nscd/selinux.c

   1 /* SELinux access controls for nscd.
   2    Copyright (C) 2004, 2005, 2006, 2007 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 int 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 };
  73
  74 /* Store an entry ref to speed AVC decisions.  */
  75 static struct avc_entry_ref aeref;
  76
  77 /* Thread to listen for SELinux status changes via netlink.  */
  78 static pthread_t avc_notify_thread;
  79
  80 #ifdef HAVE_LIBAUDIT
  81 /* Prototype for supporting the audit daemon */
  82 static void log_callback (const char *fmt, ...);
  83 #endif
  84
  85 /* Prototypes for AVC callback functions.  */
  86 static void *avc_create_thread (void (*run) (void));
  87 static void avc_stop_thread (void *thread);
  88 static void *avc_alloc_lock (void);
  89 static void avc_get_lock (void *lock);
  90 static void avc_release_lock (void *lock);
  91 static void avc_free_lock (void *lock);
  92
  93 /* AVC callback structures for use in avc_init.  */
  94 static const struct avc_log_callback log_cb =
  95 {
  96 #ifdef HAVE_LIBAUDIT
  97   .func_log = log_callback,
  98 #else
  99   .func_log = dbg_log,
 100 #endif
 101   .func_audit = NULL
 102 };
 103 static const struct avc_thread_callback thread_cb =
 104 {
 105   .func_create_thread = avc_create_thread,
 106   .func_stop_thread = avc_stop_thread
 107 };
 108 static const struct avc_lock_callback lock_cb =
 109 {
 110   .func_alloc_lock = avc_alloc_lock,
 111   .func_get_lock = avc_get_lock,
 112   .func_release_lock = avc_release_lock,
 113   .func_free_lock = avc_free_lock
 114 };
 115
 116 #ifdef HAVE_LIBAUDIT
 117 /* The audit system's netlink socket descriptor */
 118 static int audit_fd = -1;
 119
 120 /* When an avc denial occurs, log it to audit system */
 121 static void
 122 log_callback (const char *fmt, ...)
 123 {
 124   if (audit_fd >= 0)
 125     {
 126       va_list ap;
 127       va_start (ap, fmt);
 128
 129       char *buf;
 130       int e = vasprintf (&buf, fmt, ap);
 131       if (e < 0)
 132         {
 133           buf = alloca (BUFSIZ);
 134           vsnprintf (buf, BUFSIZ, fmt, ap);
 135         }
 136
 137       /* FIXME: need to attribute this to real user, using getuid for now */
 138       audit_log_user_avc_message (audit_fd, AUDIT_USER_AVC, buf, NULL, NULL,
 139                                   NULL, getuid ());
 140
 141       if (e >= 0)
 142         free (buf);
 143
 144       va_end (ap);
 145     }
 146 }
 147
 148 /* Initialize the connection to the audit system */
 149 static void
 150 audit_init (void)
 151 {
 152   audit_fd = audit_open ();
 153   if (audit_fd < 0
 154       /* If kernel doesn't support audit, bail out */
 155       && errno != EINVAL && errno != EPROTONOSUPPORT && errno != EAFNOSUPPORT)
 156     dbg_log (_("Failed opening connection to the audit subsystem: %m"));
 157 }
 158
 159
 160 # ifdef HAVE_LIBCAP
 161 static const cap_value_t new_cap_list[] =
 162   { CAP_AUDIT_WRITE };
 163 #  define nnew_cap_list (sizeof (new_cap_list) / sizeof (new_cap_list[0]))
 164 static const cap_value_t tmp_cap_list[] =
 165   { CAP_AUDIT_WRITE, CAP_SETUID, CAP_SETGID };
 166 #  define ntmp_cap_list (sizeof (tmp_cap_list) / sizeof (tmp_cap_list[0]))
 167
 168 cap_t
 169 preserve_capabilities (void)
 170 {
 171   if (getuid () != 0)
 172     /* Not root, then we cannot preserve anything.  */
 173     return NULL;
 174
 175   if (prctl (PR_SET_KEEPCAPS, 1) == -1)
 176     {
 177       dbg_log (_("Failed to set keep-capabilities"));
 178       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 179       /* NOTREACHED */
 180     }
 181
 182   cap_t tmp_caps = cap_init ();
 183   cap_t new_caps;
 184   if (tmp_caps != NULL)
 185     new_caps = cap_init ();
 186
 187   if (tmp_caps == NULL || new_caps == NULL)
 188     {
 189       if (tmp_caps != NULL)
 190         cap_free (tmp_caps);
 191
 192       dbg_log (_("Failed to initialize drop of capabilities"));
 193       error (EXIT_FAILURE, 0, _("cap_init failed"));
 194     }
 195
 196   /* There is no reason why these should not work.  */
 197   cap_set_flag (new_caps, CAP_PERMITTED, nnew_cap_list,
 198                 (cap_value_t *) new_cap_list, CAP_SET);
 199   cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list,
 200                 (cap_value_t *) new_cap_list, CAP_SET);
 201
 202   cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list,
 203                 (cap_value_t *) tmp_cap_list, CAP_SET);
 204   cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list,
 205                 (cap_value_t *) tmp_cap_list, CAP_SET);
 206
 207   int res = cap_set_proc (tmp_caps);
 208
 209   cap_free (tmp_caps);
 210
 211   if (__builtin_expect (res != 0, 0))
 212     {
 213       cap_free (new_caps);
 214       dbg_log (_("Failed to drop capabilities"));
 215       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 216     }
 217
 218   return new_caps;
 219 }
 220
 221 void
 222 install_real_capabilities (cap_t new_caps)
 223 {
 224   /* If we have no capabilities there is nothing to do here.  */
 225   if (new_caps == NULL)
 226     return;
 227
 228   if (cap_set_proc (new_caps))
 229     {
 230       cap_free (new_caps);
 231       dbg_log (_("Failed to drop capabilities"));
 232       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 233       /* NOTREACHED */
 234     }
 235
 236   cap_free (new_caps);
 237
 238   if (prctl (PR_SET_KEEPCAPS, 0) == -1)
 239     {
 240       dbg_log (_("Failed to unset keep-capabilities"));
 241       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 242       /* NOTREACHED */
 243     }
 244 }
 245 # endif /* HAVE_LIBCAP */
 246 #endif /* HAVE_LIBAUDIT */
 247
 248 /* Determine if we are running on an SELinux kernel. Set selinux_enabled
 249    to the result.  */
 250 void
 251 nscd_selinux_enabled (int *selinux_enabled)
 252 {
 253   *selinux_enabled = is_selinux_enabled ();
 254   if (*selinux_enabled < 0)
 255     {
 256       dbg_log (_("Failed to determine if kernel supports SELinux"));
 257       exit (EXIT_FAILURE);
 258     }
 259 }
 260
 261
 262 /* Create thread for AVC netlink notification.  */
 263 static void *
 264 avc_create_thread (void (*run) (void))
 265 {
 266   int rc;
 267
 268   rc =
 269     pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
 270   if (rc != 0)
 271     error (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
 272
 273   return &avc_notify_thread;
 274 }
 275
 276
 277 /* Stop AVC netlink thread.  */
 278 static void
 279 avc_stop_thread (void *thread)
 280 {
 281   pthread_cancel (*(pthread_t *) thread);
 282 }
 283
 284
 285 /* Allocate a new AVC lock.  */
 286 static void *
 287 avc_alloc_lock (void)
 288 {
 289   pthread_mutex_t *avc_mutex;
 290
 291   avc_mutex = malloc (sizeof (pthread_mutex_t));
 292   if (avc_mutex == NULL)
 293     error (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
 294   pthread_mutex_init (avc_mutex, NULL);
 295
 296   return avc_mutex;
 297 }
 298
 299
 300 /* Acquire an AVC lock.  */
 301 static void
 302 avc_get_lock (void *lock)
 303 {
 304   pthread_mutex_lock (lock);
 305 }
 306
 307
 308 /* Release an AVC lock.  */
 309 static void
 310 avc_release_lock (void *lock)
 311 {
 312   pthread_mutex_unlock (lock);
 313 }
 314
 315
 316 /* Free an AVC lock.  */
 317 static void
 318 avc_free_lock (void *lock)
 319 {
 320   pthread_mutex_destroy (lock);
 321   free (lock);
 322 }
 323
 324
 325 /* Initialize the user space access vector cache (AVC) for NSCD along with
 326    log/thread/lock callbacks.  */
 327 void
 328 nscd_avc_init (void)
 329 {
 330   avc_entry_ref_init (&aeref);
 331
 332   if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
 333     error (EXIT_FAILURE, errno, _("Failed to start AVC"));
 334   else
 335     dbg_log (_("Access Vector Cache (AVC) started"));
 336 #ifdef HAVE_LIBAUDIT
 337   audit_init ();
 338 #endif
 339 }
 340
 341
 342 /* Check the permission from the caller (via getpeercon) to nscd.
 343    Returns 0 if access is allowed, 1 if denied, and -1 on error.  */
 344 int
 345 nscd_request_avc_has_perm (int fd, request_type req)
 346 {
 347   /* Initialize to NULL so we know what to free in case of failure.  */
 348   security_context_t scon = NULL;
 349   security_context_t tcon = NULL;
 350   security_id_t ssid = NULL;
 351   security_id_t tsid = NULL;
 352   int rc = -1;
 353
 354   if (getpeercon (fd, &scon) < 0)
 355     {
 356       dbg_log (_("Error getting context of socket peer"));
 357       goto out;
 358     }
 359   if (getcon (&tcon) < 0)
 360     {
 361       dbg_log (_("Error getting context of nscd"));
 362       goto out;
 363     }
 364   if (avc_context_to_sid (scon, &ssid) < 0
 365       || avc_context_to_sid (tcon, &tsid) < 0)
 366     {
 367       dbg_log (_("Error getting sid from context"));
 368       goto out;
 369     }
 370
 371   rc = avc_has_perm (ssid, tsid, SECCLASS_NSCD, perms[req], &aeref, NULL) < 0;
 372
 373 out:
 374   if (scon)
 375     freecon (scon);
 376   if (tcon)
 377     freecon (tcon);
 378   if (ssid)
 379     sidput (ssid);
 380   if (tsid)
 381     sidput (tsid);
 382
 383   return rc;
 384 }
 385
 386
 387 /* Wrapper to get AVC statistics.  */
 388 void
 389 nscd_avc_cache_stats (struct avc_cache_stats *cstats)
 390 {
 391   avc_cache_stats (cstats);
 392 }
 393
 394
 395 /* Print the AVC statistics to stdout.  */
 396 void
 397 nscd_avc_print_stats (struct avc_cache_stats *cstats)
 398 {
 399   printf (_("\nSELinux AVC Statistics:\n\n"
 400             "%15u  entry lookups\n"
 401             "%15u  entry hits\n"
 402             "%15u  entry misses\n"
 403             "%15u  entry discards\n"
 404             "%15u  CAV lookups\n"
 405             "%15u  CAV hits\n"
 406             "%15u  CAV probes\n"
 407             "%15u  CAV misses\n"),
 408           cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
 409           cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
 410           cstats->cav_probes, cstats->cav_misses);
 411 }
 412
 413
 414 /* Clean up the AVC before exiting.  */
 415 void
 416 nscd_avc_destroy (void)
 417 {
 418   avc_destroy ();
 419 #ifdef HAVE_LIBAUDIT
 420   audit_close (audit_fd);
 421 #endif
 422 }
 423
 424 #endif /* HAVE_SELINUX */