/* 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 <linux/ipv6.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("Xtables: Packet length (Layer3,4,5) match");

  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ipt_length");
  MODULE_ALIAS("ip6t_length");

  static bool

  length_mt(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_length_info *info = par->matchinfo;

  	u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);

  	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  }

  static bool

  length_mt6(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_length_info *info = par->matchinfo;

  	const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
  				 sizeof(struct ipv6hdr);

  	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  }

  static struct xt_match length_mt_reg[] __read_mostly = {

  	{
  		.name		= "length",

  		.family		= NFPROTO_IPV4,

  		.match		= length_mt,

  		.matchsize	= sizeof(struct xt_length_info),
  		.me		= THIS_MODULE,
  	},
  	{
  		.name		= "length",

  		.family		= NFPROTO_IPV6,

  		.match		= length_mt6,

  		.matchsize	= sizeof(struct xt_length_info),
  		.me		= THIS_MODULE,
  	},

  };

  static int __init length_mt_init(void)

  {

  	return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));

  }

  static void __exit length_mt_exit(void)

  {

  	xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));

  }

  module_init(length_mt_init);
  module_exit(length_mt_exit);