auth.c

   1 /*
   2  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26 RCSID("$OpenBSD: auth.c,v 1.58 2005/03/14 11:44:42 dtucker Exp $");
  27
  28 #ifdef HAVE_LOGIN_H
  29 #include <login.h>
  30 #endif
  31 #ifdef USE_SHADOW
  32 #include <shadow.h>
  33 #endif
  34
  35 #ifdef HAVE_LIBGEN_H
  36 #include <libgen.h>
  37 #endif
  38
  39 #include "xmalloc.h"
  40 #include "match.h"
  41 #include "groupaccess.h"
  42 #include "log.h"
  43 #include "servconf.h"
  44 #include "auth.h"
  45 #include "auth-options.h"
  46 #include "canohost.h"
  47 #include "buffer.h"
  48 #include "bufaux.h"
  49 #include "uidswap.h"
  50 #include "misc.h"
  51 #include "bufaux.h"
  52 #include "packet.h"
  53 #include "loginrec.h"
  54 #include "monitor_wrap.h"
  55
  56 /* import */
  57 extern ServerOptions options;
  58 extern Buffer loginmsg;
  59
  60 /* Debugging messages */
  61 Buffer auth_debug;
  62 int auth_debug_init;
  63
  64 /*
  65  * Check if the user is allowed to log in via ssh. If user is listed
  66  * in DenyUsers or one of user's groups is listed in DenyGroups, false
  67  * will be returned. If AllowUsers isn't empty and user isn't listed
  68  * there, or if AllowGroups isn't empty and one of user's groups isn't
  69  * listed there, false will be returned.
  70  * If the user's shell is not executable, false will be returned.
  71  * Otherwise true is returned.
  72  */
  73 int
  74 allowed_user(struct passwd * pw)
  75 {
  76         struct stat st;
  77         const char *hostname = NULL, *ipaddr = NULL, *passwd = NULL;
  78         char *shell;
  79         int i;
  80 #ifdef USE_SHADOW
  81         struct spwd *spw = NULL;
  82 #endif
  83
  84         /* Shouldn't be called if pw is NULL, but better safe than sorry... */
  85         if (!pw || !pw->pw_name)
  86                 return 0;
  87
  88 #ifdef USE_SHADOW
  89         if (!options.use_pam)
  90                 spw = getspnam(pw->pw_name);
  91 #ifdef HAS_SHADOW_EXPIRE
  92         if (!options.use_pam && spw != NULL && auth_shadow_acctexpired(spw))
  93                 return 0;
  94 #endif /* HAS_SHADOW_EXPIRE */
  95 #endif /* USE_SHADOW */
  96
  97         /* grab passwd field for locked account check */
  98 #ifdef USE_SHADOW
  99         if (spw != NULL)
 100                 passwd = spw->sp_pwdp;
 101 #else
 102         passwd = pw->pw_passwd;
 103 #endif
 104
 105         /* check for locked account */
 106         if (!options.use_pam && passwd && *passwd) {
 107                 int locked = 0;
 108
 109 #ifdef LOCKED_PASSWD_STRING
 110                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 111                          locked = 1;
 112 #endif
 113 #ifdef LOCKED_PASSWD_PREFIX
 114                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 115                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 116                          locked = 1;
 117 #endif
 118 #ifdef LOCKED_PASSWD_SUBSTR
 119                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 120                         locked = 1;
 121 #endif
 122                 if (locked) {
 123                         logit("User %.100s not allowed because account is locked",
 124                             pw->pw_name);
 125                         return 0;
 126                 }
 127         }
 128
 129         /*
 130          * Get the shell from the password data.  An empty shell field is
 131          * legal, and means /bin/sh.
 132          */
 133         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 134
 135         /* deny if shell does not exists or is not executable */
 136         if (stat(shell, &st) != 0) {
 137                 logit("User %.100s not allowed because shell %.100s does not exist",
 138                     pw->pw_name, shell);
 139                 return 0;
 140         }
 141         if (S_ISREG(st.st_mode) == 0 ||
 142             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 143                 logit("User %.100s not allowed because shell %.100s is not executable",
 144                     pw->pw_name, shell);
 145                 return 0;
 146         }
 147
 148         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 149             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 150                 hostname = get_canonical_hostname(options.use_dns);
 151                 ipaddr = get_remote_ipaddr();
 152         }
 153
 154         /* Return false if user is listed in DenyUsers */
 155         if (options.num_deny_users > 0) {
 156                 for (i = 0; i < options.num_deny_users; i++)
 157                         if (match_user(pw->pw_name, hostname, ipaddr,
 158                             options.deny_users[i])) {
 159                                 logit("User %.100s from %.100s not allowed "
 160                                     "because listed in DenyUsers",
 161                                     pw->pw_name, hostname);
 162                                 return 0;
 163                         }
 164         }
 165         /* Return false if AllowUsers isn't empty and user isn't listed there */
 166         if (options.num_allow_users > 0) {
 167                 for (i = 0; i < options.num_allow_users; i++)
 168                         if (match_user(pw->pw_name, hostname, ipaddr,
 169                             options.allow_users[i]))
 170                                 break;
 171                 /* i < options.num_allow_users iff we break for loop */
 172                 if (i >= options.num_allow_users) {
 173                         logit("User %.100s from %.100s not allowed because "
 174                             "not listed in AllowUsers", pw->pw_name, hostname);
 175                         return 0;
 176                 }
 177         }
 178         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 179                 /* Get the user's group access list (primary and supplementary) */
 180                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 181                         logit("User %.100s from %.100s not allowed because "
 182                             "not in any group", pw->pw_name, hostname);
 183                         return 0;
 184                 }
 185
 186                 /* Return false if one of user's groups is listed in DenyGroups */
 187                 if (options.num_deny_groups > 0)
 188                         if (ga_match(options.deny_groups,
 189                             options.num_deny_groups)) {
 190                                 ga_free();
 191                                 logit("User %.100s from %.100s not allowed "
 192                                     "because a group is listed in DenyGroups",
 193                                     pw->pw_name, hostname);
 194                                 return 0;
 195                         }
 196                 /*
 197                  * Return false if AllowGroups isn't empty and one of user's groups
 198                  * isn't listed there
 199                  */
 200                 if (options.num_allow_groups > 0)
 201                         if (!ga_match(options.allow_groups,
 202                             options.num_allow_groups)) {
 203                                 ga_free();
 204                                 logit("User %.100s from %.100s not allowed "
 205                                     "because none of user's groups are listed "
 206                                     "in AllowGroups", pw->pw_name, hostname);
 207                                 return 0;
 208                         }
 209                 ga_free();
 210         }
 211
 212 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 213         if (!sys_auth_allowed_user(pw, &loginmsg))
 214                 return 0;
 215 #endif
 216
 217         /* We found no reason not to let this user try to log on... */
 218         return 1;
 219 }
 220
 221 void
 222 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 223 {
 224         void (*authlog) (const char *fmt,...) = verbose;
 225         char *authmsg;
 226
 227         /* Raise logging level */
 228         if (authenticated == 1 ||
 229             !authctxt->valid ||
 230             authctxt->failures >= options.max_authtries / 2 ||
 231             strcmp(method, "password") == 0)
 232                 authlog = logit;
 233
 234         if (authctxt->postponed)
 235                 authmsg = "Postponed";
 236         else
 237                 authmsg = authenticated ? "Accepted" : "Failed";
 238
 239         authlog("%s %s for %s%.100s from %.200s port %d%s",
 240             authmsg,
 241             method,
 242             authctxt->valid ? "" : "invalid user ",
 243             authctxt->user,
 244             get_remote_ipaddr(),
 245             get_remote_port(),
 246             info);
 247
 248 #ifdef CUSTOM_FAILED_LOGIN
 249         if (authenticated == 0 && !authctxt->postponed &&
 250             (strcmp(method, "password") == 0 ||
 251             strncmp(method, "keyboard-interactive", 20) == 0 ||
 252             strcmp(method, "challenge-response") == 0))
 253                 record_failed_login(authctxt->user,
 254                     get_canonical_hostname(options.use_dns), "ssh");
 255 #endif
 256 #ifdef SSH_AUDIT_EVENTS
 257         if (authenticated == 0 && !authctxt->postponed) {
 258                 ssh_audit_event_t event;
 259
 260                 debug3("audit failed auth attempt, method %s euid %d",
 261                     method, (int)geteuid());
 262                 /*
 263                  * Because the auth loop is used in both monitor and slave,
 264                  * we must be careful to send each event only once and with
 265                  * enough privs to write the event.
 266                  */
 267                 event = audit_classify_auth(method);
 268                 switch(event) {
 269                 case SSH_AUTH_FAIL_NONE:
 270                 case SSH_AUTH_FAIL_PASSWD:
 271                 case SSH_AUTH_FAIL_KBDINT:
 272                         if (geteuid() == 0)
 273                                 audit_event(event);
 274                         break;
 275                 case SSH_AUTH_FAIL_PUBKEY:
 276                 case SSH_AUTH_FAIL_HOSTBASED:
 277                 case SSH_AUTH_FAIL_GSSAPI:
 278                         /*
 279                          * This is required to handle the case where privsep
 280                          * is enabled but it's root logging in, since
 281                          * use_privsep won't be cleared until after a
 282                          * successful login.
 283                          */
 284                         if (geteuid() == 0)
 285                                 audit_event(event);
 286                         else
 287                                 PRIVSEP(audit_event(event));
 288                         break;
 289                 default:
 290                         error("unknown authentication audit event %d", event);
 291                 }
 292         }
 293 #endif
 294 }
 295
 296 /*
 297  * Check whether root logins are disallowed.
 298  */
 299 int
 300 auth_root_allowed(char *method)
 301 {
 302         switch (options.permit_root_login) {
 303         case PERMIT_YES:
 304                 return 1;
 305                 break;
 306         case PERMIT_NO_PASSWD:
 307                 if (strcmp(method, "password") != 0)
 308                         return 1;
 309                 break;
 310         case PERMIT_FORCED_ONLY:
 311                 if (forced_command) {
 312                         logit("Root login accepted for forced command.");
 313                         return 1;
 314                 }
 315                 break;
 316         }
 317         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 318         return 0;
 319 }
 320
 321
 322 /*
 323  * Given a template and a passwd structure, build a filename
 324  * by substituting % tokenised options. Currently, %% becomes '%',
 325  * %h becomes the home directory and %u the username.
 326  *
 327  * This returns a buffer allocated by xmalloc.
 328  */
 329 char *
 330 expand_filename(const char *filename, struct passwd *pw)
 331 {
 332         Buffer buffer;
 333         char *file;
 334         const char *cp;
 335
 336         /*
 337          * Build the filename string in the buffer by making the appropriate
 338          * substitutions to the given file name.
 339          */
 340         buffer_init(&buffer);
 341         for (cp = filename; *cp; cp++) {
 342                 if (cp[0] == '%' && cp[1] == '%') {
 343                         buffer_append(&buffer, "%", 1);
 344                         cp++;
 345                         continue;
 346                 }
 347                 if (cp[0] == '%' && cp[1] == 'h') {
 348                         buffer_append(&buffer, pw->pw_dir, strlen(pw->pw_dir));
 349                         cp++;
 350                         continue;
 351                 }
 352                 if (cp[0] == '%' && cp[1] == 'u') {
 353                         buffer_append(&buffer, pw->pw_name,
 354                             strlen(pw->pw_name));
 355                         cp++;
 356                         continue;
 357                 }
 358                 buffer_append(&buffer, cp, 1);
 359         }
 360         buffer_append(&buffer, "\0", 1);
 361
 362         /*
 363          * Ensure that filename starts anchored. If not, be backward
 364          * compatible and prepend the '%h/'
 365          */
 366         file = xmalloc(MAXPATHLEN);
 367         cp = buffer_ptr(&buffer);
 368         if (*cp != '/')
 369                 snprintf(file, MAXPATHLEN, "%s/%s", pw->pw_dir, cp);
 370         else
 371                 strlcpy(file, cp, MAXPATHLEN);
 372
 373         buffer_free(&buffer);
 374         return file;
 375 }
 376
 377 char *
 378 authorized_keys_file(struct passwd *pw)
 379 {
 380         return expand_filename(options.authorized_keys_file, pw);
 381 }
 382
 383 char *
 384 authorized_keys_file2(struct passwd *pw)
 385 {
 386         return expand_filename(options.authorized_keys_file2, pw);
 387 }
 388
 389 /* return ok if key exists in sysfile or userfile */
 390 HostStatus
 391 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 392     const char *sysfile, const char *userfile)
 393 {
 394         Key *found;
 395         char *user_hostfile;
 396         struct stat st;
 397         HostStatus host_status;
 398
 399         /* Check if we know the host and its host key. */
 400         found = key_new(key->type);
 401         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 402
 403         if (host_status != HOST_OK && userfile != NULL) {
 404                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 405                 if (options.strict_modes &&
 406                     (stat(user_hostfile, &st) == 0) &&
 407                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 408                     (st.st_mode & 022) != 0)) {
 409                         logit("Authentication refused for %.100s: "
 410                             "bad owner or modes for %.200s",
 411                             pw->pw_name, user_hostfile);
 412                 } else {
 413                         temporarily_use_uid(pw);
 414                         host_status = check_host_in_hostfile(user_hostfile,
 415                             host, key, found, NULL);
 416                         restore_uid();
 417                 }
 418                 xfree(user_hostfile);
 419         }
 420         key_free(found);
 421
 422         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 423             "ok" : "not found", host);
 424         return host_status;
 425 }
 426
 427
 428 /*
 429  * Check a given file for security. This is defined as all components
 430  * of the path to the file must be owned by either the owner of
 431  * of the file or root and no directories must be group or world writable.
 432  *
 433  * XXX Should any specific check be done for sym links ?
 434  *
 435  * Takes an open file descriptor, the file name, a uid and and
 436  * error buffer plus max size as arguments.
 437  *
 438  * Returns 0 on success and -1 on failure
 439  */
 440 int
 441 secure_filename(FILE *f, const char *file, struct passwd *pw,
 442     char *err, size_t errlen)
 443 {
 444         uid_t uid = pw->pw_uid;
 445         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 446         char *cp;
 447         int comparehome = 0;
 448         struct stat st;
 449
 450         if (realpath(file, buf) == NULL) {
 451                 snprintf(err, errlen, "realpath %s failed: %s", file,
 452                     strerror(errno));
 453                 return -1;
 454         }
 455         if (realpath(pw->pw_dir, homedir) != NULL)
 456                 comparehome = 1;
 457
 458         /* check the open file to avoid races */
 459         if (fstat(fileno(f), &st) < 0 ||
 460             (st.st_uid != 0 && st.st_uid != uid) ||
 461             (st.st_mode & 022) != 0) {
 462                 snprintf(err, errlen, "bad ownership or modes for file %s",
 463                     buf);
 464                 return -1;
 465         }
 466
 467         /* for each component of the canonical path, walking upwards */
 468         for (;;) {
 469                 if ((cp = dirname(buf)) == NULL) {
 470                         snprintf(err, errlen, "dirname() failed");
 471                         return -1;
 472                 }
 473                 strlcpy(buf, cp, sizeof(buf));
 474
 475                 debug3("secure_filename: checking '%s'", buf);
 476                 if (stat(buf, &st) < 0 ||
 477                     (st.st_uid != 0 && st.st_uid != uid) ||
 478                     (st.st_mode & 022) != 0) {
 479                         snprintf(err, errlen,
 480                             "bad ownership or modes for directory %s", buf);
 481                         return -1;
 482                 }
 483
 484                 /* If are passed the homedir then we can stop */
 485                 if (comparehome && strcmp(homedir, buf) == 0) {
 486                         debug3("secure_filename: terminating check at '%s'",
 487                             buf);
 488                         break;
 489                 }
 490                 /*
 491                  * dirname should always complete with a "/" path,
 492                  * but we can be paranoid and check for "." too
 493                  */
 494                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 495                         break;
 496         }
 497         return 0;
 498 }
 499
 500 struct passwd *
 501 getpwnamallow(const char *user)
 502 {
 503 #ifdef HAVE_LOGIN_CAP
 504         extern login_cap_t *lc;
 505 #ifdef BSD_AUTH
 506         auth_session_t *as;
 507 #endif
 508 #endif
 509         struct passwd *pw;
 510
 511         pw = getpwnam(user);
 512         if (pw == NULL) {
 513                 logit("Invalid user %.100s from %.100s",
 514                     user, get_remote_ipaddr());
 515 #ifdef CUSTOM_FAILED_LOGIN
 516                 record_failed_login(user,
 517                     get_canonical_hostname(options.use_dns), "ssh");
 518 #endif
 519 #ifdef SSH_AUDIT_EVENTS
 520                 audit_event(SSH_INVALID_USER);
 521 #endif /* SSH_AUDIT_EVENTS */
 522                 return (NULL);
 523         }
 524         if (!allowed_user(pw))
 525                 return (NULL);
 526 #ifdef HAVE_LOGIN_CAP
 527         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 528                 debug("unable to get login class: %s", user);
 529                 return (NULL);
 530         }
 531 #ifdef BSD_AUTH
 532         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 533             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 534                 debug("Approval failure for %s", user);
 535                 pw = NULL;
 536         }
 537         if (as != NULL)
 538                 auth_close(as);
 539 #endif
 540 #endif
 541         if (pw != NULL)
 542                 return (pwcopy(pw));
 543         return (NULL);
 544 }
 545
 546 void
 547 auth_debug_add(const char *fmt,...)
 548 {
 549         char buf[1024];
 550         va_list args;
 551
 552         if (!auth_debug_init)
 553                 return;
 554
 555         va_start(args, fmt);
 556         vsnprintf(buf, sizeof(buf), fmt, args);
 557         va_end(args);
 558         buffer_put_cstring(&auth_debug, buf);
 559 }
 560
 561 void
 562 auth_debug_send(void)
 563 {
 564         char *msg;
 565
 566         if (!auth_debug_init)
 567                 return;
 568         while (buffer_len(&auth_debug)) {
 569                 msg = buffer_get_string(&auth_debug, NULL);
 570                 packet_send_debug("%s", msg);
 571                 xfree(msg);
 572         }
 573 }
 574
 575 void
 576 auth_debug_reset(void)
 577 {
 578         if (auth_debug_init)
 579                 buffer_clear(&auth_debug);
 580         else {
 581                 buffer_init(&auth_debug);
 582                 auth_debug_init = 1;
 583         }
 584 }
 585
 586 struct passwd *
 587 fakepw(void)
 588 {
 589         static struct passwd fake;
 590
 591         memset(&fake, 0, sizeof(fake));
 592         fake.pw_name = "NOUSER";
 593         fake.pw_passwd =
 594             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 595         fake.pw_gecos = "NOUSER";
 596         fake.pw_uid = (uid_t)-1;
 597         fake.pw_gid = (gid_t)-1;
 598 #ifdef HAVE_PW_CLASS_IN_PASSWD
 599         fake.pw_class = "";
 600 #endif
 601         fake.pw_dir = "/nonexist";
 602         fake.pw_shell = "/nonexist";
 603
 604         return (&fake);
 605 }