net, netrom: convert nr_node.refcount 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/netrom.h

@@ -110,7 +110,7 @@ struct nr_node {
 	unsigned char		which;
 	unsigned char		count;
 	struct nr_route		routes[3];
-	atomic_t		refcount;
+	refcount_t		refcount;
 	spinlock_t		node_lock;
 };
 
@@ -119,11 +119,11 @@ struct nr_node {
  *********************************************************************/
 
 #define nr_node_hold(__nr_node) \
-	atomic_inc(&((__nr_node)->refcount))
+	refcount_inc(&((__nr_node)->refcount))
 
 static __inline__ void nr_node_put(struct nr_node *nr_node)
 {
-	if (atomic_dec_and_test(&nr_node->refcount)) {
+	if (refcount_dec_and_test(&nr_node->refcount)) {
 		kfree(nr_node);
 	}
 }

net/netrom/nr_route.c

@@ -184,7 +184,7 @@ static int __must_check nr_add_node(ax25_address *nr, const char *mnemonic,
 
 		nr_node->which = 0;
 		nr_node->count = 1;
-		atomic_set(&nr_node->refcount, 1);
+		refcount_set(&nr_node->refcount, 1);
 		spin_lock_init(&nr_node->node_lock);
 
 		nr_node->routes[0].quality   = quality;