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