net, decnet: convert dn_fib_info.fib_clntref 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/net/dn_fib.h b/include/net/dn_fib.h
index f2ca135..81210a8 100644
--- a/include/net/dn_fib.h
+++ b/include/net/dn_fib.h
@@ -2,6 +2,7 @@
 #define _NET_DN_FIB_H
 
 #include <linux/netlink.h>
+#include <linux/refcount.h>
 
 extern const struct nla_policy rtm_dn_policy[];
 
@@ -28,7 +29,7 @@
 	struct dn_fib_info	*fib_next;
 	struct dn_fib_info	*fib_prev;
 	int 			fib_treeref;
-	atomic_t		fib_clntref;
+	refcount_t		fib_clntref;
 	int			fib_dead;
 	unsigned int		fib_flags;
 	int			fib_protocol;
@@ -130,7 +131,7 @@
 
 static inline void dn_fib_info_put(struct dn_fib_info *fi)
 {
-	if (atomic_dec_and_test(&fi->fib_clntref))
+	if (refcount_dec_and_test(&fi->fib_clntref))
 		dn_fib_free_info(fi);
 }