net/ipv4/netfilter/ipt_ECN.c

   1 /* iptables module for the IPv4 and TCP ECN bits, Version 1.5
   2  *
   3  * (C) 2002 by Harald Welte <laforge@netfilter.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  * ipt_ECN.c,v 1.5 2002/08/18 19:36:51 laforge Exp
  10 */
  11
  12 #include <linux/in.h>
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/ip.h>
  16 #include <linux/tcp.h>
  17 #include <net/checksum.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_LICENSE("GPL");
  24 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  25 MODULE_DESCRIPTION("iptables ECN modification module");
  26
  27 /* set ECT codepoint from IP header.
  28  *      return 0 if there was an error. */
  29 static inline int
  30 set_ect_ip(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  31 {
  32         struct iphdr *iph = (*pskb)->nh.iph;
  33
  34         if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  35                 __u8 oldtos;
  36                 if (!skb_make_writable(pskb, sizeof(struct iphdr)))
  37                         return 0;
  38                 iph = (*pskb)->nh.iph;
  39                 oldtos = iph->tos;
  40                 iph->tos &= ~IPT_ECN_IP_MASK;
  41                 iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  42                 nf_csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  43         }
  44         return 1;
  45 }
  46
  47 /* Return 0 if there was an error. */
  48 static inline int
  49 set_ect_tcp(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  50 {
  51         struct tcphdr _tcph, *tcph;
  52         __be16 oldval;
  53
  54         /* Not enought header? */
  55         tcph = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
  56                                   sizeof(_tcph), &_tcph);
  57         if (!tcph)
  58                 return 0;
  59
  60         if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  61              tcph->ece == einfo->proto.tcp.ece) &&
  62             ((!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  63              tcph->cwr == einfo->proto.tcp.cwr)))
  64                 return 1;
  65
  66         if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
  67                 return 0;
  68         tcph = (void *)(*pskb)->nh.iph + (*pskb)->nh.iph->ihl*4;
  69
  70         oldval = ((__be16 *)tcph)[6];
  71         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  72                 tcph->ece = einfo->proto.tcp.ece;
  73         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  74                 tcph->cwr = einfo->proto.tcp.cwr;
  75
  76         nf_proto_csum_replace2(&tcph->check, *pskb,
  77                                 oldval, ((__be16 *)tcph)[6], 0);
  78         return 1;
  79 }
  80
  81 static unsigned int
  82 target(struct sk_buff **pskb,
  83        const struct net_device *in,
  84        const struct net_device *out,
  85        unsigned int hooknum,
  86        const struct xt_target *target,
  87        const void *targinfo)
  88 {
  89         const struct ipt_ECN_info *einfo = targinfo;
  90
  91         if (einfo->operation & IPT_ECN_OP_SET_IP)
  92                 if (!set_ect_ip(pskb, einfo))
  93                         return NF_DROP;
  94
  95         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
  96             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
  97                 if (!set_ect_tcp(pskb, einfo))
  98                         return NF_DROP;
  99
 100         return XT_CONTINUE;
 101 }
 102
 103 static int
 104 checkentry(const char *tablename,
 105            const void *e_void,
 106            const struct xt_target *target,
 107            void *targinfo,
 108            unsigned int hook_mask)
 109 {
 110         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 111         const struct ipt_entry *e = e_void;
 112
 113         if (einfo->operation & IPT_ECN_OP_MASK) {
 114                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 115                         einfo->operation);
 116                 return 0;
 117         }
 118         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 119                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 120                         einfo->ip_ect);
 121                 return 0;
 122         }
 123         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 124             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 125                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 126                        "non-tcp rule\n");
 127                 return 0;
 128         }
 129         return 1;
 130 }
 131
 132 static struct xt_target ipt_ecn_reg = {
 133         .name           = "ECN",
 134         .family         = AF_INET,
 135         .target         = target,
 136         .targetsize     = sizeof(struct ipt_ECN_info),
 137         .table          = "mangle",
 138         .checkentry     = checkentry,
 139         .me             = THIS_MODULE,
 140 };
 141
 142 static int __init ipt_ecn_init(void)
 143 {
 144         return xt_register_target(&ipt_ecn_reg);
 145 }
 146
 147 static void __exit ipt_ecn_fini(void)
 148 {
 149         xt_unregister_target(&ipt_ecn_reg);
 150 }
 151
 152 module_init(ipt_ecn_init);
 153 module_exit(ipt_ecn_fini);