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/* iptables module for setting the IPv4 DSCP field, Version 1.8

 *

 * (C) 2002 by Harald Welte <laforge@gnumonks.org>

 * based on ipt_FTOS.c (C) 2000 by Matthew G. Marsh <mgm@paktronix.com>

 * This software is distributed under GNU GPL v2, 1991

 *

 * See RFC2474 for a description of the DSCP field within the IP Header.

 *

 * ipt_DSCP.c,v 1.8 2002/08/06 18:41:57 laforge Exp

*/

#include <linux/module.h>

#include <linux/skbuff.h>

#include <linux/ip.h>

#include <net/checksum.h>

#include <linux/netfilter_ipv4/ip_tables.h>

#include <linux/netfilter_ipv4/ipt_DSCP.h>

MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");

MODULE_DESCRIPTION("IP tables DSCP modification module");

MODULE_LICENSE("GPL");

static unsigned int

target(struct sk_buff **pskb,

       unsigned int hooknum,

       const struct net_device *in,

       const struct net_device *out,

       const void *targinfo,

       void *userinfo)

{

        struct iphdr *iph = (*pskb)->nh.iph;

        const struct ipt_DSCP_info *dinfo = targinfo;

        u_int8_t sh_dscp = ((dinfo->dscp << IPT_DSCP_SHIFT) & IPT_DSCP_MASK);

        if ((iph->tos & IPT_DSCP_MASK) != sh_dscp) {

                u_int16_t diffs[2];

                /* raw socket (tcpdump) may have clone of incoming

                 * skb: don't disturb it --RR */

                if (skb_cloned(*pskb) && !(*pskb)->sk) {

                        struct sk_buff *nskb = skb_copy(*pskb, GFP_ATOMIC);

                        if (!nskb)

                                return NF_DROP;

                        kfree_skb(*pskb);

                        *pskb = nskb;

                        iph = (*pskb)->nh.iph;

                }

                diffs[0] = htons(iph->tos) ^ 0xFFFF;

                iph->tos = (iph->tos & ~IPT_DSCP_MASK) | sh_dscp;

                diffs[1] = htons(iph->tos);

                iph->check = csum_fold(csum_partial((char *)diffs,

                                                    sizeof(diffs),

                                                    iph->check^0xFFFF));

                (*pskb)->nfcache |= NFC_ALTERED;

        }

        return IPT_CONTINUE;

}

static int

checkentry(const char *tablename,

           const struct ipt_entry *e,

           void *targinfo,

           unsigned int targinfosize,

           unsigned int hook_mask)

{

        const u_int8_t dscp = ((struct ipt_DSCP_info *)targinfo)->dscp;

        if (targinfosize != IPT_ALIGN(sizeof(struct ipt_DSCP_info))) {

                printk(KERN_WARNING "DSCP: targinfosize %u != %Zu\n",

                       targinfosize,

                       IPT_ALIGN(sizeof(struct ipt_DSCP_info)));

                return 0;

        }

        if (strcmp(tablename, "mangle") != 0) {

                printk(KERN_WARNING "DSCP: can only be called from \"mangle\" table, not \"%s\"\n", tablename);

                return 0;

        }

        if ((dscp > IPT_DSCP_MAX)) {

                printk(KERN_WARNING "DSCP: dscp %x out of range\n", dscp);

                return 0;

        }

        return 1;

}

static struct ipt_target ipt_dscp_reg

= { { NULL, NULL }, "DSCP", target, checkentry, NULL, THIS_MODULE };

static int __init init(void)

{

        if (ipt_register_target(&ipt_dscp_reg))

                return -EINVAL;

        return 0;

}

static void __exit fini(void)

{

        ipt_unregister_target(&ipt_dscp_reg);

}

module_init(init);

module_exit(fini);