root/net/ipv4/netfilter/ipt_ecn.c

DEFINITIONS

1. match_ip
2. match_tcp
3. ecn_mt
4. ecn_mt_check
5. ecn_mt_init
6. ecn_mt_exit

/* IP tables module for matching the value of the IPv4 and TCP ECN bits
 *
 * (C) 2002 by Harald Welte <laforge@gnumonks.org>
 *
 * 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/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_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_ecn.h>

MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match for IPv4");
MODULE_LICENSE("GPL");

static inline bool match_ip(const struct sk_buff *skb,
                            const struct ipt_ecn_info *einfo)
{
        return (ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect;
}

static inline bool match_tcp(const struct sk_buff *skb,
                             const struct ipt_ecn_info *einfo,
                             bool *hotdrop)
{
        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, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
        if (th == NULL) {
                *hotdrop = false;
                return false;
        }

        if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
                if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
                        if (th->ece == 1)
                                return false;
                } else {
                        if (th->ece == 0)
                                return false;
                }
        }

        if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
                if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
                        if (th->cwr == 1)
                                return false;
                } else {
                        if (th->cwr == 0)
                                return false;
                }
        }

        return true;
}

static bool ecn_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
        const struct ipt_ecn_info *info = par->matchinfo;

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

        if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
                if (ip_hdr(skb)->protocol != IPPROTO_TCP)
                        return false;
                if (!match_tcp(skb, info, par->hotdrop))
                        return false;
        }

        return true;
}

static bool ecn_mt_check(const struct xt_mtchk_param *par)
{
        const struct ipt_ecn_info *info = par->matchinfo;
        const struct ipt_ip *ip = par->entryinfo;

        if (info->operation & IPT_ECN_OP_MATCH_MASK)
                return false;

        if (info->invert & IPT_ECN_OP_MATCH_MASK)
                return false;

        if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
            && ip->proto != IPPROTO_TCP) {
                printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
                       " non-tcp packets\n");
                return false;
        }

        return true;
}

static struct xt_match ecn_mt_reg __read_mostly = {
        .name           = "ecn",
        .family         = NFPROTO_IPV4,
        .match          = ecn_mt,
        .matchsize      = sizeof(struct ipt_ecn_info),
        .checkentry     = ecn_mt_check,
        .me             = THIS_MODULE,
};

static int __init ecn_mt_init(void)
{
        return xt_register_match(&ecn_mt_reg);
}

static void __exit ecn_mt_exit(void)
{
        xt_unregister_match(&ecn_mt_reg);
}

module_init(ecn_mt_init);
module_exit(ecn_mt_exit);