net/ipv4/netfilter/ipt_ecn.c

   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/module.h>
  13 #include <linux/skbuff.h>
  14 #include <linux/tcp.h>
  15
  16 #include <linux/netfilter_ipv4/ip_tables.h>
  17 #include <linux/netfilter_ipv4/ipt_ecn.h>
  18
  19 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  20 MODULE_DESCRIPTION("iptables ECN matching module");
  21 MODULE_LICENSE("GPL");
  22
  23 static inline int match_ip(const struct sk_buff *skb,
  24                            const struct ipt_ecn_info *einfo)
  25 {
  26         return ((skb->nh.iph->tos&IPT_ECN_IP_MASK) == einfo->ip_ect);
  27 }
  28
  29 static inline int match_tcp(const struct sk_buff *skb,
  30                             const struct ipt_ecn_info *einfo,
  31                             int *hotdrop)
  32 {
  33         struct tcphdr _tcph, *th;
  34
  35         /* In practice, TCP match does this, so can't fail.  But let's
  36          * be good citizens.
  37          */
  38         th = skb_header_pointer(skb, skb->nh.iph->ihl * 4,
  39                                 sizeof(_tcph), &_tcph);
  40         if (th == NULL) {
  41                 *hotdrop = 0;
  42                 return 0;
  43         }
  44
  45         if (einfo->operation & IPT_ECN_OP_MATCH_ECE) {
  46                 if (einfo->invert & IPT_ECN_OP_MATCH_ECE) {
  47                         if (th->ece == 1)
  48                                 return 0;
  49                 } else {
  50                         if (th->ece == 0)
  51                                 return 0;
  52                 }
  53         }
  54
  55         if (einfo->operation & IPT_ECN_OP_MATCH_CWR) {
  56                 if (einfo->invert & IPT_ECN_OP_MATCH_CWR) {
  57                         if (th->cwr == 1)
  58                                 return 0;
  59                 } else {
  60                         if (th->cwr == 0)
  61                                 return 0;
  62                 }
  63         }
  64
  65         return 1;
  66 }
  67
  68 static int match(const struct sk_buff *skb,
  69                  const struct net_device *in, const struct net_device *out,
  70                  const struct xt_match *match, const void *matchinfo,
  71                  int offset, unsigned int protoff, int *hotdrop)
  72 {
  73         const struct ipt_ecn_info *info = matchinfo;
  74
  75         if (info->operation & IPT_ECN_OP_MATCH_IP)
  76                 if (!match_ip(skb, info))
  77                         return 0;
  78
  79         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)) {
  80                 if (skb->nh.iph->protocol != IPPROTO_TCP)
  81                         return 0;
  82                 if (!match_tcp(skb, info, hotdrop))
  83                         return 0;
  84         }
  85
  86         return 1;
  87 }
  88
  89 static int checkentry(const char *tablename, const void *ip_void,
  90                       const struct xt_match *match,
  91                       void *matchinfo, unsigned int hook_mask)
  92 {
  93         const struct ipt_ecn_info *info = matchinfo;
  94         const struct ipt_ip *ip = ip_void;
  95
  96         if (info->operation & IPT_ECN_OP_MATCH_MASK)
  97                 return 0;
  98
  99         if (info->invert & IPT_ECN_OP_MATCH_MASK)
 100                 return 0;
 101
 102         if (info->operation & (IPT_ECN_OP_MATCH_ECE|IPT_ECN_OP_MATCH_CWR)
 103             && ip->proto != IPPROTO_TCP) {
 104                 printk(KERN_WARNING "ipt_ecn: can't match TCP bits in rule for"
 105                        " non-tcp packets\n");
 106                 return 0;
 107         }
 108
 109         return 1;
 110 }
 111
 112 static struct ipt_match ecn_match = {
 113         .name           = "ecn",
 114         .match          = match,
 115         .matchsize      = sizeof(struct ipt_ecn_info),
 116         .checkentry     = checkentry,
 117         .me             = THIS_MODULE,
 118 };
 119
 120 static int __init ipt_ecn_init(void)
 121 {
 122         return ipt_register_match(&ecn_match);
 123 }
 124
 125 static void __exit ipt_ecn_fini(void)
 126 {
 127         ipt_unregister_match(&ecn_match);
 128 }
 129
 130 module_init(ipt_ecn_init);
 131 module_exit(ipt_ecn_fini);