netfilter: add generic flow table infrastructure

This patch defines the API to interact with flow tables, this allows to
add, delete and lookup for entries in the flow table. This also adds the
generic garbage code that removes entries that have expired, ie. no
traffic has been seen for a while.

Users of the flow table infrastructure can delete entries via
flow_offload_dead(), which sets the dying bit, this signals the garbage
collector to release an entry from user context.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_flow_table.h

 #ifndef _NF_FLOW_TABLE_H
 #define _NF_FLOW_TABLE_H
 
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/netdevice.h>
 #include <linux/rhashtable.h>
+#include <linux/rcupdate.h>
+#include <net/dst.h>
 
 struct nf_flowtable;
 
@@ -20,4 +25,93 @@ struct nf_flowtable {
 	struct delayed_work		gc_work;
 };
 
+enum flow_offload_tuple_dir {
+	FLOW_OFFLOAD_DIR_ORIGINAL,
+	FLOW_OFFLOAD_DIR_REPLY,
+	__FLOW_OFFLOAD_DIR_MAX		= FLOW_OFFLOAD_DIR_REPLY,
+};
+#define FLOW_OFFLOAD_DIR_MAX	(__FLOW_OFFLOAD_DIR_MAX + 1)
+
+struct flow_offload_tuple {
+	union {
+		struct in_addr		src_v4;
+		struct in6_addr		src_v6;
+	};
+	union {
+		struct in_addr		dst_v4;
+		struct in6_addr		dst_v6;
+	};
+	struct {
+		__be16			src_port;
+		__be16			dst_port;
+	};
+
+	int				iifidx;
+
+	u8				l3proto;
+	u8				l4proto;
+	u8				dir;
+
+	int				oifidx;
+
+	struct dst_entry		*dst_cache;
+};
+
+struct flow_offload_tuple_rhash {
+	struct rhash_head		node;
+	struct flow_offload_tuple	tuple;
+};
+
+#define FLOW_OFFLOAD_SNAT	0x1
+#define FLOW_OFFLOAD_DNAT	0x2
+#define FLOW_OFFLOAD_DYING	0x4
+
+struct flow_offload {
+	struct flow_offload_tuple_rhash		tuplehash[FLOW_OFFLOAD_DIR_MAX];
+	u32					flags;
+	union {
+		/* Your private driver data here. */
+		u32		timeout;
+	};
+};
+
+#define NF_FLOW_TIMEOUT (30 * HZ)
+
+struct nf_flow_route {
+	struct {
+		struct dst_entry	*dst;
+		int			ifindex;
+	} tuple[FLOW_OFFLOAD_DIR_MAX];
+};
+
+struct flow_offload *flow_offload_alloc(struct nf_conn *ct,
+					struct nf_flow_route *route);
+void flow_offload_free(struct flow_offload *flow);
+
+int flow_offload_add(struct nf_flowtable *flow_table, struct flow_offload *flow);
+void flow_offload_del(struct nf_flowtable *flow_table, struct flow_offload *flow);
+struct flow_offload_tuple_rhash *flow_offload_lookup(struct nf_flowtable *flow_table,
+						     struct flow_offload_tuple *tuple);
+int nf_flow_table_iterate(struct nf_flowtable *flow_table,
+			  void (*iter)(struct flow_offload *flow, void *data),
+			  void *data);
+void nf_flow_offload_work_gc(struct work_struct *work);
+extern const struct rhashtable_params nf_flow_offload_rhash_params;
+
+void flow_offload_dead(struct flow_offload *flow);
+
+int nf_flow_snat_port(const struct flow_offload *flow,
+		      struct sk_buff *skb, unsigned int thoff,
+		      u8 protocol, enum flow_offload_tuple_dir dir);
+int nf_flow_dnat_port(const struct flow_offload *flow,
+		      struct sk_buff *skb, unsigned int thoff,
+		      u8 protocol, enum flow_offload_tuple_dir dir);
+
+struct flow_ports {
+	__be16 source, dest;
+};
+
+#define MODULE_ALIAS_NF_FLOWTABLE(family)	\
+	MODULE_ALIAS("nf-flowtable-" __stringify(family))
+
 #endif /* _FLOW_OFFLOAD_H */

net/netfilter/Kconfig

@@ -657,6 +657,13 @@ endif # NF_TABLES_NETDEV
 
 endif # NF_TABLES
 
+config NF_FLOW_TABLE
+	tristate "Netfilter flow table module"
+	help
+	  This option adds the flow table core infrastructure.
+
+	  To compile it as a module, choose M here.
+
 config NETFILTER_XTABLES
 	tristate "Netfilter Xtables support (required for ip_tables)"
 	default m if NETFILTER_ADVANCED=n

net/netfilter/Makefile

@@ -109,6 +109,9 @@ obj-$(CONFIG_NFT_FIB_NETDEV)	+= nft_fib_netdev.o
 obj-$(CONFIG_NFT_DUP_NETDEV)	+= nft_dup_netdev.o
 obj-$(CONFIG_NFT_FWD_NETDEV)	+= nft_fwd_netdev.o
 
+# flow table infrastructure
+obj-$(CONFIG_NF_FLOW_TABLE)	+= nf_flow_table.o
+
 # generic X tables 
 obj-$(CONFIG_NETFILTER_XTABLES) += x_tables.o xt_tcpudp.o