netfilter: xt_recent: fix namespace destroy path

recent_net_exit() is called before recent_mt_destroy() in the
destroy path of network namespaces. Make sure there are no entries
in the parent proc entry xt_recent before removing it.
Signed-off-by: Vitaly E. Lavrov <lve@guap.ru>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_recent.c

@@ -431,7 +431,8 @@ static void recent_mt_destroy(const struct xt_mtdtor_param *par)
 		list_del(&t->list);
 		spin_unlock_bh(&recent_lock);
 #ifdef CONFIG_PROC_FS
-		remove_proc_entry(t->name, recent_net->xt_recent);
+		if (recent_net->xt_recent != NULL)
+			remove_proc_entry(t->name, recent_net->xt_recent);
 #endif
 		recent_table_flush(t);
 		kfree(t);
@@ -615,6 +616,20 @@ static int __net_init recent_proc_net_init(struct net *net)
 
 static void __net_exit recent_proc_net_exit(struct net *net)
 {
+	struct recent_net *recent_net = recent_pernet(net);
+	struct recent_table *t;
+
+	/* recent_net_exit() is called before recent_mt_destroy(). Make sure
+	 * that the parent xt_recent proc entry is is empty before trying to
+	 * remove it.
+	 */
+	spin_lock_bh(&recent_lock);
+	list_for_each_entry(t, &recent_net->tables, list)
+	        remove_proc_entry(t->name, recent_net->xt_recent);
+
+	recent_net->xt_recent = NULL;
+	spin_unlock_bh(&recent_lock);
+
 	proc_net_remove(net, "xt_recent");
 }
 #else
@@ -638,9 +653,6 @@ static int __net_init recent_net_init(struct net *net)
 
 static void __net_exit recent_net_exit(struct net *net)
 {
-	struct recent_net *recent_net = recent_pernet(net);
-
-	BUG_ON(!list_empty(&recent_net->tables));
 	recent_proc_net_exit(net);
 }