netfilter: nft_inner: support for inner tunnel header matching

This new expression allows you to match on the inner headers that are
encapsulated by any of the existing tunneling protocols.

This expression parses the inner packet to set the link, network and
transport offsets, so the existing expressions (with a few updates) can
be reused to match on the inner headers.

The inner expression supports for different tunnel combinations such as:

- ethernet frame over IPv4/IPv6 packet, eg. VxLAN.
- IPv4/IPv6 packet over IPv4/IPv6 packet, eg. IPIP.
- IPv4/IPv6 packet over IPv4/IPv6 + transport header, eg. GRE.
- transport header (ESP or SCTP) over transport header (usually UDP)

The following fields are used to describe the tunnel protocol:

- flags, which describe how to parse the inner headers:

  NFT_PAYLOAD_CTX_INNER_TUN, the tunnel provides its own header.
  NFT_PAYLOAD_CTX_INNER_ETHER, the ethernet frame is available as inner header.
  NFT_PAYLOAD_CTX_INNER_NH, the network header is available as inner header.
  NFT_PAYLOAD_CTX_INNER_TH, the transport header is available as inner header.

For example, VxLAN sets on all of these flags. While GRE only sets on
NFT_PAYLOAD_CTX_INNER_NH and NFT_PAYLOAD_CTX_INNER_TH. Then, ESP over
UDP only sets on NFT_PAYLOAD_CTX_INNER_TH.

The tunnel description is composed of the following attributes:

- header size: in case the tunnel comes with its own header, eg. VxLAN.

- type: this provides a hint to userspace on how to delinearize the rule.
  This is useful for VxLAN and Geneve since they run over UDP, since
  transport does not provide a hint. This is also useful in case hardware
  offload is ever supported. The type is not currently interpreted by the
  kernel.

- expression: currently only payload supported. Follow up patch adds
  also inner meta support which is required by autogenerated
  dependencies. The exthdr expression should be supported too
  at some point. There is a new inner_ops operation that needs to be
  set on to allow to use an existing expression from the inner expression.

This patch adds a new NFT_PAYLOAD_TUN_HEADER base which allows to match
on the tunnel header fields, eg. vxlan vni.

The payload expression is embedded into nft_inner private area and this
private data area is passed to the payload inner eval function via
direct call.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -375,6 +375,10 @@ static inline void *nft_expr_priv(const struct nft_expr *expr)
 	return (void *)expr->data;
 }
 
+struct nft_expr_info;
+
+int nft_expr_inner_parse(const struct nft_ctx *ctx, const struct nlattr *nla,
+			 struct nft_expr_info *info);
 int nft_expr_clone(struct nft_expr *dst, struct nft_expr *src);
 void nft_expr_destroy(const struct nft_ctx *ctx, struct nft_expr *expr);
 int nft_expr_dump(struct sk_buff *skb, unsigned int attr,
@@ -864,6 +868,7 @@ struct nft_expr_type {
 						       const struct nlattr * const tb[]);
 	void				(*release_ops)(const struct nft_expr_ops *ops);
 	const struct nft_expr_ops	*ops;
+	const struct nft_expr_ops	*inner_ops;
 	struct list_head		list;
 	const char			*name;
 	struct module			*owner;

include/net/netfilter/nf_tables_core.h

@@ -19,6 +19,7 @@ extern struct nft_expr_type nft_rt_type;
 extern struct nft_expr_type nft_exthdr_type;
 extern struct nft_expr_type nft_last_type;
 extern struct nft_expr_type nft_objref_type;
+extern struct nft_expr_type nft_inner_type;
 
 #ifdef CONFIG_NETWORK_SECMARK
 extern struct nft_object_type nft_secmark_obj_type;
@@ -139,4 +140,27 @@ void nft_rt_get_eval(const struct nft_expr *expr,
 		     struct nft_regs *regs, const struct nft_pktinfo *pkt);
 void nft_counter_eval(const struct nft_expr *expr, struct nft_regs *regs,
                       const struct nft_pktinfo *pkt);
+
+enum {
+	NFT_PAYLOAD_CTX_INNER_TUN	= (1 << 0),
+	NFT_PAYLOAD_CTX_INNER_LL	= (1 << 1),
+	NFT_PAYLOAD_CTX_INNER_NH	= (1 << 2),
+	NFT_PAYLOAD_CTX_INNER_TH	= (1 << 3),
+};
+
+struct nft_inner_tun_ctx {
+	u16	inner_tunoff;
+	u16	inner_lloff;
+	u16	inner_nhoff;
+	u16	inner_thoff;
+	__be16	llproto;
+	u8	l4proto;
+	u8      flags;
+};
+
+int nft_payload_inner_offset(const struct nft_pktinfo *pkt);
+void nft_payload_inner_eval(const struct nft_expr *expr, struct nft_regs *regs,
+			    const struct nft_pktinfo *pkt,
+			    struct nft_inner_tun_ctx *ctx);
+
 #endif /* _NET_NF_TABLES_CORE_H */

include/uapi/linux/netfilter/nf_tables.h

@@ -760,6 +760,7 @@ enum nft_payload_bases {
 	NFT_PAYLOAD_NETWORK_HEADER,
 	NFT_PAYLOAD_TRANSPORT_HEADER,
 	NFT_PAYLOAD_INNER_HEADER,
+	NFT_PAYLOAD_TUN_HEADER,
 };
 
 /**
@@ -779,6 +780,31 @@ enum nft_payload_csum_flags {
 	NFT_PAYLOAD_L4CSUM_PSEUDOHDR = (1 << 0),
 };
 
+enum nft_inner_type {
+	NFT_INNER_UNSPEC	= 0,
+	NFT_INNER_VXLAN,
+};
+
+enum nft_inner_flags {
+	NFT_INNER_HDRSIZE	= (1 << 0),
+	NFT_INNER_LL		= (1 << 1),
+	NFT_INNER_NH		= (1 << 2),
+	NFT_INNER_TH		= (1 << 3),
+};
+#define NFT_INNER_MASK		(NFT_INNER_HDRSIZE | NFT_INNER_LL | \
+				 NFT_INNER_NH | NFT_INNER_TH)
+
+enum nft_inner_attributes {
+	NFTA_INNER_UNSPEC,
+	NFTA_INNER_NUM,
+	NFTA_INNER_TYPE,
+	NFTA_INNER_FLAGS,
+	NFTA_INNER_HDRSIZE,
+	NFTA_INNER_EXPR,
+	__NFTA_INNER_MAX
+};
+#define NFTA_INNER_MAX	(__NFTA_INNER_MAX - 1)
+
 /**
  * enum nft_payload_attributes - nf_tables payload expression netlink attributes
  *

net/netfilter/Makefile

@@ -86,7 +86,7 @@ nf_tables-objs := nf_tables_core.o nf_tables_api.o nft_chain_filter.o \
 		  nf_tables_trace.o nft_immediate.o nft_cmp.o nft_range.o \
 		  nft_bitwise.o nft_byteorder.o nft_payload.o nft_lookup.o \
 		  nft_dynset.o nft_meta.o nft_rt.o nft_exthdr.o nft_last.o \
-		  nft_counter.o nft_objref.o \
+		  nft_counter.o nft_objref.o nft_inner.o \
 		  nft_chain_route.o nf_tables_offload.o \
 		  nft_set_hash.o nft_set_bitmap.o nft_set_rbtree.o \
 		  nft_set_pipapo.o

net/netfilter/nf_tables_api.c

@@ -2857,6 +2857,43 @@ static int nf_tables_expr_parse(const struct nft_ctx *ctx,
 	return err;
 }
 
+int nft_expr_inner_parse(const struct nft_ctx *ctx, const struct nlattr *nla,
+			 struct nft_expr_info *info)
+{
+	struct nlattr *tb[NFTA_EXPR_MAX + 1];
+	const struct nft_expr_type *type;
+	int err;
+
+	err = nla_parse_nested_deprecated(tb, NFTA_EXPR_MAX, nla,
+					  nft_expr_policy, NULL);
+	if (err < 0)
+		return err;
+
+	if (!tb[NFTA_EXPR_DATA])
+		return -EINVAL;
+
+	type = __nft_expr_type_get(ctx->family, tb[NFTA_EXPR_NAME]);
+	if (IS_ERR(type))
+		return PTR_ERR(type);
+
+	if (!type->inner_ops)
+		return -EOPNOTSUPP;
+
+	err = nla_parse_nested_deprecated(info->tb, type->maxattr,
+					  tb[NFTA_EXPR_DATA],
+					  type->policy, NULL);
+	if (err < 0)
+		goto err_nla_parse;
+
+	info->attr = nla;
+	info->ops = type->inner_ops;
+
+	return 0;
+
+err_nla_parse:
+	return err;
+}
+
 static int nf_tables_newexpr(const struct nft_ctx *ctx,
 			     const struct nft_expr_info *expr_info,
 			     struct nft_expr *expr)

net/netfilter/nf_tables_core.c

@@ -341,6 +341,7 @@ static struct nft_expr_type *nft_basic_types[] = {
 	&nft_last_type,
 	&nft_counter_type,
 	&nft_objref_type,
+	&nft_inner_type,
 };
 
 static struct nft_object_type *nft_basic_objects[] = {