/*
   * Xtables module for matching the value of the IPv4/IPv6 and TCP ECN bits

   *

   * (C) 2002 by Harald Welte <laforge@gnumonks.org>

   * (C) 2011 Patrick McHardy <kaber@trash.net>

   *
   * 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.
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/in.h>
  #include <linux/ip.h>

  #include <net/ip.h>

  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/tcp.h>

  #include <linux/netfilter/x_tables.h>

  #include <linux/netfilter/xt_ecn.h>

  #include <linux/netfilter_ipv4/ip_tables.h>

  #include <linux/netfilter_ipv6/ip6_tables.h>

  
  MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");

  MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match");

  MODULE_LICENSE("GPL");

  MODULE_ALIAS("ipt_ecn");

  MODULE_ALIAS("ip6t_ecn");

  static bool match_tcp(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_ecn_info *einfo = par->matchinfo;

  	struct tcphdr _tcph;
  	const struct tcphdr *th;

  
  	/* In practice, TCP match does this, so can't fail.  But let's
  	 * be good citizens.
  	 */

  	th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);

  	if (th == NULL)

  		return false;

  	if (einfo->operation & XT_ECN_OP_MATCH_ECE) {
  		if (einfo->invert & XT_ECN_OP_MATCH_ECE) {

  			if (th->ece == 1)

  				return false;

  		} else {
  			if (th->ece == 0)

  				return false;

  		}
  	}

  	if (einfo->operation & XT_ECN_OP_MATCH_CWR) {
  		if (einfo->invert & XT_ECN_OP_MATCH_CWR) {

  			if (th->cwr == 1)

  				return false;

  		} else {
  			if (th->cwr == 0)

  				return false;

  		}
  	}

  	return true;

  }

  static inline bool match_ip(const struct sk_buff *skb,
  			    const struct xt_ecn_info *einfo)
  {
  	return ((ip_hdr(skb)->tos & XT_ECN_IP_MASK) == einfo->ip_ect) ^
  	       !!(einfo->invert & XT_ECN_OP_MATCH_IP);
  }
  
  static bool ecn_mt4(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	const struct xt_ecn_info *info = par->matchinfo;

  	if (info->operation & XT_ECN_OP_MATCH_IP && !match_ip(skb, info))
  		return false;

  	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
  	    !match_tcp(skb, par))
  		return false;

  	return true;

  }

  static int ecn_mt_check4(const struct xt_mtchk_param *par)

  {

  	const struct xt_ecn_info *info = par->matchinfo;

  	const struct ipt_ip *ip = par->entryinfo;

  	if (info->operation & XT_ECN_OP_MATCH_MASK)

  		return -EINVAL;

  	if (info->invert & XT_ECN_OP_MATCH_MASK)

  		return -EINVAL;

  	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&

  	    (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {

  		pr_info("cannot match TCP bits in rule for non-tcp packets
  ");

  		return -EINVAL;

  	}

  	return 0;

  }

  static inline bool match_ipv6(const struct sk_buff *skb,
  			      const struct xt_ecn_info *einfo)
  {
  	return (((ipv6_hdr(skb)->flow_lbl[0] >> 4) & XT_ECN_IP_MASK) ==
  	        einfo->ip_ect) ^
  	       !!(einfo->invert & XT_ECN_OP_MATCH_IP);
  }
  
  static bool ecn_mt6(const struct sk_buff *skb, struct xt_action_param *par)
  {
  	const struct xt_ecn_info *info = par->matchinfo;
  
  	if (info->operation & XT_ECN_OP_MATCH_IP && !match_ipv6(skb, info))
  		return false;
  
  	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
  	    !match_tcp(skb, par))
  		return false;
  
  	return true;
  }
  
  static int ecn_mt_check6(const struct xt_mtchk_param *par)
  {
  	const struct xt_ecn_info *info = par->matchinfo;
  	const struct ip6t_ip6 *ip = par->entryinfo;
  
  	if (info->operation & XT_ECN_OP_MATCH_MASK)
  		return -EINVAL;
  
  	if (info->invert & XT_ECN_OP_MATCH_MASK)
  		return -EINVAL;
  
  	if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
  	    (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
  		pr_info("cannot match TCP bits in rule for non-tcp packets
  ");
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static struct xt_match ecn_mt_reg[] __read_mostly = {
  	{
  		.name		= "ecn",
  		.family		= NFPROTO_IPV4,
  		.match		= ecn_mt4,
  		.matchsize	= sizeof(struct xt_ecn_info),
  		.checkentry	= ecn_mt_check4,
  		.me		= THIS_MODULE,
  	},
  	{
  		.name		= "ecn",
  		.family		= NFPROTO_IPV6,
  		.match		= ecn_mt6,
  		.matchsize	= sizeof(struct xt_ecn_info),
  		.checkentry	= ecn_mt_check6,
  		.me		= THIS_MODULE,
  	},

  };

  static int __init ecn_mt_init(void)

  {

  	return xt_register_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));

  }

  static void __exit ecn_mt_exit(void)

  {

  	xt_unregister_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));

  }

  module_init(ecn_mt_init);
  module_exit(ecn_mt_exit);