net, x25: convert x25_route.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

@@ -11,6 +11,7 @@
 #define _X25_H 
 #include <linux/x25.h>
 #include <linux/slab.h>
+#include <linux/refcount.h>
 #include <net/sock.h>
 
 #define	X25_ADDR_LEN			16
@@ -129,7 +130,7 @@ struct x25_route {
 	struct x25_address	address;
 	unsigned int		sigdigits;
 	struct net_device	*dev;
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 };
 
 struct x25_neigh {
@@ -265,12 +266,12 @@ void x25_route_free(void);
 
 static __inline__ void x25_route_hold(struct x25_route *rt)
 {
-	atomic_inc(&rt->refcnt);
+	refcount_inc(&rt->refcnt);
 }
 
 static __inline__ void x25_route_put(struct x25_route *rt)
 {
-	if (atomic_dec_and_test(&rt->refcnt))
+	if (refcount_dec_and_test(&rt->refcnt))
 		kfree(rt);
 }
 

net/x25/x25_route.c

@@ -55,7 +55,7 @@ static int x25_add_route(struct x25_address *address, unsigned int sigdigits,
 
 	rt->sigdigits = sigdigits;
 	rt->dev       = dev;
-	atomic_set(&rt->refcnt, 1);
+	refcount_set(&rt->refcnt, 1);
 
 	list_add(&rt->node, &x25_route_list);
 	rc = 0;