net: convert netpoll_info.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>
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index 1828900..27c0aaa 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -11,6 +11,7 @@
 #include <linux/interrupt.h>
 #include <linux/rcupdate.h>
 #include <linux/list.h>
+#include <linux/refcount.h>
 
 union inet_addr {
 	__u32		all[4];
@@ -34,7 +35,7 @@ struct netpoll {
 };
 
 struct netpoll_info {
-	atomic_t refcnt;
+	refcount_t refcnt;
 
 	struct semaphore dev_lock;