netfilter: nft_ct: Add ct id support

The 'id' key returns the unique id of the conntrack entry as returned
by nf_ct_get_id().
Signed-off-by: Brett Mastbergen <bmastbergen@untangle.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -967,6 +967,7 @@ enum nft_socket_keys {
  * @NFT_CT_SRC_IP6: conntrack layer 3 protocol source (IPv6 address)
  * @NFT_CT_DST_IP6: conntrack layer 3 protocol destination (IPv6 address)
  * @NFT_CT_TIMEOUT: connection tracking timeout policy assigned to conntrack
+ * @NFT_CT_ID: conntrack id
  */
 enum nft_ct_keys {
 	NFT_CT_STATE,
@@ -993,6 +994,7 @@ enum nft_ct_keys {
 	NFT_CT_SRC_IP6,
 	NFT_CT_DST_IP6,
 	NFT_CT_TIMEOUT,
+	NFT_CT_ID,
 	__NFT_CT_MAX
 };
 #define NFT_CT_MAX		(__NFT_CT_MAX - 1)

net/netfilter/nft_ct.c

@@ -178,6 +178,11 @@ static void nft_ct_get_eval(const struct nft_expr *expr,
 		return;
 	}
 #endif
+	case NFT_CT_ID:
+		if (!nf_ct_is_confirmed(ct))
+			goto err;
+		*dest = nf_ct_get_id(ct);
+		return;
 	default:
 		break;
 	}
@@ -479,6 +484,9 @@ static int nft_ct_get_init(const struct nft_ctx *ctx,
 		len = sizeof(u16);
 		break;
 #endif
+	case NFT_CT_ID:
+		len = sizeof(u32);
+		break;
 	default:
 		return -EOPNOTSUPP;
 	}