[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, 98 insertions, 0 deletions

diff --git a/net/netfilter/xt_length.c b/net/netfilter/xt_length.c
new file mode 100644
index 000000000000..ab6c710cf88f
--- /dev/null
+++ b/net/netfilter/xt_length.c
@@ -0,0 +1,98 @@
+/* Kernel module to match packet length. */
+/* (C) 1999-2001 James Morris <jmorros@intercode.com.au>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <net/ip.h>
+
+#include <linux/netfilter/xt_length.h>
+#include <linux/netfilter/x_tables.h>
+
+MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
+MODULE_DESCRIPTION("IP tables packet length matching module");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_length");
+MODULE_ALIAS("ip6t_length");
+
+static int
+match(const struct sk_buff *skb,
+      const struct net_device *in,
+      const struct net_device *out,
+      const void *matchinfo,
+      int offset,
+      unsigned int protoff,
+      int *hotdrop)
+{
+	const struct xt_length_info *info = matchinfo;
+	u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
+	
+	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
+}
+
+static int
+match6(const struct sk_buff *skb,
+       const struct net_device *in,
+       const struct net_device *out,
+       const void *matchinfo,
+       int offset,
+       unsigned int protoff,
+       int *hotdrop)
+{
+	const struct xt_length_info *info = matchinfo;
+	u_int16_t pktlen = ntohs(skb->nh.ipv6h->payload_len) + sizeof(struct ipv6hdr);
+	
+	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
+}
+
+static int
+checkentry(const char *tablename,
+           const void *ip,
+           void *matchinfo,
+           unsigned int matchsize,
+           unsigned int hook_mask)
+{
+	if (matchsize != XT_ALIGN(sizeof(struct xt_length_info)))
+		return 0;
+
+	return 1;
+}
+
+static struct xt_match length_match = {
+	.name		= "length",
+	.match		= &match,
+	.checkentry	= &checkentry,
+	.me		= THIS_MODULE,
+};
+static struct xt_match length6_match = {
+	.name		= "length",
+	.match		= &match6,
+	.checkentry	= &checkentry,
+	.me		= THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	int ret;
+	ret = xt_register_match(AF_INET, &length_match);
+	if (ret)
+		return ret;
+	ret = xt_register_match(AF_INET6, &length6_match);
+	if (ret)
+		xt_unregister_match(AF_INET, &length_match);
+
+	return ret;
+}
+
+static void __exit fini(void)
+{
+	xt_unregister_match(AF_INET, &length_match);
+	xt_unregister_match(AF_INET6, &length6_match);
+}
+
+module_init(init);
+module_exit(fini);