net, netrom: convert nr_neigh.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

@@ -11,6 +11,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <net/sock.h>
+#include <linux/refcount.h>
 
 #define	NR_NETWORK_LEN			15
 #define	NR_TRANSPORT_LEN		5
@@ -93,7 +94,7 @@ struct nr_neigh {
 	unsigned short		count;
 	unsigned int		number;
 	unsigned char		failed;
-	atomic_t		refcount;
+	refcount_t		refcount;
 };
 
 struct nr_route {
@@ -128,11 +129,11 @@ static __inline__ void nr_node_put(struct nr_node *nr_node)
 }
 
 #define nr_neigh_hold(__nr_neigh) \
-	atomic_inc(&((__nr_neigh)->refcount))
+	refcount_inc(&((__nr_neigh)->refcount))
 
 static __inline__ void nr_neigh_put(struct nr_neigh *nr_neigh)
 {
-	if (atomic_dec_and_test(&nr_neigh->refcount)) {
+	if (refcount_dec_and_test(&nr_neigh->refcount)) {
 		if (nr_neigh->ax25)
 			ax25_cb_put(nr_neigh->ax25);
 		kfree(nr_neigh->digipeat);

net/netrom/nr_route.c

@@ -149,7 +149,7 @@ static int __must_check nr_add_node(ax25_address *nr, const char *mnemonic,
 		nr_neigh->count    = 0;
 		nr_neigh->number   = nr_neigh_no++;
 		nr_neigh->failed   = 0;
-		atomic_set(&nr_neigh->refcount, 1);
+		refcount_set(&nr_neigh->refcount, 1);
 
 		if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
 			nr_neigh->digipeat = kmemdup(ax25_digi,
@@ -431,7 +431,7 @@ static int __must_check nr_add_neigh(ax25_address *callsign,
 	nr_neigh->count    = 0;
 	nr_neigh->number   = nr_neigh_no++;
 	nr_neigh->failed   = 0;
-	atomic_set(&nr_neigh->refcount, 1);
+	refcount_set(&nr_neigh->refcount, 1);
 
 	if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
 		nr_neigh->digipeat = kmemdup(ax25_digi, sizeof(*ax25_digi),