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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_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         }
  47         return 1;
  48 }
  49
  50 /* Return 0 if there was an error. */
  51 static inline int
  52 set_ect_tcp(struct sk_buff **pskb, const struct ipt_ECN_info *einfo, int inward)
  53 {
  54         struct tcphdr _tcph, *tcph;
  55         u_int16_t diffs[2];
  56
  57         /* Not enought header? */
  58         tcph = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
  59                                   sizeof(_tcph), &_tcph);
  60         if (!tcph)
  61                 return 0;
  62
  63         if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  64              tcph->ece == einfo->proto.tcp.ece) &&
  65             ((!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  66              tcph->cwr == einfo->proto.tcp.cwr)))
  67                 return 1;
  68
  69         if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
  70                 return 0;
  71         tcph = (void *)(*pskb)->nh.iph + (*pskb)->nh.iph->ihl*4;
  72
  73         if ((*pskb)->ip_summed == CHECKSUM_HW &&
  74             skb_checksum_help(*pskb, inward))
  75                 return 0;
  76
  77         diffs[0] = ((u_int16_t *)tcph)[6];
  78         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  79                 tcph->ece = einfo->proto.tcp.ece;
  80         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  81                 tcph->cwr = einfo->proto.tcp.cwr;
  82         diffs[1] = ((u_int16_t *)tcph)[6];
  83         diffs[0] = diffs[0] ^ 0xFFFF;
  84
  85         if ((*pskb)->ip_summed != CHECKSUM_UNNECESSARY)
  86                 tcph->check = csum_fold(csum_partial((char *)diffs,
  87                                                      sizeof(diffs),
  88                                                      tcph->check^0xFFFF));
  89         return 1;
  90 }
  91
  92 static unsigned int
  93 target(struct sk_buff **pskb,
  94        const struct net_device *in,
  95        const struct net_device *out,
  96        unsigned int hooknum,
  97        const struct xt_target *target,
  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 void *e_void,
 118            const struct xt_target *target,
 119            void *targinfo,
 120            unsigned int targinfosize,
 121            unsigned int hook_mask)
 122 {
 123         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 124         const struct ipt_entry *e = e_void;
 125
 126         if (einfo->operation & IPT_ECN_OP_MASK) {
 127                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 128                         einfo->operation);
 129                 return 0;
 130         }
 131         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 132                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 133                         einfo->ip_ect);
 134                 return 0;
 135         }
 136         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 137             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & IPT_INV_PROTO))) {
 138                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 139                        "non-tcp rule\n");
 140                 return 0;
 141         }
 142         return 1;
 143 }
 144
 145 static struct ipt_target ipt_ecn_reg = {
 146         .name           = "ECN",
 147         .target         = target,
 148         .targetsize     = sizeof(struct ipt_ECN_info),
 149         .table          = "mangle",
 150         .checkentry     = checkentry,
 151         .me             = THIS_MODULE,
 152 };
 153
 154 static int __init ipt_ecn_init(void)
 155 {
 156         return ipt_register_target(&ipt_ecn_reg);
 157 }
 158
 159 static void __exit ipt_ecn_fini(void)
 160 {
 161         ipt_unregister_target(&ipt_ecn_reg);
 162 }
 163
 164 module_init(ipt_ecn_init);
 165 module_exit(ipt_ecn_fini);