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         free_caps (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, new_cap_list, CAP_SET);
 198   cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list, new_cap_list, CAP_SET);
 199
 200   cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list, tmp_cap_list, CAP_SET);
 201   cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list, tmp_cap_list, CAP_SET);
 202
 203   int res = cap_set_proc (tmp_caps);
 204
 205   cap_free (tmp_caps);
 206
 207   if (__builtin_expect (res != 0, 0))
 208     {
 209       cap_free (new_caps);
 210       dbg_log (_("Failed to drop capabilities"));
 211       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 212     }
 213
 214   return new_caps;
 215 }
 216
 217 void
 218 install_real_capabilities (cap_t new_caps)
 219 {
 220   /* If we have no capabilities there is nothing to do here.  */
 221   if (new_caps == NULL)
 222     return;
 223
 224   if (cap_set_proc (new_caps))
 225     {
 226       cap_free (new_caps);
 227       dbg_log (_("Failed to drop capabilities"));
 228       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 229       /* NOTREACHED */
 230     }
 231
 232   cap_free (new_caps);
 233
 234   if (prctl (PR_SET_KEEPCAPS, 0) == -1)
 235     {
 236       dbg_log (_("Failed to unset keep-capabilities"));
 237       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 238       /* NOTREACHED */
 239     }
 240 }
 241 # endif /* HAVE_LIBCAP */
 242 #endif /* HAVE_LIBAUDIT */
 243
 244 /* Determine if we are running on an SELinux kernel. Set selinux_enabled
 245    to the result.  */
 246 void
 247 nscd_selinux_enabled (int *selinux_enabled)
 248 {
 249   *selinux_enabled = is_selinux_enabled ();
 250   if (*selinux_enabled < 0)
 251     {
 252       dbg_log (_("Failed to determine if kernel supports SELinux"));
 253       exit (EXIT_FAILURE);
 254     }
 255 }
 256
 257
 258 /* Create thread for AVC netlink notification.  */
 259 static void *
 260 avc_create_thread (void (*run) (void))
 261 {
 262   int rc;
 263
 264   rc =
 265     pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
 266   if (rc != 0)
 267     error (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
 268
 269   return &avc_notify_thread;
 270 }
 271
 272
 273 /* Stop AVC netlink thread.  */
 274 static void
 275 avc_stop_thread (void *thread)
 276 {
 277   pthread_cancel (*(pthread_t *) thread);
 278 }
 279
 280
 281 /* Allocate a new AVC lock.  */
 282 static void *
 283 avc_alloc_lock (void)
 284 {
 285   pthread_mutex_t *avc_mutex;
 286
 287   avc_mutex = malloc (sizeof (pthread_mutex_t));
 288   if (avc_mutex == NULL)
 289     error (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
 290   pthread_mutex_init (avc_mutex, NULL);
 291
 292   return avc_mutex;
 293 }
 294
 295
 296 /* Acquire an AVC lock.  */
 297 static void
 298 avc_get_lock (void *lock)
 299 {
 300   pthread_mutex_lock (lock);
 301 }
 302
 303
 304 /* Release an AVC lock.  */
 305 static void
 306 avc_release_lock (void *lock)
 307 {
 308   pthread_mutex_unlock (lock);
 309 }
 310
 311
 312 /* Free an AVC lock.  */
 313 static void
 314 avc_free_lock (void *lock)
 315 {
 316   pthread_mutex_destroy (lock);
 317   free (lock);
 318 }
 319
 320
 321 /* Initialize the user space access vector cache (AVC) for NSCD along with
 322    log/thread/lock callbacks.  */
 323 void
 324 nscd_avc_init (void)
 325 {
 326   avc_entry_ref_init (&aeref);
 327
 328   if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
 329     error (EXIT_FAILURE, errno, _("Failed to start AVC"));
 330   else
 331     dbg_log (_("Access Vector Cache (AVC) started"));
 332 #ifdef HAVE_LIBAUDIT
 333   audit_init ();
 334 #endif
 335 }
 336
 337
 338 /* Check the permission from the caller (via getpeercon) to nscd.
 339    Returns 0 if access is allowed, 1 if denied, and -1 on error.  */
 340 int
 341 nscd_request_avc_has_perm (int fd, request_type req)
 342 {
 343   /* Initialize to NULL so we know what to free in case of failure.  */
 344   security_context_t scon = NULL;
 345   security_context_t tcon = NULL;
 346   security_id_t ssid = NULL;
 347   security_id_t tsid = NULL;
 348   int rc = -1;
 349
 350   if (getpeercon (fd, &scon) < 0)
 351     {
 352       dbg_log (_("Error getting context of socket peer"));
 353       goto out;
 354     }
 355   if (getcon (&tcon) < 0)
 356     {
 357       dbg_log (_("Error getting context of nscd"));
 358       goto out;
 359     }
 360   if (avc_context_to_sid (scon, &ssid) < 0
 361       || avc_context_to_sid (tcon, &tsid) < 0)
 362     {
 363       dbg_log (_("Error getting sid from context"));
 364       goto out;
 365     }
 366
 367   rc = avc_has_perm (ssid, tsid, SECCLASS_NSCD, perms[req], &aeref, NULL) < 0;
 368
 369 out:
 370   if (scon)
 371     freecon (scon);
 372   if (tcon)
 373     freecon (tcon);
 374   if (ssid)
 375     sidput (ssid);
 376   if (tsid)
 377     sidput (tsid);
 378
 379   return rc;
 380 }
 381
 382
 383 /* Wrapper to get AVC statistics.  */
 384 void
 385 nscd_avc_cache_stats (struct avc_cache_stats *cstats)
 386 {
 387   avc_cache_stats (cstats);
 388 }
 389
 390
 391 /* Print the AVC statistics to stdout.  */
 392 void
 393 nscd_avc_print_stats (struct avc_cache_stats *cstats)
 394 {
 395   printf (_("\nSELinux AVC Statistics:\n\n"
 396             "%15u  entry lookups\n"
 397             "%15u  entry hits\n"
 398             "%15u  entry misses\n"
 399             "%15u  entry discards\n"
 400             "%15u  CAV lookups\n"
 401             "%15u  CAV hits\n"
 402             "%15u  CAV probes\n"
 403             "%15u  CAV misses\n"),
 404           cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
 405           cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
 406           cstats->cav_probes, cstats->cav_misses);
 407 }
 408
 409
 410 /* Clean up the AVC before exiting.  */
 411 void
 412 nscd_avc_destroy (void)
 413 {
 414   avc_destroy ();
 415 #ifdef HAVE_LIBAUDIT
 416   audit_close (audit_fd);
 417 #endif
 418 }
 419
 420 #endif /* HAVE_SELINUX */