Hi, I'm having a problem where calling avc_destroy doesn't seem to close the netlink socket, because a subsequent avc_init is unable to bind to the socket, and gets an error "Address already in use". The attached test program lets me reproduce the problem - the very interesting thing is it seems to only happen about 50% of the time. Is there some race here in the kernel? As far as I can tell the close() is being called so the socket should be shut down.
#include <errno.h>
#include <pthread.h>
#include <syslog.h>
#include <selinux/selinux.h>
#include <selinux/avc.h>
#include <selinux/av_permissions.h>
#include <selinux/flask.h>
#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#define HAVE_SELINUX
#ifdef HAVE_SELINUX
/* Store the value telling us if SELinux is enabled in the kernel. */
static int selinux_enabled = 0;
/* Store an avc_entry_ref to speed AVC decisions. */
static struct avc_entry_ref aeref;
/* Store the SID of the bus itself to use as the default. */
static security_id_t bus_sid = SECSID_WILD;
/* Thread to listen for SELinux status changes via netlink. */
static pthread_t avc_notify_thread;
/* Prototypes for AVC callback functions. */
static void log_callback (const char *fmt, ...);
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_memory_callback mem_cb =
{
.func_malloc = malloc,
.func_free = free
};
static const struct avc_log_callback log_cb =
{
.func_log = log_callback,
.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
};
#endif /* HAVE_SELINUX */
/**
* Log callback to log denial messages from the AVC.
* This is used in avc_init. Logs to both standard
* error and syslogd.
*
* @param fmt the format string
* @param variable argument list
*/
#ifdef HAVE_SELINUX
static void
log_callback (const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vsyslog (LOG_INFO, fmt, ap);
va_end(ap);
}
/**
* On a policy reload we need to reparse the SELinux configuration file, since
* this could have changed. Send a SIGHUP to reload all configs.
*/
static int
policy_reload_callback (u_int32_t event, security_id_t ssid,
security_id_t tsid, security_class_t tclass,
access_vector_t perms, access_vector_t *out_retained)
{
if (event == AVC_CALLBACK_RESET)
return raise (SIGHUP);
return 0;
}
/**
* Create thread to notify the AVC of enforcing and policy reload
* changes via netlink.
*
* @param run the thread run function
* @return pointer to the thread
*/
static void *
avc_create_thread (void (*run) (void))
{
int rc;
rc = pthread_create (&avc_notify_thread, NULL, (void *(*) (void *)) run, NULL);
if (rc != 0)
{
fprintf (stderr, "Failed to start AVC thread: %s\n", strerror (rc));
exit (1);
}
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)
{
fprintf (stderr, "Could not create mutex: %s\n", strerror (errno));
exit (1);
}
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);
}
#endif /* HAVE_SELINUX */
/**
* Initialize the user space access vector cache (AVC) for D-BUS and set up
* logging callbacks.
*/
int
bus_selinux_init (void)
{
#ifdef HAVE_SELINUX
int r;
char *bus_context;
/* Determine if we are running an SELinux kernel. */
r = is_selinux_enabled ();
if (r < 0)
{
fprintf (stderr, "Could not tell if SELinux is enabled: %s\n",
strerror (errno));
return 0;
}
selinux_enabled = r != 0;
if (!selinux_enabled)
{
fprintf (stderr, "SELinux not enabled in this kernel.\n");
return 1;
}
fprintf (stderr, "SELinux is enabled in this kernel.\n");
avc_entry_ref_init (&aeref);
if (avc_init ("avc", &mem_cb, &log_cb, &thread_cb, &lock_cb) < 0)
{
fprintf (stderr, "Failed to start Access Vector Cache (AVC).\n");
return 0;
}
else
{
openlog ("dbus", LOG_PERROR, LOG_USER);
fprintf (stderr, "Access Vector Cache (AVC) started.\n");
}
if (avc_add_callback (policy_reload_callback, AVC_CALLBACK_RESET,
NULL, NULL, 0, 0) < 0)
{
fprintf (stderr, "Failed to add policy reload callback: %s\n",
strerror (errno));
avc_destroy ();
return 0;
}
bus_context = NULL;
bus_sid = SECSID_WILD;
if (getcon (&bus_context) < 0)
{
fprintf (stderr, "Error getting context of bus: %s\n",
strerror (errno));
return 0;
}
if (avc_context_to_sid (bus_context, &bus_sid) < 0)
{
fprintf (stderr, "Error getting SID from bus context: %s\n",
strerror (errno));
freecon (bus_context);
return 0;
}
freecon (bus_context);
return 1;
#else
return 1;
#endif /* HAVE_SELINUX */
}
void
bus_selinux_shutdown (void)
{
#ifdef HAVE_SELINUX
if (!selinux_enabled)
return;
sidput (bus_sid);
bus_sid = SECSID_WILD;
#ifdef DBUS_ENABLE_VERBOSE_MODE
bus_avc_print_stats ();
#endif /* DBUS_ENABLE_VERBOSE_MODE */
avc_destroy ();
#endif /* HAVE_SELINUX */
}
int
main(int argc, char **argv)
{
if (!bus_selinux_init ()) {
fprintf (stderr, "couldn't init selinux\n");
exit (1);
}
bus_selinux_shutdown ();
if (!bus_selinux_init ()) {
fprintf (stderr, "couldn't init selinux\n");
exit (1);
}
bus_selinux_shutdown ();
return 0;
}
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