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