crypto/openssh-4/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 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 101                 passwd = get_iaf_password(pw);
 102 #else
 103                 passwd = spw->sp_pwdp;
 104 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 105 #else
 106         passwd = pw->pw_passwd;
 107 #endif
 108
 109         /* check for locked account */
 110         if (!options.use_pam && passwd && *passwd) {
 111                 int locked = 0;
 112
 113 #ifdef LOCKED_PASSWD_STRING
 114                 if (strcmp(passwd, LOCKED_PASSWD_STRING) == 0)
 115                          locked = 1;
 116 #endif
 117 #ifdef LOCKED_PASSWD_PREFIX
 118                 if (strncmp(passwd, LOCKED_PASSWD_PREFIX,
 119                     strlen(LOCKED_PASSWD_PREFIX)) == 0)
 120                          locked = 1;
 121 #endif
 122 #ifdef LOCKED_PASSWD_SUBSTR
 123                 if (strstr(passwd, LOCKED_PASSWD_SUBSTR))
 124                         locked = 1;
 125 #endif
 126 #if defined(HAVE_LIBIAF)  &&  !defined(BROKEN_LIBIAF)
 127                 free(passwd);
 128 #endif /* HAVE_LIBIAF  && !BROKEN_LIBIAF */
 129                 if (locked) {
 130                         logit("User %.100s not allowed because account is locked",
 131                             pw->pw_name);
 132                         return 0;
 133                 }
 134         }
 135
 136         /*
 137          * Get the shell from the password data.  An empty shell field is
 138          * legal, and means /bin/sh.
 139          */
 140         shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;
 141
 142         /* deny if shell does not exists or is not executable */
 143         if (stat(shell, &st) != 0) {
 144                 logit("User %.100s not allowed because shell %.100s does not exist",
 145                     pw->pw_name, shell);
 146                 return 0;
 147         }
 148         if (S_ISREG(st.st_mode) == 0 ||
 149             (st.st_mode & (S_IXOTH|S_IXUSR|S_IXGRP)) == 0) {
 150                 logit("User %.100s not allowed because shell %.100s is not executable",
 151                     pw->pw_name, shell);
 152                 return 0;
 153         }
 154
 155         if (options.num_deny_users > 0 || options.num_allow_users > 0 ||
 156             options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 157                 hostname = get_canonical_hostname(options.use_dns);
 158                 ipaddr = get_remote_ipaddr();
 159         }
 160
 161         /* Return false if user is listed in DenyUsers */
 162         if (options.num_deny_users > 0) {
 163                 for (i = 0; i < options.num_deny_users; i++)
 164                         if (match_user(pw->pw_name, hostname, ipaddr,
 165                             options.deny_users[i])) {
 166                                 logit("User %.100s from %.100s not allowed "
 167                                     "because listed in DenyUsers",
 168                                     pw->pw_name, hostname);
 169                                 return 0;
 170                         }
 171         }
 172         /* Return false if AllowUsers isn't empty and user isn't listed there */
 173         if (options.num_allow_users > 0) {
 174                 for (i = 0; i < options.num_allow_users; i++)
 175                         if (match_user(pw->pw_name, hostname, ipaddr,
 176                             options.allow_users[i]))
 177                                 break;
 178                 /* i < options.num_allow_users iff we break for loop */
 179                 if (i >= options.num_allow_users) {
 180                         logit("User %.100s from %.100s not allowed because "
 181                             "not listed in AllowUsers", pw->pw_name, hostname);
 182                         return 0;
 183                 }
 184         }
 185         if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
 186                 /* Get the user's group access list (primary and supplementary) */
 187                 if (ga_init(pw->pw_name, pw->pw_gid) == 0) {
 188                         logit("User %.100s from %.100s not allowed because "
 189                             "not in any group", pw->pw_name, hostname);
 190                         return 0;
 191                 }
 192
 193                 /* Return false if one of user's groups is listed in DenyGroups */
 194                 if (options.num_deny_groups > 0)
 195                         if (ga_match(options.deny_groups,
 196                             options.num_deny_groups)) {
 197                                 ga_free();
 198                                 logit("User %.100s from %.100s not allowed "
 199                                     "because a group is listed in DenyGroups",
 200                                     pw->pw_name, hostname);
 201                                 return 0;
 202                         }
 203                 /*
 204                  * Return false if AllowGroups isn't empty and one of user's groups
 205                  * isn't listed there
 206                  */
 207                 if (options.num_allow_groups > 0)
 208                         if (!ga_match(options.allow_groups,
 209                             options.num_allow_groups)) {
 210                                 ga_free();
 211                                 logit("User %.100s from %.100s not allowed "
 212                                     "because none of user's groups are listed "
 213                                     "in AllowGroups", pw->pw_name, hostname);
 214                                 return 0;
 215                         }
 216                 ga_free();
 217         }
 218
 219 #ifdef CUSTOM_SYS_AUTH_ALLOWED_USER
 220         if (!sys_auth_allowed_user(pw, &loginmsg))
 221                 return 0;
 222 #endif
 223
 224         /* We found no reason not to let this user try to log on... */
 225         return 1;
 226 }
 227
 228 void
 229 auth_log(Authctxt *authctxt, int authenticated, char *method, char *info)
 230 {
 231         void (*authlog) (const char *fmt,...) = verbose;
 232         char *authmsg;
 233
 234         /* Raise logging level */
 235         if (authenticated == 1 ||
 236             !authctxt->valid ||
 237             authctxt->failures >= options.max_authtries / 2 ||
 238             strcmp(method, "password") == 0)
 239                 authlog = logit;
 240
 241         if (authctxt->postponed)
 242                 authmsg = "Postponed";
 243         else
 244                 authmsg = authenticated ? "Accepted" : "Failed";
 245
 246         authlog("%s %s for %s%.100s from %.200s port %d%s",
 247             authmsg,
 248             method,
 249             authctxt->valid ? "" : "invalid user ",
 250             authctxt->user,
 251             get_remote_ipaddr(),
 252             get_remote_port(),
 253             info);
 254
 255 #ifdef CUSTOM_FAILED_LOGIN
 256         if (authenticated == 0 && !authctxt->postponed &&
 257             (strcmp(method, "password") == 0 ||
 258             strncmp(method, "keyboard-interactive", 20) == 0 ||
 259             strcmp(method, "challenge-response") == 0))
 260                 record_failed_login(authctxt->user,
 261                     get_canonical_hostname(options.use_dns), "ssh");
 262 #endif
 263 #ifdef SSH_AUDIT_EVENTS
 264         if (authenticated == 0 && !authctxt->postponed) {
 265                 ssh_audit_event_t event;
 266
 267                 debug3("audit failed auth attempt, method %s euid %d",
 268                     method, (int)geteuid());
 269                 /*
 270                  * Because the auth loop is used in both monitor and slave,
 271                  * we must be careful to send each event only once and with
 272                  * enough privs to write the event.
 273                  */
 274                 event = audit_classify_auth(method);
 275                 switch(event) {
 276                 case SSH_AUTH_FAIL_NONE:
 277                 case SSH_AUTH_FAIL_PASSWD:
 278                 case SSH_AUTH_FAIL_KBDINT:
 279                         if (geteuid() == 0)
 280                                 audit_event(event);
 281                         break;
 282                 case SSH_AUTH_FAIL_PUBKEY:
 283                 case SSH_AUTH_FAIL_HOSTBASED:
 284                 case SSH_AUTH_FAIL_GSSAPI:
 285                         /*
 286                          * This is required to handle the case where privsep
 287                          * is enabled but it's root logging in, since
 288                          * use_privsep won't be cleared until after a
 289                          * successful login.
 290                          */
 291                         if (geteuid() == 0)
 292                                 audit_event(event);
 293                         else
 294                                 PRIVSEP(audit_event(event));
 295                         break;
 296                 default:
 297                         error("unknown authentication audit event %d", event);
 298                 }
 299         }
 300 #endif
 301 }
 302
 303 /*
 304  * Check whether root logins are disallowed.
 305  */
 306 int
 307 auth_root_allowed(char *method)
 308 {
 309         switch (options.permit_root_login) {
 310         case PERMIT_YES:
 311                 return 1;
 312                 break;
 313         case PERMIT_NO_PASSWD:
 314                 if (strcmp(method, "password") != 0)
 315                         return 1;
 316                 break;
 317         case PERMIT_FORCED_ONLY:
 318                 if (forced_command) {
 319                         logit("Root login accepted for forced command.");
 320                         return 1;
 321                 }
 322                 break;
 323         }
 324         logit("ROOT LOGIN REFUSED FROM %.200s", get_remote_ipaddr());
 325         return 0;
 326 }
 327
 328
 329 /*
 330  * Given a template and a passwd structure, build a filename
 331  * by substituting % tokenised options. Currently, %% becomes '%',
 332  * %h becomes the home directory and %u the username.
 333  *
 334  * This returns a buffer allocated by xmalloc.
 335  */
 336 static char *
 337 expand_authorized_keys(const char *filename, struct passwd *pw)
 338 {
 339         char *file, *ret;
 340
 341         file = percent_expand(filename, "h", pw->pw_dir,
 342             "u", pw->pw_name, (char *)NULL);
 343
 344         /*
 345          * Ensure that filename starts anchored. If not, be backward
 346          * compatible and prepend the '%h/'
 347          */
 348         if (*file == '/')
 349                 return (file);
 350
 351         ret = xmalloc(MAXPATHLEN);
 352         if (strlcpy(ret, pw->pw_dir, MAXPATHLEN) >= MAXPATHLEN ||
 353             strlcat(ret, "/", MAXPATHLEN) >= MAXPATHLEN ||
 354             strlcat(ret, file, MAXPATHLEN) >= MAXPATHLEN)
 355                 fatal("expand_authorized_keys: path too long");
 356
 357         xfree(file);
 358         return (ret);
 359 }
 360
 361 char *
 362 authorized_keys_file(struct passwd *pw)
 363 {
 364         return expand_authorized_keys(options.authorized_keys_file, pw);
 365 }
 366
 367 char *
 368 authorized_keys_file2(struct passwd *pw)
 369 {
 370         return expand_authorized_keys(options.authorized_keys_file2, pw);
 371 }
 372
 373 /* return ok if key exists in sysfile or userfile */
 374 HostStatus
 375 check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
 376     const char *sysfile, const char *userfile)
 377 {
 378         Key *found;
 379         char *user_hostfile;
 380         struct stat st;
 381         HostStatus host_status;
 382
 383         /* Check if we know the host and its host key. */
 384         found = key_new(key->type);
 385         host_status = check_host_in_hostfile(sysfile, host, key, found, NULL);
 386
 387         if (host_status != HOST_OK && userfile != NULL) {
 388                 user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
 389                 if (options.strict_modes &&
 390                     (stat(user_hostfile, &st) == 0) &&
 391                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 392                     (st.st_mode & 022) != 0)) {
 393                         logit("Authentication refused for %.100s: "
 394                             "bad owner or modes for %.200s",
 395                             pw->pw_name, user_hostfile);
 396                 } else {
 397                         temporarily_use_uid(pw);
 398                         host_status = check_host_in_hostfile(user_hostfile,
 399                             host, key, found, NULL);
 400                         restore_uid();
 401                 }
 402                 xfree(user_hostfile);
 403         }
 404         key_free(found);
 405
 406         debug2("check_key_in_hostfiles: key %s for %s", host_status == HOST_OK ?
 407             "ok" : "not found", host);
 408         return host_status;
 409 }
 410
 411
 412 /*
 413  * Check a given file for security. This is defined as all components
 414  * of the path to the file must be owned by either the owner of
 415  * of the file or root and no directories must be group or world writable.
 416  *
 417  * XXX Should any specific check be done for sym links ?
 418  *
 419  * Takes an open file descriptor, the file name, a uid and and
 420  * error buffer plus max size as arguments.
 421  *
 422  * Returns 0 on success and -1 on failure
 423  */
 424 int
 425 secure_filename(FILE *f, const char *file, struct passwd *pw,
 426     char *err, size_t errlen)
 427 {
 428         uid_t uid = pw->pw_uid;
 429         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
 430         char *cp;
 431         int comparehome = 0;
 432         struct stat st;
 433
 434         if (realpath(file, buf) == NULL) {
 435                 snprintf(err, errlen, "realpath %s failed: %s", file,
 436                     strerror(errno));
 437                 return -1;
 438         }
 439         if (realpath(pw->pw_dir, homedir) != NULL)
 440                 comparehome = 1;
 441
 442         /* check the open file to avoid races */
 443         if (fstat(fileno(f), &st) < 0 ||
 444             (st.st_uid != 0 && st.st_uid != uid) ||
 445             (st.st_mode & 022) != 0) {
 446                 snprintf(err, errlen, "bad ownership or modes for file %s",
 447                     buf);
 448                 return -1;
 449         }
 450
 451         /* for each component of the canonical path, walking upwards */
 452         for (;;) {
 453                 if ((cp = dirname(buf)) == NULL) {
 454                         snprintf(err, errlen, "dirname() failed");
 455                         return -1;
 456                 }
 457                 strlcpy(buf, cp, sizeof(buf));
 458
 459                 debug3("secure_filename: checking '%s'", buf);
 460                 if (stat(buf, &st) < 0 ||
 461                     (st.st_uid != 0 && st.st_uid != uid) ||
 462                     (st.st_mode & 022) != 0) {
 463                         snprintf(err, errlen,
 464                             "bad ownership or modes for directory %s", buf);
 465                         return -1;
 466                 }
 467
 468                 /* If are passed the homedir then we can stop */
 469                 if (comparehome && strcmp(homedir, buf) == 0) {
 470                         debug3("secure_filename: terminating check at '%s'",
 471                             buf);
 472                         break;
 473                 }
 474                 /*
 475                  * dirname should always complete with a "/" path,
 476                  * but we can be paranoid and check for "." too
 477                  */
 478                 if ((strcmp("/", buf) == 0) || (strcmp(".", buf) == 0))
 479                         break;
 480         }
 481         return 0;
 482 }
 483
 484 struct passwd *
 485 getpwnamallow(const char *user)
 486 {
 487 #ifdef HAVE_LOGIN_CAP
 488         extern login_cap_t *lc;
 489 #ifdef BSD_AUTH
 490         auth_session_t *as;
 491 #endif
 492 #endif
 493         struct passwd *pw;
 494
 495         pw = getpwnam(user);
 496         if (pw == NULL) {
 497                 logit("Invalid user %.100s from %.100s",
 498                     user, get_remote_ipaddr());
 499 #ifdef CUSTOM_FAILED_LOGIN
 500                 record_failed_login(user,
 501                     get_canonical_hostname(options.use_dns), "ssh");
 502 #endif
 503 #ifdef SSH_AUDIT_EVENTS
 504                 audit_event(SSH_INVALID_USER);
 505 #endif /* SSH_AUDIT_EVENTS */
 506                 return (NULL);
 507         }
 508         if (!allowed_user(pw))
 509                 return (NULL);
 510 #ifdef HAVE_LOGIN_CAP
 511         if ((lc = login_getclass(pw->pw_class)) == NULL) {
 512                 debug("unable to get login class: %s", user);
 513                 return (NULL);
 514         }
 515 #ifdef BSD_AUTH
 516         if ((as = auth_open()) == NULL || auth_setpwd(as, pw) != 0 ||
 517             auth_approval(as, lc, pw->pw_name, "ssh") <= 0) {
 518                 debug("Approval failure for %s", user);
 519                 pw = NULL;
 520         }
 521         if (as != NULL)
 522                 auth_close(as);
 523 #endif
 524 #endif
 525         if (pw != NULL)
 526                 return (pwcopy(pw));
 527         return (NULL);
 528 }
 529
 530 void
 531 auth_debug_add(const char *fmt,...)
 532 {
 533         char buf[1024];
 534         va_list args;
 535
 536         if (!auth_debug_init)
 537                 return;
 538
 539         va_start(args, fmt);
 540         vsnprintf(buf, sizeof(buf), fmt, args);
 541         va_end(args);
 542         buffer_put_cstring(&auth_debug, buf);
 543 }
 544
 545 void
 546 auth_debug_send(void)
 547 {
 548         char *msg;
 549
 550         if (!auth_debug_init)
 551                 return;
 552         while (buffer_len(&auth_debug)) {
 553                 msg = buffer_get_string(&auth_debug, NULL);
 554                 packet_send_debug("%s", msg);
 555                 xfree(msg);
 556         }
 557 }
 558
 559 void
 560 auth_debug_reset(void)
 561 {
 562         if (auth_debug_init)
 563                 buffer_clear(&auth_debug);
 564         else {
 565                 buffer_init(&auth_debug);
 566                 auth_debug_init = 1;
 567         }
 568 }
 569
 570 struct passwd *
 571 fakepw(void)
 572 {
 573         static struct passwd fake;
 574
 575         memset(&fake, 0, sizeof(fake));
 576         fake.pw_name = "NOUSER";
 577         fake.pw_passwd =
 578             "$2a$06$r3.juUaHZDlIbQaO2dS9FuYxL1W9M81R1Tc92PoSNmzvpEqLkLGrK";
 579         fake.pw_gecos = "NOUSER";
 580         fake.pw_uid = (uid_t)-1;
 581         fake.pw_gid = (gid_t)-1;
 582 #ifdef HAVE_PW_CLASS_IN_PASSWD
 583         fake.pw_class = "";
 584 #endif
 585         fake.pw_dir = "/nonexist";
 586         fake.pw_shell = "/nonexist";
 587
 588         return (&fake);
 589 }