netfilter: nf_tables: disallow updates of implicit chain

Updates on existing implicit chain make no sense, disallow this.

Fixes: d0e2c7de ("netfilter: nf_tables: add NFT_CHAIN_BINDING")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -2574,6 +2574,9 @@ static int nf_tables_newchain(struct sk_buff *skb, const struct nfnl_info *info,
 	nft_ctx_init(&ctx, net, skb, info->nlh, family, table, chain, nla);
 
 	if (chain != NULL) {
+		if (chain->flags & NFT_CHAIN_BINDING)
+			return -EINVAL;
+
 		if (info->nlh->nlmsg_flags & NLM_F_EXCL) {
 			NL_SET_BAD_ATTR(extack, attr);
 			return -EEXIST;