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 };
  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         cap_free (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,
 193                 (cap_value_t *) new_cap_list, CAP_SET);
 194   cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list,
 195                 (cap_value_t *) new_cap_list, CAP_SET);
 196
 197   cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list,
 198                 (cap_value_t *) tmp_cap_list, CAP_SET);
 199   cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list,
 200                 (cap_value_t *) tmp_cap_list, CAP_SET);
 201
 202   int res = cap_set_proc (tmp_caps);
 203
 204   cap_free (tmp_caps);
 205
 206   if (__builtin_expect (res != 0, 0))
 207     {
 208       cap_free (new_caps);
 209       dbg_log (_("Failed to drop capabilities\n"));
 210       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 211     }
 212
 213   return new_caps;
 214 }
 215
 216 void
 217 install_real_capabilities (cap_t new_caps)
 218 {
 219   /* If we have no capabilities there is nothing to do here.  */
 220   if (new_caps == NULL)
 221     return;
 222
 223   if (cap_set_proc (new_caps))
 224     {
 225       cap_free (new_caps);
 226       dbg_log (_("Failed to drop capabilities"));
 227       error (EXIT_FAILURE, 0, _("cap_set_proc failed"));
 228       /* NOTREACHED */
 229     }
 230
 231   cap_free (new_caps);
 232
 233   if (prctl (PR_SET_KEEPCAPS, 0) == -1)
 234     {
 235       dbg_log (_("Failed to unset keep-capabilities"));
 236       error (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
 237       /* NOTREACHED */
 238     }
 239 }
 240 # endif /* HAVE_LIBCAP */
 241 #endif /* HAVE_LIBAUDIT */
 242
 243 /* Determine if we are running on an SELinux kernel. Set selinux_enabled
 244    to the result.  */
 245 void
 246 nscd_selinux_enabled (int *selinux_enabled)
 247 {
 248   *selinux_enabled = is_selinux_enabled ();
 249   if (*selinux_enabled < 0)
 250     {
 251       dbg_log (_("Failed to determine if kernel supports SELinux"));
 252       exit (EXIT_FAILURE);
 253     }
 254 }
 255
 256
 257 /* Create thread for AVC netlink notification.  */
 258 static void *
 259 avc_create_thread (void (*run) (void))
 260 {
 261   int rc;
 262
 263   rc =
 264     pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
 265   if (rc != 0)
 266     error (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
 267
 268   return &avc_notify_thread;
 269 }
 270
 271
 272 /* Stop AVC netlink thread.  */
 273 static void
 274 avc_stop_thread (void *thread)
 275 {
 276   pthread_cancel (*(pthread_t *) thread);
 277 }
 278
 279
 280 /* Allocate a new AVC lock.  */
 281 static void *
 282 avc_alloc_lock (void)
 283 {
 284   pthread_mutex_t *avc_mutex;
 285
 286   avc_mutex = malloc (sizeof (pthread_mutex_t));
 287   if (avc_mutex == NULL)
 288     error (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
 289   pthread_mutex_init (avc_mutex, NULL);
 290
 291   return avc_mutex;
 292 }
 293
 294
 295 /* Acquire an AVC lock.  */
 296 static void
 297 avc_get_lock (void *lock)
 298 {
 299   pthread_mutex_lock (lock);
 300 }
 301
 302
 303 /* Release an AVC lock.  */
 304 static void
 305 avc_release_lock (void *lock)
 306 {
 307   pthread_mutex_unlock (lock);
 308 }
 309
 310
 311 /* Free an AVC lock.  */
 312 static void
 313 avc_free_lock (void *lock)
 314 {
 315   pthread_mutex_destroy (lock);
 316   free (lock);
 317 }
 318
 319
 320 /* Initialize the user space access vector cache (AVC) for NSCD along with
 321    log/thread/lock callbacks.  */
 322 void
 323 nscd_avc_init (void)
 324 {
 325   avc_entry_ref_init (&aeref);
 326
 327   if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
 328     error (EXIT_FAILURE, errno, _("Failed to start AVC"));
 329   else
 330     dbg_log (_("Access Vector Cache (AVC) started"));
 331 #ifdef HAVE_LIBAUDIT
 332   audit_init ();
 333 #endif
 334 }
 335
 336
 337 /* Check the permission from the caller (via getpeercon) to nscd.
 338    Returns 0 if access is allowed, 1 if denied, and -1 on error.  */
 339 int
 340 nscd_request_avc_has_perm (int fd, request_type req)
 341 {
 342   /* Initialize to NULL so we know what to free in case of failure.  */
 343   security_context_t scon = NULL;
 344   security_context_t tcon = NULL;
 345   security_id_t ssid = NULL;
 346   security_id_t tsid = NULL;
 347   int rc = -1;
 348
 349   if (getpeercon (fd, &scon) < 0)
 350     {
 351       dbg_log (_("Error getting context of socket peer"));
 352       goto out;
 353     }
 354   if (getcon (&tcon) < 0)
 355     {
 356       dbg_log (_("Error getting context of nscd"));
 357       goto out;
 358     }
 359   if (avc_context_to_sid (scon, &ssid) < 0
 360       || avc_context_to_sid (tcon, &tsid) < 0)
 361     {
 362       dbg_log (_("Error getting sid from context"));
 363       goto out;
 364     }
 365
 366   rc = avc_has_perm (ssid, tsid, SECCLASS_NSCD, perms[req], &aeref, NULL) < 0;
 367
 368 out:
 369   if (scon)
 370     freecon (scon);
 371   if (tcon)
 372     freecon (tcon);
 373   if (ssid)
 374     sidput (ssid);
 375   if (tsid)
 376     sidput (tsid);
 377
 378   return rc;
 379 }
 380
 381
 382 /* Wrapper to get AVC statistics.  */
 383 void
 384 nscd_avc_cache_stats (struct avc_cache_stats *cstats)
 385 {
 386   avc_cache_stats (cstats);
 387 }
 388
 389
 390 /* Print the AVC statistics to stdout.  */
 391 void
 392 nscd_avc_print_stats (struct avc_cache_stats *cstats)
 393 {
 394   printf (_("\nSELinux AVC Statistics:\n\n"
 395             "%15u  entry lookups\n"
 396             "%15u  entry hits\n"
 397             "%15u  entry misses\n"
 398             "%15u  entry discards\n"
 399             "%15u  CAV lookups\n"
 400             "%15u  CAV hits\n"
 401             "%15u  CAV probes\n"
 402             "%15u  CAV misses\n"),
 403           cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
 404           cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
 405           cstats->cav_probes, cstats->cav_misses);
 406 }
 407
 408
 409 /* Clean up the AVC before exiting.  */
 410 void
 411 nscd_avc_destroy (void)
 412 {
 413   avc_destroy ();
 414 #ifdef HAVE_LIBAUDIT
 415   audit_close (audit_fd);
 416 #endif
 417 }
 418
 419 #endif /* HAVE_SELINUX */