[NETFILTER]: Add nf_conntrack subsystem.

The existing connection tracking subsystem in netfilter can only
handle ipv4.  There were basically two choices present to add
connection tracking support for ipv6.  We could either duplicate all
of the ipv4 connection tracking code into an ipv6 counterpart, or (the
choice taken by these patches) we could design a generic layer that
could handle both ipv4 and ipv6 and thus requiring only one sub-protocol
(TCP, UDP, etc.) connection tracking helper module to be written.

In fact nf_conntrack is capable of working with any layer 3
protocol.

The existing ipv4 specific conntrack code could also not deal
with the pecularities of doing connection tracking on ipv6,
which is also cured here.  For example, these issues include:

1) ICMPv6 handling, which is used for neighbour discovery in
   ipv6 thus some messages such as these should not participate
   in connection tracking since effectively they are like ARP
   messages

2) fragmentation must be handled differently in ipv6, because
   the simplistic "defrag, connection track and NAT, refrag"
   (which the existing ipv4 connection tracking does) approach simply
   isn't feasible in ipv6

3) ipv6 extension header parsing must occur at the correct spots
   before and after connection tracking decisions, and there were
   no provisions for this in the existing connection tracking
   design

4) ipv6 has no need for stateful NAT

The ipv4 specific conntrack layer is kept around, until all of
the ipv4 specific conntrack helpers are ported over to nf_conntrack
and it is feature complete.  Once that occurs, the old conntrack
stuff will get placed into the feature-removal-schedule and we will
fully kill it off 6 months later.

Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

1 files changed, 93 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_conntrack_l3proto.h b/include/net/netfilter/nf_conntrack_l3proto.h
new file mode 100644
index 00000000000..01663e5b33d
--- /dev/null
+++ b/include/net/netfilter/nf_conntrack_l3proto.h
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C)2003,2004 USAGI/WIDE Project
+ *
+ * Header for use in defining a given L3 protocol for connection tracking.
+ *
+ * Author:
+ *	Yasuyuki Kozakai @USAGI	<yasuyuki.kozakai@toshiba.co.jp>
+ *
+ * Derived from include/netfilter_ipv4/ip_conntrack_protocol.h
+ */
+
+#ifndef _NF_CONNTRACK_L3PROTO_H
+#define _NF_CONNTRACK_L3PROTO_H
+#include <linux/seq_file.h>
+#include <net/netfilter/nf_conntrack.h>
+
+struct nf_conntrack_l3proto
+{
+	/* Next pointer. */
+	struct list_head list;
+
+	/* L3 Protocol Family number. ex) PF_INET */
+	u_int16_t l3proto;
+
+	/* Protocol name */
+	const char *name;
+
+	/*
+	 * Try to fill in the third arg: nhoff is offset of l3 proto
+         * hdr.  Return true if possible.
+	 */
+	int (*pkt_to_tuple)(const struct sk_buff *skb, unsigned int nhoff,
+			    struct nf_conntrack_tuple *tuple);
+
+	/*
+	 * Invert the per-proto part of the tuple: ie. turn xmit into reply.
+	 * Some packets can't be inverted: return 0 in that case.
+	 */
+	int (*invert_tuple)(struct nf_conntrack_tuple *inverse,
+			    const struct nf_conntrack_tuple *orig);
+
+	/* Print out the per-protocol part of the tuple. */
+	int (*print_tuple)(struct seq_file *s,
+			   const struct nf_conntrack_tuple *);
+
+	/* Print out the private part of the conntrack. */
+	int (*print_conntrack)(struct seq_file *s, const struct nf_conn *);
+
+	/* Returns verdict for packet, or -1 for invalid. */
+	int (*packet)(struct nf_conn *conntrack,
+		      const struct sk_buff *skb,
+		      enum ip_conntrack_info ctinfo);
+
+	/*
+	 * Called when a new connection for this protocol found;
+	 * returns TRUE if it's OK.  If so, packet() called next.
+	 */
+	int (*new)(struct nf_conn *conntrack, const struct sk_buff *skb);
+
+	/* Called when a conntrack entry is destroyed */
+	void (*destroy)(struct nf_conn *conntrack);
+
+	/*
+	 * Called before tracking. 
+	 *	*dataoff: offset of protocol header (TCP, UDP,...) in *pskb
+	 *	*protonum: protocol number
+	 */
+	int (*prepare)(struct sk_buff **pskb, unsigned int hooknum,
+		       unsigned int *dataoff, u_int8_t *protonum);
+
+	u_int32_t (*get_features)(const struct nf_conntrack_tuple *tuple);
+
+	/* Module (if any) which this is connected to. */
+	struct module *me;
+};
+
+extern struct nf_conntrack_l3proto *nf_ct_l3protos[AF_MAX];
+
+/* Protocol registration. */
+extern int nf_conntrack_l3proto_register(struct nf_conntrack_l3proto *proto);
+extern void nf_conntrack_l3proto_unregister(struct nf_conntrack_l3proto *proto);
+
+static inline struct nf_conntrack_l3proto *
+nf_ct_find_l3proto(u_int16_t l3proto)
+{
+	return nf_ct_l3protos[l3proto];
+}
+
+/* Existing built-in protocols */
+extern struct nf_conntrack_l3proto nf_conntrack_l3proto_ipv4;
+extern struct nf_conntrack_l3proto nf_conntrack_l3proto_ipv6;
+extern struct nf_conntrack_l3proto nf_conntrack_generic_l3proto;
+#endif /*_NF_CONNTRACK_L3PROTO_H*/