netfilter: nf_tables: add NFTA_VERDICT_CHAIN_ID attribute

This netlink attribute allows you to identify the chain to jump/goto by
means of the chain ID.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -471,11 +471,13 @@ enum nft_data_attributes {
  *
  * @NFTA_VERDICT_CODE: nf_tables verdict (NLA_U32: enum nft_verdicts)
  * @NFTA_VERDICT_CHAIN: jump target chain name (NLA_STRING)
+ * @NFTA_VERDICT_CHAIN_ID: jump target chain ID (NLA_U32)
  */
 enum nft_verdict_attributes {
 	NFTA_VERDICT_UNSPEC,
 	NFTA_VERDICT_CODE,
 	NFTA_VERDICT_CHAIN,
+	NFTA_VERDICT_CHAIN_ID,
 	__NFTA_VERDICT_MAX
 };
 #define NFTA_VERDICT_MAX	(__NFTA_VERDICT_MAX - 1)

net/netfilter/nf_tables_api.c

@@ -8242,6 +8242,7 @@ static const struct nla_policy nft_verdict_policy[NFTA_VERDICT_MAX + 1] = {
 	[NFTA_VERDICT_CODE]	= { .type = NLA_U32 },
 	[NFTA_VERDICT_CHAIN]	= { .type = NLA_STRING,
 				    .len = NFT_CHAIN_MAXNAMELEN - 1 },
+	[NFTA_VERDICT_CHAIN_ID]	= { .type = NLA_U32 },
 };
 
 static int nft_verdict_init(const struct nft_ctx *ctx, struct nft_data *data,
@@ -8278,10 +8279,19 @@ static int nft_verdict_init(const struct nft_ctx *ctx, struct nft_data *data,
 		break;
 	case NFT_JUMP:
 	case NFT_GOTO:
-		if (!tb[NFTA_VERDICT_CHAIN])
+		if (tb[NFTA_VERDICT_CHAIN]) {
+			chain = nft_chain_lookup(ctx->net, ctx->table,
+						 tb[NFTA_VERDICT_CHAIN],
+						 genmask);
+		} else if (tb[NFTA_VERDICT_CHAIN_ID]) {
+			chain = nft_chain_lookup_byid(ctx->net,
+						      tb[NFTA_VERDICT_CHAIN_ID]);
+			if (IS_ERR(chain))
+				return PTR_ERR(chain);
+		} else {
 			return -EINVAL;
-		chain = nft_chain_lookup(ctx->net, ctx->table,
-					 tb[NFTA_VERDICT_CHAIN], genmask);
+		}
+
 		if (IS_ERR(chain))
 			return PTR_ERR(chain);
 		if (nft_is_base_chain(chain))