net, ax25: convert ax25_uid_assoc.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/ax25.h

@@ -11,7 +11,7 @@
 #include <linux/timer.h>
 #include <linux/list.h>
 #include <linux/slab.h>
-#include <linux/atomic.h>
+#include <linux/refcount.h>
 #include <net/neighbour.h>
 #include <net/sock.h>
 
@@ -158,7 +158,7 @@ enum {
 
 typedef struct ax25_uid_assoc {
 	struct hlist_node	uid_node;
-	atomic_t		refcount;
+	refcount_t		refcount;
 	kuid_t			uid;
 	ax25_address		call;
 } ax25_uid_assoc;
@@ -167,11 +167,11 @@ typedef struct ax25_uid_assoc {
 	hlist_for_each_entry(__ax25, list, uid_node)
 
 #define ax25_uid_hold(ax25) \
-	atomic_inc(&((ax25)->refcount))
+	refcount_inc(&((ax25)->refcount))
 
 static inline void ax25_uid_put(ax25_uid_assoc *assoc)
 {
-	if (atomic_dec_and_test(&assoc->refcount)) {
+	if (refcount_dec_and_test(&assoc->refcount)) {
 		kfree(assoc);
 	}
 }

net/ax25/ax25_uid.c

@@ -107,7 +107,7 @@ int ax25_uid_ioctl(int cmd, struct sockaddr_ax25 *sax)
 		if ((ax25_uid = kmalloc(sizeof(*ax25_uid), GFP_KERNEL)) == NULL)
 			return -ENOMEM;
 
-		atomic_set(&ax25_uid->refcount, 1);
+		refcount_set(&ax25_uid->refcount, 1);
 		ax25_uid->uid  = sax25_kuid;
 		ax25_uid->call = sax->sax25_call;