nscd/selinux.c

   1 /* SELinux access controls for nscd.
   2    Copyright (C) 2004,2005,2006,2007,2009,2011 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Matthew Rickard <mjricka@epoch.ncsc.mil>, 2004.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include "config.h"
  22 #include <error.h>
  23 #include <errno.h>
  24 #include <libintl.h>
  25 #include <pthread.h>
  26 #include <stdarg.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <syslog.h>
  30 #include <unistd.h>
  31 #include <sys/prctl.h>
  32 #include <selinux/av_permissions.h>
  33 #include <selinux/avc.h>
  34 #include <selinux/flask.h>
  35 #include <selinux/selinux.h>
  36 #ifdef HAVE_LIBAUDIT
  37 # include <libaudit.h>
  38 #endif
  39
  40 #include "dbg_log.h"
  41 #include "selinux.h"
  42
  43
  44 #ifdef HAVE_SELINUX
  45 /* Global variable to tell if the kernel has SELinux support.  */
  46 int selinux_enabled;
  47
  48 /* Define mappings of access vector permissions to request types.  */
  49 static const access_vector_t perms[LASTREQ] =
  50 {
  51   [GETPWBYNAME] = NSCD__GETPWD,
  52   [GETPWBYUID] = NSCD__GETPWD,
  53   [GETGRBYNAME] = NSCD__GETGRP,
  54   [GETGRBYGID] = NSCD__GETGRP,
  55   [GETHOSTBYNAME] = NSCD__GETHOST,
  56   [GETHOSTBYNAMEv6] = NSCD__GETHOST,
  57   [GETHOSTBYADDR] = NSCD__GETHOST,
  58   [GETHOSTBYADDRv6] = NSCD__GETHOST,
  59   [GETSTAT] = NSCD__GETSTAT,
  60   [SHUTDOWN] = NSCD__ADMIN,
  61   [INVALIDATE] = NSCD__ADMIN,
  62   [GETFDPW] = NSCD__SHMEMPWD,
  63   [GETFDGR] = NSCD__SHMEMGRP,
  64   [GETFDHST] = NSCD__SHMEMHOST,
  65   [GETAI] = NSCD__GETHOST,
  66   [INITGROUPS] = NSCD__GETGRP,
  67 #ifdef NSCD__GETSERV
  68   [GETSERVBYNAME] = NSCD__GETSERV,
  69   [GETSERVBYPORT] = NSCD__GETSERV,
  70   [GETFDSERV] = NSCD__SHMEMSERV,
  71 #endif
  72 #ifdef NSCD__GETNETGRP
  73   [GETNETGRENT] = NSCD__GETNETGRP,
  74   [INNETGR] = NSCD__GETNETGRP,
  75   [GETFDNETGR] = NSCD__SHMEMNETGRP,
  76 #endif
  77 };
  78
  79 /* Store an entry ref to speed AVC decisions.  */
  80 static struct avc_entry_ref aeref;
  81
  82 /* Thread to listen for SELinux status changes via netlink.  */
  83 static pthread_t avc_notify_thread;
  84
  85 #ifdef HAVE_LIBAUDIT
  86 /* Prototype for supporting the audit daemon */
  87 static void log_callback (const char *fmt, ...);
  88 #endif
  89
  90 /* Prototypes for AVC callback functions.  */
  91 static void *avc_create_thread (void (*run) (void));
  92 static void avc_stop_thread (void *thread);
  93 static void *avc_alloc_lock (void);
  94 static void avc_get_lock (void *lock);
  95 static void avc_release_lock (void *lock);
  96 static void avc_free_lock (void *lock);
  97
  98 /* AVC callback structures for use in avc_init.  */
  99 static const struct avc_log_callback log_cb =
 100 {
 101 #ifdef HAVE_LIBAUDIT
 102   .func_log = log_callback,
 103 #else
 104   .func_log = dbg_log,
 105 #endif
 106   .func_audit = NULL
 107 };
 108 static const struct avc_thread_callback thread_cb =
 109 {
 110   .func_create_thread = avc_create_thread,
 111   .func_stop_thread = avc_stop_thread
 112 };
 113 static const struct avc_lock_callback lock_cb =
 114 {
 115   .func_alloc_lock = avc_alloc_lock,
 116   .func_get_lock = avc_get_lock,
 117   .func_release_lock = avc_release_lock,
 118   .func_free_lock = avc_free_lock
 119 };
 120
 121 #ifdef HAVE_LIBAUDIT
 122 /* The audit system's netlink socket descriptor */
 123 static int audit_fd = -1;
 124
 125 /* When an avc denial occurs, log it to audit system */
 126 static void
 127 log_callback (const char *fmt, ...)
 128 {
 129   if (audit_fd >= 0)
 130     {
 131       va_list ap;
 132       va_start (ap, fmt);
 133
 134       char *buf;
 135       int e = vasprintf (&buf, fmt, ap);
 136       if (e < 0)
 137         {
 138           buf = alloca (BUFSIZ);
 139           vsnprintf (buf, BUFSIZ, fmt, ap);
 140         }
 141
 142       /* FIXME: need to attribute this to real user, using getuid for now */
 143       audit_log_user_avc_message (audit_fd, AUDIT_USER_AVC, buf, NULL, NULL,
 144                                   NULL, getuid ());
 145
 146       if (e >= 0)
 147         free (buf);
 148
 149       va_end (ap);
 150     }
 151 }
 152
 153 /* Initialize the connection to the audit system */
 154 static void
 155 audit_init (void)
 156 {
 157   audit_fd = audit_open ();
 158   if (audit_fd < 0
 159       /* If kernel doesn't support audit, bail out */
 160       && errno != EINVAL && errno != EPROTONOSUPPORT && errno != EAFNOSUPPORT)
 161     dbg_log (_("Failed opening connection to the audit subsystem: %m"));
 162 }
 163
 164
 165 # ifdef HAVE_LIBCAP
 166 static const cap_value_t new_cap_list[] =
 167   { CAP_AUDIT_WRITE };
 168 #  define nnew_cap_list (sizeof (new_cap_list) / sizeof (new_cap_list[0]))
 169 static const cap_value_t tmp_cap_list[] =
 170   { CAP_AUDIT_WRITE, CAP_SETUID, CAP_SETGID };
 171 #  define ntmp_cap_list (sizeof (tmp_cap_list) / sizeof (tmp_cap_list[0]))
 172
 173 cap_t
 174 preserve_capabilities (void)
 175 {
 176   if (getuid () != 0)
 177     /* Not root, then we cannot preserve anything.  */
 178     return NULL;
 179
 180   if (prctl (PR_SET_KEEPCAPS, 1) == -1)
 181     {
 182       dbg_log (_("Failed to set keep-capabilities"));
 183       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 184       /* NOTREACHED */
 185     }
 186
 187   cap_t tmp_caps = cap_init ();
 188   cap_t new_caps = NULL;
 189   if (tmp_caps != NULL)
 190     new_caps = cap_init ();
 191
 192   if (tmp_caps == NULL || new_caps == NULL)
 193     {
 194       if (tmp_caps != NULL)
 195         cap_free (tmp_caps);
 196
 197       dbg_log (_("Failed to initialize drop of capabilities"));
 198       error (EXIT_FAILURE, 0, _("cap_init failed"));
 199     }
 200
 201   /* There is no reason why these should not work.  */
 202   cap_set_flag (new_caps, CAP_PERMITTED, nnew_cap_list,
 203                 (cap_value_t *) new_cap_list, CAP_SET);
 204   cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list,
 205                 (cap_value_t *) new_cap_list, CAP_SET);
 206
 207   cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list,
 208                 (cap_value_t *) tmp_cap_list, CAP_SET);
 209   cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list,
 210                 (cap_value_t *) tmp_cap_list, CAP_SET);
 211
 212   int res = cap_set_proc (tmp_caps);
 213
 214   cap_free (tmp_caps);
 215
 216   if (__builtin_expect (res != 0, 0))
 217     {
 218       cap_free (new_caps);
 219       dbg_log (_("Failed to drop capabilities"));
 220       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 221     }
 222
 223   return new_caps;
 224 }
 225
 226 void
 227 install_real_capabilities (cap_t new_caps)
 228 {
 229   /* If we have no capabilities there is nothing to do here.  */
 230   if (new_caps == NULL)
 231     return;
 232
 233   if (cap_set_proc (new_caps))
 234     {
 235       cap_free (new_caps);
 236       dbg_log (_("Failed to drop capabilities"));
 237       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 238       /* NOTREACHED */
 239     }
 240
 241   cap_free (new_caps);
 242
 243   if (prctl (PR_SET_KEEPCAPS, 0) == -1)
 244     {
 245       dbg_log (_("Failed to unset keep-capabilities"));
 246       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 247       /* NOTREACHED */
 248     }
 249 }
 250 # endif /* HAVE_LIBCAP */
 251 #endif /* HAVE_LIBAUDIT */
 252
 253 /* Determine if we are running on an SELinux kernel. Set selinux_enabled
 254    to the result.  */
 255 void
 256 nscd_selinux_enabled (int *selinux_enabled)
 257 {
 258   *selinux_enabled = is_selinux_enabled ();
 259   if (*selinux_enabled < 0)
 260     {
 261       dbg_log (_("Failed to determine if kernel supports SELinux"));
 262       exit (EXIT_FAILURE);
 263     }
 264 }
 265
 266
 267 /* Create thread for AVC netlink notification.  */
 268 static void *
 269 avc_create_thread (void (*run) (void))
 270 {
 271   int rc;
 272
 273   rc =
 274     pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
 275   if (rc != 0)
 276     error (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
 277
 278   return &avc_notify_thread;
 279 }
 280
 281
 282 /* Stop AVC netlink thread.  */
 283 static void
 284 avc_stop_thread (void *thread)
 285 {
 286   pthread_cancel (*(pthread_t *) thread);
 287 }
 288
 289
 290 /* Allocate a new AVC lock.  */
 291 static void *
 292 avc_alloc_lock (void)
 293 {
 294   pthread_mutex_t *avc_mutex;
 295
 296   avc_mutex = malloc (sizeof (pthread_mutex_t));
 297   if (avc_mutex == NULL)
 298     error (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
 299   pthread_mutex_init (avc_mutex, NULL);
 300
 301   return avc_mutex;
 302 }
 303
 304
 305 /* Acquire an AVC lock.  */
 306 static void
 307 avc_get_lock (void *lock)
 308 {
 309   pthread_mutex_lock (lock);
 310 }
 311
 312
 313 /* Release an AVC lock.  */
 314 static void
 315 avc_release_lock (void *lock)
 316 {
 317   pthread_mutex_unlock (lock);
 318 }
 319
 320
 321 /* Free an AVC lock.  */
 322 static void
 323 avc_free_lock (void *lock)
 324 {
 325   pthread_mutex_destroy (lock);
 326   free (lock);
 327 }
 328
 329
 330 /* Initialize the user space access vector cache (AVC) for NSCD along with
 331    log/thread/lock callbacks.  */
 332 void
 333 nscd_avc_init (void)
 334 {
 335   avc_entry_ref_init (&aeref);
 336
 337   if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
 338     error (EXIT_FAILURE, errno, _("Failed to start AVC"));
 339   else
 340     dbg_log (_("Access Vector Cache (AVC) started"));
 341 #ifdef HAVE_LIBAUDIT
 342   audit_init ();
 343 #endif
 344 }
 345
 346
 347 /* Check the permission from the caller (via getpeercon) to nscd.
 348    Returns 0 if access is allowed, 1 if denied, and -1 on error.  */
 349 int
 350 nscd_request_avc_has_perm (int fd, request_type req)
 351 {
 352   /* Initialize to NULL so we know what to free in case of failure.  */
 353   security_context_t scon = NULL;
 354   security_context_t tcon = NULL;
 355   security_id_t ssid = NULL;
 356   security_id_t tsid = NULL;
 357   int rc = -1;
 358
 359   if (getpeercon (fd, &scon) < 0)
 360     {
 361       dbg_log (_("Error getting context of socket peer"));
 362       goto out;
 363     }
 364   if (getcon (&tcon) < 0)
 365     {
 366       dbg_log (_("Error getting context of nscd"));
 367       goto out;
 368     }
 369   if (avc_context_to_sid (scon, &ssid) < 0
 370       || avc_context_to_sid (tcon, &tsid) < 0)
 371     {
 372       dbg_log (_("Error getting sid from context"));
 373       goto out;
 374     }
 375
 376 #ifndef NSCD__GETSERV
 377   if (perms[req] == 0)
 378     {
 379       dbg_log (_("compile-time support for database policy missing"));
 380       goto out;
 381     }
 382 #endif
 383
 384   rc = avc_has_perm (ssid, tsid, SECCLASS_NSCD, perms[req], &aeref, NULL) < 0;
 385
 386 out:
 387   if (scon)
 388     freecon (scon);
 389   if (tcon)
 390     freecon (tcon);
 391   if (ssid)
 392     sidput (ssid);
 393   if (tsid)
 394     sidput (tsid);
 395
 396   return rc;
 397 }
 398
 399
 400 /* Wrapper to get AVC statistics.  */
 401 void
 402 nscd_avc_cache_stats (struct avc_cache_stats *cstats)
 403 {
 404   avc_cache_stats (cstats);
 405 }
 406
 407
 408 /* Print the AVC statistics to stdout.  */
 409 void
 410 nscd_avc_print_stats (struct avc_cache_stats *cstats)
 411 {
 412   printf (_("\nSELinux AVC Statistics:\n\n"
 413             "%15u  entry lookups\n"
 414             "%15u  entry hits\n"
 415             "%15u  entry misses\n"
 416             "%15u  entry discards\n"
 417             "%15u  CAV lookups\n"
 418             "%15u  CAV hits\n"
 419             "%15u  CAV probes\n"
 420             "%15u  CAV misses\n"),
 421           cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
 422           cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
 423           cstats->cav_probes, cstats->cav_misses);
 424 }
 425
 426 #endif /* HAVE_SELINUX */