[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, 51 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
new file mode 100644
index 000000000000..5a66b2a3a623
--- /dev/null
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -0,0 +1,51 @@
+/*
+ * connection tracking helpers.
+ *
+ * 16 Dec 2003: Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
+ *	- generalize L3 protocol dependent part.
+ *
+ * Derived from include/linux/netfiter_ipv4/ip_conntrack_helper.h
+ */
+
+#ifndef _NF_CONNTRACK_HELPER_H
+#define _NF_CONNTRACK_HELPER_H
+#include <net/netfilter/nf_conntrack.h>
+
+struct module;
+
+struct nf_conntrack_helper
+{	
+	struct list_head list; 		/* Internal use. */
+
+	const char *name;		/* name of the module */
+	struct module *me;		/* pointer to self */
+	unsigned int max_expected;	/* Maximum number of concurrent 
+					 * expected connections */
+	unsigned int timeout;		/* timeout for expecteds */
+
+	/* Mask of things we will help (compared against server response) */
+	struct nf_conntrack_tuple tuple;
+	struct nf_conntrack_tuple mask;
+	
+	/* Function to call when data passes; return verdict, or -1 to
+           invalidate. */
+	int (*help)(struct sk_buff **pskb,
+		    unsigned int protoff,
+		    struct nf_conn *ct,
+		    enum ip_conntrack_info conntrackinfo);
+};
+
+extern int nf_conntrack_helper_register(struct nf_conntrack_helper *);
+extern void nf_conntrack_helper_unregister(struct nf_conntrack_helper *);
+
+/* Allocate space for an expectation: this is mandatory before calling
+   nf_conntrack_expect_related.  You will have to call put afterwards. */
+extern struct nf_conntrack_expect *
+nf_conntrack_expect_alloc(struct nf_conn *master);
+extern void nf_conntrack_expect_put(struct nf_conntrack_expect *exp);
+
+/* Add an expected connection: can have more than one per connection */
+extern int nf_conntrack_expect_related(struct nf_conntrack_expect *exp);
+extern void nf_conntrack_unexpect_related(struct nf_conntrack_expect *exp);
+
+#endif /*_NF_CONNTRACK_HELPER_H*/