1 /* $NetBSD: auth2.c,v 1.7 2013/03/29 16:19:44 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 1.7 2013/03/29 16:19:44 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 static int method_allowed(Authctxt *, const char *); 113 static int list_starts_with(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 xfree(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 || 167 strcasecmp(options.banner, "none") == 0 || 168 (datafellows & SSH_BUG_BANNER) != 0) 169 return; 170 171 if ((banner = PRIVSEP(auth2_read_banner())) == NULL) 172 goto done; 173 174 userauth_send_banner(banner); 175 done: 176 if (banner) 177 xfree(banner); 178 } 179 180 /* 181 * loop until authctxt->success == TRUE 182 */ 183 void 184 do_authentication2(Authctxt *authctxt) 185 { 186 dispatch_init(&dispatch_protocol_error); 187 dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request); 188 dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt); 189 } 190 191 /*ARGSUSED*/ 192 static void 193 input_service_request(int type, u_int32_t seq, void *ctxt) 194 { 195 Authctxt *authctxt = ctxt; 196 u_int len; 197 int acceptit = 0; 198 char *service = packet_get_cstring(&len); 199 packet_check_eom(); 200 201 if (authctxt == NULL) 202 fatal("input_service_request: no authctxt"); 203 204 if (strcmp(service, "ssh-userauth") == 0) { 205 if (!authctxt->success) { 206 acceptit = 1; 207 /* now we can handle user-auth requests */ 208 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request); 209 } 210 } 211 /* XXX all other service requests are denied */ 212 213 if (acceptit) { 214 packet_start(SSH2_MSG_SERVICE_ACCEPT); 215 packet_put_cstring(service); 216 packet_send(); 217 packet_write_wait(); 218 } else { 219 debug("bad service request %s", service); 220 packet_disconnect("bad service request %s", service); 221 } 222 xfree(service); 223 } 224 225 /*ARGSUSED*/ 226 static void 227 input_userauth_request(int type, u_int32_t seq, void *ctxt) 228 { 229 Authctxt *authctxt = ctxt; 230 Authmethod *m = NULL; 231 char *user, *service, *method, *style = NULL; 232 int authenticated = 0; 233 234 if (authctxt == NULL) 235 fatal("input_userauth_request: no authctxt"); 236 237 user = packet_get_cstring(NULL); 238 service = packet_get_cstring(NULL); 239 method = packet_get_cstring(NULL); 240 debug("userauth-request for user %s service %s method %s", user, service, method); 241 if (!log_flag) { 242 logit("SSH: Server;Ltype: Authname;Remote: %s-%d;Name: %s", 243 get_remote_ipaddr(), get_remote_port(), user); 244 log_flag = 1; 245 } 246 debug("attempt %d failures %d", authctxt->attempt, authctxt->failures); 247 248 if ((style = strchr(user, ':')) != NULL) 249 *style++ = 0; 250 251 if (authctxt->attempt++ == 0) { 252 /* setup auth context */ 253 authctxt->pw = PRIVSEP(getpwnamallow(user)); 254 authctxt->user = xstrdup(user); 255 if (authctxt->pw && strcmp(service, "ssh-connection")==0) { 256 authctxt->valid = 1; 257 debug2("input_userauth_request: setting up authctxt for %s", user); 258 } else { 259 logit("input_userauth_request: invalid user %s", user); 260 authctxt->pw = fakepw(); 261 } 262 #ifdef USE_PAM 263 if (options.use_pam) 264 PRIVSEP(start_pam(authctxt)); 265 #endif 266 setproctitle("%s%s", authctxt->valid ? user : "unknown", 267 use_privsep ? " [net]" : ""); 268 authctxt->service = xstrdup(service); 269 authctxt->style = style ? xstrdup(style) : NULL; 270 if (use_privsep) 271 mm_inform_authserv(service, style); 272 userauth_banner(); 273 if (auth2_setup_methods_lists(authctxt) != 0) 274 packet_disconnect("no authentication methods enabled"); 275 } else if (strcmp(user, authctxt->user) != 0 || 276 strcmp(service, authctxt->service) != 0) { 277 packet_disconnect("Change of username or service not allowed: " 278 "(%s,%s) -> (%s,%s)", 279 authctxt->user, authctxt->service, user, service); 280 } 281 /* reset state */ 282 auth2_challenge_stop(authctxt); 283 #ifdef JPAKE 284 auth2_jpake_stop(authctxt); 285 #endif 286 287 #ifdef GSSAPI 288 /* XXX move to auth2_gssapi_stop() */ 289 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL); 290 dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL); 291 #endif 292 293 authctxt->postponed = 0; 294 authctxt->server_caused_failure = 0; 295 296 /* try to authenticate user */ 297 m = authmethod_lookup(authctxt, method); 298 if (m != NULL && authctxt->failures < options.max_authtries) { 299 debug2("input_userauth_request: try method %s", method); 300 authenticated = m->userauth(authctxt); 301 } 302 userauth_finish(authctxt, authenticated, method, NULL); 303 304 xfree(service); 305 xfree(user); 306 xfree(method); 307 } 308 309 void 310 userauth_finish(Authctxt *authctxt, int authenticated, const char *method, 311 const char *submethod) 312 { 313 char *methods; 314 int partial = 0; 315 316 if (!authctxt->valid && authenticated) 317 fatal("INTERNAL ERROR: authenticated invalid user %s", 318 authctxt->user); 319 if (authenticated && authctxt->postponed) 320 fatal("INTERNAL ERROR: authenticated and postponed"); 321 322 /* Special handling for root */ 323 if (authenticated && authctxt->pw->pw_uid == 0 && 324 !auth_root_allowed(method)) { 325 authenticated = 0; 326 #ifdef SSH_AUDIT_EVENTS 327 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 328 #endif 329 } 330 331 #ifdef USE_PAM 332 if (options.use_pam && authenticated) { 333 if (!PRIVSEP(do_pam_account())) { 334 /* if PAM returned a message, send it to the user */ 335 if (buffer_len(&loginmsg) > 0) { 336 buffer_append(&loginmsg, "\0", 1); 337 userauth_send_banner(buffer_ptr(&loginmsg)); 338 packet_write_wait(); 339 } 340 fatal("Access denied for user %s by PAM account " 341 "configuration", authctxt->user); 342 } 343 } 344 #endif 345 346 if (authenticated && options.num_auth_methods != 0) { 347 if (!auth2_update_methods_lists(authctxt, method)) { 348 authenticated = 0; 349 partial = 1; 350 } 351 } 352 353 /* Log before sending the reply */ 354 auth_log(authctxt, authenticated, partial, method, submethod, " ssh2"); 355 356 if (authctxt->postponed) 357 return; 358 359 if (authenticated == 1) { 360 /* turn off userauth */ 361 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore); 362 packet_start(SSH2_MSG_USERAUTH_SUCCESS); 363 packet_send(); 364 packet_write_wait(); 365 /* now we can break out */ 366 authctxt->success = 1; 367 } else { 368 /* Allow initial try of "none" auth without failure penalty */ 369 if (!authctxt->server_caused_failure && 370 (authctxt->attempt > 1 || strcmp(method, "none") != 0)) 371 authctxt->failures++; 372 if (authctxt->failures >= options.max_authtries) { 373 packet_disconnect(AUTH_FAIL_MSG, authctxt->user); 374 #ifdef SSH_AUDIT_EVENTS 375 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 376 #endif 377 } 378 methods = authmethods_get(authctxt); 379 debug3("%s: failure partial=%d next methods=\"%s\"", __func__, 380 partial, methods); 381 packet_start(SSH2_MSG_USERAUTH_FAILURE); 382 packet_put_cstring(methods); 383 packet_put_char(partial); 384 packet_send(); 385 packet_write_wait(); 386 xfree(methods); 387 } 388 } 389 390 /* 391 * Checks whether method is allowed by at least one AuthenticationMethods 392 * methods list. Returns 1 if allowed, or no methods lists configured. 393 * 0 otherwise. 394 */ 395 static int 396 method_allowed(Authctxt *authctxt, const char *method) 397 { 398 u_int i; 399 400 /* 401 * NB. authctxt->num_auth_methods might be zero as a result of 402 * auth2_setup_methods_lists(), so check the configuration. 403 */ 404 if (options.num_auth_methods == 0) 405 return 1; 406 for (i = 0; i < authctxt->num_auth_methods; i++) { 407 if (list_starts_with(authctxt->auth_methods[i], method)) 408 return 1; 409 } 410 return 0; 411 } 412 413 static char * 414 authmethods_get(Authctxt *authctxt) 415 { 416 Buffer b; 417 char *list; 418 u_int i; 419 420 buffer_init(&b); 421 for (i = 0; authmethods[i] != NULL; i++) { 422 if (strcmp(authmethods[i]->name, "none") == 0) 423 continue; 424 if (authmethods[i]->enabled == NULL || 425 *(authmethods[i]->enabled) == 0) 426 continue; 427 if (!method_allowed(authctxt, authmethods[i]->name)) 428 continue; 429 if (buffer_len(&b) > 0) 430 buffer_append(&b, ",", 1); 431 buffer_append(&b, authmethods[i]->name, 432 strlen(authmethods[i]->name)); 433 } 434 buffer_append(&b, "\0", 1); 435 list = xstrdup(buffer_ptr(&b)); 436 buffer_free(&b); 437 return list; 438 } 439 440 static Authmethod * 441 authmethod_lookup(Authctxt *authctxt, const char *name) 442 { 443 int i; 444 445 if (name != NULL) 446 for (i = 0; authmethods[i] != NULL; i++) 447 if (authmethods[i]->enabled != NULL && 448 *(authmethods[i]->enabled) != 0 && 449 strcmp(name, authmethods[i]->name) == 0 && 450 method_allowed(authctxt, authmethods[i]->name)) 451 return authmethods[i]; 452 debug2("Unrecognized authentication method name: %s", 453 name ? name : "NULL"); 454 return NULL; 455 } 456 457 /* 458 * Check a comma-separated list of methods for validity. Is need_enable is 459 * non-zero, then also require that the methods are enabled. 460 * Returns 0 on success or -1 if the methods list is invalid. 461 */ 462 int 463 auth2_methods_valid(const char *_methods, int need_enable) 464 { 465 char *methods, *omethods, *method; 466 u_int i, found; 467 int ret = -1; 468 469 if (*_methods == '\0') { 470 error("empty authentication method list"); 471 return -1; 472 } 473 omethods = methods = xstrdup(_methods); 474 while ((method = strsep(&methods, ",")) != NULL) { 475 for (found = i = 0; !found && authmethods[i] != NULL; i++) { 476 if (strcmp(method, authmethods[i]->name) != 0) 477 continue; 478 if (need_enable) { 479 if (authmethods[i]->enabled == NULL || 480 *(authmethods[i]->enabled) == 0) { 481 error("Disabled method \"%s\" in " 482 "AuthenticationMethods list \"%s\"", 483 method, _methods); 484 goto out; 485 } 486 } 487 found = 1; 488 break; 489 } 490 if (!found) { 491 error("Unknown authentication method \"%s\" in list", 492 method); 493 goto out; 494 } 495 } 496 ret = 0; 497 out: 498 free(omethods); 499 return ret; 500 } 501 502 /* 503 * Prune the AuthenticationMethods supplied in the configuration, removing 504 * any methods lists that include disabled methods. Note that this might 505 * leave authctxt->num_auth_methods == 0, even when multiple required auth 506 * has been requested. For this reason, all tests for whether multiple is 507 * enabled should consult options.num_auth_methods directly. 508 */ 509 int 510 auth2_setup_methods_lists(Authctxt *authctxt) 511 { 512 u_int i; 513 514 if (options.num_auth_methods == 0) 515 return 0; 516 debug3("%s: checking methods", __func__); 517 authctxt->auth_methods = xcalloc(options.num_auth_methods, 518 sizeof(*authctxt->auth_methods)); 519 authctxt->num_auth_methods = 0; 520 for (i = 0; i < options.num_auth_methods; i++) { 521 if (auth2_methods_valid(options.auth_methods[i], 1) != 0) { 522 logit("Authentication methods list \"%s\" contains " 523 "disabled method, skipping", 524 options.auth_methods[i]); 525 continue; 526 } 527 debug("authentication methods list %d: %s", 528 authctxt->num_auth_methods, options.auth_methods[i]); 529 authctxt->auth_methods[authctxt->num_auth_methods++] = 530 xstrdup(options.auth_methods[i]); 531 } 532 if (authctxt->num_auth_methods == 0) { 533 error("No AuthenticationMethods left after eliminating " 534 "disabled methods"); 535 return -1; 536 } 537 return 0; 538 } 539 540 static int 541 list_starts_with(const char *methods, const char *method) 542 { 543 size_t l = strlen(method); 544 545 if (strncmp(methods, method, l) != 0) 546 return 0; 547 if (methods[l] != ',' && methods[l] != '\0') 548 return 0; 549 return 1; 550 } 551 552 /* 553 * Remove method from the start of a comma-separated list of methods. 554 * Returns 0 if the list of methods did not start with that method or 1 555 * if it did. 556 */ 557 static int 558 remove_method(char **methods, const char *method) 559 { 560 char *omethods = *methods; 561 size_t l = strlen(method); 562 563 if (!list_starts_with(omethods, method)) 564 return 0; 565 *methods = xstrdup(omethods + l + (omethods[l] == ',' ? 1 : 0)); 566 free(omethods); 567 return 1; 568 } 569 570 /* 571 * Called after successful authentication. Will remove the successful method 572 * from the start of each list in which it occurs. If it was the last method 573 * in any list, then authentication is deemed successful. 574 * Returns 1 if the method completed any authentication list or 0 otherwise. 575 */ 576 int 577 auth2_update_methods_lists(Authctxt *authctxt, const char *method) 578 { 579 u_int i, found = 0; 580 581 debug3("%s: updating methods list after \"%s\"", __func__, method); 582 for (i = 0; i < authctxt->num_auth_methods; i++) { 583 if (!remove_method(&(authctxt->auth_methods[i]), method)) 584 continue; 585 found = 1; 586 if (*authctxt->auth_methods[i] == '\0') { 587 debug2("authentication methods list %d complete", i); 588 return 1; 589 } 590 debug3("authentication methods list %d remaining: \"%s\"", 591 i, authctxt->auth_methods[i]); 592 } 593 /* This should not happen, but would be bad if it did */ 594 if (!found) 595 fatal("%s: method not in AuthenticationMethods", __func__); 596 return 0; 597 } 598 599 600