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 <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/dn_fib.h

···
 struct dn_fib_info {
 	struct dn_fib_info	*fib_next;
 	struct dn_fib_info	*fib_prev;
-	int 			fib_treeref;
+	refcount_t		fib_treeref;
 	refcount_t		fib_clntref;
 	int			fib_dead;
 	unsigned int		fib_flags;

include/net/ip_fib.h

···
 	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;

net/decnet/dn_fib.c

···
 void dn_fib_release_info(struct dn_fib_info *fi)
 {
 	spin_lock(&dn_fib_info_lock);
-	if (fi && --fi->fib_treeref == 0) {
+	if (fi && refcount_dec_and_test(&fi->fib_treeref)) {
 		if (fi->fib_next)
 			fi->fib_next->fib_prev = fi->fib_prev;
 		if (fi->fib_prev)
···
 	if ((ofi = dn_fib_find_info(fi)) != NULL) {
 		fi->fib_dead = 1;
 		dn_fib_free_info(fi);
-		ofi->fib_treeref++;
+		refcount_inc(&ofi->fib_treeref);
 		return ofi;
 	}
 
-	fi->fib_treeref++;
+	refcount_inc(&fi->fib_treeref);
 	refcount_set(&fi->fib_clntref, 1);
 	spin_lock(&dn_fib_info_lock);
 	fi->fib_next = dn_fib_info_list;

net/ipv4/fib_semantics.c

···
 void fib_release_info(struct fib_info *fi)
 {
 	spin_lock_bh(&fib_info_lock);
-	if (fi && --fi->fib_treeref == 0) {
+	if (fi && refcount_dec_and_test(&fi->fib_treeref)) {
 		hlist_del(&fi->fib_hash);
 		if (fi->fib_prefsrc)
 			hlist_del(&fi->fib_lhash);
···
 		if (!cfg->fc_mx) {
 			fi = fib_find_info_nh(net, cfg);
 			if (fi) {
-				fi->fib_treeref++;
+				refcount_inc(&fi->fib_treeref);
 				return fi;
 			}
 		}
···
 	if (ofi) {
 		fi->fib_dead = 1;
 		free_fib_info(fi);
-		ofi->fib_treeref++;
+		refcount_inc(&ofi->fib_treeref);
 		return ofi;
 	}
 
-	fi->fib_treeref++;
+	refcount_inc(&fi->fib_treeref);
 	refcount_set(&fi->fib_clntref, 1);
 	spin_lock_bh(&fib_info_lock);
 	hlist_add_head(&fi->fib_hash,