netfilter: nf_tables: use NLM_F_NONREC for deletion requests

Bail out if user requests non-recursive deletion for tables and sets.
This new flags tells nf_tables netlink interface to reject deletions if
tables and sets have content.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -860,6 +860,10 @@ static int nf_tables_deltable(struct net *net, struct sock *nlsk,
 	if (IS_ERR(table))
 		return PTR_ERR(table);
 
+	if (nlh->nlmsg_flags & NLM_F_NONREC &&
+	    table->use > 0)
+		return -EBUSY;
+
 	ctx.afi = afi;
 	ctx.table = table;
 
@@ -3225,7 +3229,9 @@ static int nf_tables_delset(struct net *net, struct sock *nlsk,
 	set = nf_tables_set_lookup(ctx.table, nla[NFTA_SET_NAME], genmask);
 	if (IS_ERR(set))
 		return PTR_ERR(set);
-	if (!list_empty(&set->bindings))
+
+	if (!list_empty(&set->bindings) ||
+	    (nlh->nlmsg_flags & NLM_F_NONREC && atomic_read(&set->nelems) > 0))
 		return -EBUSY;
 
 	return nft_delset(&ctx, set);