xt_CHECKSUM.c

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/* iptables module for the packet checksum mangling
 *
 * (C) 2002 by Harald Welte <[email protected]>
 * (C) 2010 Red Hat, Inc.
 *
 * Author: Michael S. Tsirkin <[email protected]>
 *
 * 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 <[email protected]>");
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\n", einfo->operation);
        return -EINVAL;
    }
    if (!einfo->operation) {
        pr_info("no CHECKSUM operation enabled\n");
        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);