net: convert fib_treeref from int to refcount_t

refcount_t type should be used instead of int when fib_treeref is used as
a reference counter,and avoid use-after-free risks.

Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20210729071350.28919-1-yajun.deng@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 3ab2563..21c5386 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -133,7 +133,7 @@ struct fib_info {
 	struct hlist_node	fib_lhash;
 	struct list_head	nh_list;
 	struct net		*fib_net;
-	int			fib_treeref;
+	refcount_t		fib_treeref;
 	refcount_t		fib_clntref;
 	unsigned int		fib_flags;
 	unsigned char		fib_dead;