netfilter: xtables: add CT target

Add a new target for the raw table, which can be used to specify conntrack
parameters for specific connections, f.i. the conntrack helper.

The target attaches a "template" connection tracking entry to the skb, which
is used by the conntrack core when initializing a new conntrack.

Signed-off-by: Patrick McHardy <kaber@trash.net>

include/linux/netfilter/Kbuild

@@ -6,6 +6,7 @@ header-y += nfnetlink_queue.h
 header-y += xt_CLASSIFY.h
 header-y += xt_CONNMARK.h
 header-y += xt_CONNSECMARK.h
+header-y += xt_CT.h
 header-y += xt_DSCP.h
 header-y += xt_LED.h
 header-y += xt_MARK.h

include/linux/netfilter/xt_CT.h

@@ -0,0 +1,17 @@
+#ifndef _XT_CT_H
+#define _XT_CT_H
+
+#define XT_CT_NOTRACK	0x1
+
+struct xt_ct_target_info {
+	u_int16_t	flags;
+	u_int16_t	__unused;
+	u_int32_t	ct_events;
+	u_int32_t	exp_events;
+	char		helper[16];
+
+	/* Used internally by the kernel */
+	struct nf_conn	*ct __attribute__((aligned(8)));
+};
+
+#endif /* _XT_CT_H */