crypto/openssh/auth2.c

   1 /* $OpenBSD: auth2.c,v 1.136 2016/05/02 08:49:03 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 "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 Authmethod *authmethods[] = {
  78         &method_none,
  79         &method_pubkey,
  80 #ifdef GSSAPI
  81         &method_gssapi,
  82 #endif
  83         &method_passwd,
  84         &method_kbdint,
  85         &method_hostbased,
  86         NULL
  87 };
  88
  89 /* protocol */
  90
  91 static int input_service_request(int, u_int32_t, void *);
  92 static int input_userauth_request(int, u_int32_t, void *);
  93
  94 /* helper */
  95 static Authmethod *authmethod_lookup(Authctxt *, const char *);
  96 static char *authmethods_get(Authctxt *authctxt);
  97
  98 #define MATCH_NONE      0       /* method or submethod mismatch */
  99 #define MATCH_METHOD    1       /* method matches (no submethod specified) */
 100 #define MATCH_BOTH      2       /* method and submethod match */
 101 #define MATCH_PARTIAL   3       /* method matches, submethod can't be checked */
 102 static int list_starts_with(const char *, const char *, const char *);
 103
 104 char *
 105 auth2_read_banner(void)
 106 {
 107         struct stat st;
 108         char *banner = NULL;
 109         size_t len, n;
 110         int fd;
 111
 112         if ((fd = open(options.banner, O_RDONLY)) == -1)
 113                 return (NULL);
 114         if (fstat(fd, &st) == -1) {
 115                 close(fd);
 116                 return (NULL);
 117         }
 118         if (st.st_size <= 0 || st.st_size > 1*1024*1024) {
 119                 close(fd);
 120                 return (NULL);
 121         }
 122
 123         len = (size_t)st.st_size;               /* truncate */
 124         banner = xmalloc(len + 1);
 125         n = atomicio(read, fd, banner, len);
 126         close(fd);
 127
 128         if (n != len) {
 129                 free(banner);
 130                 return (NULL);
 131         }
 132         banner[n] = '\0';
 133
 134         return (banner);
 135 }
 136
 137 void
 138 userauth_send_banner(const char *msg)
 139 {
 140         if (datafellows & SSH_BUG_BANNER)
 141                 return;
 142
 143         packet_start(SSH2_MSG_USERAUTH_BANNER);
 144         packet_put_cstring(msg);
 145         packet_put_cstring("");         /* language, unused */
 146         packet_send();
 147         debug("%s: sent", __func__);
 148 }
 149
 150 static void
 151 userauth_banner(void)
 152 {
 153         char *banner = NULL;
 154
 155         if (options.banner == NULL || (datafellows & SSH_BUG_BANNER) != 0)
 156                 return;
 157
 158         if ((banner = PRIVSEP(auth2_read_banner())) == NULL)
 159                 goto done;
 160         userauth_send_banner(banner);
 161
 162 done:
 163         free(banner);
 164 }
 165
 166 /*
 167  * loop until authctxt->success == TRUE
 168  */
 169 void
 170 do_authentication2(Authctxt *authctxt)
 171 {
 172         dispatch_init(&dispatch_protocol_error);
 173         dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
 174         dispatch_run(DISPATCH_BLOCK, &authctxt->success, authctxt);
 175 }
 176
 177 /*ARGSUSED*/
 178 static int
 179 input_service_request(int type, u_int32_t seq, void *ctxt)
 180 {
 181         Authctxt *authctxt = ctxt;
 182         u_int len;
 183         int acceptit = 0;
 184         char *service = packet_get_cstring(&len);
 185         packet_check_eom();
 186
 187         if (authctxt == NULL)
 188                 fatal("input_service_request: no authctxt");
 189
 190         if (strcmp(service, "ssh-userauth") == 0) {
 191                 if (!authctxt->success) {
 192                         acceptit = 1;
 193                         /* now we can handle user-auth requests */
 194                         dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
 195                 }
 196         }
 197         /* XXX all other service requests are denied */
 198
 199         if (acceptit) {
 200                 packet_start(SSH2_MSG_SERVICE_ACCEPT);
 201                 packet_put_cstring(service);
 202                 packet_send();
 203                 packet_write_wait();
 204         } else {
 205                 debug("bad service request %s", service);
 206                 packet_disconnect("bad service request %s", service);
 207         }
 208         free(service);
 209         return 0;
 210 }
 211
 212 /*ARGSUSED*/
 213 static int
 214 input_userauth_request(int type, u_int32_t seq, void *ctxt)
 215 {
 216         Authctxt *authctxt = ctxt;
 217         Authmethod *m = NULL;
 218         char *user, *service, *method, *style = NULL;
 219         int authenticated = 0;
 220
 221         if (authctxt == NULL)
 222                 fatal("input_userauth_request: no authctxt");
 223
 224         user = packet_get_cstring(NULL);
 225         service = packet_get_cstring(NULL);
 226         method = packet_get_cstring(NULL);
 227         debug("userauth-request for user %s service %s method %s", user, service, method);
 228         debug("attempt %d failures %d", authctxt->attempt, authctxt->failures);
 229
 230         if ((style = strchr(user, ':')) != NULL)
 231                 *style++ = 0;
 232
 233         if (authctxt->attempt++ == 0) {
 234                 /* setup auth context */
 235                 authctxt->pw = PRIVSEP(getpwnamallow(user));
 236                 authctxt->user = xstrdup(user);
 237                 if (authctxt->pw && strcmp(service, "ssh-connection")==0) {
 238                         authctxt->valid = 1;
 239                         debug2("input_userauth_request: setting up authctxt for %s", user);
 240                 } else {
 241                         logit("input_userauth_request: invalid user %s", user);
 242                         authctxt->pw = fakepw();
 243 #ifdef SSH_AUDIT_EVENTS
 244                         PRIVSEP(audit_event(SSH_INVALID_USER));
 245 #endif
 246                 }
 247 #ifdef USE_PAM
 248                 if (options.use_pam)
 249                         PRIVSEP(start_pam(authctxt));
 250 #endif
 251                 setproctitle("%s%s", authctxt->valid ? user : "unknown",
 252                     use_privsep ? " [net]" : "");
 253                 authctxt->service = xstrdup(service);
 254                 authctxt->style = style ? xstrdup(style) : NULL;
 255                 if (use_privsep)
 256                         mm_inform_authserv(service, style);
 257                 userauth_banner();
 258                 if (auth2_setup_methods_lists(authctxt) != 0)
 259                         packet_disconnect("no authentication methods enabled");
 260         } else if (strcmp(user, authctxt->user) != 0 ||
 261             strcmp(service, authctxt->service) != 0) {
 262                 packet_disconnect("Change of username or service not allowed: "
 263                     "(%s,%s) -> (%s,%s)",
 264                     authctxt->user, authctxt->service, user, service);
 265         }
 266         /* reset state */
 267         auth2_challenge_stop(authctxt);
 268
 269 #ifdef GSSAPI
 270         /* XXX move to auth2_gssapi_stop() */
 271         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
 272         dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 273 #endif
 274
 275         authctxt->postponed = 0;
 276         authctxt->server_caused_failure = 0;
 277
 278         /* try to authenticate user */
 279         m = authmethod_lookup(authctxt, method);
 280         if (m != NULL && authctxt->failures < options.max_authtries) {
 281                 debug2("input_userauth_request: try method %s", method);
 282                 authenticated = m->userauth(authctxt);
 283         }
 284         userauth_finish(authctxt, authenticated, method, NULL);
 285
 286         free(service);
 287         free(user);
 288         free(method);
 289         return 0;
 290 }
 291
 292 void
 293 userauth_finish(Authctxt *authctxt, int authenticated, const char *method,
 294     const char *submethod)
 295 {
 296         char *methods;
 297         int partial = 0;
 298
 299         if (!authctxt->valid && authenticated)
 300                 fatal("INTERNAL ERROR: authenticated invalid user %s",
 301                     authctxt->user);
 302         if (authenticated && authctxt->postponed)
 303                 fatal("INTERNAL ERROR: authenticated and postponed");
 304
 305         /* Special handling for root */
 306         if (authenticated && authctxt->pw->pw_uid == 0 &&
 307             !auth_root_allowed(method)) {
 308                 authenticated = 0;
 309 #ifdef SSH_AUDIT_EVENTS
 310                 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 311 #endif
 312         }
 313
 314         if (authenticated && options.num_auth_methods != 0) {
 315                 if (!auth2_update_methods_lists(authctxt, method, submethod)) {
 316                         authenticated = 0;
 317                         partial = 1;
 318                 }
 319         }
 320
 321         /* Log before sending the reply */
 322         auth_log(authctxt, authenticated, partial, method, submethod);
 323
 324         if (authctxt->postponed)
 325                 return;
 326
 327 #ifdef USE_PAM
 328         if (options.use_pam && authenticated) {
 329                 if (!PRIVSEP(do_pam_account())) {
 330                         /* if PAM returned a message, send it to the user */
 331                         if (buffer_len(&loginmsg) > 0) {
 332                                 buffer_append(&loginmsg, "\0", 1);
 333                                 userauth_send_banner(buffer_ptr(&loginmsg));
 334                                 packet_write_wait();
 335                         }
 336                         fatal("Access denied for user %s by PAM account "
 337                             "configuration", authctxt->user);
 338                 }
 339         }
 340 #endif
 341
 342 #ifdef _UNICOS
 343         if (authenticated && cray_access_denied(authctxt->user)) {
 344                 authenticated = 0;
 345                 fatal("Access denied for user %s.", authctxt->user);
 346         }
 347 #endif /* _UNICOS */
 348
 349         if (authenticated == 1) {
 350                 /* turn off userauth */
 351                 dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &dispatch_protocol_ignore);
 352                 packet_start(SSH2_MSG_USERAUTH_SUCCESS);
 353                 packet_send();
 354                 packet_write_wait();
 355                 /* now we can break out */
 356                 authctxt->success = 1;
 357         } else {
 358
 359                 /* Allow initial try of "none" auth without failure penalty */
 360                 if (!partial && !authctxt->server_caused_failure &&
 361                     (authctxt->attempt > 1 || strcmp(method, "none") != 0))
 362                         authctxt->failures++;
 363                 if (authctxt->failures >= options.max_authtries) {
 364 #ifdef SSH_AUDIT_EVENTS
 365                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 366 #endif
 367                         auth_maxtries_exceeded(authctxt);
 368                 }
 369                 methods = authmethods_get(authctxt);
 370                 debug3("%s: failure partial=%d next methods=\"%s\"", __func__,
 371                     partial, methods);
 372                 packet_start(SSH2_MSG_USERAUTH_FAILURE);
 373                 packet_put_cstring(methods);
 374                 packet_put_char(partial);
 375                 packet_send();
 376                 packet_write_wait();
 377                 free(methods);
 378         }
 379 }
 380
 381 /*
 382  * Checks whether method is allowed by at least one AuthenticationMethods
 383  * methods list. Returns 1 if allowed, or no methods lists configured.
 384  * 0 otherwise.
 385  */
 386 int
 387 auth2_method_allowed(Authctxt *authctxt, const char *method,
 388     const char *submethod)
 389 {
 390         u_int i;
 391
 392         /*
 393          * NB. authctxt->num_auth_methods might be zero as a result of
 394          * auth2_setup_methods_lists(), so check the configuration.
 395          */
 396         if (options.num_auth_methods == 0)
 397                 return 1;
 398         for (i = 0; i < authctxt->num_auth_methods; i++) {
 399                 if (list_starts_with(authctxt->auth_methods[i], method,
 400                     submethod) != MATCH_NONE)
 401                         return 1;
 402         }
 403         return 0;
 404 }
 405
 406 static char *
 407 authmethods_get(Authctxt *authctxt)
 408 {
 409         Buffer b;
 410         char *list;
 411         u_int i;
 412
 413         buffer_init(&b);
 414         for (i = 0; authmethods[i] != NULL; i++) {
 415                 if (strcmp(authmethods[i]->name, "none") == 0)
 416                         continue;
 417                 if (authmethods[i]->enabled == NULL ||
 418                     *(authmethods[i]->enabled) == 0)
 419                         continue;
 420                 if (!auth2_method_allowed(authctxt, authmethods[i]->name,
 421                     NULL))
 422                         continue;
 423                 if (buffer_len(&b) > 0)
 424                         buffer_append(&b, ",", 1);
 425                 buffer_append(&b, authmethods[i]->name,
 426                     strlen(authmethods[i]->name));
 427         }
 428         if ((list = sshbuf_dup_string(&b)) == NULL)
 429                 fatal("%s: sshbuf_dup_string failed", __func__);
 430         buffer_free(&b);
 431         return list;
 432 }
 433
 434 static Authmethod *
 435 authmethod_lookup(Authctxt *authctxt, const char *name)
 436 {
 437         int i;
 438
 439         if (name != NULL)
 440                 for (i = 0; authmethods[i] != NULL; i++)
 441                         if (authmethods[i]->enabled != NULL &&
 442                             *(authmethods[i]->enabled) != 0 &&
 443                             strcmp(name, authmethods[i]->name) == 0 &&
 444                             auth2_method_allowed(authctxt,
 445                             authmethods[i]->name, NULL))
 446                                 return authmethods[i];
 447         debug2("Unrecognized authentication method name: %s",
 448             name ? name : "NULL");
 449         return NULL;
 450 }
 451
 452 /*
 453  * Check a comma-separated list of methods for validity. Is need_enable is
 454  * non-zero, then also require that the methods are enabled.
 455  * Returns 0 on success or -1 if the methods list is invalid.
 456  */
 457 int
 458 auth2_methods_valid(const char *_methods, int need_enable)
 459 {
 460         char *methods, *omethods, *method, *p;
 461         u_int i, found;
 462         int ret = -1;
 463
 464         if (*_methods == '\0') {
 465                 error("empty authentication method list");
 466                 return -1;
 467         }
 468         omethods = methods = xstrdup(_methods);
 469         while ((method = strsep(&methods, ",")) != NULL) {
 470                 for (found = i = 0; !found && authmethods[i] != NULL; i++) {
 471                         if ((p = strchr(method, ':')) != NULL)
 472                                 *p = '\0';
 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  */
 506 int
 507 auth2_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
 537 static int
 538 list_starts_with(const char *methods, const char *method,
 539     const char *submethod)
 540 {
 541         size_t l = strlen(method);
 542         int match;
 543         const char *p;
 544
 545         if (strncmp(methods, method, l) != 0)
 546                 return MATCH_NONE;
 547         p = methods + l;
 548         match = MATCH_METHOD;
 549         if (*p == ':') {
 550                 if (!submethod)
 551                         return MATCH_PARTIAL;
 552                 l = strlen(submethod);
 553                 p += 1;
 554                 if (strncmp(submethod, p, l))
 555                         return MATCH_NONE;
 556                 p += l;
 557                 match = MATCH_BOTH;
 558         }
 559         if (*p != ',' && *p != '\0')
 560                 return MATCH_NONE;
 561         return match;
 562 }
 563
 564 /*
 565  * Remove method from the start of a comma-separated list of methods.
 566  * Returns 0 if the list of methods did not start with that method or 1
 567  * if it did.
 568  */
 569 static int
 570 remove_method(char **methods, const char *method, const char *submethod)
 571 {
 572         char *omethods = *methods, *p;
 573         size_t l = strlen(method);
 574         int match;
 575
 576         match = list_starts_with(omethods, method, submethod);
 577         if (match != MATCH_METHOD && match != MATCH_BOTH)
 578                 return 0;
 579         p = omethods + l;
 580         if (submethod && match == MATCH_BOTH)
 581                 p += 1 + strlen(submethod); /* include colon */
 582         if (*p == ',')
 583                 p++;
 584         *methods = xstrdup(p);
 585         free(omethods);
 586         return 1;
 587 }
 588
 589 /*
 590  * Called after successful authentication. Will remove the successful method
 591  * from the start of each list in which it occurs. If it was the last method
 592  * in any list, then authentication is deemed successful.
 593  * Returns 1 if the method completed any authentication list or 0 otherwise.
 594  */
 595 int
 596 auth2_update_methods_lists(Authctxt *authctxt, const char *method,
 597     const char *submethod)
 598 {
 599         u_int i, found = 0;
 600
 601         debug3("%s: updating methods list after \"%s\"", __func__, method);
 602         for (i = 0; i < authctxt->num_auth_methods; i++) {
 603                 if (!remove_method(&(authctxt->auth_methods[i]), method,
 604                     submethod))
 605                         continue;
 606                 found = 1;
 607                 if (*authctxt->auth_methods[i] == '\0') {
 608                         debug2("authentication methods list %d complete", i);
 609                         return 1;
 610                 }
 611                 debug3("authentication methods list %d remaining: \"%s\"",
 612                     i, authctxt->auth_methods[i]);
 613         }
 614         /* This should not happen, but would be bad if it did */
 615         if (!found)
 616                 fatal("%s: method not in AuthenticationMethods", __func__);
 617         return 0;
 618 }
 619
 620