fsnotify: convert fsnotify_mark.refcnt from atomic_t to refcount_t
atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable fsnotify_mark.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index f3a32ea..e9191b4 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -105,8 +105,8 @@ static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
void fsnotify_get_mark(struct fsnotify_mark *mark)
{
- WARN_ON_ONCE(!atomic_read(&mark->refcnt));
- atomic_inc(&mark->refcnt);
+ WARN_ON_ONCE(!refcount_read(&mark->refcnt));
+ refcount_inc(&mark->refcnt);
}
static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
@@ -201,7 +201,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
/* Catch marks that were actually never attached to object */
if (!mark->connector) {
- if (atomic_dec_and_test(&mark->refcnt))
+ if (refcount_dec_and_test(&mark->refcnt))
fsnotify_final_mark_destroy(mark);
return;
}
@@ -210,7 +210,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
* We have to be careful so that traversals of obj_list under lock can
* safely grab mark reference.
*/
- if (!atomic_dec_and_lock(&mark->refcnt, &mark->connector->lock))
+ if (!refcount_dec_and_lock(&mark->refcnt, &mark->connector->lock))
return;
conn = mark->connector;
@@ -258,7 +258,7 @@ static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
if (!mark)
return true;
- if (atomic_inc_not_zero(&mark->refcnt)) {
+ if (refcount_inc_not_zero(&mark->refcnt)) {
spin_lock(&mark->lock);
if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
/* mark is attached, group is still alive then */
@@ -335,7 +335,7 @@ void fsnotify_detach_mark(struct fsnotify_mark *mark)
WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
- atomic_read(&mark->refcnt) < 1 +
+ refcount_read(&mark->refcnt) < 1 +
!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
spin_lock(&mark->lock);
@@ -737,7 +737,7 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
{
memset(mark, 0, sizeof(*mark));
spin_lock_init(&mark->lock);
- atomic_set(&mark->refcnt, 1);
+ refcount_set(&mark->refcnt, 1);
fsnotify_get_group(group);
mark->group = group;
}