netfilter: nf_tables: match on tunnel metadata

This patch allows us to match on the tunnel metadata that is available
of the packet. We can use this to validate if the packet comes from/goes
to tunnel and the corresponding tunnel ID.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -1647,4 +1647,19 @@ enum nft_tunnel_key_attributes {
 };
 #define NFTA_TUNNEL_KEY_MAX	(__NFTA_TUNNEL_KEY_MAX - 1)
 
+enum nft_tunnel_keys {
+	NFT_TUNNEL_PATH,
+	NFT_TUNNEL_ID,
+	__NFT_TUNNEL_MAX
+};
+#define NFT_TUNNEL_MAX	(__NFT_TUNNEL_MAX - 1)
+
+enum nft_tunnel_attributes {
+	NFTA_TUNNEL_UNSPEC,
+	NFTA_TUNNEL_KEY,
+	NFTA_TUNNEL_DREG,
+	__NFTA_TUNNEL_MAX
+};
+#define NFTA_TUNNEL_MAX	(__NFTA_TUNNEL_MAX - 1)
+
 #endif /* _LINUX_NF_TABLES_H */

net/netfilter/nft_tunnel.c

@@ -12,6 +12,104 @@
 #include <net/vxlan.h>
 #include <net/erspan.h>
 
+struct nft_tunnel {
+	enum nft_tunnel_keys	key:8;
+	enum nft_registers	dreg:8;
+};
+
+static void nft_tunnel_get_eval(const struct nft_expr *expr,
+				struct nft_regs *regs,
+				const struct nft_pktinfo *pkt)
+{
+	const struct nft_tunnel *priv = nft_expr_priv(expr);
+	u32 *dest = &regs->data[priv->dreg];
+	struct ip_tunnel_info *tun_info;
+
+	tun_info = skb_tunnel_info(pkt->skb);
+
+	switch (priv->key) {
+	case NFT_TUNNEL_PATH:
+		nft_reg_store8(dest, !!tun_info);
+		break;
+	case NFT_TUNNEL_ID:
+		if (!tun_info) {
+			regs->verdict.code = NFT_BREAK;
+			return;
+		}
+		*dest = ntohl(tunnel_id_to_key32(tun_info->key.tun_id));
+		break;
+	default:
+		WARN_ON(1);
+		regs->verdict.code = NFT_BREAK;
+	}
+}
+
+static const struct nla_policy nft_tunnel_policy[NFTA_TUNNEL_MAX + 1] = {
+	[NFTA_TUNNEL_KEY]	= { .type = NLA_U32 },
+	[NFTA_TUNNEL_DREG]	= { .type = NLA_U32 },
+};
+
+static int nft_tunnel_get_init(const struct nft_ctx *ctx,
+			       const struct nft_expr *expr,
+			       const struct nlattr * const tb[])
+{
+	struct nft_tunnel *priv = nft_expr_priv(expr);
+	u32 len;
+
+	if (!tb[NFTA_TUNNEL_KEY] &&
+	    !tb[NFTA_TUNNEL_DREG])
+		return -EINVAL;
+
+	priv->key = ntohl(nla_get_be32(tb[NFTA_TUNNEL_KEY]));
+	switch (priv->key) {
+	case NFT_TUNNEL_PATH:
+		len = sizeof(u8);
+		break;
+	case NFT_TUNNEL_ID:
+		len = sizeof(u32);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	priv->dreg = nft_parse_register(tb[NFTA_TUNNEL_DREG]);
+
+	return nft_validate_register_store(ctx, priv->dreg, NULL,
+					   NFT_DATA_VALUE, len);
+}
+
+static int nft_tunnel_get_dump(struct sk_buff *skb,
+			       const struct nft_expr *expr)
+{
+	const struct nft_tunnel *priv = nft_expr_priv(expr);
+
+	if (nla_put_be32(skb, NFTA_TUNNEL_KEY, htonl(priv->key)))
+		goto nla_put_failure;
+	if (nft_dump_register(skb, NFTA_TUNNEL_DREG, priv->dreg))
+		goto nla_put_failure;
+	return 0;
+
+nla_put_failure:
+	return -1;
+}
+
+static struct nft_expr_type nft_tunnel_type;
+static const struct nft_expr_ops nft_tunnel_get_ops = {
+	.type		= &nft_tunnel_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_tunnel)),
+	.eval		= nft_tunnel_get_eval,
+	.init		= nft_tunnel_get_init,
+	.dump		= nft_tunnel_get_dump,
+};
+
+static struct nft_expr_type nft_tunnel_type __read_mostly = {
+	.name		= "tunnel",
+	.ops		= &nft_tunnel_get_ops,
+	.policy		= nft_tunnel_policy,
+	.maxattr	= NFTA_TUNNEL_MAX,
+	.owner		= THIS_MODULE,
+};
+
 struct nft_tunnel_opts {
 	union {
 		struct vxlan_metadata	vxlan;
@@ -442,12 +540,23 @@ static struct nft_object_type nft_tunnel_obj_type __read_mostly = {
 
 static int __init nft_tunnel_module_init(void)
 {
-	return nft_register_obj(&nft_tunnel_obj_type);
+	int err;
+
+	err = nft_register_expr(&nft_tunnel_type);
+	if (err < 0)
+		return err;
+
+	err = nft_register_obj(&nft_tunnel_obj_type);
+	if (err < 0)
+		nft_unregister_expr(&nft_tunnel_type);
+
+	return err;
 }
 
 static void __exit nft_tunnel_module_exit(void)
 {
 	nft_unregister_obj(&nft_tunnel_obj_type);
+	nft_unregister_expr(&nft_tunnel_type);
 }
 
 module_init(nft_tunnel_module_init);
@@ -455,4 +564,5 @@ module_exit(nft_tunnel_module_exit);
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
+MODULE_ALIAS_NFT_EXPR("tunnel");
 MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_TUNNEL);