LXR linux/net/ipv4/netfilter/ipt

   1/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
   2 *
   3 * (C) 2002 by Harald Welte <laforge@netfilter.org>
   4 *
   5 * This program is free software; you can redistribute it and/or modify
   6 * it under the terms of the GNU General Public License version 2 as
   7 * published by the Free Software Foundation.
   8*/
   9
  10#include <linux/in.h>
  11#include <linux/module.h>
  12#include <linux/skbuff.h>
  13#include <linux/ip.h>
  14#include <net/ip.h>
  15#include <linux/tcp.h>
  16#include <net/checksum.h>
  17
  18#include <linux/netfilter/x_tables.h>
  19#include <linux/netfilter_ipv4/ip_tables.h>
  20#include <linux/netfilter_ipv4/ipt_ECN.h>
  21
  22MODULE_LICENSE("GPL");
  23MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  24MODULE_DESCRIPTION("iptables ECN modification module");
  25
  26/* set ECT codepoint from IP header.
  27 *      return false if there was an error. */
  28static inline bool
  29set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  30{
  31        struct iphdr *iph = ip_hdr(skb);
  32
  33        if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  34                __u8 oldtos;
  35                if (!skb_make_writable(skb, sizeof(struct iphdr)))
  36                        return false;
  37                iph = ip_hdr(skb);
  38                oldtos = iph->tos;
  39                iph->tos &= ~IPT_ECN_IP_MASK;
  40                iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  41                nf_csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  42        }
  43        return true;
  44}
  45
  46/* Return false if there was an error. */
  47static inline bool
  48set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  49{
  50        struct tcphdr _tcph, *tcph;
  51        __be16 oldval;
  52
  53        /* Not enought header? */
  54        tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  55        if (!tcph)
  56                return false;
  57
  58        if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  59             tcph->ece == einfo->proto.tcp.ece) &&
  60            (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  61             tcph->cwr == einfo->proto.tcp.cwr))
  62                return true;
  63
  64        if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
  65                return false;
  66        tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
  67
  68        oldval = ((__be16 *)tcph)[6];
  69        if (einfo->operation & IPT_ECN_OP_SET_ECE)
  70                tcph->ece = einfo->proto.tcp.ece;
  71        if (einfo->operation & IPT_ECN_OP_SET_CWR)
  72                tcph->cwr = einfo->proto.tcp.cwr;
  73
  74        nf_proto_csum_replace2(&tcph->check, skb,
  75                                oldval, ((__be16 *)tcph)[6], 0);
  76        return true;
  77}
  78
  79static unsigned int
  80target(struct sk_buff *skb,
  81       const struct net_device *in,
  82       const struct net_device *out,
  83       unsigned int hooknum,
  84       const struct xt_target *target,
  85       const void *targinfo)
  86{
  87        const struct ipt_ECN_info *einfo = targinfo;
  88
  89        if (einfo->operation & IPT_ECN_OP_SET_IP)
  90                if (!set_ect_ip(skb, einfo))
  91                        return NF_DROP;
  92
  93        if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
  94            && ip_hdr(skb)->protocol == IPPROTO_TCP)
  95                if (!set_ect_tcp(skb, einfo))
  96                        return NF_DROP;
  97
  98        return XT_CONTINUE;
  99}
 100
 101static bool
 102checkentry(const char *tablename,
 103           const void *e_void,
 104           const struct xt_target *target,
 105           void *targinfo,
 106           unsigned int hook_mask)
 107{
 108        const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 109        const struct ipt_entry *e = e_void;
 110
 111        if (einfo->operation & IPT_ECN_OP_MASK) {
 112                printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 113                        einfo->operation);
 114                return false;
 115        }
 116        if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 117                printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 118                        einfo->ip_ect);
 119                return false;
 120        }
 121        if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 122            && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 123                printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 124                       "non-tcp rule\n");
 125                return false;
 126        }
 127        return true;
 128}
 129
 130static struct xt_target ipt_ecn_reg __read_mostly = {
 131        .name           = "ECN",
 132        .family         = AF_INET,
 133        .target         = target,
 134        .targetsize     = sizeof(struct ipt_ECN_info),
 135        .table          = "mangle",
 136        .checkentry     = checkentry,
 137        .me             = THIS_MODULE,
 138};
 139
 140static int __init ipt_ecn_init(void)
 141{
 142        return xt_register_target(&ipt_ecn_reg);
 143}
 144
 145static void __exit ipt_ecn_fini(void)
 146{
 147        xt_unregister_target(&ipt_ecn_reg);
 148}
 149
 150module_init(ipt_ecn_init);
 151module_exit(ipt_ecn_fini);
 152