root/net/ipv4/netfilter/ipt_ECN.c

DEFINITIONS

1. set_ect_ip
2. set_ect_tcp
3. ecn_tg
4. ecn_tg_check
5. ecn_tg_init
6. ecn_tg_exit

/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
 *
 * (C) 2002 by Harald Welte <laforge@netfilter.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/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/ip.h>
#include <linux/tcp.h>
#include <net/checksum.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv4/ipt_ECN.h>

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

/* set ECT codepoint from IP header.
 *      return false if there was an error. */
static inline bool
set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
{
        struct iphdr *iph = ip_hdr(skb);

        if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
                __u8 oldtos;
                if (!skb_make_writable(skb, sizeof(struct iphdr)))
                        return false;
                iph = ip_hdr(skb);
                oldtos = iph->tos;
                iph->tos &= ~IPT_ECN_IP_MASK;
                iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
                csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
        }
        return true;
}

/* Return false if there was an error. */
static inline bool
set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
{
        struct tcphdr _tcph, *tcph;
        __be16 oldval;

        /* Not enought header? */
        tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
        if (!tcph)
                return false;

        if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
             tcph->ece == einfo->proto.tcp.ece) &&
            (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
             tcph->cwr == einfo->proto.tcp.cwr))
                return true;

        if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
                return false;
        tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);

        oldval = ((__be16 *)tcph)[6];
        if (einfo->operation & IPT_ECN_OP_SET_ECE)
                tcph->ece = einfo->proto.tcp.ece;
        if (einfo->operation & IPT_ECN_OP_SET_CWR)
                tcph->cwr = einfo->proto.tcp.cwr;

        inet_proto_csum_replace2(&tcph->check, skb,
                                 oldval, ((__be16 *)tcph)[6], 0);
        return true;
}

static unsigned int
ecn_tg(struct sk_buff *skb, const struct xt_target_param *par)
{
        const struct ipt_ECN_info *einfo = par->targinfo;

        if (einfo->operation & IPT_ECN_OP_SET_IP)
                if (!set_ect_ip(skb, einfo))
                        return NF_DROP;

        if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
            && ip_hdr(skb)->protocol == IPPROTO_TCP)
                if (!set_ect_tcp(skb, einfo))
                        return NF_DROP;

        return XT_CONTINUE;
}

static bool ecn_tg_check(const struct xt_tgchk_param *par)
{
        const struct ipt_ECN_info *einfo = par->targinfo;
        const struct ipt_entry *e = par->entryinfo;

        if (einfo->operation & IPT_ECN_OP_MASK) {
                printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
                        einfo->operation);
                return false;
        }
        if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
                printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
                        einfo->ip_ect);
                return false;
        }
        if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
            && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
                printk(KERN_WARNING "ECN: cannot use TCP operations on a "
                       "non-tcp rule\n");
                return false;
        }
        return true;
}

static struct xt_target ecn_tg_reg __read_mostly = {
        .name           = "ECN",
        .family         = NFPROTO_IPV4,
        .target         = ecn_tg,
        .targetsize     = sizeof(struct ipt_ECN_info),
        .table          = "mangle",
        .checkentry     = ecn_tg_check,
        .me             = THIS_MODULE,
};

static int __init ecn_tg_init(void)
{
        return xt_register_target(&ecn_tg_reg);
}

static void __exit ecn_tg_exit(void)
{
        xt_unregister_target(&ecn_tg_reg);
}

module_init(ecn_tg_init);
module_exit(ecn_tg_exit);