/* iptables module to match on related connections */
  /*
   * (C) 2001 Martin Josefsson <gandalf@wlug.westbo.se>
   *
   * 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/module.h>
  #include <linux/skbuff.h>
  #include <linux/netfilter.h>

  #include <net/netfilter/nf_conntrack.h>
  #include <net/netfilter/nf_conntrack_core.h>
  #include <net/netfilter/nf_conntrack_helper.h>

  #include <linux/netfilter/x_tables.h>
  #include <linux/netfilter/xt_helper.h>

  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Martin Josefsson <gandalf@netfilter.org>");

  MODULE_DESCRIPTION("Xtables: Related connection matching");

  MODULE_ALIAS("ipt_helper");
  MODULE_ALIAS("ip6t_helper");

  static bool

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

  {

  	const struct xt_helper_info *info = par->matchinfo;

  	const struct nf_conn *ct;
  	const struct nf_conn_help *master_help;

  	const struct nf_conntrack_helper *helper;

  	enum ip_conntrack_info ctinfo;

  	bool ret = info->invert;

  	ct = nf_ct_get(skb, &ctinfo);

  	if (!ct || !ct->master)

  		return ret;

  	master_help = nfct_help(ct->master);

  	if (!master_help)
  		return ret;

  	/* rcu_read_lock()ed by nf_hook_slow */
  	helper = rcu_dereference(master_help->helper);
  	if (!helper)
  		return ret;

  
  	if (info->name[0] == '\0')

  		ret = !ret;

  	else

  		ret ^= !strncmp(helper->name, info->name,
  				strlen(helper->name));

  	return ret;
  }

  static int helper_mt_check(const struct xt_mtchk_param *par)

  {

  	struct xt_helper_info *info = par->matchinfo;

  	int ret;

  	ret = nf_ct_l3proto_try_module_get(par->family);
  	if (ret < 0) {

  		pr_info("cannot load conntrack support for proto=%u
  ",
  			par->family);

  		return ret;

  	}

  	info->name[29] = '\0';

  	return 0;

  }

  static void helper_mt_destroy(const struct xt_mtdtor_param *par)

  {

  	nf_ct_l3proto_module_put(par->family);

  }

  static struct xt_match helper_mt_reg __read_mostly = {
  	.name       = "helper",
  	.revision   = 0,
  	.family     = NFPROTO_UNSPEC,
  	.checkentry = helper_mt_check,
  	.match      = helper_mt,
  	.destroy    = helper_mt_destroy,
  	.matchsize  = sizeof(struct xt_helper_info),
  	.me         = THIS_MODULE,

  };

  static int __init helper_mt_init(void)

  {

  	return xt_register_match(&helper_mt_reg);

  }

  static void __exit helper_mt_exit(void)

  {

  	xt_unregister_match(&helper_mt_reg);

  }

  module_init(helper_mt_init);
  module_exit(helper_mt_exit);