net/netfilter/xt_ecn.c

   1 /* IP tables module for matching the value of the IPv4 and TCP ECN bits
   2  *
   3  * (C) 2002 by Harald Welte <laforge@gnumonks.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/ip.h>
  12 #include <net/ip.h>
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/tcp.h>
  16
  17 #include <linux/netfilter/x_tables.h>
  18 #include <linux/netfilter_ipv4/ip_tables.h>
  19 #include <linux/netfilter_ipv4/ipt_ecn.h>
  20
  21 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  22 MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match for IPv4");
  23 MODULE_LICENSE("GPL");
  24 MODULE_ALIAS("ipt_ecn");
  25
  26 static inline bool match_ip(const struct sk_buff *skb,
  27                             const struct ipt_ecn_info *einfo)
  28 {
  29         return ((ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect) ^
  30                !!(einfo->invert & IPT_ECN_OP_MATCH_IP);
  31 }
  32
  33 static inline bool match_tcp(const struct sk_buff *skb,
  34                              const struct ipt_ecn_info *einfo,
  35                              bool *hotdrop)
  36 {
  37         struct tcphdr _tcph;
  38         const struct tcphdr *th;
  39
  40         /* In practice, TCP match does this, so can't fail.  But let's
  41          * be good citizens.
  42          */
  43         th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  44         if (th == NULL) {
  45                 *hotdrop = false;
  46                 return false;
  47         }
  48
  49         if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
  50                 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
  51                         if (th->ece == 1)
  52                                 return false;
  53                 } else {
  54                         if (th->ece == 0)
  55                                 return false;
  56                 }
  57         }
  58
  59         if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
  60                 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
  61                         if (th->cwr == 1)
  62                                 return false;
  63                 } else {
  64                         if (th->cwr == 0)
  65                                 return false;
  66                 }
  67         }
  68
  69         return true;
  70 }
  71
  72 static bool ecn_mt(const struct sk_buff *skb, struct xt_action_param *par)
  73 {
  74         const struct ipt_ecn_info *info = par->matchinfo;
  75
  76         if (info->operation & IPT_ECN_OP_MATCH_IP)
  77                 if (!match_ip(skb, info))
  78                         return false;
  79
  80         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  81                 if (!match_tcp(skb, info, &par->hotdrop))
  82                         return false;
  83         }
  84
  85         return true;
  86 }
  87
  88 static int ecn_mt_check(const struct xt_mtchk_param *par)
  89 {
  90         const struct ipt_ecn_info *info = par->matchinfo;
  91         const struct ipt_ip *ip = par->entryinfo;
  92
  93         if (info->operation & IPT_ECN_OP_MATCH_MASK)
  94                 return -EINVAL;
  95
  96         if (info->invert & IPT_ECN_OP_MATCH_MASK)
  97                 return -EINVAL;
  98
  99         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR) &&
 100             (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
 101                 pr_info("cannot match TCP bits in rule for non-tcp packets\n");
 102                 return -EINVAL;
 103         }
 104
 105         return 0;
 106 }
 107
 108 static struct xt_match ecn_mt_reg __read_mostly = {
 109         .name           = "ecn",
 110         .family         = NFPROTO_IPV4,
 111         .match          = ecn_mt,
 112         .matchsize      = sizeof(struct ipt_ecn_info),
 113         .checkentry     = ecn_mt_check,
 114         .me             = THIS_MODULE,
 115 };
 116
 117 static int __init ecn_mt_init(void)
 118 {
 119         return xt_register_match(&ecn_mt_reg);
 120 }
 121
 122 static void __exit ecn_mt_exit(void)
 123 {
 124         xt_unregister_match(&ecn_mt_reg);
 125 }
 126
 127 module_init(ecn_mt_init);
 128 module_exit(ecn_mt_exit);