net, x25: convert x25_neigh.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>

include/net/x25.h

@@ -142,7 +142,7 @@ struct x25_neigh {
 	unsigned long		t20;
 	struct timer_list	t20timer;
 	unsigned long		global_facil_mask;
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 };
 
 struct x25_sock {
@@ -243,12 +243,12 @@ void x25_link_free(void);
 /* x25_neigh.c */
 static __inline__ void x25_neigh_hold(struct x25_neigh *nb)
 {
-	atomic_inc(&nb->refcnt);
+	refcount_inc(&nb->refcnt);
 }
 
 static __inline__ void x25_neigh_put(struct x25_neigh *nb)
 {
-	if (atomic_dec_and_test(&nb->refcnt))
+	if (refcount_dec_and_test(&nb->refcnt))
 		kfree(nb);
 }
 

net/x25/x25_link.c

@@ -266,7 +266,7 @@ void x25_link_device_up(struct net_device *dev)
 				       X25_MASK_PACKET_SIZE |
 				       X25_MASK_WINDOW_SIZE;
 	nb->t20      = sysctl_x25_restart_request_timeout;
-	atomic_set(&nb->refcnt, 1);
+	refcount_set(&nb->refcnt, 1);
 
 	write_lock_bh(&x25_neigh_list_lock);
 	list_add(&nb->node, &x25_neigh_list);