1/* $OpenBSD: auth2.c,v 1.126 2012/12/02 20:34:09 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 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 "servconf.h" 45#include "compat.h" 46#include "key.h" 47#include "hostfile.h" 48#include "auth.h" 49#include "dispatch.h" 50#include "pathnames.h" 51#include "buffer.h" 52 53#ifdef GSSAPI 54#include "ssh-gss.h" 55#endif 56#include "monitor_wrap.h" 57 58/* import */ 59extern ServerOptions options; 60extern u_char *session_id2; 61extern u_int session_id2_len; 62extern Buffer loginmsg; 63 64/* methods */ 65 66extern Authmethod method_none; 67extern Authmethod method_pubkey; 68extern Authmethod method_passwd; 69extern Authmethod method_kbdint; 70extern Authmethod method_hostbased; 71#ifdef GSSAPI 72extern Authmethod method_gsskeyex; 73extern Authmethod method_gssapi; 74#endif 75#ifdef JPAKE 76extern Authmethod method_jpake; 77#endif 78 79Authmethod *authmethods[] = { 80 &method_none, 81 &method_pubkey, 82#ifdef GSSAPI 83 &method_gsskeyex, 84 &method_gssapi, 85#endif 86#ifdef JPAKE 87 &method_jpake, 88#endif 89 &method_passwd, 90 &method_kbdint, 91 &method_hostbased, 92 NULL 93}; 94 95/* protocol */ 96 97static void input_service_request(int, u_int32_t, void *); 98static void input_userauth_request(int, u_int32_t, void *); 99 100/* helper */ 101static Authmethod *authmethod_lookup(Authctxt *, const char *); 102static char *authmethods_get(Authctxt *authctxt); 103static int method_allowed(Authctxt *, const char *); 104static int list_starts_with(const char *, const char *); 105 106char * 107auth2_read_banner(void) 108{ 109 struct stat st; 110 char *banner = NULL; 111 size_t len, n; 112 int fd; 113 114 if ((fd = open(options.banner, O_RDONLY)) == -1) 115 return (NULL); 116 if (fstat(fd, &st) == -1) { 117 close(fd); 118 return (NULL); 119 } 120 if (st.st_size <= 0 || st.st_size > 1*1024*1024) { 121 close(fd); 122 return (NULL); 123 } 124 125 len = (size_t)st.st_size; /* truncate */ 126 banner = xmalloc(len + 1); 127 n = atomicio(read, fd, banner, len); 128 close(fd); 129 130 if (n != len) { 131 xfree(banner); 132 return (NULL); 133 } 134 banner[n] = '\0'; 135 136 return (banner); 137} 138 139void 140userauth_send_banner(const char *msg) 141{ 142 if (datafellows & SSH_BUG_BANNER) 143 return; 144 145 packet_start(SSH2_MSG_USERAUTH_BANNER); 146 packet_put_cstring(msg); 147 packet_put_cstring(""); /* language, unused */ 148 packet_send(); 149 debug("%s: sent", __func__); 150} 151 152static void 153userauth_banner(void) 154{ 155 char *banner = NULL; 156 157 if (options.banner == NULL || 158 strcasecmp(options.banner, "none") == 0 || 159 (datafellows & SSH_BUG_BANNER) != 0) 160 return; 161 162 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 163 goto done; 164 userauth_send_banner(banner); 165 166done: 167 if (banner) 168 xfree(banner); 169} 170 171/* 172 * loop until authctxt->success == TRUE 173 */ 174void 175do_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*/ 183static void 184input_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 xfree(service); 214} 215 216/*ARGSUSED*/ 217static void 218input_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; 224 225 if (authctxt == NULL) 226 fatal("input_userauth_request: no authctxt"); 227 228 user = packet_get_cstring(NULL); 229 service = packet_get_cstring(NULL); 230 method = packet_get_cstring(NULL); 231 debug("userauth-request for user %s service %s method %s", user, service, method); 232 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 233 234 if ((style = strchr(user, ':')) != NULL) 235 *style++ = 0; 236 237 if (authctxt->attempt++ == 0) { 238 /* setup auth context */ 239 authctxt->pw = PRIVSEP(getpwnamallow(user)); 240 authctxt->user = xstrdup(user); 241 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 242 authctxt->valid = 1; 243 debug2("input_userauth_request: setting up authctxt for %s", user); 244 } else { 245 logit("input_userauth_request: invalid user %s", user); 246 authctxt->pw = fakepw(); 247#ifdef SSH_AUDIT_EVENTS 248 PRIVSEP(audit_event(SSH_INVALID_USER)); 249#endif 250 } 251#ifdef USE_PAM 252 if (options.use_pam) 253 PRIVSEP(start_pam(authctxt)); 254#endif 255 setproctitle("%s%s", authctxt->valid ? user : "unknown", 256 use_privsep ? " [net]" : ""); 257 authctxt->service = xstrdup(service); 258 authctxt->style = style ? xstrdup(style) : NULL; 259 if (use_privsep) 260 mm_inform_authserv(service, style); 261 userauth_banner(); 262 if (auth2_setup_methods_lists(authctxt) != 0) 263 packet_disconnect("no authentication methods enabled"); 264 } else if (strcmp(user, authctxt->user) != 0 || 265 strcmp(service, authctxt->service) != 0) { 266 packet_disconnect("Change of username or service not allowed: " 267 "(%s,%s) -> (%s,%s)", 268 authctxt->user, authctxt->service, user, service); 269 } 270 /* reset state */ 271 auth2_challenge_stop(authctxt); 272#ifdef JPAKE 273 auth2_jpake_stop(authctxt); 274#endif 275 276#ifdef GSSAPI 277 /* XXX move to auth2_gssapi_stop() */ 278 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 279 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 280#endif 281 282 authctxt->postponed = 0; 283 authctxt->server_caused_failure = 0; 284 285 /* try to authenticate user */ 286 m = authmethod_lookup(authctxt, method); 287 if (m != NULL && authctxt->failures < options.max_authtries) { 288 debug2("input_userauth_request: try method %s", method); 289 authenticated = m->userauth(authctxt); 290 } 291 userauth_finish(authctxt, authenticated, method, NULL); 292 293 xfree(service); 294 xfree(user); 295 xfree(method); 296} 297 298void 299userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 300 const char *submethod) 301{ 302 char *methods; 303 int partial = 0; 304 305 if (!authctxt->valid && authenticated) 306 fatal("INTERNAL ERROR: authenticated invalid user %s", 307 authctxt->user); 308 if (authenticated && authctxt->postponed) 309 fatal("INTERNAL ERROR: authenticated and postponed"); 310 311 /* Special handling for root */ 312 if (authenticated && authctxt->pw->pw_uid == 0 && 313 !auth_root_allowed(method)) { 314 authenticated = 0; 315#ifdef SSH_AUDIT_EVENTS 316 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 317#endif 318 } 319 320 if (authenticated && options.num_auth_methods != 0) { 321 if (!auth2_update_methods_lists(authctxt, method)) { 322 authenticated = 0; 323 partial = 1; 324 } 325 } 326 327 /* Log before sending the reply */ 328 auth_log(authctxt, authenticated, partial, method, submethod, " ssh2"); 329 330 if (authctxt->postponed) 331 return; 332 333#ifdef USE_PAM 334 if (options.use_pam && authenticated) { 335 if (!PRIVSEP(do_pam_account())) { 336 /* if PAM returned a message, send it to the user */ 337 if (buffer_len(&loginmsg) > 0) { 338 buffer_append(&loginmsg, "\0", 1); 339 userauth_send_banner(buffer_ptr(&loginmsg)); 340 packet_write_wait(); 341 } 342 fatal("Access denied for user %s by PAM account " 343 "configuration", authctxt->user); 344 } 345 } 346#endif 347 348#ifdef _UNICOS 349 if (authenticated && cray_access_denied(authctxt->user)) { 350 authenticated = 0; 351 fatal("Access denied for user %s.", authctxt->user); 352 } 353#endif /* _UNICOS */ 354 355 if (authenticated == 1) { 356 /* turn off userauth */ 357 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 358 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 359 packet_send(); 360 packet_write_wait(); 361 /* now we can break out */ 362 authctxt->success = 1; 363 } else { 364 365 /* Allow initial try of "none" auth without failure penalty */ 366 if (!authctxt->server_caused_failure && 367 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 368 authctxt->failures++; 369 if (authctxt->failures >= options.max_authtries) { 370#ifdef SSH_AUDIT_EVENTS 371 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 372#endif 373 packet_disconnect(AUTH_FAIL_MSG, authctxt->user); 374 } 375 methods = authmethods_get(authctxt); 376 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 377 partial, methods); 378 packet_start(SSH2_MSG_USERAUTH_FAILURE); 379 packet_put_cstring(methods); 380 packet_put_char(partial); 381 packet_send(); 382 packet_write_wait(); 383 xfree(methods); 384 } 385} 386 387/* 388 * Checks whether method is allowed by at least one AuthenticationMethods 389 * methods list. Returns 1 if allowed, or no methods lists configured. 390 * 0 otherwise. 391 */ 392static int 393method_allowed(Authctxt *authctxt, const char *method) 394{ 395 u_int i; 396 397 /* 398 * NB. authctxt->num_auth_methods might be zero as a result of 399 * auth2_setup_methods_lists(), so check the configuration. 400 */ 401 if (options.num_auth_methods == 0) 402 return 1; 403 for (i = 0; i < authctxt->num_auth_methods; i++) { 404 if (list_starts_with(authctxt->auth_methods[i], method)) 405 return 1; 406 } 407 return 0; 408} 409 410static char * 411authmethods_get(Authctxt *authctxt) 412{ 413 Buffer b; 414 char *list; 415 u_int i; 416 417 buffer_init(&b); 418 for (i = 0; authmethods[i] != NULL; i++) { 419 if (strcmp(authmethods[i]->name, "none") == 0) 420 continue; 421 if (authmethods[i]->enabled == NULL || 422 *(authmethods[i]->enabled) == 0) 423 continue; 424 if (!method_allowed(authctxt, authmethods[i]->name)) 425 continue; 426 if (buffer_len(&b) > 0) 427 buffer_append(&b, ",", 1); 428 buffer_append(&b, authmethods[i]->name, 429 strlen(authmethods[i]->name)); 430 } 431 buffer_append(&b, "\0", 1); 432 list = xstrdup(buffer_ptr(&b)); 433 buffer_free(&b); 434 return list; 435} 436 437static Authmethod * 438authmethod_lookup(Authctxt *authctxt, const char *name) 439{ 440 int i; 441 442 if (name != NULL) 443 for (i = 0; authmethods[i] != NULL; i++) 444 if (authmethods[i]->enabled != NULL && 445 *(authmethods[i]->enabled) != 0 && 446 strcmp(name, authmethods[i]->name) == 0 && 447 method_allowed(authctxt, authmethods[i]->name)) 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 */ 459int 460auth2_methods_valid(const char *_methods, int need_enable) 461{ 462 char *methods, *omethods, *method; 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 (strcmp(method, authmethods[i]->name) != 0) 474 continue; 475 if (need_enable) { 476 if (authmethods[i]->enabled == NULL || 477 *(authmethods[i]->enabled) == 0) { 478 error("Disabled method \"%s\" in " 479 "AuthenticationMethods list \"%s\"", 480 method, _methods); 481 goto out; 482 } 483 } 484 found = 1; 485 break; 486 } 487 if (!found) { 488 error("Unknown authentication method \"%s\" in list", 489 method); 490 goto out; 491 } 492 } 493 ret = 0; 494 out: 495 free(omethods); 496 return ret; 497} 498 499/* 500 * Prune the AuthenticationMethods supplied in the configuration, removing 501 * any methods lists that include disabled methods. Note that this might 502 * leave authctxt->num_auth_methods == 0, even when multiple required auth 503 * has been requested. For this reason, all tests for whether multiple is 504 * enabled should consult options.num_auth_methods directly. 505 */ 506int 507auth2_setup_methods_lists(Authctxt *authctxt) 508{ 509 u_int i; 510 511 if (options.num_auth_methods == 0) 512 return 0; 513 debug3("%s: checking methods", __func__); 514 authctxt->auth_methods = xcalloc(options.num_auth_methods, 515 sizeof(*authctxt->auth_methods)); 516 authctxt->num_auth_methods = 0; 517 for (i = 0; i < options.num_auth_methods; i++) { 518 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 519 logit("Authentication methods list \"%s\" contains " 520 "disabled method, skipping", 521 options.auth_methods[i]); 522 continue; 523 } 524 debug("authentication methods list %d: %s", 525 authctxt->num_auth_methods, options.auth_methods[i]); 526 authctxt->auth_methods[authctxt->num_auth_methods++] = 527 xstrdup(options.auth_methods[i]); 528 } 529 if (authctxt->num_auth_methods == 0) { 530 error("No AuthenticationMethods left after eliminating " 531 "disabled methods"); 532 return -1; 533 } 534 return 0; 535} 536 537static int 538list_starts_with(const char *methods, const char *method) 539{ 540 size_t l = strlen(method); 541 542 if (strncmp(methods, method, l) != 0) 543 return 0; 544 if (methods[l] != ',' && methods[l] != '\0') 545 return 0; 546 return 1; 547} 548 549/* 550 * Remove method from the start of a comma-separated list of methods. 551 * Returns 0 if the list of methods did not start with that method or 1 552 * if it did. 553 */ 554static int 555remove_method(char **methods, const char *method) 556{ 557 char *omethods = *methods; 558 size_t l = strlen(method); 559 560 if (!list_starts_with(omethods, method)) 561 return 0; 562 *methods = xstrdup(omethods + l + (omethods[l] == ',' ? 1 : 0)); 563 free(omethods); 564 return 1; 565} 566 567/* 568 * Called after successful authentication. Will remove the successful method 569 * from the start of each list in which it occurs. If it was the last method 570 * in any list, then authentication is deemed successful. 571 * Returns 1 if the method completed any authentication list or 0 otherwise. 572 */ 573int 574auth2_update_methods_lists(Authctxt *authctxt, const char *method) 575{ 576 u_int i, found = 0; 577 578 debug3("%s: updating methods list after \"%s\"", __func__, method); 579 for (i = 0; i < authctxt->num_auth_methods; i++) { 580 if (!remove_method(&(authctxt->auth_methods[i]), method)) 581 continue; 582 found = 1; 583 if (*authctxt->auth_methods[i] == '\0') { 584 debug2("authentication methods list %d complete", i); 585 return 1; 586 } 587 debug3("authentication methods list %d remaining: \"%s\"", 588 i, authctxt->auth_methods[i]); 589 } 590 /* This should not happen, but would be bad if it did */ 591 if (!found) 592 fatal("%s: method not in AuthenticationMethods", __func__); 593 return 0; 594} 595 596 597