net/ipv4/netfilter/ipt_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
  25 static inline bool match_ip(const struct sk_buff *skb,
  26                             const struct ipt_ecn_info *einfo)
  27 {
  28         return (ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect;
  29 }
  30
  31 static inline bool match_tcp(const struct sk_buff *skb,
  32                              const struct ipt_ecn_info *einfo,
  33                              bool *hotdrop)
  34 {
  35         struct tcphdr _tcph;
  36         const struct tcphdr *th;
  37
  38         /* In practice, TCP match does this, so can't fail.  But let's
  39          * be good citizens.
  40          */
  41         th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  42         if (th == NULL) {
  43                 *hotdrop = false;
  44                 return false;
  45         }
  46
  47         if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
  48                 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
  49                         if (th->ece == 1)
  50                                 return false;
  51                 } else {
  52                         if (th->ece == 0)
  53                                 return false;
  54                 }
  55         }
  56
  57         if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
  58                 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
  59                         if (th->cwr == 1)
  60                                 return false;
  61                 } else {
  62                         if (th->cwr == 0)
  63                                 return false;
  64                 }
  65         }
  66
  67         return true;
  68 }
  69
  70 static bool ecn_mt(const struct sk_buff *skb, struct xt_action_param *par)
  71 {
  72         const struct ipt_ecn_info *info = par->matchinfo;
  73
  74         if (info->operation & IPT_ECN_OP_MATCH_IP)
  75                 if (!match_ip(skb, info))
  76                         return false;
  77
  78         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  79                 if (ip_hdr(skb)->protocol != IPPROTO_TCP)
  80                         return false;
  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) {
 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);