auth.c

   1 /* $OpenBSD: auth.c,v 1.160 2023/03/05 05:34:09 dtucker 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/socket.h>
  31 #include <sys/wait.h>
  32
  33 #include <netinet/in.h>
  34
  35 #include <stdlib.h>
  36 #include <errno.h>
  37 #include <fcntl.h>
  38 #ifdef HAVE_PATHS_H
  39 # include <paths.h>
  40 #endif
  41 #include <pwd.h>
  42 #ifdef HAVE_LOGIN_H
  43 #include <login.h>
  44 #endif
  45 #ifdef USE_SHADOW
  46 #include <shadow.h>
  47 #endif
  48 #include <stdarg.h>
  49 #include <stdio.h>
  50 #include <string.h>
  51 #include <unistd.h>
  52 #include <limits.h>
  53 #include <netdb.h>
  54 #include <time.h>
  55
  56 #include "xmalloc.h"
  57 #include "match.h"
  58 #include "groupaccess.h"
  59 #include "log.h"
  60 #include "sshbuf.h"
  61 #include "misc.h"
  62 #include "servconf.h"
  63 #include "sshkey.h"
  64 #include "hostfile.h"
  65 #include "auth.h"
  66 #include "auth-options.h"
  67 #include "canohost.h"
  68 #include "uidswap.h"
  69 #include "packet.h"
  70 #include "loginrec.h"
  71 #ifdef GSSAPI
  72 #include "ssh-gss.h"
  73 #endif
  74 #include "authfile.h"
  75 #include "monitor_wrap.h"
  76 #include "ssherr.h"
  77 #include "channels.h"
  78
  79 /* import */
  80 extern ServerOptions options;
  81 extern struct include_list includes;
  82 extern int use_privsep;
  83 extern struct sshbuf *loginmsg;
  84 extern struct passwd *privsep_pw;
  85 extern struct sshauthopt *auth_opts;
  86
  87 /* Debugging messages */
  88 static struct sshbuf *auth_debug;
  89
  90 /*
  91  * Check if the user is allowed to log in via ssh. If user is listed
  92  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  93  * will be returned. If AllowUsers isn't empty and user isn't listed
  94  * there, or if AllowGroups isn't empty and one of user's groups isn't
  95  * listed there, false will be returned.
  96  * If the user's shell is not executable, false will be returned.
  97  * Otherwise true is returned.
  98  */
  99 int
 100 allowed_user(struct ssh *ssh, struct passwd * pw)
 101 {
 102         struct stat st;
 103         const char *hostname = NULL, *ipaddr = NULL;
 104         u_int i;
 105         int r;
 106
 107         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
 108         if (!pw || !pw->pw_name)
 109                 return 0;
 110
 111         if (!options.use_pam && platform_locked_account(pw)) {
 112                 logit("User %.100s not allowed because account is locked",
 113                     pw->pw_name);
 114                 return 0;
 115         }
 116
 117         /*
 118          * Deny if shell does not exist or is not executable unless we
 119          * are chrooting.
 120          */
 121         if (options.chroot_directory == NULL ||
 122             strcasecmp(options.chroot_directory, "none") == 0) {
 123                 char *shell = xstrdup((pw->pw_shell[0] == '\0') ?
 124                     _PATH_BSHELL : pw->pw_shell); /* empty = /bin/sh */
 125
 126                 if (stat(shell, &st) == -1) {
 127                         logit("User %.100s not allowed because shell %.100s "
 128                             "does not exist", pw->pw_name, shell);
 129                         free(shell);
 130                         return 0;
 131                 }
 132                 if (S_ISREG(st.st_mode) == 0 ||
 133                     (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 134                         logit("User %.100s not allowed because shell %.100s "
 135                             "is not executable", pw->pw_name, shell);
 136                         free(shell);
 137                         return 0;
 138                 }
 139                 free(shell);
 140         }
 141
 142         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 143             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 144                 hostname = auth_get_canonical_hostname(ssh, options.use_dns);
 145                 ipaddr = ssh_remote_ipaddr(ssh);
 146         }
 147
 148         /* Return false if user is listed in DenyUsers */
 149         if (options.num_deny_users > 0) {
 150                 for (i = 0; i < options.num_deny_users; i++) {
 151                         r = match_user(pw->pw_name, hostname, ipaddr,
 152                             options.deny_users[i]);
 153                         if (r < 0) {
 154                                 fatal("Invalid DenyUsers pattern \"%.100s\"",
 155                                     options.deny_users[i]);
 156                         } else if (r != 0) {
 157                                 logit("User %.100s from %.100s not allowed "
 158                                     "because listed in DenyUsers",
 159                                     pw->pw_name, hostname);
 160                                 return 0;
 161                         }
 162                 }
 163         }
 164         /* Return false if AllowUsers isn't empty and user isn't listed there */
 165         if (options.num_allow_users > 0) {
 166                 for (i = 0; i < options.num_allow_users; i++) {
 167                         r = match_user(pw->pw_name, hostname, ipaddr,
 168                             options.allow_users[i]);
 169                         if (r < 0) {
 170                                 fatal("Invalid AllowUsers pattern \"%.100s\"",
 171                                     options.allow_users[i]);
 172                         } else if (r == 1)
 173                                 break;
 174                 }
 175                 /* i < options.num_allow_users iff we break for loop */
 176                 if (i >= options.num_allow_users) {
 177                         logit("User %.100s from %.100s not allowed because "
 178                             "not listed in AllowUsers", pw->pw_name, hostname);
 179                         return 0;
 180                 }
 181         }
 182         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 183                 /* Get the user's group access list (primary and supplementary) */
 184                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 185                         logit("User %.100s from %.100s not allowed because "
 186                             "not in any group", pw->pw_name, hostname);
 187                         return 0;
 188                 }
 189
 190                 /* Return false if one of user's groups is listed in DenyGroups */
 191                 if (options.num_deny_groups > 0)
 192                         if (ga_match(options.deny_groups,
 193                             options.num_deny_groups)) {
 194                                 ga_free();
 195                                 logit("User %.100s from %.100s not allowed "
 196                                     "because a group is listed in DenyGroups",
 197                                     pw->pw_name, hostname);
 198                                 return 0;
 199                         }
 200                 /*
 201                  * Return false if AllowGroups isn't empty and one of user's groups
 202                  * isn't listed there
 203                  */
 204                 if (options.num_allow_groups > 0)
 205                         if (!ga_match(options.allow_groups,
 206                             options.num_allow_groups)) {
 207                                 ga_free();
 208                                 logit("User %.100s from %.100s not allowed "
 209                                     "because none of user's groups are listed "
 210                                     "in AllowGroups", pw->pw_name, hostname);
 211                                 return 0;
 212                         }
 213                 ga_free();
 214         }
 215
 216 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 217         if (!sys_auth_allowed_user(pw, loginmsg))
 218                 return 0;
 219 #endif
 220
 221         /* We found no reason not to let this user try to log on... */
 222         return 1;
 223 }
 224
 225 /*
 226  * Formats any key left in authctxt->auth_method_key for inclusion in
 227  * auth_log()'s message. Also includes authxtct->auth_method_info if present.
 228  */
 229 static char *
 230 format_method_key(Authctxt *authctxt)
 231 {
 232         const struct sshkey *key = authctxt->auth_method_key;
 233         const char *methinfo = authctxt->auth_method_info;
 234         char *fp, *cafp, *ret = NULL;
 235
 236         if (key == NULL)
 237                 return NULL;
 238
 239         if (sshkey_is_cert(key)) {
 240                 fp = sshkey_fingerprint(key,
 241                     options.fingerprint_hash, SSH_FP_DEFAULT);
 242                 cafp = sshkey_fingerprint(key->cert->signature_key,
 243                     options.fingerprint_hash, SSH_FP_DEFAULT);
 244                 xasprintf(&ret, "%s %s ID %s (serial %llu) CA %s %s%s%s",
 245                     sshkey_type(key), fp == NULL ? "(null)" : fp,
 246                     key->cert->key_id,
 247                     (unsigned long long)key->cert->serial,
 248                     sshkey_type(key->cert->signature_key),
 249                     cafp == NULL ? "(null)" : cafp,
 250                     methinfo == NULL ? "" : ", ",
 251                     methinfo == NULL ? "" : methinfo);
 252                 free(fp);
 253                 free(cafp);
 254         } else {
 255                 fp = sshkey_fingerprint(key, options.fingerprint_hash,
 256                     SSH_FP_DEFAULT);
 257                 xasprintf(&ret, "%s %s%s%s", sshkey_type(key),
 258                     fp == NULL ? "(null)" : fp,
 259                     methinfo == NULL ? "" : ", ",
 260                     methinfo == NULL ? "" : methinfo);
 261                 free(fp);
 262         }
 263         return ret;
 264 }
 265
 266 void
 267 auth_log(struct ssh *ssh, int authenticated, int partial,
 268     const char *method, const char *submethod)
 269 {
 270         Authctxt *authctxt = (Authctxt *)ssh->authctxt;
 271         int level = SYSLOG_LEVEL_VERBOSE;
 272         const char *authmsg;
 273         char *extra = NULL;
 274
 275         if (use_privsep && !mm_is_monitor() && !authctxt->postponed)
 276                 return;
 277
 278         /* Raise logging level */
 279         if (authenticated == 1 ||
 280             !authctxt->valid ||
 281             authctxt->failures >= options.max_authtries / 2 ||
 282             strcmp(method, "password") == 0)
 283                 level = SYSLOG_LEVEL_INFO;
 284
 285         if (authctxt->postponed)
 286                 authmsg = "Postponed";
 287         else if (partial)
 288                 authmsg = "Partial";
 289         else
 290                 authmsg = authenticated ? "Accepted" : "Failed";
 291
 292         if ((extra = format_method_key(authctxt)) == NULL) {
 293                 if (authctxt->auth_method_info != NULL)
 294                         extra = xstrdup(authctxt->auth_method_info);
 295         }
 296
 297         do_log2(level, "%s %s%s%s for %s%.100s from %.200s port %d ssh2%s%s",
 298             authmsg,
 299             method,
 300             submethod != NULL ? "/" : "", submethod == NULL ? "" : submethod,
 301             authctxt->valid ? "" : "invalid user ",
 302             authctxt->user,
 303             ssh_remote_ipaddr(ssh),
 304             ssh_remote_port(ssh),
 305             extra != NULL ? ": " : "",
 306             extra != NULL ? extra : "");
 307
 308         free(extra);
 309
 310 #if defined(CUSTOM_FAILED_LOGIN) || defined(SSH_AUDIT_EVENTS)
 311         if (authenticated == 0 && !(authctxt->postponed || partial)) {
 312                 /* Log failed login attempt */
 313 # ifdef CUSTOM_FAILED_LOGIN
 314                 if (strcmp(method, "password") == 0 ||
 315                     strncmp(method, "keyboard-interactive", 20) == 0 ||
 316                     strcmp(method, "challenge-response") == 0)
 317                         record_failed_login(ssh, authctxt->user,
 318                             auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
 319 # endif
 320 # ifdef SSH_AUDIT_EVENTS
 321                 audit_event(ssh, audit_classify_auth(method));
 322 # endif
 323         }
 324 #endif
 325 #if defined(CUSTOM_FAILED_LOGIN) && defined(WITH_AIXAUTHENTICATE)
 326         if (authenticated)
 327                 sys_auth_record_login(authctxt->user,
 328                     auth_get_canonical_hostname(ssh, options.use_dns), "ssh",
 329                     loginmsg);
 330 #endif
 331 }
 332
 333 void
 334 auth_maxtries_exceeded(struct ssh *ssh)
 335 {
 336         Authctxt *authctxt = (Authctxt *)ssh->authctxt;
 337
 338         error("maximum authentication attempts exceeded for "
 339             "%s%.100s from %.200s port %d ssh2",
 340             authctxt->valid ? "" : "invalid user ",
 341             authctxt->user,
 342             ssh_remote_ipaddr(ssh),
 343             ssh_remote_port(ssh));
 344         ssh_packet_disconnect(ssh, "Too many authentication failures");
 345         /* NOTREACHED */
 346 }
 347
 348 /*
 349  * Check whether root logins are disallowed.
 350  */
 351 int
 352 auth_root_allowed(struct ssh *ssh, const char *method)
 353 {
 354         switch (options.permit_root_login) {
 355         case PERMIT_YES:
 356                 return 1;
 357         case PERMIT_NO_PASSWD:
 358                 if (strcmp(method, "publickey") == 0 ||
 359                     strcmp(method, "hostbased") == 0 ||
 360                     strcmp(method, "gssapi-with-mic") == 0)
 361                         return 1;
 362                 break;
 363         case PERMIT_FORCED_ONLY:
 364                 if (auth_opts->force_command != NULL) {
 365                         logit("Root login accepted for forced command.");
 366                         return 1;
 367                 }
 368                 break;
 369         }
 370         logit("ROOT LOGIN REFUSED FROM %.200s port %d",
 371             ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
 372         return 0;
 373 }
 374
 375
 376 /*
 377  * Given a template and a passwd structure, build a filename
 378  * by substituting % tokenised options. Currently, %% becomes '%',
 379  * %h becomes the home directory and %u the username.
 380  *
 381  * This returns a buffer allocated by xmalloc.
 382  */
 383 char *
 384 expand_authorized_keys(const char *filename, struct passwd *pw)
 385 {
 386         char *file, uidstr[32], ret[PATH_MAX];
 387         int i;
 388
 389         snprintf(uidstr, sizeof(uidstr), "%llu",
 390             (unsigned long long)pw->pw_uid);
 391         file = percent_expand(filename, "h", pw->pw_dir,
 392             "u", pw->pw_name, "U", uidstr, (char *)NULL);
 393
 394         /*
 395          * Ensure that filename starts anchored. If not, be backward
 396          * compatible and prepend the '%h/'
 397          */
 398         if (path_absolute(file))
 399                 return (file);
 400
 401         i = snprintf(ret, sizeof(ret), "%s/%s", pw->pw_dir, file);
 402         if (i < 0 || (size_t)i >= sizeof(ret))
 403                 fatal("expand_authorized_keys: path too long");
 404         free(file);
 405         return (xstrdup(ret));
 406 }
 407
 408 char *
 409 authorized_principals_file(struct passwd *pw)
 410 {
 411         if (options.authorized_principals_file == NULL)
 412                 return NULL;
 413         return expand_authorized_keys(options.authorized_principals_file, pw);
 414 }
 415
 416 /* return ok if key exists in sysfile or userfile */
 417 HostStatus
 418 check_key_in_hostfiles(struct passwd *pw, struct sshkey *key, const char *host,
 419     const char *sysfile, const char *userfile)
 420 {
 421         char *user_hostfile;
 422         struct stat st;
 423         HostStatus host_status;
 424         struct hostkeys *hostkeys;
 425         const struct hostkey_entry *found;
 426
 427         hostkeys = init_hostkeys();
 428         load_hostkeys(hostkeys, host, sysfile, 0);
 429         if (userfile != NULL) {
 430                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 431                 if (options.strict_modes &&
 432                     (stat(user_hostfile, &st) == 0) &&
 433                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 434                     (st.st_mode & 022) != 0)) {
 435                         logit("Authentication refused for %.100s: "
 436                             "bad owner or modes for %.200s",
 437                             pw->pw_name, user_hostfile);
 438                         auth_debug_add("Ignored %.200s: bad ownership or modes",
 439                             user_hostfile);
 440                 } else {
 441                         temporarily_use_uid(pw);
 442                         load_hostkeys(hostkeys, host, user_hostfile, 0);
 443                         restore_uid();
 444                 }
 445                 free(user_hostfile);
 446         }
 447         host_status = check_key_in_hostkeys(hostkeys, key, &found);
 448         if (host_status == HOST_REVOKED)
 449                 error("WARNING: revoked key for %s attempted authentication",
 450                     host);
 451         else if (host_status == HOST_OK)
 452                 debug_f("key for %s found at %s:%ld",
 453                     found->host, found->file, found->line);
 454         else
 455                 debug_f("key for host %s not found", host);
 456
 457         free_hostkeys(hostkeys);
 458
 459         return host_status;
 460 }
 461
 462 struct passwd *
 463 getpwnamallow(struct ssh *ssh, const char *user)
 464 {
 465 #ifdef HAVE_LOGIN_CAP
 466         extern login_cap_t *lc;
 467 #ifdef BSD_AUTH
 468         auth_session_t *as;
 469 #endif
 470 #endif
 471         struct passwd *pw;
 472         struct connection_info *ci;
 473         u_int i;
 474
 475         ci = get_connection_info(ssh, 1, options.use_dns);
 476         ci->user = user;
 477         parse_server_match_config(&options, &includes, ci);
 478         log_change_level(options.log_level);
 479         log_verbose_reset();
 480         for (i = 0; i < options.num_log_verbose; i++)
 481                 log_verbose_add(options.log_verbose[i]);
 482         process_permitopen(ssh, &options);
 483
 484 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
 485         aix_setauthdb(user);
 486 #endif
 487
 488         pw = getpwnam(user);
 489
 490 #if defined(_AIX) && defined(HAVE_SETAUTHDB)
 491         aix_restoreauthdb();
 492 #endif
 493         if (pw == NULL) {
 494                 logit("Invalid user %.100s from %.100s port %d",
 495                     user, ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
 496 #ifdef CUSTOM_FAILED_LOGIN
 497                 record_failed_login(ssh, user,
 498                     auth_get_canonical_hostname(ssh, options.use_dns), "ssh");
 499 #endif
 500 #ifdef SSH_AUDIT_EVENTS
 501                 audit_event(ssh, SSH_INVALID_USER);
 502 #endif /* SSH_AUDIT_EVENTS */
 503                 return (NULL);
 504         }
 505         if (!allowed_user(ssh, pw))
 506                 return (NULL);
 507 #ifdef HAVE_LOGIN_CAP
 508         if ((lc = login_getpwclass(pw)) == NULL) {
 509                 debug("unable to get login class: %s", user);
 510                 return (NULL);
 511         }
 512 #ifdef BSD_AUTH
 513         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 514             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 515                 debug("Approval failure for %s", user);
 516                 pw = NULL;
 517         }
 518         if (as != NULL)
 519                 auth_close(as);
 520 #endif
 521 #endif
 522         if (pw != NULL)
 523                 return (pwcopy(pw));
 524         return (NULL);
 525 }
 526
 527 /* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
 528 int
 529 auth_key_is_revoked(struct sshkey *key)
 530 {
 531         char *fp = NULL;
 532         int r;
 533
 534         if (options.revoked_keys_file == NULL)
 535                 return 0;
 536         if ((fp = sshkey_fingerprint(key, options.fingerprint_hash,
 537             SSH_FP_DEFAULT)) == NULL) {
 538                 r = SSH_ERR_ALLOC_FAIL;
 539                 error_fr(r, "fingerprint key");
 540                 goto out;
 541         }
 542
 543         r = sshkey_check_revoked(key, options.revoked_keys_file);
 544         switch (r) {
 545         case 0:
 546                 break; /* not revoked */
 547         case SSH_ERR_KEY_REVOKED:
 548                 error("Authentication key %s %s revoked by file %s",
 549                     sshkey_type(key), fp, options.revoked_keys_file);
 550                 goto out;
 551         default:
 552                 error_r(r, "Error checking authentication key %s %s in "
 553                     "revoked keys file %s", sshkey_type(key), fp,
 554                     options.revoked_keys_file);
 555                 goto out;
 556         }
 557
 558         /* Success */
 559         r = 0;
 560
 561  out:
 562         free(fp);
 563         return r == 0 ? 0 : 1;
 564 }
 565
 566 void
 567 auth_debug_add(const char *fmt,...)
 568 {
 569         char buf[1024];
 570         va_list args;
 571         int r;
 572
 573         va_start(args, fmt);
 574         vsnprintf(buf, sizeof(buf), fmt, args);
 575         va_end(args);
 576         debug3("%s", buf);
 577         if (auth_debug != NULL)
 578                 if ((r = sshbuf_put_cstring(auth_debug, buf)) != 0)
 579                         fatal_fr(r, "sshbuf_put_cstring");
 580 }
 581
 582 void
 583 auth_debug_send(struct ssh *ssh)
 584 {
 585         char *msg;
 586         int r;
 587
 588         if (auth_debug == NULL)
 589                 return;
 590         while (sshbuf_len(auth_debug) != 0) {
 591                 if ((r = sshbuf_get_cstring(auth_debug, &msg, NULL)) != 0)
 592                         fatal_fr(r, "sshbuf_get_cstring");
 593                 ssh_packet_send_debug(ssh, "%s", msg);
 594                 free(msg);
 595         }
 596 }
 597
 598 void
 599 auth_debug_reset(void)
 600 {
 601         if (auth_debug != NULL)
 602                 sshbuf_reset(auth_debug);
 603         else if ((auth_debug = sshbuf_new()) == NULL)
 604                 fatal_f("sshbuf_new failed");
 605 }
 606
 607 struct passwd *
 608 fakepw(void)
 609 {
 610         static int done = 0;
 611         static struct passwd fake;
 612         const char hashchars[] = "./ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 613             "abcdefghijklmnopqrstuvwxyz0123456789"; /* from bcrypt.c */
 614         char *cp;
 615
 616         if (done)
 617                 return (&fake);
 618
 619         memset(&fake, 0, sizeof(fake));
 620         fake.pw_name = "NOUSER";
 621         fake.pw_passwd = xstrdup("$2a$10$"
 622             "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
 623         for (cp = fake.pw_passwd + 7; *cp != '\0'; cp++)
 624                 *cp = hashchars[arc4random_uniform(sizeof(hashchars) - 1)];
 625 #ifdef HAVE_STRUCT_PASSWD_PW_GECOS
 626         fake.pw_gecos = "NOUSER";
 627 #endif
 628         fake.pw_uid = privsep_pw == NULL ? (uid_t)-1 : privsep_pw->pw_uid;
 629         fake.pw_gid = privsep_pw == NULL ? (gid_t)-1 : privsep_pw->pw_gid;
 630 #ifdef HAVE_STRUCT_PASSWD_PW_CLASS
 631         fake.pw_class = "";
 632 #endif
 633         fake.pw_dir = "/nonexist";
 634         fake.pw_shell = "/nonexist";
 635         done = 1;
 636
 637         return (&fake);
 638 }
 639
 640 /*
 641  * Returns the remote DNS hostname as a string. The returned string must not
 642  * be freed. NB. this will usually trigger a DNS query the first time it is
 643  * called.
 644  * This function does additional checks on the hostname to mitigate some
 645  * attacks on based on conflation of hostnames and IP addresses.
 646  */
 647
 648 static char *
 649 remote_hostname(struct ssh *ssh)
 650 {
 651         struct sockaddr_storage from;
 652         socklen_t fromlen;
 653         struct addrinfo hints, *ai, *aitop;
 654         char name[NI_MAXHOST], ntop2[NI_MAXHOST];
 655         const char *ntop = ssh_remote_ipaddr(ssh);
 656
 657         /* Get IP address of client. */
 658         fromlen = sizeof(from);
 659         memset(&from, 0, sizeof(from));
 660         if (getpeername(ssh_packet_get_connection_in(ssh),
 661             (struct sockaddr *)&from, &fromlen) == -1) {
 662                 debug("getpeername failed: %.100s", strerror(errno));
 663                 return xstrdup(ntop);
 664         }
 665
 666         ipv64_normalise_mapped(&from, &fromlen);
 667         if (from.ss_family == AF_INET6)
 668                 fromlen = sizeof(struct sockaddr_in6);
 669
 670         debug3("Trying to reverse map address %.100s.", ntop);
 671         /* Map the IP address to a host name. */
 672         if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
 673             NULL, 0, NI_NAMEREQD) != 0) {
 674                 /* Host name not found.  Use ip address. */
 675                 return xstrdup(ntop);
 676         }
 677
 678         /*
 679          * if reverse lookup result looks like a numeric hostname,
 680          * someone is trying to trick us by PTR record like following:
 681          *      1.1.1.10.in-addr.arpa.  IN PTR  2.3.4.5
 682          */
 683         memset(&hints, 0, sizeof(hints));
 684         hints.ai_socktype = SOCK_DGRAM; /*dummy*/
 685         hints.ai_flags = AI_NUMERICHOST;
 686         if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
 687                 logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
 688                     name, ntop);
 689                 freeaddrinfo(ai);
 690                 return xstrdup(ntop);
 691         }
 692
 693         /* Names are stored in lowercase. */
 694         lowercase(name);
 695
 696         /*
 697          * Map it back to an IP address and check that the given
 698          * address actually is an address of this host.  This is
 699          * necessary because anyone with access to a name server can
 700          * define arbitrary names for an IP address. Mapping from
 701          * name to IP address can be trusted better (but can still be
 702          * fooled if the intruder has access to the name server of
 703          * the domain).
 704          */
 705         memset(&hints, 0, sizeof(hints));
 706         hints.ai_family = from.ss_family;
 707         hints.ai_socktype = SOCK_STREAM;
 708         if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
 709                 logit("reverse mapping checking getaddrinfo for %.700s "
 710                     "[%s] failed.", name, ntop);
 711                 return xstrdup(ntop);
 712         }
 713         /* Look for the address from the list of addresses. */
 714         for (ai = aitop; ai; ai = ai->ai_next) {
 715                 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
 716                     sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
 717                     (strcmp(ntop, ntop2) == 0))
 718                                 break;
 719         }
 720         freeaddrinfo(aitop);
 721         /* If we reached the end of the list, the address was not there. */
 722         if (ai == NULL) {
 723                 /* Address not found for the host name. */
 724                 logit("Address %.100s maps to %.600s, but this does not "
 725                     "map back to the address.", ntop, name);
 726                 return xstrdup(ntop);
 727         }
 728         return xstrdup(name);
 729 }
 730
 731 /*
 732  * Return the canonical name of the host in the other side of the current
 733  * connection.  The host name is cached, so it is efficient to call this
 734  * several times.
 735  */
 736
 737 const char *
 738 auth_get_canonical_hostname(struct ssh *ssh, int use_dns)
 739 {
 740         static char *dnsname;
 741
 742         if (!use_dns)
 743                 return ssh_remote_ipaddr(ssh);
 744         else if (dnsname != NULL)
 745                 return dnsname;
 746         else {
 747                 dnsname = remote_hostname(ssh);
 748                 return dnsname;
 749         }
 750 }
 751
 752 /* These functions link key/cert options to the auth framework */
 753
 754 /* Log sshauthopt options locally and (optionally) for remote transmission */
 755 void
 756 auth_log_authopts(const char *loc, const struct sshauthopt *opts, int do_remote)
 757 {
 758         int do_env = options.permit_user_env && opts->nenv > 0;
 759         int do_permitopen = opts->npermitopen > 0 &&
 760             (options.allow_tcp_forwarding & FORWARD_LOCAL) != 0;
 761         int do_permitlisten = opts->npermitlisten > 0 &&
 762             (options.allow_tcp_forwarding & FORWARD_REMOTE) != 0;
 763         size_t i;
 764         char msg[1024], buf[64];
 765
 766         snprintf(buf, sizeof(buf), "%d", opts->force_tun_device);
 767         /* Try to keep this alphabetically sorted */
 768         snprintf(msg, sizeof(msg), "key options:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
 769             opts->permit_agent_forwarding_flag ? " agent-forwarding" : "",
 770             opts->force_command == NULL ? "" : " command",
 771             do_env ?  " environment" : "",
 772             opts->valid_before == 0 ? "" : "expires",
 773             opts->no_require_user_presence ? " no-touch-required" : "",
 774             do_permitopen ?  " permitopen" : "",
 775             do_permitlisten ?  " permitlisten" : "",
 776             opts->permit_port_forwarding_flag ? " port-forwarding" : "",
 777             opts->cert_principals == NULL ? "" : " principals",
 778             opts->permit_pty_flag ? " pty" : "",
 779             opts->require_verify ? " uv" : "",
 780             opts->force_tun_device == -1 ? "" : " tun=",
 781             opts->force_tun_device == -1 ? "" : buf,
 782             opts->permit_user_rc ? " user-rc" : "",
 783             opts->permit_x11_forwarding_flag ? " x11-forwarding" : "");
 784
 785         debug("%s: %s", loc, msg);
 786         if (do_remote)
 787                 auth_debug_add("%s: %s", loc, msg);
 788
 789         if (options.permit_user_env) {
 790                 for (i = 0; i < opts->nenv; i++) {
 791                         debug("%s: environment: %s", loc, opts->env[i]);
 792                         if (do_remote) {
 793                                 auth_debug_add("%s: environment: %s",
 794                                     loc, opts->env[i]);
 795                         }
 796                 }
 797         }
 798
 799         /* Go into a little more details for the local logs. */
 800         if (opts->valid_before != 0) {
 801                 format_absolute_time(opts->valid_before, buf, sizeof(buf));
 802                 debug("%s: expires at %s", loc, buf);
 803         }
 804         if (opts->cert_principals != NULL) {
 805                 debug("%s: authorized principals: \"%s\"",
 806                     loc, opts->cert_principals);
 807         }
 808         if (opts->force_command != NULL)
 809                 debug("%s: forced command: \"%s\"", loc, opts->force_command);
 810         if (do_permitopen) {
 811                 for (i = 0; i < opts->npermitopen; i++) {
 812                         debug("%s: permitted open: %s",
 813                             loc, opts->permitopen[i]);
 814                 }
 815         }
 816         if (do_permitlisten) {
 817                 for (i = 0; i < opts->npermitlisten; i++) {
 818                         debug("%s: permitted listen: %s",
 819                             loc, opts->permitlisten[i]);
 820                 }
 821         }
 822 }
 823
 824 /* Activate a new set of key/cert options; merging with what is there. */
 825 int
 826 auth_activate_options(struct ssh *ssh, struct sshauthopt *opts)
 827 {
 828         struct sshauthopt *old = auth_opts;
 829         const char *emsg = NULL;
 830
 831         debug_f("setting new authentication options");
 832         if ((auth_opts = sshauthopt_merge(old, opts, &emsg)) == NULL) {
 833                 error("Inconsistent authentication options: %s", emsg);
 834                 return -1;
 835         }
 836         return 0;
 837 }
 838
 839 /* Disable forwarding, etc for the session */
 840 void
 841 auth_restrict_session(struct ssh *ssh)
 842 {
 843         struct sshauthopt *restricted;
 844
 845         debug_f("restricting session");
 846
 847         /* A blank sshauthopt defaults to permitting nothing */
 848         if ((restricted = sshauthopt_new()) == NULL)
 849                 fatal_f("sshauthopt_new failed");
 850         restricted->permit_pty_flag = 1;
 851         restricted->restricted = 1;
 852
 853         if (auth_activate_options(ssh, restricted) != 0)
 854                 fatal_f("failed to restrict session");
 855         sshauthopt_free(restricted);
 856 }