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/module.h>
  13 #include <linux/skbuff.h>
  14 #include <linux/ip.h>
  15 #include <linux/tcp.h>
  16 #include <net/checksum.h>
  17
  18 #include <linux/netfilter_ipv4/ip_tables.h>
  19 #include <linux/netfilter_ipv4/ipt_ECN.h>
  20
  21 MODULE_LICENSE("GPL");
  22 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  23 MODULE_DESCRIPTION("iptables ECN modification module");
  24
  25 /* set ECT codepoint from IP header.
  26  *      return 0 if there was an error. */
  27 static inline int
  28 set_ect_ip(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  29 {
  30         struct iphdr *iph = (*pskb)->nh.iph;
  31
  32         if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  33                 __u8 oldtos;
  34                 if (!skb_make_writable(pskb, sizeof(struct iphdr)))
  35                         return 0;
  36                 iph = (*pskb)->nh.iph;
  37                 oldtos = iph->tos;
  38                 iph->tos &= ~IPT_ECN_IP_MASK;
  39                 iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  40                 nf_csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  41         }
  42         return 1;
  43 }
  44
  45 /* Return 0 if there was an error. */
  46 static inline int
  47 set_ect_tcp(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  48 {
  49         struct tcphdr _tcph, *tcph;
  50         __be16 oldval;
  51
  52         /* Not enought header? */
  53         tcph = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
  54                                   sizeof(_tcph), &_tcph);
  55         if (!tcph)
  56                 return 0;
  57
  58         if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  59              tcph->ece == einfo->proto.tcp.ece) &&
  60             ((!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  61              tcph->cwr == einfo->proto.tcp.cwr)))
  62                 return 1;
  63
  64         if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
  65                 return 0;
  66         tcph = (void *)(*pskb)->nh.iph + (*pskb)->nh.iph->ihl*4;
  67
  68         oldval = ((__be16 *)tcph)[6];
  69         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  70                 tcph->ece = einfo->proto.tcp.ece;
  71         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  72                 tcph->cwr = einfo->proto.tcp.cwr;
  73
  74         nf_proto_csum_replace2(&tcph->check, *pskb,
  75                                 oldval, ((__be16 *)tcph)[6], 0);
  76         return 1;
  77 }
  78
  79 static unsigned int
  80 target(struct sk_buff **pskb,
  81        const struct net_device *in,
  82        const struct net_device *out,
  83        unsigned int hooknum,
  84        const struct xt_target *target,
  85        const void *targinfo)
  86 {
  87         const struct ipt_ECN_info *einfo = targinfo;
  88
  89         if (einfo->operation & IPT_ECN_OP_SET_IP)
  90                 if (!set_ect_ip(pskb, einfo))
  91                         return NF_DROP;
  92
  93         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
  94             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
  95                 if (!set_ect_tcp(pskb, einfo))
  96                         return NF_DROP;
  97
  98         return IPT_CONTINUE;
  99 }
 100
 101 static int
 102 checkentry(const char *tablename,
 103            const void *e_void,
 104            const struct xt_target *target,
 105            void *targinfo,
 106            unsigned int hook_mask)
 107 {
 108         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 109         const struct ipt_entry *e = e_void;
 110
 111         if (einfo->operation & IPT_ECN_OP_MASK) {
 112                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 113                         einfo->operation);
 114                 return 0;
 115         }
 116         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 117                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 118                         einfo->ip_ect);
 119                 return 0;
 120         }
 121         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 122             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & IPT_INV_PROTO))) {
 123                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 124                        "non-tcp rule\n");
 125                 return 0;
 126         }
 127         return 1;
 128 }
 129
 130 static struct ipt_target ipt_ecn_reg = {
 131         .name           = "ECN",
 132         .target         = target,
 133         .targetsize     = sizeof(struct ipt_ECN_info),
 134         .table          = "mangle",
 135         .checkentry     = checkentry,
 136         .me             = THIS_MODULE,
 137 };
 138
 139 static int __init ipt_ecn_init(void)
 140 {
 141         return ipt_register_target(&ipt_ecn_reg);
 142 }
 143
 144 static void __exit ipt_ecn_fini(void)
 145 {
 146         ipt_unregister_target(&ipt_ecn_reg);
 147 }
 148
 149 module_init(ipt_ecn_init);
 150 module_exit(ipt_ecn_fini);