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         if (((*pskb)->nh.iph->tos & IPT_ECN_IP_MASK)
  31             != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  32                 u_int16_t diffs[2];
  33
  34                 if (!skb_ip_make_writable(pskb, sizeof(struct iphdr)))
  35                         return 0;
  36
  37                 diffs[0] = htons((*pskb)->nh.iph->tos) ^ 0xFFFF;
  38                 (*pskb)->nh.iph->tos &= ~IPT_ECN_IP_MASK;
  39                 (*pskb)->nh.iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  40                 diffs[1] = htons((*pskb)->nh.iph->tos);
  41                 (*pskb)->nh.iph->check
  42                         = csum_fold(csum_partial((char *)diffs,
  43                                                  sizeof(diffs),
  44                                                  (*pskb)->nh.iph->check
  45                                                  ^0xFFFF));
  46                 (*pskb)->nfcache |= NFC_ALTERED;
  47         }
  48         return 1;
  49 }
  50
  51 /* Return 0 if there was an error. */
  52 static inline int
  53 set_ect_tcp(struct sk_buff **pskb, const struct ipt_ECN_info *einfo)
  54 {
  55         struct tcphdr tcph;
  56         u_int16_t diffs[2];
  57
  58         /* Not enought header? */
  59         if (skb_copy_bits(*pskb, (*pskb)->nh.iph->ihl*4, &tcph, sizeof(tcph))
  60             < 0)
  61                 return 0;
  62
  63         diffs[0] = ((u_int16_t *)&tcph)[6];
  64         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  65                 tcph.ece = einfo->proto.tcp.ece;
  66
  67         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  68                 tcph.cwr = einfo->proto.tcp.cwr;
  69         diffs[1] = ((u_int16_t *)&tcph)[6];
  70
  71         /* Only mangle if it's changed. */
  72         if (diffs[0] != diffs[1]) {
  73                 diffs[0] = diffs[0] ^ 0xFFFF;
  74                 if (!skb_ip_make_writable(pskb,
  75                                           (*pskb)->nh.iph->ihl*4+sizeof(tcph)))
  76                         return 0;
  77                 tcph.check = csum_fold(csum_partial((char *)diffs,
  78                                                     sizeof(diffs),
  79                                                     tcph.check^0xFFFF));
  80                 memcpy((*pskb)->data + (*pskb)->nh.iph->ihl*4,
  81                        &tcph, sizeof(tcph));
  82                 (*pskb)->nfcache |= NFC_ALTERED;
  83         }
  84         return 1;
  85 }
  86
  87 static unsigned int
  88 target(struct sk_buff **pskb,
  89        const struct net_device *in,
  90        const struct net_device *out,
  91        unsigned int hooknum,
  92        const void *targinfo,
  93        void *userinfo)
  94 {
  95         const struct ipt_ECN_info *einfo = targinfo;
  96
  97         if (einfo->operation & IPT_ECN_OP_SET_IP)
  98                 if (!set_ect_ip(pskb, einfo))
  99                         return NF_DROP;
 100
 101         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
 102             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
 103                 if (!set_ect_tcp(pskb, einfo))
 104                         return NF_DROP;
 105
 106         return IPT_CONTINUE;
 107 }
 108
 109 static int
 110 checkentry(const char *tablename,
 111            const struct ipt_entry *e,
 112            void *targinfo,
 113            unsigned int targinfosize,
 114            unsigned int hook_mask)
 115 {
 116         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 117
 118         if (targinfosize != IPT_ALIGN(sizeof(struct ipt_ECN_info))) {
 119                 printk(KERN_WARNING "ECN: targinfosize %u != %Zu\n",
 120                        targinfosize,
 121                        IPT_ALIGN(sizeof(struct ipt_ECN_info)));
 122                 return 0;
 123         }
 124
 125         if (strcmp(tablename, "mangle") != 0) {
 126                 printk(KERN_WARNING "ECN: can only be called from \"mangle\" table, not \"%s\"\n", tablename);
 127                 return 0;
 128         }
 129
 130         if (einfo->operation & IPT_ECN_OP_MASK) {
 131                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 132                         einfo->operation);
 133                 return 0;
 134         }
 135         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 136                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 137                         einfo->ip_ect);
 138                 return 0;
 139         }
 140
 141         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 142             && e->ip.proto != IPPROTO_TCP) {
 143                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 144                        "non-tcp rule\n");
 145                 return 0;
 146         }
 147
 148         return 1;
 149 }
 150
 151 static struct ipt_target ipt_ecn_reg = {
 152         .name           = "ECN",
 153         .target         = target,
 154         .checkentry     = checkentry,
 155         .me             = THIS_MODULE,
 156 };
 157
 158 static int __init init(void)
 159 {
 160         return ipt_register_target(&ipt_ecn_reg);
 161 }
 162
 163 static void __exit fini(void)
 164 {
 165         ipt_unregister_target(&ipt_ecn_reg);
 166 }
 167
 168 module_init(init);
 169 module_exit(fini);