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, int inward)
  54 {
  55         struct tcphdr _tcph, *th;
  56         u_int16_t diffs[2];
  57
  58         /* Not enought header? */
  59         th = skb_header_pointer(*pskb, (*pskb)->nh.iph->ihl*4,
  60                                 sizeof(_tcph), &_tcph);
  61         if (th == NULL)
  62                 return 0;
  63
  64         diffs[0] = ((u_int16_t *)th)[6];
  65         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  66                 th->ece = einfo->proto.tcp.ece;
  67
  68         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  69                 th->cwr = einfo->proto.tcp.cwr;
  70         diffs[1] = ((u_int16_t *)&th)[6];
  71
  72         /* Only mangle if it's changed. */
  73         if (diffs[0] != diffs[1]) {
  74                 diffs[0] = diffs[0] ^ 0xFFFF;
  75                 if (!skb_ip_make_writable(pskb,
  76                                           (*pskb)->nh.iph->ihl*4+sizeof(_tcph)))
  77                         return 0;
  78
  79                 if (th != &_tcph)
  80                         memcpy(&_tcph, th, sizeof(_tcph));
  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                 memcpy((*pskb)->data + (*pskb)->nh.iph->ihl*4,
  87                        &_tcph, sizeof(_tcph));
  88                 if ((*pskb)->ip_summed == CHECKSUM_HW)
  89                         if (skb_checksum_help(pskb, inward))
  90                                 return 0;
  91                 (*pskb)->nfcache |= NFC_ALTERED;
  92         }
  93         return 1;
  94 }
  95
  96 static unsigned int
  97 target(struct sk_buff **pskb,
  98        const struct net_device *in,
  99        const struct net_device *out,
 100        unsigned int hooknum,
 101        const void *targinfo,
 102        void *userinfo)
 103 {
 104         const struct ipt_ECN_info *einfo = targinfo;
 105
 106         if (einfo->operation & IPT_ECN_OP_SET_IP)
 107                 if (!set_ect_ip(pskb, einfo))
 108                         return NF_DROP;
 109
 110         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
 111             && (*pskb)->nh.iph->protocol == IPPROTO_TCP)
 112                 if (!set_ect_tcp(pskb, einfo, (out == NULL)))
 113                         return NF_DROP;
 114
 115         return IPT_CONTINUE;
 116 }
 117
 118 static int
 119 checkentry(const char *tablename,
 120            const struct ipt_entry *e,
 121            void *targinfo,
 122            unsigned int targinfosize,
 123            unsigned int hook_mask)
 124 {
 125         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 126
 127         if (targinfosize != IPT_ALIGN(sizeof(struct ipt_ECN_info))) {
 128                 printk(KERN_WARNING "ECN: targinfosize %u != %Zu\n",
 129                        targinfosize,
 130                        IPT_ALIGN(sizeof(struct ipt_ECN_info)));
 131                 return 0;
 132         }
 133
 134         if (strcmp(tablename, "mangle") != 0) {
 135                 printk(KERN_WARNING "ECN: can only be called from \"mangle\" table, not \"%s\"\n", tablename);
 136                 return 0;
 137         }
 138
 139         if (einfo->operation & IPT_ECN_OP_MASK) {
 140                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 141                         einfo->operation);
 142                 return 0;
 143         }
 144         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 145                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 146                         einfo->ip_ect);
 147                 return 0;
 148         }
 149
 150         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 151             && e->ip.proto != IPPROTO_TCP) {
 152                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 153                        "non-tcp rule\n");
 154                 return 0;
 155         }
 156
 157         return 1;
 158 }
 159
 160 static struct ipt_target ipt_ecn_reg = {
 161         .name           = "ECN",
 162         .target         = target,
 163         .checkentry     = checkentry,
 164         .me             = THIS_MODULE,
 165 };
 166
 167 static int __init init(void)
 168 {
 169         return ipt_register_target(&ipt_ecn_reg);
 170 }
 171
 172 static void __exit fini(void)
 173 {
 174         ipt_unregister_target(&ipt_ecn_reg);
 175 }
 176
 177 module_init(init);
 178 module_exit(fini);