net/netfilter/xt_ecn.c

   1 /*
   2  * Xtables module for matching the value of the IPv4/IPv6 and TCP ECN bits
   3  *
   4  * (C) 2002 by Harald Welte <laforge@gnumonks.org>
   5  * (C) 2011 Patrick McHardy <kaber@trash.net>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  12 #include <linux/in.h>
  13 #include <linux/ip.h>
  14 #include <net/ip.h>
  15 #include <linux/module.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/tcp.h>
  18
  19 #include <linux/netfilter/x_tables.h>
  20 #include <linux/netfilter/xt_ecn.h>
  21 #include <linux/netfilter_ipv4/ip_tables.h>
  22 #include <linux/netfilter_ipv6/ip6_tables.h>
  23
  24 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  25 MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag match");
  26 MODULE_LICENSE("GPL");
  27 MODULE_ALIAS("ipt_ecn");
  28 MODULE_ALIAS("ip6t_ecn");
  29
  30 static bool match_tcp(const struct sk_buff *skb, struct xt_action_param *par)
  31 {
  32         const struct xt_ecn_info *einfo = par->matchinfo;
  33         struct tcphdr _tcph;
  34         const struct tcphdr *th;
  35
  36         /* In practice, TCP match does this, so can't fail.  But let's
  37          * be good citizens.
  38          */
  39         th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
  40         if (th == NULL)
  41                 return false;
  42
  43         if (einfo->operation & XT_ECN_OP_MATCH_ECE) {
  44                 if (einfo->invert & XT_ECN_OP_MATCH_ECE) {
  45                         if (th->ece == 1)
  46                                 return false;
  47                 } else {
  48                         if (th->ece == 0)
  49                                 return false;
  50                 }
  51         }
  52
  53         if (einfo->operation & XT_ECN_OP_MATCH_CWR) {
  54                 if (einfo->invert & XT_ECN_OP_MATCH_CWR) {
  55                         if (th->cwr == 1)
  56                                 return false;
  57                 } else {
  58                         if (th->cwr == 0)
  59                                 return false;
  60                 }
  61         }
  62
  63         return true;
  64 }
  65
  66 static inline bool match_ip(const struct sk_buff *skb,
  67                             const struct xt_ecn_info *einfo)
  68 {
  69         return ((ip_hdr(skb)->tos & XT_ECN_IP_MASK) == einfo->ip_ect) ^
  70                !!(einfo->invert & XT_ECN_OP_MATCH_IP);
  71 }
  72
  73 static bool ecn_mt4(const struct sk_buff *skb, struct xt_action_param *par)
  74 {
  75         const struct xt_ecn_info *info = par->matchinfo;
  76
  77         if (info->operation & XT_ECN_OP_MATCH_IP && !match_ip(skb, info))
  78                 return false;
  79
  80         if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
  81             !match_tcp(skb, par))
  82                 return false;
  83
  84         return true;
  85 }
  86
  87 static int ecn_mt_check4(const struct xt_mtchk_param *par)
  88 {
  89         const struct xt_ecn_info *info = par->matchinfo;
  90         const struct ipt_ip *ip = par->entryinfo;
  91
  92         if (info->operation & XT_ECN_OP_MATCH_MASK)
  93                 return -EINVAL;
  94
  95         if (info->invert & XT_ECN_OP_MATCH_MASK)
  96                 return -EINVAL;
  97
  98         if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_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 inline bool match_ipv6(const struct sk_buff *skb,
 108                               const struct xt_ecn_info *einfo)
 109 {
 110         return (((ipv6_hdr(skb)->flow_lbl[0] >> 4) & XT_ECN_IP_MASK) ==
 111                 einfo->ip_ect) ^
 112                !!(einfo->invert & XT_ECN_OP_MATCH_IP);
 113 }
 114
 115 static bool ecn_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 116 {
 117         const struct xt_ecn_info *info = par->matchinfo;
 118
 119         if (info->operation & XT_ECN_OP_MATCH_IP && !match_ipv6(skb, info))
 120                 return false;
 121
 122         if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
 123             !match_tcp(skb, par))
 124                 return false;
 125
 126         return true;
 127 }
 128
 129 static int ecn_mt_check6(const struct xt_mtchk_param *par)
 130 {
 131         const struct xt_ecn_info *info = par->matchinfo;
 132         const struct ip6t_ip6 *ip = par->entryinfo;
 133
 134         if (info->operation & XT_ECN_OP_MATCH_MASK)
 135                 return -EINVAL;
 136
 137         if (info->invert & XT_ECN_OP_MATCH_MASK)
 138                 return -EINVAL;
 139
 140         if (info->operation & (XT_ECN_OP_MATCH_ECE | XT_ECN_OP_MATCH_CWR) &&
 141             (ip->proto != IPPROTO_TCP || ip->invflags & IP6T_INV_PROTO)) {
 142                 pr_info("cannot match TCP bits in rule for non-tcp packets\n");
 143                 return -EINVAL;
 144         }
 145
 146         return 0;
 147 }
 148
 149 static struct xt_match ecn_mt_reg[] __read_mostly = {
 150         {
 151                 .name           = "ecn",
 152                 .family         = NFPROTO_IPV4,
 153                 .match          = ecn_mt4,
 154                 .matchsize      = sizeof(struct xt_ecn_info),
 155                 .checkentry     = ecn_mt_check4,
 156                 .me             = THIS_MODULE,
 157         },
 158         {
 159                 .name           = "ecn",
 160                 .family         = NFPROTO_IPV6,
 161                 .match          = ecn_mt6,
 162                 .matchsize      = sizeof(struct xt_ecn_info),
 163                 .checkentry     = ecn_mt_check6,
 164                 .me             = THIS_MODULE,
 165         },
 166 };
 167
 168 static int __init ecn_mt_init(void)
 169 {
 170         return xt_register_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
 171 }
 172
 173 static void __exit ecn_mt_exit(void)
 174 {
 175         xt_unregister_matches(ecn_mt_reg, ARRAY_SIZE(ecn_mt_reg));
 176 }
 177
 178 module_init(ecn_mt_init);
 179 module_exit(ecn_mt_exit);