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   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
  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("iptables ECN matching module");
  23 MODULE_LICENSE("GPL");
  24
  25 static inline int 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 int match_tcp(const struct sk_buff *skb,
  32                             const struct ipt_ecn_info *einfo,
  33                             bool *hotdrop)
  34 {
  35         struct tcphdr _tcph, *th;
  36
  37         /* In practice, TCP match does this, so can't fail.  But let's
  38          * be good citizens.
  39          */
  40         th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  41         if (th == NULL) {
  42                 *hotdrop = false;
  43                 return 0;
  44         }
  45
  46         if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
  47                 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
  48                         if (th->ece == 1)
  49                                 return 0;
  50                 } else {
  51                         if (th->ece == 0)
  52                                 return 0;
  53                 }
  54         }
  55
  56         if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
  57                 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
  58                         if (th->cwr == 1)
  59                                 return 0;
  60                 } else {
  61                         if (th->cwr == 0)
  62                                 return 0;
  63                 }
  64         }
  65
  66         return 1;
  67 }
  68
  69 static int match(const struct sk_buff *skb,
  70                  const struct net_device *in, const struct net_device *out,
  71                  const struct xt_match *match, const void *matchinfo,
  72                  int offset, unsigned int protoff, bool *hotdrop)
  73 {
  74         const struct ipt_ecn_info *info = matchinfo;
  75
  76         if (info->operation & IPT_ECN_OP_MATCH_IP)
  77                 if (!match_ip(skb, info))
  78                         return 0;
  79
  80         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  81                 if (ip_hdr(skb)->protocol != IPPROTO_TCP)
  82                         return 0;
  83                 if (!match_tcp(skb, info, hotdrop))
  84                         return 0;
  85         }
  86
  87         return 1;
  88 }
  89
  90 static int checkentry(const char *tablename, const void *ip_void,
  91                       const struct xt_match *match,
  92                       void *matchinfo, unsigned int hook_mask)
  93 {
  94         const struct ipt_ecn_info *info = matchinfo;
  95         const struct ipt_ip *ip = ip_void;
  96
  97         if (info->operation & IPT_ECN_OP_MATCH_MASK)
  98                 return 0;
  99
 100         if (info->invert & IPT_ECN_OP_MATCH_MASK)
 101                 return 0;
 102
 103         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
 104             && ip->proto != IPPROTO_TCP) {
 105                 printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
 106                        " non-tcp packets\n");
 107                 return 0;
 108         }
 109
 110         return 1;
 111 }
 112
 113 static struct xt_match ecn_match = {
 114         .name           = "ecn",
 115         .family         = AF_INET,
 116         .match          = match,
 117         .matchsize      = sizeof(struct ipt_ecn_info),
 118         .checkentry     = checkentry,
 119         .me             = THIS_MODULE,
 120 };
 121
 122 static int __init ipt_ecn_init(void)
 123 {
 124         return xt_register_match(&ecn_match);
 125 }
 126
 127 static void __exit ipt_ecn_fini(void)
 128 {
 129         xt_unregister_match(&ecn_match);
 130 }
 131
 132 module_init(ipt_ecn_init);
 133 module_exit(ipt_ecn_fini);