[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables

This monster-patch tries to do the best job for unifying the data
structures and backend interfaces for the three evil clones ip_tables,
ip6_tables and arp_tables.  In an ideal world we would never have
allowed this kind of copy+paste programming... but well, our world
isn't (yet?) ideal.

o introduce a new x_tables module
o {ip,arp,ip6}_tables depend on this x_tables module
o registration functions for tables, matches and targets are only
  wrappers around x_tables provided functions
o all matches/targets that are used from ip_tables and ip6_tables
  are now implemented as xt_FOOBAR.c files and provide module aliases
  to ipt_FOOBAR and ip6t_FOOBAR
o header files for xt_matches are in include/linux/netfilter/,
  include/linux/netfilter_{ipv4,ipv6} contains compatibility wrappers
  around the xt_FOOBAR.h headers

Based on this patchset we're going to further unify the code,
gradually getting rid of all the layer 3 specific assumptions.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 92 insertions, 0 deletions

diff --git a/net/netfilter/xt_NOTRACK.c b/net/netfilter/xt_NOTRACK.c
new file mode 100644
index 00000000000000..24d477afa9398b
--- /dev/null
+++ b/net/netfilter/xt_NOTRACK.c
@@ -0,0 +1,92 @@
+/* This is a module which is used for setting up fake conntracks
+ * on packets so that they are not seen by the conntrack/NAT code.
+ */
+#include <linux/module.h>
+#include <linux/skbuff.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <net/netfilter/nf_conntrack_compat.h>
+
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_NOTRACK");
+
+static unsigned int
+target(struct sk_buff **pskb,
+       const struct net_device *in,
+       const struct net_device *out,
+       unsigned int hooknum,
+       const void *targinfo,
+       void *userinfo)
+{
+	/* Previously seen (loopback)? Ignore. */
+	if ((*pskb)->nfct != NULL)
+		return XT_CONTINUE;
+
+	/* Attach fake conntrack entry. 
+	   If there is a real ct entry correspondig to this packet, 
+	   it'll hang aroun till timing out. We don't deal with it
+	   for performance reasons. JK */
+	nf_ct_untrack(*pskb);
+	(*pskb)->nfctinfo = IP_CT_NEW;
+	nf_conntrack_get((*pskb)->nfct);
+
+	return XT_CONTINUE;
+}
+
+static int
+checkentry(const char *tablename,
+	   const void *entry,
+           void *targinfo,
+           unsigned int targinfosize,
+           unsigned int hook_mask)
+{
+	if (targinfosize != 0) {
+		printk(KERN_WARNING "NOTRACK: targinfosize %u != 0\n",
+		       targinfosize);
+		return 0;
+	}
+
+	if (strcmp(tablename, "raw") != 0) {
+		printk(KERN_WARNING "NOTRACK: can only be called from \"raw\" table, not \"%s\"\n", tablename);
+		return 0;
+	}
+
+	return 1;
+}
+
+static struct xt_target notrack_reg = { 
+	.name = "NOTRACK", 
+	.target = target, 
+	.checkentry = checkentry,
+	.me = THIS_MODULE,
+};
+static struct xt_target notrack6_reg = { 
+	.name = "NOTRACK", 
+	.target = target, 
+	.checkentry = checkentry,
+	.me = THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	int ret;
+
+	ret = xt_register_target(AF_INET, &notrack_reg);
+	if (ret)
+		return ret;
+
+	ret = xt_register_target(AF_INET6, &notrack6_reg);
+	if (ret)
+		xt_unregister_target(AF_INET, &notrack_reg);
+
+	return ret;
+}
+
+static void __exit fini(void)
+{
+	xt_unregister_target(AF_INET6, &notrack6_reg);
+	xt_unregister_target(AF_INET, &notrack_reg);
+}
+
+module_init(init);
+module_exit(fini);