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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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("Xtables: Explicit Congestion Notification (ECN) flag modification");
  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                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 enough 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        inet_proto_csum_replace2(&tcph->check, skb,
  75                                 oldval, ((__be16 *)tcph)[6], 0);
  76        return true;
  77}
  78
  79static unsigned int
  80ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
  81{
  82        const struct ipt_ECN_info *einfo = par->targinfo;
  83
  84        if (einfo->operation & IPT_ECN_OP_SET_IP)
  85                if (!set_ect_ip(skb, einfo))
  86                        return NF_DROP;
  87
  88        if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
  89            ip_hdr(skb)->protocol == IPPROTO_TCP)
  90                if (!set_ect_tcp(skb, einfo))
  91                        return NF_DROP;
  92
  93        return XT_CONTINUE;
  94}
  95
  96static int ecn_tg_check(const struct xt_tgchk_param *par)
  97{
  98        const struct ipt_ECN_info *einfo = par->targinfo;
  99        const struct ipt_entry *e = par->entryinfo;
 100
 101        if (einfo->operation & IPT_ECN_OP_MASK) {
 102                pr_info("unsupported ECN operation %x\n", einfo->operation);
 103                return -EINVAL;
 104        }
 105        if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 106                pr_info("new ECT codepoint %x out of mask\n", einfo->ip_ect);
 107                return -EINVAL;
 108        }
 109        if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
 110            (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 111                pr_info("cannot use TCP operations on a non-tcp rule\n");
 112                return -EINVAL;
 113        }
 114        return 0;
 115}
 116
 117static struct xt_target ecn_tg_reg __read_mostly = {
 118        .name           = "ECN",
 119        .family         = NFPROTO_IPV4,
 120        .target         = ecn_tg,
 121        .targetsize     = sizeof(struct ipt_ECN_info),
 122        .table          = "mangle",
 123        .checkentry     = ecn_tg_check,
 124        .me             = THIS_MODULE,
 125};
 126
 127static int __init ecn_tg_init(void)
 128{
 129        return xt_register_target(&ecn_tg_reg);
 130}
 131
 132static void __exit ecn_tg_exit(void)
 133{
 134        xt_unregister_target(&ecn_tg_reg);
 135}
 136
 137module_init(ecn_tg_init);
 138module_exit(ecn_tg_exit);
 139