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 <net/ip.h>
  17 #include <linux/tcp.h>
  18 #include <net/checksum.h>
  19
  20 #include <linux/netfilter/x_tables.h>
  21 #include <linux/netfilter_ipv4/ip_tables.h>
  22 #include <linux/netfilter_ipv4/ipt_ECN.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  26 MODULE_DESCRIPTION("iptables ECN modification module");
  27
  28 /* set ECT codepoint from IP header.
  29  *      return 0 if there was an error. */
  30 static inline int
  31 set_ect_ip(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  32 {
  33         struct iphdr *iph = (*pskb)->nh.iph;
  34
  35         if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  36                 __u8 oldtos;
  37                 if (!skb_make_writable(pskb, sizeof(struct iphdr)))
  38                         return 0;
  39                 iph = (*pskb)->nh.iph;
  40                 oldtos = iph->tos;
  41                 iph->tos &= ~IPT_ECN_IP_MASK;
  42                 iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  43                 nf_csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  44         }
  45         return 1;
  46 }
  47
  48 /* Return 0 if there was an error. */
  49 static inline int
  50 set_ect_tcp(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  51 {
  52         struct tcphdr _tcph, *tcph;
  53         __be16 oldval;
  54
  55         /* Not enought header? */
  56         tcph = skb_header_pointer(*pskb, ip_hdrlen(*pskb),
  57                                   sizeof(_tcph), &_tcph);
  58         if (!tcph)
  59                 return 0;
  60
  61         if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  62              tcph->ece == einfo->proto.tcp.ece) &&
  63             ((!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  64              tcph->cwr == einfo->proto.tcp.cwr)))
  65                 return 1;
  66
  67         if (!skb_make_writable(pskb, ip_hdrlen(*pskb) + sizeof(*tcph)))
  68                 return 0;
  69         tcph = (void *)(*pskb)->nh.iph + ip_hdrlen(*pskb);
  70
  71         oldval = ((__be16 *)tcph)[6];
  72         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  73                 tcph->ece = einfo->proto.tcp.ece;
  74         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  75                 tcph->cwr = einfo->proto.tcp.cwr;
  76
  77         nf_proto_csum_replace2(&tcph->check, *pskb,
  78                                 oldval, ((__be16 *)tcph)[6], 0);
  79         return 1;
  80 }
  81
  82 static unsigned int
  83 target(struct sk_buff **pskb,
  84        const struct net_device *in,
  85        const struct net_device *out,
  86        unsigned int hooknum,
  87        const struct xt_target *target,
  88        const void *targinfo)
  89 {
  90         const struct ipt_ECN_info *einfo = targinfo;
  91
  92         if (einfo->operation & IPT_ECN_OP_SET_IP)
  93                 if (!set_ect_ip(pskb, einfo))
  94                         return NF_DROP;
  95
  96         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
  97             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
  98                 if (!set_ect_tcp(pskb, einfo))
  99                         return NF_DROP;
 100
 101         return XT_CONTINUE;
 102 }
 103
 104 static int
 105 checkentry(const char *tablename,
 106            const void *e_void,
 107            const struct xt_target *target,
 108            void *targinfo,
 109            unsigned int hook_mask)
 110 {
 111         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 112         const struct ipt_entry *e = e_void;
 113
 114         if (einfo->operation & IPT_ECN_OP_MASK) {
 115                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 116                         einfo->operation);
 117                 return 0;
 118         }
 119         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 120                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 121                         einfo->ip_ect);
 122                 return 0;
 123         }
 124         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 125             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 126                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 127                        "non-tcp rule\n");
 128                 return 0;
 129         }
 130         return 1;
 131 }
 132
 133 static struct xt_target ipt_ecn_reg = {
 134         .name           = "ECN",
 135         .family         = AF_INET,
 136         .target         = target,
 137         .targetsize     = sizeof(struct ipt_ECN_info),
 138         .table          = "mangle",
 139         .checkentry     = checkentry,
 140         .me             = THIS_MODULE,
 141 };
 142
 143 static int __init ipt_ecn_init(void)
 144 {
 145         return xt_register_target(&ipt_ecn_reg);
 146 }
 147
 148 static void __exit ipt_ecn_fini(void)
 149 {
 150         xt_unregister_target(&ipt_ecn_reg);
 151 }
 152
 153 module_init(ipt_ecn_init);
 154 module_exit(ipt_ecn_fini);