netfilter: nf_tables: do not allow to delete table with owner by handle

nft_table_lookup_byhandle() also needs to validate the netlink PortID
owner when deleting a table by handle.

Fixes: 6001a93 ("netfilter: nftables: introduce table ownership")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -583,15 +583,19 @@ static struct nft_table *nft_table_lookup(const struct net *net,
 
 static struct nft_table *nft_table_lookup_byhandle(const struct net *net,
 						   const struct nlattr *nla,
-						   u8 genmask)
+						   u8 genmask, u32 nlpid)
 {
 	struct nftables_pernet *nft_net;
 	struct nft_table *table;
 
 	nft_net = nft_pernet(net);
 	list_for_each_entry(table, &nft_net->tables, list) {
 		if (be64_to_cpu(nla_get_be64(nla)) == table->handle &&
-		    nft_active_genmask(table, genmask))
+		    nft_active_genmask(table, genmask)) {
+			if (nft_table_has_owner(table) &&
+			    nlpid && table->nlpid != nlpid)
+				return ERR_PTR(-EPERM);
+
 			return table;
 	}
 
@@ -1279,7 +1283,8 @@ static int nf_tables_deltable(struct sk_buff *skb, const struct nfnl_info *info,
 
 	if (nla[NFTA_TABLE_HANDLE]) {
 		attr = nla[NFTA_TABLE_HANDLE];
-		table = nft_table_lookup_byhandle(net, attr, genmask);
+		table = nft_table_lookup_byhandle(net, attr, genmask,
+						  NETLINK_CB(skb).portid);
 	} else {
 		attr = nla[NFTA_TABLE_NAME];
 		table = nft_table_lookup(net, attr, family, genmask,