/* iptables module for the packet checksum mangling
   *
   * (C) 2002 by Harald Welte <laforge@netfilter.org>
   * (C) 2010 Red Hat, Inc.
   *
   * Author: Michael S. Tsirkin <mst@redhat.com>
   *
   * 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/x_tables.h>
  #include <linux/netfilter/xt_CHECKSUM.h>
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Michael S. Tsirkin <mst@redhat.com>");
  MODULE_DESCRIPTION("Xtables: checksum modification");
  MODULE_ALIAS("ipt_CHECKSUM");
  MODULE_ALIAS("ip6t_CHECKSUM");
  
  static unsigned int
  checksum_tg(struct sk_buff *skb, const struct xt_action_param *par)
  {
  	if (skb->ip_summed == CHECKSUM_PARTIAL)
  		skb_checksum_help(skb);
  
  	return XT_CONTINUE;
  }
  
  static int checksum_tg_check(const struct xt_tgchk_param *par)
  {
  	const struct xt_CHECKSUM_info *einfo = par->targinfo;
  
  	if (einfo->operation & ~XT_CHECKSUM_OP_FILL) {
  		pr_info("unsupported CHECKSUM operation %x
  ", einfo->operation);
  		return -EINVAL;
  	}
  	if (!einfo->operation) {
  		pr_info("no CHECKSUM operation enabled
  ");
  		return -EINVAL;
  	}
  	return 0;
  }
  
  static struct xt_target checksum_tg_reg __read_mostly = {
  	.name		= "CHECKSUM",
  	.family		= NFPROTO_UNSPEC,
  	.target		= checksum_tg,
  	.targetsize	= sizeof(struct xt_CHECKSUM_info),
  	.table		= "mangle",
  	.checkentry	= checksum_tg_check,
  	.me		= THIS_MODULE,
  };
  
  static int __init checksum_tg_init(void)
  {
  	return xt_register_target(&checksum_tg_reg);
  }
  
  static void __exit checksum_tg_exit(void)
  {
  	xt_unregister_target(&checksum_tg_reg);
  }
  
  module_init(checksum_tg_init);
  module_exit(checksum_tg_exit);