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   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, int inward)
  54 {
  55         struct tcphdr _tcph, *tcph;
  56         u_int16_t diffs[2];
  57
  58         /* Not enought header? */
  59         tcph = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
  60                                   sizeof(_tcph), &_tcph);
  61         if (!tcph)
  62                 return 0;
  63
  64         if (!(einfo->operation & IPT_ECN_OP_SET_ECE
  65               || tcph->ece == einfo->proto.tcp.ece)
  66             && (!(einfo->operation & IPT_ECN_OP_SET_CWR
  67                   || tcph->cwr == einfo->proto.tcp.cwr)))
  68                 return 1;
  69
  70         if (!skb_ip_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
  71                 return 0;
  72         tcph = (void *)(*pskb)->nh.iph + (*pskb)->nh.iph->ihl*4;
  73
  74         diffs[0] = ((u_int16_t *)tcph)[6];
  75         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  76                 tcph->ece = einfo->proto.tcp.ece;
  77         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  78                 tcph->cwr = einfo->proto.tcp.cwr;
  79         diffs[1] = ((u_int16_t *)tcph)[6];
  80         diffs[0] = diffs[0] ^ 0xFFFF;
  81
  82         if ((*pskb)->ip_summed != CHECKSUM_HW)
  83                 tcph->check = csum_fold(csum_partial((char *)diffs,
  84                                                      sizeof(diffs),
  85                                                      tcph->check^0xFFFF));
  86         else
  87                 if (skb_checksum_help(*pskb, inward))
  88                         return 0;
  89         (*pskb)->nfcache |= NFC_ALTERED;
  90         return 1;
  91 }
  92
  93 static unsigned int
  94 target(struct sk_buff **pskb,
  95        const struct net_device *in,
  96        const struct net_device *out,
  97        unsigned int hooknum,
  98        const void *targinfo,
  99        void *userinfo)
 100 {
 101         const struct ipt_ECN_info *einfo = targinfo;
 102
 103         if (einfo->operation & IPT_ECN_OP_SET_IP)
 104                 if (!set_ect_ip(pskb, einfo))
 105                         return NF_DROP;
 106
 107         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
 108             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
 109                 if (!set_ect_tcp(pskb, einfo, (out == NULL)))
 110                         return NF_DROP;
 111
 112         return IPT_CONTINUE;
 113 }
 114
 115 static int
 116 checkentry(const char *tablename,
 117            const struct ipt_entry *e,
 118            void *targinfo,
 119            unsigned int targinfosize,
 120            unsigned int hook_mask)
 121 {
 122         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 123
 124         if (targinfosize != IPT_ALIGN(sizeof(struct ipt_ECN_info))) {
 125                 printk(KERN_WARNING "ECN: targinfosize %u != %Zu\n",
 126                        targinfosize,
 127                        IPT_ALIGN(sizeof(struct ipt_ECN_info)));
 128                 return 0;
 129         }
 130
 131         if (strcmp(tablename, "mangle") != 0) {
 132                 printk(KERN_WARNING "ECN: can only be called from \"mangle\" table, not \"%s\"\n", tablename);
 133                 return 0;
 134         }
 135
 136         if (einfo->operation & IPT_ECN_OP_MASK) {
 137                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 138                         einfo->operation);
 139                 return 0;
 140         }
 141         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 142                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 143                         einfo->ip_ect);
 144                 return 0;
 145         }
 146
 147         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 148             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & IPT_INV_PROTO))) {
 149                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 150                        "non-tcp rule\n");
 151                 return 0;
 152         }
 153
 154         return 1;
 155 }
 156
 157 static struct ipt_target ipt_ecn_reg = {
 158         .name           = "ECN",
 159         .target         = target,
 160         .checkentry     = checkentry,
 161         .me             = THIS_MODULE,
 162 };
 163
 164 static int __init init(void)
 165 {
 166         return ipt_register_target(&ipt_ecn_reg);
 167 }
 168
 169 static void __exit fini(void)
 170 {
 171         ipt_unregister_target(&ipt_ecn_reg);
 172 }
 173
 174 module_init(init);
 175 module_exit(fini);