXX all other service requests are denied */ 209 210 if (acceptit) { 211 packet_start(SSH2_MSG_SERVICE_ACCEPT); 212 packet_put_cstring(service); 213 packet_send(); 214 packet_write_wait(); 215 } else { 216 debug("bad service request %s", service); 217 packet_disconnect("bad service request %s", service); 218 } 219 free(service); 220 return 0; 221 } 222 223 /*ARGSUSED*/ 224 static int 225 input_userauth_request(int type, u_int32_t seq, void *ctxt) 226 { 227 Authctxt *authctxt = ctxt; 228 Authmethod *m = NULL; 229 char *user, *service, *method, *style = NULL; 230 int authenticated = 0; 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 pfilter_notify(1); 260 } 261 #ifdef USE_PAM 262 if (options.use_pam) 263 PRIVSEP(start_pam(authctxt)); 264 #endif 265 setproctitle("%s%s", authctxt->valid ? user : "unknown", 266 use_privsep ? " [net]" : ""); 267 authctxt->service = xstrdup(service); 268 authctxt->style = style ? xstrdup(style) : NULL; 269 if (use_privsep) 270 mm_inform_authserv(service, style); 271 userauth_banner(); 272 if (auth2_setup_methods_lists(authctxt) != 0) 273 packet_disconnect("no authentication methods enabled"); 274 } else if (strcmp(user, authctxt->user) != 0 || 275 strcmp(service, authctxt->service) != 0) { 276 packet_disconnect("Change of username or service not allowed: " 277 "(%s,%s) -> (%s,%s)", 278 authctxt->user, authctxt->service, user, service); 279 } 280 /* reset state */ 281 auth2_challenge_stop(authctxt); 282 283 #ifdef GSSAPI 284 /* XXX move to auth2_gssapi_stop() */ 285 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 286 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 287 #endif 288 289 authctxt->postponed = 0; 290 authctxt->server_caused_failure = 0; 291 292 /* try to authenticate user */ 293 m = authmethod_lookup(authctxt, method); 294 if (m != NULL && authctxt->failures < options.max_authtries) { 295 debug2("input_userauth_request: try method %s", method); 296 authenticated = m->userauth(authctxt); 297 } 298 userauth_finish(authctxt, authenticated, method, NULL); 299 300 free(service); 301 free(user); 302 free(method); 303 return 0; 304 } 305 306 void 307 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 308 const char *submethod) 309 { 310 char *methods; 311 int partial = 0; 312 313 if (!authctxt->valid && authenticated) 314 fatal("INTERNAL ERROR: authenticated invalid user %s", 315 authctxt->user); 316 if (authenticated && authctxt->postponed) 317 fatal("INTERNAL ERROR: authenticated and postponed"); 318 319 /* Special handling for root */ 320 if (authenticated && authctxt->pw->pw_uid == 0 && 321 !auth_root_allowed(method)) { 322 authenticated = 0; 323 #ifdef SSH_AUDIT_EVENTS 324 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 325 #endif 326 } 327 328 #ifdef USE_PAM 329 if (options.use_pam && authenticated) { 330 if (!PRIVSEP(do_pam_account())) { 331 /* if PAM returned a message, send it to the user */ 332 if (buffer_len(&loginmsg) > 0) { 333 buffer_append(&loginmsg, "\0", 1); 334 userauth_send_banner((const char *)buffer_ptr(&loginmsg)); 335 packet_write_wait(); 336 } 337 fatal("Access denied for user %s by PAM account " 338 "configuration", authctxt->user); 339 } 340 } 341 #endif 342 343 if (authenticated && options.num_auth_methods != 0) { 344 if (!auth2_update_methods_lists(authctxt, method, submethod)) { 345 authenticated = 0; 346 partial = 1; 347 } 348 } 349 350 /* Log before sending the reply */ 351 auth_log(authctxt, authenticated, partial, method, submethod); 352 353 if (authctxt->postponed) 354 return; 355 356 if (authenticated == 1) { 357 /* turn off userauth */ 358 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 359 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 360 packet_send(); 361 packet_write_wait(); 362 /* now we can break out */ 363 authctxt->success = 1; 364 } else { 365 /* Allow initial try of "none" auth without failure penalty */ 366 if (!partial && !authctxt->server_caused_failure && 367 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 368 authctxt->failures++; 369 if (authctxt->failures >= options.max_authtries) 370 auth_maxtries_exceeded(authctxt); 371 methods = authmethods_get(authctxt); 372 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 373 partial, methods); 374 packet_start(SSH2_MSG_USERAUTH_FAILURE); 375 packet_put_cstring(methods); 376 packet_put_char(partial); 377 packet_send(); 378 packet_write_wait(); 379 free(methods); 380 } 381 } 382 383 /* 384 * Checks whether method is allowed by at least one AuthenticationMethods 385 * methods list. Returns 1 if allowed, or no methods lists configured. 386 * 0 otherwise. 387 */ 388 int 389 auth2_method_allowed(Authctxt *authctxt, const char *method, 390 const char *submethod) 391 { 392 u_int i; 393 394 /* 395 * NB. authctxt->num_auth_methods might be zero as a result of 396 * auth2_setup_methods_lists(), so check the configuration. 397 */ 398 if (options.num_auth_methods == 0) 399 return 1; 400 for (i = 0; i < authctxt->num_auth_methods; i++) { 401 if (list_starts_with(authctxt->auth_methods[i], method, 402 submethod) != MATCH_NONE) 403 return 1; 404 } 405 return 0; 406 } 407 408 static char * 409 authmethods_get(Authctxt *authctxt) 410 { 411 Buffer b; 412 char *list; 413 u_int i; 414 415 buffer_init(&b); 416 for (i = 0; authmethods[i] != NULL; i++) { 417 if (strcmp(authmethods[i]->name, "none") == 0) 418 continue; 419 if (authmethods[i]->enabled == NULL || 420 *(authmethods[i]->enabled) == 0) 421 continue; 422 if (!auth2_method_allowed(authctxt, authmethods[i]->name, 423 NULL)) 424 continue; 425 if (buffer_len(&b) > 0) 426 buffer_append(&b, ",", 1); 427 buffer_append(&b, authmethods[i]->name, 428 strlen(authmethods[i]->name)); 429 } 430 buffer_append(&b, "\0", 1); 431 list = xstrdup((const char *)buffer_ptr(&b)); 432 buffer_free(&b); 433 return list; 434 } 435 436 static Authmethod * 437 authmethod_lookup(Authctxt *authctxt, const char *name) 438 { 439 int i; 440 441 if (name != NULL) 442 for (i = 0; authmethods[i] != NULL; i++) 443 if (authmethods[i]->enabled != NULL && 444 *(authmethods[i]->enabled) != 0 && 445 strcmp(name, authmethods[i]->name) == 0 && 446 auth2_method_allowed(authctxt, 447 authmethods[i]->name, NULL)) 448 return authmethods[i]; 449 debug2("Unrecognized authentication method name: %s", 450 name ? name : "NULL"); 451 return NULL; 452 } 453 454 /* 455 * Check a comma-separated list of methods for validity. Is need_enable is 456 * non-zero, then also require that the methods are enabled. 457 * Returns 0 on success or -1 if the methods list is invalid. 458 */ 459 int 460 auth2_methods_valid(const char *_methods, int need_enable) 461 { 462 char *methods, *omethods, *method, *p; 463 u_int i, found; 464 int ret = -1; 465 466 if (*_methods == '\0') { 467 error("empty authentication method list"); 468 return -1; 469 } 470 omethods = methods = xstrdup(_methods); 471 while ((method = strsep(&methods, ",")) != NULL) { 472 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 473 if ((p = strchr(method, ':')) != NULL) 474 *p = '\0'; 475 if (strcmp(method, authmethods[i]->name) != 0) 476 continue; 477 if (need_enable) { 478 if (authmethods[i]->enabled == NULL || 479 *(authmethods[i]->enabled) == 0) { 480 error("Disabled method \"%s\" in " 481 "AuthenticationMethods list \"%s\"", 482 method, _methods); 483 goto out; 484 } 485 } 486 found = 1; 487 break; 488 } 489 if (!found) { 490 error("Unknown authentication method \"%s\" in list", 491 method); 492 goto out; 493 } 494 } 495 ret = 0; 496 out: 497 free(omethods); 498 return ret; 499 } 500 501 /* 502 * Prune the AuthenticationMethods supplied in the configuration, removing 503 * any methods lists that include disabled methods. Note that this might 504 * leave authctxt->num_auth_methods == 0, even when multiple required auth 505 * has been requested. For this reason, all tests for whether multiple is 506 * enabled should consult options.num_auth_methods directly. 507 */ 508 int 509 auth2_setup_methods_lists(Authctxt *authctxt) 510 { 511 u_int i; 512 513 if (options.num_auth_methods == 0) 514 return 0; 515 debug3("%s: checking methods", __func__); 516 authctxt->auth_methods = xcalloc(options.num_auth_methods, 517 sizeof(*authctxt->auth_methods)); 518 authctxt->num_auth_methods = 0; 519 for (i = 0; i < options.num_auth_methods; i++) { 520 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 521 logit("Authentication methods list \"%s\" contains " 522 "disabled method, skipping", 523 options.auth_methods[i]); 524 continue; 525 } 526 debug("authentication methods list %d: %s", 527 authctxt->num_auth_methods, options.auth_methods[i]); 528 authctxt->auth_methods[authctxt->num_auth_methods++] = 529 xstrdup(options.auth_methods[i]); 530 } 531 if (authctxt->num_auth_methods == 0) { 532 error("No AuthenticationMethods left after eliminating " 533 "disabled methods"); 534 return -1; 535 } 536 return 0; 537 } 538 539 static int 540 list_starts_with(const char *methods, const char *method, 541 const char *submethod) 542 { 543 size_t l = strlen(method); 544 int match; 545 const char *p; 546 547 if (strncmp(methods, method, l) != 0) 548 return MATCH_NONE; 549 p = methods + l; 550 match = MATCH_METHOD; 551 if (*p == ':') { 552 if (!submethod) 553 return MATCH_PARTIAL; 554 l = strlen(submethod); 555 p += 1; 556 if (strncmp(submethod, p, l)) 557 return MATCH_NONE; 558 p += l; 559 match = MATCH_BOTH; 560 } 561 if (*p != ',' && *p != '\0') 562 return MATCH_NONE; 563 return match; 564 } 565 566 /* 567 * Remove method from the start of a comma-separated list of methods. 568 * Returns 0 if the list of methods did not start with that method or 1 569 * if it did. 570 */ 571 static int 572 remove_method(char **methods, const char *method, const char *submethod) 573 { 574 char *omethods = *methods, *p; 575 size_t l = strlen(method); 576 int match; 577 578 match = list_starts_with(omethods, method, submethod); 579 if (match != MATCH_METHOD && match != MATCH_BOTH) 580 return 0; 581 p = omethods + l; 582 if (submethod && match == MATCH_BOTH) 583 p += 1 + strlen(submethod); /* include colon */ 584 if (*p == ',') 585 p++; 586 *methods = xstrdup(p); 587 free(omethods); 588 return 1; 589 } 590 591 /* 592 * Called after successful authentication. Will remove the successful method 593 * from the start of each list in which it occurs. If it was the last method 594 * in any list, then authentication is deemed successful. 595 * Returns 1 if the method completed any authentication list or 0 otherwise. 596 */ 597 int 598 auth2_update_methods_lists(Authctxt *authctxt, const char *method, 599 const char *submethod) 600 { 601 u_int i, found = 0; 602 603 debug3("%s: updating methods list after \"%s\"", __func__, method); 604 for (i = 0; i < authctxt->num_auth_methods; i++) { 605 if (!remove_method(&(authctxt->auth_methods[i]), method, 606 submethod)) 607 continue; 608 found = 1; 609 if (*authctxt->auth_methods[i] == '\0') { 610 debug2("authentication methods list %d complete", i); 611 return 1; 612 } 613 debug3("authentication methods list %d remaining: \"%s\"", 614 i, authctxt->auth_methods[i]); 615 } 616 /* This should not happen, but would be bad if it did */ 617 if (!found) 618 fatal("%s: method not in AuthenticationMethods", __func__); 619 return 0; 620 } 621 622 623