/* SELinux access controls for nscd.
Copyright (C) 2004-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Matthew Rickard <mjricka@epoch.ncsc.mil>, 2004.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include "config.h"
#include <error.h>
#include <errno.h>
#include <libintl.h>
#include <pthread.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <syslog.h>
#include <unistd.h>
#include <sys/prctl.h>
#include <selinux/avc.h>
#include <selinux/selinux.h>
#ifdef HAVE_LIBAUDIT
# include <libaudit.h>
#endif
#include "dbg_log.h"
#include "selinux.h"
#ifdef HAVE_SELINUX
/* Global variable to tell if the kernel has SELinux support. */
int selinux_enabled;
/* Define mappings of request type to AVC permission name. */
static const char *perms[LASTREQ] =
{
[GETPWBYNAME] = "getpwd",
[GETPWBYUID] = "getpwd",
[GETGRBYNAME] = "getgrp",
[GETGRBYGID] = "getgrp",
[GETHOSTBYNAME] = "gethost",
[GETHOSTBYNAMEv6] = "gethost",
[GETHOSTBYADDR] = "gethost",
[GETHOSTBYADDRv6] = "gethost",
[SHUTDOWN] = "admin",
[GETSTAT] = "getstat",
[INVALIDATE] = "admin",
[GETFDPW] = "shmempwd",
[GETFDGR] = "shmemgrp",
[GETFDHST] = "shmemhost",
[GETAI] = "gethost",
[INITGROUPS] = "getgrp",
[GETSERVBYNAME] = "getserv",
[GETSERVBYPORT] = "getserv",
[GETFDSERV] = "shmemserv",
[GETNETGRENT] = "getnetgrp",
[INNETGR] = "getnetgrp",
[GETFDNETGR] = "shmemnetgrp",
};
/* Store an entry ref to speed AVC decisions. */
static struct avc_entry_ref aeref;
/* Thread to listen for SELinux status changes via netlink. */
static pthread_t avc_notify_thread;
#ifdef HAVE_LIBAUDIT
/* Prototype for supporting the audit daemon */
static void log_callback (const char *fmt, ...);
#endif
/* Prototypes for AVC callback functions. */
static void *avc_create_thread (void (*run) (void));
static void avc_stop_thread (void *thread);
static void *avc_alloc_lock (void);
static void avc_get_lock (void *lock);
static void avc_release_lock (void *lock);
static void avc_free_lock (void *lock);
/* AVC callback structures for use in avc_init. */
static const struct avc_log_callback log_cb =
{
#ifdef HAVE_LIBAUDIT
.func_log = log_callback,
#else
.func_log = dbg_log,
#endif
.func_audit = NULL
};
static const struct avc_thread_callback thread_cb =
{
.func_create_thread = avc_create_thread,
.func_stop_thread = avc_stop_thread
};
static const struct avc_lock_callback lock_cb =
{
.func_alloc_lock = avc_alloc_lock,
.func_get_lock = avc_get_lock,
.func_release_lock = avc_release_lock,
.func_free_lock = avc_free_lock
};
#ifdef HAVE_LIBAUDIT
/* The audit system's netlink socket descriptor */
static int audit_fd = -1;
/* When an avc denial occurs, log it to audit system */
static void
log_callback (const char *fmt, ...)
{
if (audit_fd >= 0)
{
va_list ap;
va_start (ap, fmt);
char *buf;
int e = vasprintf (&buf, fmt, ap);
if (e < 0)
{
buf = alloca (BUFSIZ);
vsnprintf (buf, BUFSIZ, fmt, ap);
}
/* FIXME: need to attribute this to real user, using getuid for now */
audit_log_user_avc_message (audit_fd, AUDIT_USER_AVC, buf, NULL, NULL,
NULL, getuid ());
if (e >= 0)
free (buf);
va_end (ap);
}
}
/* Initialize the connection to the audit system */
static void
audit_init (void)
{
audit_fd = audit_open ();
if (audit_fd < 0
/* If kernel doesn't support audit, bail out */
&& errno != EINVAL && errno != EPROTONOSUPPORT && errno != EAFNOSUPPORT)
dbg_log (_("Failed opening connection to the audit subsystem: %m"));
}
# ifdef HAVE_LIBCAP
static const cap_value_t new_cap_list[] =
{ CAP_AUDIT_WRITE };
# define nnew_cap_list (sizeof (new_cap_list) / sizeof (new_cap_list[0]))
static const cap_value_t tmp_cap_list[] =
{ CAP_AUDIT_WRITE, CAP_SETUID, CAP_SETGID };
# define ntmp_cap_list (sizeof (tmp_cap_list) / sizeof (tmp_cap_list[0]))
cap_t
preserve_capabilities (void)
{
if (getuid () != 0)
/* Not root, then we cannot preserve anything. */
return NULL;
if (prctl (PR_SET_KEEPCAPS, 1) == -1)
{
dbg_log (_("Failed to set keep-capabilities"));
do_exit (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
/* NOTREACHED */
}
cap_t tmp_caps = cap_init ();
cap_t new_caps = NULL;
if (tmp_caps != NULL)
new_caps = cap_init ();
if (tmp_caps == NULL || new_caps == NULL)
{
if (tmp_caps != NULL)
cap_free (tmp_caps);
dbg_log (_("Failed to initialize drop of capabilities"));
do_exit (EXIT_FAILURE, 0, _("cap_init failed"));
}
/* There is no reason why these should not work. */
cap_set_flag (new_caps, CAP_PERMITTED, nnew_cap_list,
(cap_value_t *) new_cap_list, CAP_SET);
cap_set_flag (new_caps, CAP_EFFECTIVE, nnew_cap_list,
(cap_value_t *) new_cap_list, CAP_SET);
cap_set_flag (tmp_caps, CAP_PERMITTED, ntmp_cap_list,
(cap_value_t *) tmp_cap_list, CAP_SET);
cap_set_flag (tmp_caps, CAP_EFFECTIVE, ntmp_cap_list,
(cap_value_t *) tmp_cap_list, CAP_SET);
int res = cap_set_proc (tmp_caps);
cap_free (tmp_caps);
if (__glibc_unlikely (res != 0))
{
cap_free (new_caps);
dbg_log (_("Failed to drop capabilities"));
do_exit (EXIT_FAILURE, 0, _("cap_set_proc failed"));
}
return new_caps;
}
void
install_real_capabilities (cap_t new_caps)
{
/* If we have no capabilities there is nothing to do here. */
if (new_caps == NULL)
return;
if (cap_set_proc (new_caps))
{
cap_free (new_caps);
dbg_log (_("Failed to drop capabilities"));
do_exit (EXIT_FAILURE, 0, _("cap_set_proc failed"));
/* NOTREACHED */
}
cap_free (new_caps);
if (prctl (PR_SET_KEEPCAPS, 0) == -1)
{
dbg_log (_("Failed to unset keep-capabilities"));
do_exit (EXIT_FAILURE, errno, _("prctl(KEEPCAPS) failed"));
/* NOTREACHED */
}
}
# endif /* HAVE_LIBCAP */
#endif /* HAVE_LIBAUDIT */
/* Determine if we are running on an SELinux kernel. Set selinux_enabled
to the result. */
void
nscd_selinux_enabled (int *selinux_enabled)
{
*selinux_enabled = is_selinux_enabled ();
if (*selinux_enabled < 0)
{
dbg_log (_("Failed to determine if kernel supports SELinux"));
do_exit (EXIT_FAILURE, 0, NULL);
}
}
/* Create thread for AVC netlink notification. */
static void *
avc_create_thread (void (*run) (void))
{
int rc;
rc =
pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
if (rc != 0)
do_exit (EXIT_FAILURE, rc, _("Failed to start AVC thread"));
return &avc_notify_thread;
}
/* Stop AVC netlink thread. */
static void
avc_stop_thread (void *thread)
{
pthread_cancel (*(pthread_t *) thread);
}
/* Allocate a new AVC lock. */
static void *
avc_alloc_lock (void)
{
pthread_mutex_t *avc_mutex;
avc_mutex = malloc (sizeof (pthread_mutex_t));
if (avc_mutex == NULL)
do_exit (EXIT_FAILURE, errno, _("Failed to create AVC lock"));
pthread_mutex_init (avc_mutex, NULL);
return avc_mutex;
}
/* Acquire an AVC lock. */
static void
avc_get_lock (void *lock)
{
pthread_mutex_lock (lock);
}
/* Release an AVC lock. */
static void
avc_release_lock (void *lock)
{
pthread_mutex_unlock (lock);
}
/* Free an AVC lock. */
static void
avc_free_lock (void *lock)
{
pthread_mutex_destroy (lock);
free (lock);
}
/* Initialize the user space access vector cache (AVC) for NSCD along with
log/thread/lock callbacks. */
void
nscd_avc_init (void)
{
avc_entry_ref_init (&aeref);
if (avc_init ("avc", NULL, &log_cb, &thread_cb, &lock_cb) < 0)
do_exit (EXIT_FAILURE, errno, _("Failed to start AVC"));
else
dbg_log (_("Access Vector Cache (AVC) started"));
#ifdef HAVE_LIBAUDIT
audit_init ();
#endif
}
/* Check the permission from the caller (via getpeercon) to nscd.
Returns 0 if access is allowed, 1 if denied, and -1 on error.
The SELinux policy, enablement, and permission bits are all dynamic and the
caching done by glibc is not entirely correct. This nscd support should be
rewritten to use selinux_check_permission. A rewrite is risky though and
requires some refactoring. Currently we use symbolic mappings instead of
compile time constants (which SELinux upstream says are going away), and we
use security_deny_unknown to determine what to do if selinux-policy* doesn't
have a definition for the the permission or object class we are looking
up. */
int
nscd_request_avc_has_perm (int fd, request_type req)
{
/* Initialize to NULL so we know what to free in case of failure. */
security_context_t scon = NULL;
security_context_t tcon = NULL;
security_id_t ssid = NULL;
security_id_t tsid = NULL;
int rc = -1;
security_class_t sc_nscd;
access_vector_t perm;
int avc_deny_unknown;
/* Check if SELinux denys or allows unknown object classes
and permissions. It is 0 if they are allowed, 1 if they
are not allowed and -1 on error. */
if ((avc_deny_unknown = security_deny_unknown ()) == -1)
dbg_log (_("Error querying policy for undefined object classes "
"or permissions."));
/* Get the security class for nscd. If this fails we will likely be
unable to do anything unless avc_deny_unknown is 0. */
sc_nscd = string_to_security_class ("nscd");
if (sc_nscd == 0 && avc_deny_unknown == 1)
dbg_log (_("Error getting security class for nscd."));
/* Convert permission to AVC bits. */
perm = string_to_av_perm (sc_nscd, perms[req]);
if (perm == 0 && avc_deny_unknown == 1)
dbg_log (_("Error translating permission name "
"\"%s\" to access vector bit."), perms[req]);
/* If the nscd security class was not found or perms were not
found and AVC does not deny unknown values then allow it. */
if ((sc_nscd == 0 || perm == 0) && avc_deny_unknown == 0)
return 0;
if (getpeercon (fd, &scon) < 0)
{
dbg_log (_("Error getting context of socket peer"));
goto out;
}
if (getcon (&tcon) < 0)
{
dbg_log (_("Error getting context of nscd"));
goto out;
}
if (avc_context_to_sid (scon, &ssid) < 0
|| avc_context_to_sid (tcon, &tsid) < 0)
{
dbg_log (_("Error getting sid from context"));
goto out;
}
/* The SELinux API for avc_has_perm conflates access denied and error into
the return code -1, while nscd_request_avs_has_perm has distinct error
(-1) and denied (1) return codes. We map the avc_has_perm access denied or
error into an access denied at the nscd interface level (we do accurately
report error for the getpeercon, getcon, and avc_context_to_sid interfaces
used above). */
rc = avc_has_perm (ssid, tsid, sc_nscd, perm, &aeref, NULL) < 0;
out:
if (scon)
freecon (scon);
if (tcon)
freecon (tcon);
if (ssid)
sidput (ssid);
if (tsid)
sidput (tsid);
return rc;
}
/* Wrapper to get AVC statistics. */
void
nscd_avc_cache_stats (struct avc_cache_stats *cstats)
{
avc_cache_stats (cstats);
}
/* Print the AVC statistics to stdout. */
void
nscd_avc_print_stats (struct avc_cache_stats *cstats)
{
printf (_("\nSELinux AVC Statistics:\n\n"
"%15u entry lookups\n"
"%15u entry hits\n"
"%15u entry misses\n"
"%15u entry discards\n"
"%15u CAV lookups\n"
"%15u CAV hits\n"
"%15u CAV probes\n"
"%15u CAV misses\n"),
cstats->entry_lookups, cstats->entry_hits, cstats->entry_misses,
cstats->entry_discards, cstats->cav_lookups, cstats->cav_hits,
cstats->cav_probes, cstats->cav_misses);
}
#endif /* HAVE_SELINUX */