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 1.60 2005/06/17 02:44:32 djm 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         u_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 static char *
 330 expand_authorized_keys(const char *filename, struct passwd *pw)
 331 {
 332         char *file, *ret;
 333
 334         file = percent_expand(filename, "h", pw->pw_dir,
 335             "u", pw->pw_name, (char *)NULL);
 336
 337         /*
 338          * Ensure that filename starts anchored. If not, be backward
 339          * compatible and prepend the '%h/'
 340          */
 341         if (*file == '/')
 342                 return (file);
 343
 344         ret = xmalloc(MAXPATHLEN);
 345         if (strlcpy(ret, pw->pw_dir, MAXPATHLEN) >= MAXPATHLEN ||
 346             strlcat(ret, "/", MAXPATHLEN) >= MAXPATHLEN ||
 347             strlcat(ret, file, MAXPATHLEN) >= MAXPATHLEN)
 348                 fatal("expand_authorized_keys: path too long");
 349
 350         xfree(file);
 351         return (ret);
 352 }
 353
 354 char *
 355 authorized_keys_file(struct passwd *pw)
 356 {
 357         return expand_authorized_keys(options.authorized_keys_file, pw);
 358 }
 359
 360 char *
 361 authorized_keys_file2(struct passwd *pw)
 362 {
 363         return expand_authorized_keys(options.authorized_keys_file2, pw);
 364 }
 365
 366 /* return ok if key exists in sysfile or userfile */
 367 HostStatus
 368 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 369     const char *sysfile, const char *userfile)
 370 {
 371         Key *found;
 372         char *user_hostfile;
 373         struct stat st;
 374         HostStatus host_status;
 375
 376         /* Check if we know the host and its host key. */
 377         found = key_new(key->type);
 378         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 379
 380         if (host_status != HOST_OK && userfile != NULL) {
 381                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 382                 if (options.strict_modes &&
 383                     (stat(user_hostfile, &st) == 0) &&
 384                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 385                     (st.st_mode & 022) != 0)) {
 386                         logit("Authentication refused for %.100s: "
 387                             "bad owner or modes for %.200s",
 388                             pw->pw_name, user_hostfile);
 389                 } else {
 390                         temporarily_use_uid(pw);
 391                         host_status = check_host_in_hostfile(user_hostfile,
 392                             host, key, found, NULL);
 393                         restore_uid();
 394                 }
 395                 xfree(user_hostfile);
 396         }
 397         key_free(found);
 398
 399         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 400             "ok" : "not found", host);
 401         return host_status;
 402 }
 403
 404
 405 /*
 406  * Check a given file for security. This is defined as all components
 407  * of the path to the file must be owned by either the owner of
 408  * of the file or root and no directories must be group or world writable.
 409  *
 410  * XXX Should any specific check be done for sym links ?
 411  *
 412  * Takes an open file descriptor, the file name, a uid and and
 413  * error buffer plus max size as arguments.
 414  *
 415  * Returns 0 on success and -1 on failure
 416  */
 417 int
 418 secure_filename(FILE *f, const char *file, struct passwd *pw,
 419     char *err, size_t errlen)
 420 {
 421         uid_t uid = pw->pw_uid;
 422         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 423         char *cp;
 424         int comparehome = 0;
 425         struct stat st;
 426
 427         if (realpath(file, buf) == NULL) {
 428                 snprintf(err, errlen, "realpath %s failed: %s", file,
 429                     strerror(errno));
 430                 return -1;
 431         }
 432         if (realpath(pw->pw_dir, homedir) != NULL)
 433                 comparehome = 1;
 434
 435         /* check the open file to avoid races */
 436         if (fstat(fileno(f), &st) < 0 ||
 437             (st.st_uid != 0 && st.st_uid != uid) ||
 438             (st.st_mode & 022) != 0) {
 439                 snprintf(err, errlen, "bad ownership or modes for file %s",
 440                     buf);
 441                 return -1;
 442         }
 443
 444         /* for each component of the canonical path, walking upwards */
 445         for (;;) {
 446                 if ((cp = dirname(buf)) == NULL) {
 447                         snprintf(err, errlen, "dirname() failed");
 448                         return -1;
 449                 }
 450                 strlcpy(buf, cp, sizeof(buf));
 451
 452                 debug3("secure_filename: checking '%s'", buf);
 453                 if (stat(buf, &st) < 0 ||
 454                     (st.st_uid != 0 && st.st_uid != uid) ||
 455                     (st.st_mode & 022) != 0) {
 456                         snprintf(err, errlen,
 457                             "bad ownership or modes for directory %s", buf);
 458                         return -1;
 459                 }
 460
 461                 /* If are passed the homedir then we can stop */
 462                 if (comparehome && strcmp(homedir, buf) == 0) {
 463                         debug3("secure_filename: terminating check at '%s'",
 464                             buf);
 465                         break;
 466                 }
 467                 /*
 468                  * dirname should always complete with a "/" path,
 469                  * but we can be paranoid and check for "." too
 470                  */
 471                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 472                         break;
 473         }
 474         return 0;
 475 }
 476
 477 struct passwd *
 478 getpwnamallow(const char *user)
 479 {
 480 #ifdef HAVE_LOGIN_CAP
 481         extern login_cap_t *lc;
 482 #ifdef BSD_AUTH
 483         auth_session_t *as;
 484 #endif
 485 #endif
 486         struct passwd *pw;
 487
 488         pw = getpwnam(user);
 489         if (pw == NULL) {
 490                 logit("Invalid user %.100s from %.100s",
 491                     user, get_remote_ipaddr());
 492 #ifdef CUSTOM_FAILED_LOGIN
 493                 record_failed_login(user,
 494                     get_canonical_hostname(options.use_dns), "ssh");
 495 #endif
 496 #ifdef SSH_AUDIT_EVENTS
 497                 audit_event(SSH_INVALID_USER);
 498 #endif /* SSH_AUDIT_EVENTS */
 499                 return (NULL);
 500         }
 501         if (!allowed_user(pw))
 502                 return (NULL);
 503 #ifdef HAVE_LOGIN_CAP
 504         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 505                 debug("unable to get login class: %s", user);
 506                 return (NULL);
 507         }
 508 #ifdef BSD_AUTH
 509         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 510             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 511                 debug("Approval failure for %s", user);
 512                 pw = NULL;
 513         }
 514         if (as != NULL)
 515                 auth_close(as);
 516 #endif
 517 #endif
 518         if (pw != NULL)
 519                 return (pwcopy(pw));
 520         return (NULL);
 521 }
 522
 523 void
 524 auth_debug_add(const char *fmt,...)
 525 {
 526         char buf[1024];
 527         va_list args;
 528
 529         if (!auth_debug_init)
 530                 return;
 531
 532         va_start(args, fmt);
 533         vsnprintf(buf, sizeof(buf), fmt, args);
 534         va_end(args);
 535         buffer_put_cstring(&auth_debug, buf);
 536 }
 537
 538 void
 539 auth_debug_send(void)
 540 {
 541         char *msg;
 542
 543         if (!auth_debug_init)
 544                 return;
 545         while (buffer_len(&auth_debug)) {
 546                 msg = buffer_get_string(&auth_debug, NULL);
 547                 packet_send_debug("%s", msg);
 548                 xfree(msg);
 549         }
 550 }
 551
 552 void
 553 auth_debug_reset(void)
 554 {
 555         if (auth_debug_init)
 556                 buffer_clear(&auth_debug);
 557         else {
 558                 buffer_init(&auth_debug);
 559                 auth_debug_init = 1;
 560         }
 561 }
 562
 563 struct passwd *
 564 fakepw(void)
 565 {
 566         static struct passwd fake;
 567
 568         memset(&fake, 0, sizeof(fake));
 569         fake.pw_name = "NOUSER";
 570         fake.pw_passwd =
 571             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 572         fake.pw_gecos = "NOUSER";
 573         fake.pw_uid = (uid_t)-1;
 574         fake.pw_gid = (gid_t)-1;
 575 #ifdef HAVE_PW_CLASS_IN_PASSWD
 576         fake.pw_class = "";
 577 #endif
 578         fake.pw_dir = "/nonexist";
 579         fake.pw_shell = "/nonexist";
 580
 581         return (&fake);
 582 }