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   1 /* IP tables module for matching the value of the IPv4 and TCP ECN bits
   2  *
   3  * ipt_ecn.c,v 1.3 2002/05/29 15:09:00 laforge Exp
   4  *
   5  * (C) 2002 by Harald Welte <laforge@gnumonks.org>
   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
  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_ipv4/ip_tables.h>
  21 #include <linux/netfilter_ipv4/ipt_ecn.h>
  22
  23 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  24 MODULE_DESCRIPTION("iptables ECN matching module");
  25 MODULE_LICENSE("GPL");
  26
  27 static inline int match_ip(const struct sk_buff *skb,
  28                            const struct ipt_ecn_info *einfo)
  29 {
  30         return (ip_hdr(skb)->tos & IPT_ECN_IP_MASK) == einfo->ip_ect;
  31 }
  32
  33 static inline int match_tcp(const struct sk_buff *skb,
  34                             const struct ipt_ecn_info *einfo,
  35                             int *hotdrop)
  36 {
  37         struct tcphdr _tcph, *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 = 0;
  45                 return 0;
  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 0;
  52                 } else {
  53                         if (th->ece == 0)
  54                                 return 0;
  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 0;
  62                 } else {
  63                         if (th->cwr == 0)
  64                                 return 0;
  65                 }
  66         }
  67
  68         return 1;
  69 }
  70
  71 static int match(const struct sk_buff *skb,
  72                  const struct net_device *in, const struct net_device *out,
  73                  const struct xt_match *match, const void *matchinfo,
  74                  int offset, unsigned int protoff, int *hotdrop)
  75 {
  76         const struct ipt_ecn_info *info = matchinfo;
  77
  78         if (info->operation & IPT_ECN_OP_MATCH_IP)
  79                 if (!match_ip(skb, info))
  80                         return 0;
  81
  82         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  83                 if (ip_hdr(skb)->protocol != IPPROTO_TCP)
  84                         return 0;
  85                 if (!match_tcp(skb, info, hotdrop))
  86                         return 0;
  87         }
  88
  89         return 1;
  90 }
  91
  92 static int checkentry(const char *tablename, const void *ip_void,
  93                       const struct xt_match *match,
  94                       void *matchinfo, unsigned int hook_mask)
  95 {
  96         const struct ipt_ecn_info *info = matchinfo;
  97         const struct ipt_ip *ip = ip_void;
  98
  99         if (info->operation & IPT_ECN_OP_MATCH_MASK)
 100                 return 0;
 101
 102         if (info->invert & IPT_ECN_OP_MATCH_MASK)
 103                 return 0;
 104
 105         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
 106             && ip->proto != IPPROTO_TCP) {
 107                 printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
 108                        " non-tcp packets\n");
 109                 return 0;
 110         }
 111
 112         return 1;
 113 }
 114
 115 static struct xt_match ecn_match = {
 116         .name           = "ecn",
 117         .family         = AF_INET,
 118         .match          = match,
 119         .matchsize      = sizeof(struct ipt_ecn_info),
 120         .checkentry     = checkentry,
 121         .me             = THIS_MODULE,
 122 };
 123
 124 static int __init ipt_ecn_init(void)
 125 {
 126         return xt_register_match(&ecn_match);
 127 }
 128
 129 static void __exit ipt_ecn_fini(void)
 130 {
 131         xt_unregister_match(&ecn_match);
 132 }
 133
 134 module_init(ipt_ecn_init);
 135 module_exit(ipt_ecn_fini);