nscd/selinux.c

   1 /* SELinux access controls for nscd.
   2    Copyright (C) 2004, 2005, 2006 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 };
  68
  69 /* Store an entry ref to speed AVC decisions.  */
  70 static struct avc_entry_ref aeref;
  71
  72 /* Thread to listen for SELinux status changes via netlink.  */
  73 static pthread_t avc_notify_thread;
  74
  75 #ifdef HAVE_LIBAUDIT
  76 /* Prototype for supporting the audit daemon */
  77 static void log_callback (const char *fmt, ...);
  78 #endif
  79
  80 /* Prototypes for AVC callback functions.  */
  81 static void *avc_create_thread (void (*run) (void));
  82 static void avc_stop_thread (void *thread);
  83 static void *avc_alloc_lock (void);
  84 static void avc_get_lock (void *lock);
  85 static void avc_release_lock (void *lock);
  86 static void avc_free_lock (void *lock);
  87
  88 /* AVC callback structures for use in avc_init.  */
  89 static const struct avc_log_callback log_cb =
  90 {
  91 #ifdef HAVE_LIBAUDIT
  92   .func_log = log_callback,
  93 #else
  94   .func_log = dbg_log,
  95 #endif
  96   .func_audit = NULL
  97 };
  98 static const struct avc_thread_callback thread_cb =
  99 {
 100   .func_create_thread = avc_create_thread,
 101   .func_stop_thread = avc_stop_thread
 102 };
 103 static const struct avc_lock_callback lock_cb =
 104 {
 105   .func_alloc_lock = avc_alloc_lock,
 106   .func_get_lock = avc_get_lock,
 107   .func_release_lock = avc_release_lock,
 108   .func_free_lock = avc_free_lock
 109 };
 110
 111 #ifdef HAVE_LIBAUDIT
 112 /* The audit system's netlink socket descriptor */
 113 static int audit_fd = -1;
 114
 115 /* When an avc denial occurs, log it to audit system */
 116 static void
 117 log_callback (const char *fmt, ...)
 118 {
 119   if (audit_fd >= 0)
 120     {
 121       va_list ap;
 122       va_start (ap, fmt);
 123
 124       char *buf;
 125       int e = vasprintf (&buf, fmt, ap);
 126       if (e < 0)
 127         {
 128           buf = alloca (BUFSIZ);
 129           vsnprintf (buf, BUFSIZ, fmt, ap);
 130         }
 131
 132       /* FIXME: need to attribute this to real user, using getuid for now */
 133       audit_log_user_avc_message (audit_fd, AUDIT_USER_AVC, buf, NULL, NULL,
 134                                   NULL, getuid ());
 135
 136       if (e >= 0)
 137         free (buf);
 138
 139       va_end (ap);
 140     }
 141 }
 142
 143 /* Initialize the connection to the audit system */
 144 static void
 145 audit_init (void)
 146 {
 147   audit_fd = audit_open ();
 148   if (audit_fd < 0
 149       /* If kernel doesn't support audit, bail out */
 150       && errno != EINVAL && errno != EPROTONOSUPPORT && errno != EAFNOSUPPORT)
 151     dbg_log (_("Failed opening connection to the audit subsystem: %m"));
 152 }
 153
 154
 155 # ifdef HAVE_LIBCAP
 156 static const cap_value_t new_cap_list[] =
 157   { CAP_AUDIT_WRITE };
 158 #  define nnew_cap_list (sizeof (new_cap_list) / sizeof (new_cap_list[0]))
 159 static const cap_value_t tmp_cap_list[] =
 160   { CAP_AUDIT_WRITE, CAP_SETUID, CAP_SETGID };
 161 #  define ntmp_cap_list (sizeof (tmp_cap_list) / sizeof (tmp_cap_list[0]))
 162
 163 cap_t
 164 preserve_capabilities (void)
 165 {
 166   if (getuid () != 0)
 167     /* Not root, then we cannot preserve anything.  */
 168     return NULL;
 169
 170   if (prctl (PR_SET_KEEPCAPS, 1) == -1)
 171     {
 172       dbg_log (_("Failed to set keep-capabilities"));
 173       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 174       /* NOTREACHED */
 175     }
 176
 177   cap_t tmp_caps = cap_init ();
 178   cap_t new_caps;
 179   if (tmp_caps != NULL)
 180     new_caps = cap_init ();
 181
 182   if (tmp_caps == NULL || new_caps == NULL)
 183     {
 184       if (tmp_caps != NULL)
 185         free_caps (tmp_caps);
 186
 187       dbg_log (_("Failed to initialize drop of capabilities"));
 188       error (EXIT_FAILURE, 0, _("cap_init failed"));
 189     }
 190
 191   /* There is no reason why these should not work.  */
 192   cap_set_flag (new_caps, CAP_PERMITTED, nnew_cap_list, new_cap_list, CAP_SET);
 193   cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list, new_cap_list, CAP_SET);
 194
 195   cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list, tmp_cap_list, CAP_SET);
 196   cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list, tmp_cap_list, CAP_SET);
 197
 198   int res = cap_set_proc (tmp_caps);
 199
 200   cap_free (tmp_caps);
 201
 202   if (__builtin_expect (res != 0, 0))
 203     {
 204       cap_free (new_caps);
 205       dbg_log (_("Failed to drop capabilities\n"));
 206       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 207     }
 208
 209   return new_caps;
 210 }
 211
 212 void
 213 install_real_capabilities (cap_t new_caps)
 214 {
 215   /* If we have no capabilities there is nothing to do here.  */
 216   if (new_caps == NULL)
 217     return;
 218
 219   if (cap_set_proc (new_caps))
 220     {
 221       cap_free (new_caps);
 222       dbg_log (_("Failed to drop capabilities"));
 223       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 224       /* NOTREACHED */
 225     }
 226
 227   cap_free (new_caps);
 228
 229   if (prctl (PR_SET_KEEPCAPS, 0) == -1)
 230     {
 231       dbg_log (_("Failed to unset keep-capabilities"));
 232       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 233       /* NOTREACHED */
 234     }
 235 }
 236 # endif /* HAVE_LIBCAP */
 237 #endif /* HAVE_LIBAUDIT */
 238
 239 /* Determine if we are running on an SELinux kernel. Set selinux_enabled
 240    to the result.  */
 241 void
 242 nscd_selinux_enabled (int *selinux_enabled)
 243 {
 244   *selinux_enabled = is_selinux_enabled ();
 245   if (*selinux_enabled < 0)
 246     {
 247       dbg_log (_("Failed to determine if kernel supports SELinux"));
 248       exit (EXIT_FAILURE);
 249     }
 250 }
 251
 252
 253 /* Create thread for AVC netlink notification.  */
 254 static void *
 255 avc_create_thread (void (*run) (void))
 256 {
 257   int rc;
 258
 259   rc =
 260     pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
 261   if (rc != 0)
 262     error (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
 263
 264   return &avc_notify_thread;
 265 }
 266
 267
 268 /* Stop AVC netlink thread.  */
 269 static void
 270 avc_stop_thread (void *thread)
 271 {
 272   pthread_cancel (*(pthread_t *) thread);
 273 }
 274
 275
 276 /* Allocate a new AVC lock.  */
 277 static void *
 278 avc_alloc_lock (void)
 279 {
 280   pthread_mutex_t *avc_mutex;
 281
 282   avc_mutex = malloc (sizeof (pthread_mutex_t));
 283   if (avc_mutex == NULL)
 284     error (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
 285   pthread_mutex_init (avc_mutex, NULL);
 286
 287   return avc_mutex;
 288 }
 289
 290
 291 /* Acquire an AVC lock.  */
 292 static void
 293 avc_get_lock (void *lock)
 294 {
 295   pthread_mutex_lock (lock);
 296 }
 297
 298
 299 /* Release an AVC lock.  */
 300 static void
 301 avc_release_lock (void *lock)
 302 {
 303   pthread_mutex_unlock (lock);
 304 }
 305
 306
 307 /* Free an AVC lock.  */
 308 static void
 309 avc_free_lock (void *lock)
 310 {
 311   pthread_mutex_destroy (lock);
 312   free (lock);
 313 }
 314
 315
 316 /* Initialize the user space access vector cache (AVC) for NSCD along with
 317    log/thread/lock callbacks.  */
 318 void
 319 nscd_avc_init (void)
 320 {
 321   avc_entry_ref_init (&aeref);
 322
 323   if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
 324     error (EXIT_FAILURE, errno, _("Failed to start AVC"));
 325   else
 326     dbg_log (_("Access Vector Cache (AVC) started"));
 327 #ifdef HAVE_LIBAUDIT
 328   audit_init ();
 329 #endif
 330 }
 331
 332
 333 /* Check the permission from the caller (via getpeercon) to nscd.
 334    Returns 0 if access is allowed, 1 if denied, and -1 on error.  */
 335 int
 336 nscd_request_avc_has_perm (int fd, request_type req)
 337 {
 338   /* Initialize to NULL so we know what to free in case of failure.  */
 339   security_context_t scon = NULL;
 340   security_context_t tcon = NULL;
 341   security_id_t ssid = NULL;
 342   security_id_t tsid = NULL;
 343   int rc = -1;
 344
 345   if (getpeercon (fd, &scon) < 0)
 346     {
 347       dbg_log (_("Error getting context of socket peer"));
 348       goto out;
 349     }
 350   if (getcon (&tcon) < 0)
 351     {
 352       dbg_log (_("Error getting context of nscd"));
 353       goto out;
 354     }
 355   if (avc_context_to_sid (scon, &ssid) < 0
 356       || avc_context_to_sid (tcon, &tsid) < 0)
 357     {
 358       dbg_log (_("Error getting sid from context"));
 359       goto out;
 360     }
 361
 362   rc = avc_has_perm (ssid, tsid, SECCLASS_NSCD, perms[req], &aeref, NULL) < 0;
 363
 364 out:
 365   if (scon)
 366     freecon (scon);
 367   if (tcon)
 368     freecon (tcon);
 369   if (ssid)
 370     sidput (ssid);
 371   if (tsid)
 372     sidput (tsid);
 373
 374   return rc;
 375 }
 376
 377
 378 /* Wrapper to get AVC statistics.  */
 379 void
 380 nscd_avc_cache_stats (struct avc_cache_stats *cstats)
 381 {
 382   avc_cache_stats (cstats);
 383 }
 384
 385
 386 /* Print the AVC statistics to stdout.  */
 387 void
 388 nscd_avc_print_stats (struct avc_cache_stats *cstats)
 389 {
 390   printf (_("\nSELinux AVC Statistics:\n\n"
 391             "%15u  entry lookups\n"
 392             "%15u  entry hits\n"
 393             "%15u  entry misses\n"
 394             "%15u  entry discards\n"
 395             "%15u  CAV lookups\n"
 396             "%15u  CAV hits\n"
 397             "%15u  CAV probes\n"
 398             "%15u  CAV misses\n"),
 399           cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
 400           cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
 401           cstats->cav_probes, cstats->cav_misses);
 402 }
 403
 404
 405 /* Clean up the AVC before exiting.  */
 406 void
 407 nscd_avc_destroy (void)
 408 {
 409   avc_destroy ();
 410 #ifdef HAVE_LIBAUDIT
 411   audit_close (audit_fd);
 412 #endif
 413 }
 414
 415 #endif /* HAVE_SELINUX */