netfilter: nf_tables: Fix potential data-race in __nft_obj_type_get()

nft_unregister_obj() can concurrent with __nft_obj_type_get(),
and there is not any protection when iterate over nf_tables_objects
list in __nft_obj_type_get(). Therefore, there is potential data-race
of nf_tables_objects list entry.

Use list_for_each_entry_rcu() to iterate over nf_tables_objects
list in __nft_obj_type_get(), and use rcu_read_lock() in the caller
nft_obj_type_get() to protect the entire type query process.

Fixes: e500924 ("netfilter: nf_tables: add stateful objects")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: Ziyang Xuan

net/netfilter/nf_tables_api.c

@@ -7611,7 +7611,7 @@ static const struct nft_object_type *__nft_obj_type_get(u32 objtype, u8 family)
 {
 	const struct nft_object_type *type;
 
-	list_for_each_entry(type, &nf_tables_objects, list) {
+	list_for_each_entry_rcu(type, &nf_tables_objects, list) {
 		if (type->family != NFPROTO_UNSPEC &&
 		    type->family != family)
 			continue;
@@ -7627,9 +7627,13 @@ nft_obj_type_get(struct net *net, u32 objtype, u8 family)
 {
 	const struct nft_object_type *type;
 
+	rcu_read_lock();
 	type = __nft_obj_type_get(objtype, family);
-	if (type != NULL && try_module_get(type->owner))
+	if (type != NULL && try_module_get(type->owner)) {
+		rcu_read_unlock();
 		return type;
+	}
+	rcu_read_unlock();
 
 	lockdep_nfnl_nft_mutex_not_held();
 #ifdef CONFIG_MODULES