net: convert inet_frag_queue.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 975779d..440c1e9 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -50,7 +50,7 @@ struct inet_frag_queue {
 	spinlock_t		lock;
 	struct timer_list	timer;
 	struct hlist_node	list;
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	struct sk_buff		*fragments;
 	struct sk_buff		*fragments_tail;
 	ktime_t			stamp;
@@ -129,7 +129,7 @@ void inet_frag_maybe_warn_overflow(struct inet_frag_queue *q,
 
 static inline void inet_frag_put(struct inet_frag_queue *q, struct inet_frags *f)
 {
-	if (atomic_dec_and_test(&q->refcnt))
+	if (refcount_dec_and_test(&q->refcnt))
 		inet_frag_destroy(q, f);
 }