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                !!(einfo->invert & IPT_ECN_OP_MATCH_IP);
  30 }
  31
  32 static inline bool match_tcp(const struct sk_buff *skb,
  33                              const struct ipt_ecn_info *einfo,
  34                              bool *hotdrop)
  35 {
  36         struct tcphdr _tcph;
  37         const struct tcphdr *th;
  38
  39         /* In practice, TCP match does this, so can't fail.  But let's
  40          * be good citizens.
  41          */
  42         th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  43         if (th == NULL) {
  44                 *hotdrop = false;
  45                 return false;
  46         }
  47
  48         if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
  49                 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
  50                         if (th->ece == 1)
  51                                 return false;
  52                 } else {
  53                         if (th->ece == 0)
  54                                 return false;
  55                 }
  56         }
  57
  58         if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
  59                 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
  60                         if (th->cwr == 1)
  61                                 return false;
  62                 } else {
  63                         if (th->cwr == 0)
  64                                 return false;
  65                 }
  66         }
  67
  68         return true;
  69 }
  70
  71 static bool ecn_mt(const struct sk_buff *skb, struct xt_action_param *par)
  72 {
  73         const struct ipt_ecn_info *info = par->matchinfo;
  74
  75         if (info->operation & IPT_ECN_OP_MATCH_IP)
  76                 if (!match_ip(skb, info))
  77                         return false;
  78
  79         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  80                 if (!match_tcp(skb, info, &par->hotdrop))
  81                         return false;
  82         }
  83
  84         return true;
  85 }
  86
  87 static int ecn_mt_check(const struct xt_mtchk_param *par)
  88 {
  89         const struct ipt_ecn_info *info = par->matchinfo;
  90         const struct ipt_ip *ip = par->entryinfo;
  91
  92         if (info->operation & IPT_ECN_OP_MATCH_MASK)
  93                 return -EINVAL;
  94
  95         if (info->invert & IPT_ECN_OP_MATCH_MASK)
  96                 return -EINVAL;
  97
  98         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR) &&
  99             (ip->proto != IPPROTO_TCP || ip->invflags & IPT_INV_PROTO)) {
 100                 pr_info("cannot match TCP bits in rule for non-tcp packets\n");
 101                 return -EINVAL;
 102         }
 103
 104         return 0;
 105 }
 106
 107 static struct xt_match ecn_mt_reg __read_mostly = {
 108         .name           = "ecn",
 109         .family         = NFPROTO_IPV4,
 110         .match          = ecn_mt,
 111         .matchsize      = sizeof(struct ipt_ecn_info),
 112         .checkentry     = ecn_mt_check,
 113         .me             = THIS_MODULE,
 114 };
 115
 116 static int __init ecn_mt_init(void)
 117 {
 118         return xt_register_match(&ecn_mt_reg);
 119 }
 120
 121 static void __exit ecn_mt_exit(void)
 122 {
 123         xt_unregister_match(&ecn_mt_reg);
 124 }
 125
 126 module_init(ecn_mt_init);
 127 module_exit(ecn_mt_exit);