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/* 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("iptables ECN modification module");
/* set ECT codepoint from IP header.
* return false if there was an error. */
static inline bool
set_ect_ip(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
{
struct iphdr *iph = ip_hdr(*pskb);
if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
__u8 oldtos;
if (!skb_make_writable(*pskb, sizeof(struct iphdr)))
return false;
iph = ip_hdr(*pskb);
oldtos = iph->tos;
iph->tos &= ~IPT_ECN_IP_MASK;
iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
nf_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 **pskb, const struct ipt_ECN_info *einfo)
{
struct tcphdr _tcph, *tcph;
__be16 oldval;
/* Not enought header? */
tcph = skb_header_pointer(*pskb, ip_hdrlen(*pskb),
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(*pskb, ip_hdrlen(*pskb) + sizeof(*tcph)))
return false;
tcph = (void *)ip_hdr(*pskb) + ip_hdrlen(*pskb);
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;
nf_proto_csum_replace2(&tcph->check, *pskb,
oldval, ((__be16 *)tcph)[6], 0);
return true;
}
static unsigned int
target(struct sk_buff **pskb,
const struct net_device *in,
const struct net_device *out,
unsigned int hooknum,
const struct xt_target *target,
const void *targinfo)
{
const struct ipt_ECN_info *einfo = targinfo;
if (einfo->operation & IPT_ECN_OP_SET_IP)
if (!set_ect_ip(pskb, einfo))
return NF_DROP;
if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
&& ip_hdr(*pskb)->protocol == IPPROTO_TCP)
if (!set_ect_tcp(pskb, einfo))
return NF_DROP;
return XT_CONTINUE;
}
static bool
checkentry(const char *tablename,
const void *e_void,
const struct xt_target *target,
void *targinfo,
unsigned int hook_mask)
{
const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
const struct ipt_entry *e = e_void;
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 ipt_ecn_reg __read_mostly = {
.name = "ECN",
.family = AF_INET,
.target = target,
.targetsize = sizeof(struct ipt_ECN_info),
.table = "mangle",
.checkentry = checkentry,
.me = THIS_MODULE,
};
static int __init ipt_ecn_init(void)
{
return xt_register_target(&ipt_ecn_reg);
}
static void __exit ipt_ecn_fini(void)
{
xt_unregister_target(&ipt_ecn_reg);
}
module_init(ipt_ecn_init);
module_exit(ipt_ecn_fini);
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