crypto/openssh/auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.34 2013/02/14 21:35:59 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/wait.h>
  31
  32 #include <errno.h>
  33 #include <fcntl.h>
  34 #ifdef HAVE_PATHS_H
  35 # include <paths.h>
  36 #endif
  37 #include <pwd.h>
  38 #include <signal.h>
  39 #include <stdio.h>
  40 #include <stdarg.h>
  41 #include <string.h>
  42 #include <time.h>
  43 #include <unistd.h>
  44
  45 #include "xmalloc.h"
  46 #include "ssh.h"
  47 #include "ssh2.h"
  48 #include "packet.h"
  49 #include "buffer.h"
  50 #include "log.h"
  51 #include "servconf.h"
  52 #include "compat.h"
  53 #include "key.h"
  54 #include "hostfile.h"
  55 #include "auth.h"
  56 #include "pathnames.h"
  57 #include "uidswap.h"
  58 #include "auth-options.h"
  59 #include "canohost.h"
  60 #ifdef GSSAPI
  61 #include "ssh-gss.h"
  62 #endif
  63 #include "monitor_wrap.h"
  64 #include "misc.h"
  65 #include "authfile.h"
  66 #include "match.h"
  67
  68 /* import */
  69 extern ServerOptions options;
  70 extern u_char *session_id2;
  71 extern u_int session_id2_len;
  72
  73 static int
  74 userauth_pubkey(Authctxt *authctxt)
  75 {
  76         Buffer b;
  77         Key *key = NULL;
  78         char *pkalg;
  79         u_char *pkblob, *sig;
  80         u_int alen, blen, slen;
  81         int have_sig, pktype;
  82         int authenticated = 0;
  83
  84         if (!authctxt->valid) {
  85                 debug2("userauth_pubkey: disabled because of invalid user");
  86                 return 0;
  87         }
  88         have_sig = packet_get_char();
  89         if (datafellows & SSH_BUG_PKAUTH) {
  90                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  91                 /* no explicit pkalg given */
  92                 pkblob = packet_get_string(&blen);
  93                 buffer_init(&b);
  94                 buffer_append(&b, pkblob, blen);
  95                 /* so we have to extract the pkalg from the pkblob */
  96                 pkalg = buffer_get_string(&b, &alen);
  97                 buffer_free(&b);
  98         } else {
  99                 pkalg = packet_get_string(&alen);
 100                 pkblob = packet_get_string(&blen);
 101         }
 102         pktype = key_type_from_name(pkalg);
 103         if (pktype == KEY_UNSPEC) {
 104                 /* this is perfectly legal */
 105                 logit("userauth_pubkey: unsupported public key algorithm: %s",
 106                     pkalg);
 107                 goto done;
 108         }
 109         key = key_from_blob(pkblob, blen);
 110         if (key == NULL) {
 111                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 112                 goto done;
 113         }
 114         if (key->type != pktype) {
 115                 error("userauth_pubkey: type mismatch for decoded key "
 116                     "(received %d, expected %d)", key->type, pktype);
 117                 goto done;
 118         }
 119         if (have_sig) {
 120                 sig = packet_get_string(&slen);
 121                 packet_check_eom();
 122                 buffer_init(&b);
 123                 if (datafellows & SSH_OLD_SESSIONID) {
 124                         buffer_append(&b, session_id2, session_id2_len);
 125                 } else {
 126                         buffer_put_string(&b, session_id2, session_id2_len);
 127                 }
 128                 /* reconstruct packet */
 129                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 130                 buffer_put_cstring(&b, authctxt->user);
 131                 buffer_put_cstring(&b,
 132                     datafellows & SSH_BUG_PKSERVICE ?
 133                     "ssh-userauth" :
 134                     authctxt->service);
 135                 if (datafellows & SSH_BUG_PKAUTH) {
 136                         buffer_put_char(&b, have_sig);
 137                 } else {
 138                         buffer_put_cstring(&b, "publickey");
 139                         buffer_put_char(&b, have_sig);
 140                         buffer_put_cstring(&b, pkalg);
 141                 }
 142                 buffer_put_string(&b, pkblob, blen);
 143 #ifdef DEBUG_PK
 144                 buffer_dump(&b);
 145 #endif
 146                 /* test for correct signature */
 147                 authenticated = 0;
 148                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 149                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 150                     buffer_len(&b))) == 1)
 151                         authenticated = 1;
 152                 buffer_free(&b);
 153                 xfree(sig);
 154         } else {
 155                 debug("test whether pkalg/pkblob are acceptable");
 156                 packet_check_eom();
 157
 158                 /* XXX fake reply and always send PK_OK ? */
 159                 /*
 160                  * XXX this allows testing whether a user is allowed
 161                  * to login: if you happen to have a valid pubkey this
 162                  * message is sent. the message is NEVER sent at all
 163                  * if a user is not allowed to login. is this an
 164                  * issue? -markus
 165                  */
 166                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 167                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 168                         packet_put_string(pkalg, alen);
 169                         packet_put_string(pkblob, blen);
 170                         packet_send();
 171                         packet_write_wait();
 172                         authctxt->postponed = 1;
 173                 }
 174         }
 175         if (authenticated != 1)
 176                 auth_clear_options();
 177 done:
 178         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 179         if (key != NULL)
 180                 key_free(key);
 181         xfree(pkalg);
 182         xfree(pkblob);
 183         return authenticated;
 184 }
 185
 186 static int
 187 match_principals_option(const char *principal_list, struct KeyCert *cert)
 188 {
 189         char *result;
 190         u_int i;
 191
 192         /* XXX percent_expand() sequences for authorized_principals? */
 193
 194         for (i = 0; i < cert->nprincipals; i++) {
 195                 if ((result = match_list(cert->principals[i],
 196                     principal_list, NULL)) != NULL) {
 197                         debug3("matched principal from key options \"%.100s\"",
 198                             result);
 199                         xfree(result);
 200                         return 1;
 201                 }
 202         }
 203         return 0;
 204 }
 205
 206 static int
 207 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
 208 {
 209         FILE *f;
 210         char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 211         u_long linenum = 0;
 212         u_int i;
 213
 214         temporarily_use_uid(pw);
 215         debug("trying authorized principals file %s", file);
 216         if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
 217                 restore_uid();
 218                 return 0;
 219         }
 220         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 221                 /* Skip leading whitespace. */
 222                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 223                         ;
 224                 /* Skip blank and comment lines. */
 225                 if ((ep = strchr(cp, '#')) != NULL)
 226                         *ep = '\0';
 227                 if (!*cp || *cp == '\n')
 228                         continue;
 229                 /* Trim trailing whitespace. */
 230                 ep = cp + strlen(cp) - 1;
 231                 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
 232                         *ep-- = '\0';
 233                 /*
 234                  * If the line has internal whitespace then assume it has
 235                  * key options.
 236                  */
 237                 line_opts = NULL;
 238                 if ((ep = strrchr(cp, ' ')) != NULL ||
 239                     (ep = strrchr(cp, '\t')) != NULL) {
 240                         for (; *ep == ' ' || *ep == '\t'; ep++)
 241                                 ;
 242                         line_opts = cp;
 243                         cp = ep;
 244                 }
 245                 for (i = 0; i < cert->nprincipals; i++) {
 246                         if (strcmp(cp, cert->principals[i]) == 0) {
 247                                 debug3("matched principal \"%.100s\" "
 248                                     "from file \"%s\" on line %lu",
 249                                     cert->principals[i], file, linenum);
 250                                 if (auth_parse_options(pw, line_opts,
 251                                     file, linenum) != 1)
 252                                         continue;
 253                                 fclose(f);
 254                                 restore_uid();
 255                                 return 1;
 256                         }
 257                 }
 258         }
 259         fclose(f);
 260         restore_uid();
 261         return 0;
 262 }
 263
 264 /*
 265  * Checks whether key is allowed in authorized_keys-format file,
 266  * returns 1 if the key is allowed or 0 otherwise.
 267  */
 268 static int
 269 check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
 270 {
 271         char line[SSH_MAX_PUBKEY_BYTES];
 272         const char *reason;
 273         int found_key = 0;
 274         u_long linenum = 0;
 275         Key *found;
 276         char *fp;
 277
 278         found_key = 0;
 279         found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 280
 281         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 282                 char *cp, *key_options = NULL;
 283
 284                 auth_clear_options();
 285
 286                 /* Skip leading whitespace, empty and comment lines. */
 287                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 288                         ;
 289                 if (!*cp || *cp == '\n' || *cp == '#')
 290                         continue;
 291
 292                 if (key_read(found, &cp) != 1) {
 293                         /* no key?  check if there are options for this key */
 294                         int quoted = 0;
 295                         debug2("user_key_allowed: check options: '%s'", cp);
 296                         key_options = cp;
 297                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 298                                 if (*cp == '\\' && cp[1] == '"')
 299                                         cp++;   /* Skip both */
 300                                 else if (*cp == '"')
 301                                         quoted = !quoted;
 302                         }
 303                         /* Skip remaining whitespace. */
 304                         for (; *cp == ' ' || *cp == '\t'; cp++)
 305                                 ;
 306                         if (key_read(found, &cp) != 1) {
 307                                 debug2("user_key_allowed: advance: '%s'", cp);
 308                                 /* still no key?  advance to next line*/
 309                                 continue;
 310                         }
 311                 }
 312                 if (key_is_cert(key)) {
 313                         if (!key_equal(found, key->cert->signature_key))
 314                                 continue;
 315                         if (auth_parse_options(pw, key_options, file,
 316                             linenum) != 1)
 317                                 continue;
 318                         if (!key_is_cert_authority)
 319                                 continue;
 320                         fp = key_fingerprint(found, SSH_FP_MD5,
 321                             SSH_FP_HEX);
 322                         debug("matching CA found: file %s, line %lu, %s %s",
 323                             file, linenum, key_type(found), fp);
 324                         /*
 325                          * If the user has specified a list of principals as
 326                          * a key option, then prefer that list to matching
 327                          * their username in the certificate principals list.
 328                          */
 329                         if (authorized_principals != NULL &&
 330                             !match_principals_option(authorized_principals,
 331                             key->cert)) {
 332                                 reason = "Certificate does not contain an "
 333                                     "authorized principal";
 334  fail_reason:
 335                                 xfree(fp);
 336                                 error("%s", reason);
 337                                 auth_debug_add("%s", reason);
 338                                 continue;
 339                         }
 340                         if (key_cert_check_authority(key, 0, 0,
 341                             authorized_principals == NULL ? pw->pw_name : NULL,
 342                             &reason) != 0)
 343                                 goto fail_reason;
 344                         if (auth_cert_options(key, pw) != 0) {
 345                                 xfree(fp);
 346                                 continue;
 347                         }
 348                         verbose("Accepted certificate ID \"%s\" "
 349                             "signed by %s CA %s via %s", key->cert->key_id,
 350                             key_type(found), fp, file);
 351                         xfree(fp);
 352                         found_key = 1;
 353                         break;
 354                 } else if (key_equal(found, key)) {
 355                         if (auth_parse_options(pw, key_options, file,
 356                             linenum) != 1)
 357                                 continue;
 358                         if (key_is_cert_authority)
 359                                 continue;
 360                         found_key = 1;
 361                         debug("matching key found: file %s, line %lu",
 362                             file, linenum);
 363                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 364                         verbose("Found matching %s key: %s",
 365                             key_type(found), fp);
 366                         xfree(fp);
 367                         break;
 368                 }
 369         }
 370         key_free(found);
 371         if (!found_key)
 372                 debug2("key not found");
 373         return found_key;
 374 }
 375
 376 /* Authenticate a certificate key against TrustedUserCAKeys */
 377 static int
 378 user_cert_trusted_ca(struct passwd *pw, Key *key)
 379 {
 380         char *ca_fp, *principals_file = NULL;
 381         const char *reason;
 382         int ret = 0;
 383
 384         if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 385                 return 0;
 386
 387         ca_fp = key_fingerprint(key->cert->signature_key,
 388             SSH_FP_MD5, SSH_FP_HEX);
 389
 390         if (key_in_file(key->cert->signature_key,
 391             options.trusted_user_ca_keys, 1) != 1) {
 392                 debug2("%s: CA %s %s is not listed in %s", __func__,
 393                     key_type(key->cert->signature_key), ca_fp,
 394                     options.trusted_user_ca_keys);
 395                 goto out;
 396         }
 397         /*
 398          * If AuthorizedPrincipals is in use, then compare the certificate
 399          * principals against the names in that file rather than matching
 400          * against the username.
 401          */
 402         if ((principals_file = authorized_principals_file(pw)) != NULL) {
 403                 if (!match_principals_file(principals_file, pw, key->cert)) {
 404                         reason = "Certificate does not contain an "
 405                             "authorized principal";
 406  fail_reason:
 407                         error("%s", reason);
 408                         auth_debug_add("%s", reason);
 409                         goto out;
 410                 }
 411         }
 412         if (key_cert_check_authority(key, 0, 1,
 413             principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
 414                 goto fail_reason;
 415         if (auth_cert_options(key, pw) != 0)
 416                 goto out;
 417
 418         verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
 419             key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
 420             options.trusted_user_ca_keys);
 421         ret = 1;
 422
 423  out:
 424         if (principals_file != NULL)
 425                 xfree(principals_file);
 426         if (ca_fp != NULL)
 427                 xfree(ca_fp);
 428         return ret;
 429 }
 430
 431 /*
 432  * Checks whether key is allowed in file.
 433  * returns 1 if the key is allowed or 0 otherwise.
 434  */
 435 static int
 436 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 437 {
 438         FILE *f;
 439         int found_key = 0;
 440
 441         /* Temporarily use the user's uid. */
 442         temporarily_use_uid(pw);
 443
 444         debug("trying public key file %s", file);
 445         if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
 446                 found_key = check_authkeys_file(f, file, key, pw);
 447                 fclose(f);
 448         }
 449
 450         restore_uid();
 451         return found_key;
 452 }
 453
 454 /*
 455  * Checks whether key is allowed in output of command.
 456  * returns 1 if the key is allowed or 0 otherwise.
 457  */
 458 static int
 459 user_key_command_allowed2(struct passwd *user_pw, Key *key)
 460 {
 461         FILE *f;
 462         int ok, found_key = 0;
 463         struct passwd *pw;
 464         struct stat st;
 465         int status, devnull, p[2], i;
 466         pid_t pid;
 467         char *username, errmsg[512];
 468
 469         if (options.authorized_keys_command == NULL ||
 470             options.authorized_keys_command[0] != '/')
 471                 return 0;
 472
 473         if (options.authorized_keys_command_user == NULL) {
 474                 error("No user for AuthorizedKeysCommand specified, skipping");
 475                 return 0;
 476         }
 477
 478         username = percent_expand(options.authorized_keys_command_user,
 479             "u", user_pw->pw_name, (char *)NULL);
 480         pw = getpwnam(username);
 481         if (pw == NULL) {
 482                 error("AuthorizedKeysCommandUser \"%s\" not found: %s",
 483                     username, strerror(errno));
 484                 free(username);
 485                 return 0;
 486         }
 487         free(username);
 488
 489         temporarily_use_uid(pw);
 490
 491         if (stat(options.authorized_keys_command, &st) < 0) {
 492                 error("Could not stat AuthorizedKeysCommand \"%s\": %s",
 493                     options.authorized_keys_command, strerror(errno));
 494                 goto out;
 495         }
 496         if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
 497             errmsg, sizeof(errmsg)) != 0) {
 498                 error("Unsafe AuthorizedKeysCommand: %s", errmsg);
 499                 goto out;
 500         }
 501
 502         if (pipe(p) != 0) {
 503                 error("%s: pipe: %s", __func__, strerror(errno));
 504                 goto out;
 505         }
 506
 507         debug3("Running AuthorizedKeysCommand: \"%s %s\" as \"%s\"",
 508             options.authorized_keys_command, user_pw->pw_name, pw->pw_name);
 509
 510         /*
 511          * Don't want to call this in the child, where it can fatal() and
 512          * run cleanup_exit() code.
 513          */
 514         restore_uid();
 515
 516         switch ((pid = fork())) {
 517         case -1: /* error */
 518                 error("%s: fork: %s", __func__, strerror(errno));
 519                 close(p[0]);
 520                 close(p[1]);
 521                 return 0;
 522         case 0: /* child */
 523                 for (i = 0; i < NSIG; i++)
 524                         signal(i, SIG_DFL);
 525
 526                 if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
 527                         error("%s: open %s: %s", __func__, _PATH_DEVNULL,
 528                             strerror(errno));
 529                         _exit(1);
 530                 }
 531                 /* Keep stderr around a while longer to catch errors */
 532                 if (dup2(devnull, STDIN_FILENO) == -1 ||
 533                     dup2(p[1], STDOUT_FILENO) == -1) {
 534                         error("%s: dup2: %s", __func__, strerror(errno));
 535                         _exit(1);
 536                 }
 537                 closefrom(STDERR_FILENO + 1);
 538
 539                 /* Don't use permanently_set_uid() here to avoid fatal() */
 540                 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
 541                         error("setresgid %u: %s", (u_int)pw->pw_gid,
 542                             strerror(errno));
 543                         _exit(1);
 544                 }
 545                 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
 546                         error("setresuid %u: %s", (u_int)pw->pw_uid,
 547                             strerror(errno));
 548                         _exit(1);
 549                 }
 550                 /* stdin is pointed to /dev/null at this point */
 551                 if (dup2(STDIN_FILENO, STDERR_FILENO) == -1) {
 552                         error("%s: dup2: %s", __func__, strerror(errno));
 553                         _exit(1);
 554                 }
 555
 556                 execl(options.authorized_keys_command,
 557                     options.authorized_keys_command, user_pw->pw_name, NULL);
 558
 559                 error("AuthorizedKeysCommand %s exec failed: %s",
 560                     options.authorized_keys_command, strerror(errno));
 561                 _exit(127);
 562         default: /* parent */
 563                 break;
 564         }
 565
 566         temporarily_use_uid(pw);
 567
 568         close(p[1]);
 569         if ((f = fdopen(p[0], "r")) == NULL) {
 570                 error("%s: fdopen: %s", __func__, strerror(errno));
 571                 close(p[0]);
 572                 /* Don't leave zombie child */
 573                 kill(pid, SIGTERM);
 574                 while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
 575                         ;
 576                 goto out;
 577         }
 578         ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
 579         fclose(f);
 580
 581         while (waitpid(pid, &status, 0) == -1) {
 582                 if (errno != EINTR) {
 583                         error("%s: waitpid: %s", __func__, strerror(errno));
 584                         goto out;
 585                 }
 586         }
 587         if (WIFSIGNALED(status)) {
 588                 error("AuthorizedKeysCommand %s exited on signal %d",
 589                     options.authorized_keys_command, WTERMSIG(status));
 590                 goto out;
 591         } else if (WEXITSTATUS(status) != 0) {
 592                 error("AuthorizedKeysCommand %s returned status %d",
 593                     options.authorized_keys_command, WEXITSTATUS(status));
 594                 goto out;
 595         }
 596         found_key = ok;
 597  out:
 598         restore_uid();
 599         return found_key;
 600 }
 601
 602 /*
 603  * Check whether key authenticates and authorises the user.
 604  */
 605 int
 606 user_key_allowed(struct passwd *pw, Key *key)
 607 {
 608         u_int success, i;
 609         char *file;
 610
 611         if (auth_key_is_revoked(key))
 612                 return 0;
 613         if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
 614                 return 0;
 615
 616         success = user_cert_trusted_ca(pw, key);
 617         if (success)
 618                 return success;
 619
 620         success = user_key_command_allowed2(pw, key);
 621         if (success > 0)
 622                 return success;
 623
 624         for (i = 0; !success && i < options.num_authkeys_files; i++) {
 625
 626                 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
 627                         continue;
 628                 file = expand_authorized_keys(
 629                     options.authorized_keys_files[i], pw);
 630
 631                 success = user_key_allowed2(pw, key, file);
 632                 xfree(file);
 633         }
 634
 635         return success;
 636 }
 637
 638 Authmethod method_pubkey = {
 639         "publickey",
 640         userauth_pubkey,
 641         &options.pubkey_authentication
 642 };