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("Xtables: Explicit Congestion Notification (ECN) flag modification");
  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 *skb, const struct ipt_ECN_info *einfo)
  30 {
  31         struct iphdr *iph = ip_hdr(skb);
  32
  33         if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  34                 __u8 oldtos;
  35                 if (!skb_make_writable(skb, sizeof(struct iphdr)))
  36                         return false;
  37                 iph = ip_hdr(skb);
  38                 oldtos = iph->tos;
  39                 iph->tos &= ~IPT_ECN_IP_MASK;
  40                 iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  41                 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 *skb, 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(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  55         if (!tcph)
  56                 return false;
  57
  58         if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  59              tcph->ece == einfo->proto.tcp.ece) &&
  60             (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  61              tcph->cwr == einfo->proto.tcp.cwr))
  62                 return true;
  63
  64         if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
  65                 return false;
  66         tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
  67
  68         oldval = ((__be16 *)tcph)[6];
  69         if (einfo->operation & IPT_ECN_OP_SET_ECE)
  70                 tcph->ece = einfo->proto.tcp.ece;
  71         if (einfo->operation & IPT_ECN_OP_SET_CWR)
  72                 tcph->cwr = einfo->proto.tcp.cwr;
  73
  74         inet_proto_csum_replace2(&tcph->check, skb,
  75                                  oldval, ((__be16 *)tcph)[6], 0);
  76         return true;
  77 }
  78
  79 static unsigned int
  80 ecn_tg(struct sk_buff *skb, const struct net_device *in,
  81        const struct net_device *out, unsigned int hooknum,
  82        const struct xt_target *target, const void *targinfo)
  83 {
  84         const struct ipt_ECN_info *einfo = targinfo;
  85
  86         if (einfo->operation & IPT_ECN_OP_SET_IP)
  87                 if (!set_ect_ip(skb, einfo))
  88                         return NF_DROP;
  89
  90         if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR)
  91             && ip_hdr(skb)->protocol == IPPROTO_TCP)
  92                 if (!set_ect_tcp(skb, einfo))
  93                         return NF_DROP;
  94
  95         return XT_CONTINUE;
  96 }
  97
  98 static bool
  99 ecn_tg_check(const char *tablename, const void *e_void,
 100              const struct xt_target *target, void *targinfo,
 101              unsigned int hook_mask)
 102 {
 103         const struct ipt_ECN_info *einfo = (struct ipt_ECN_info *)targinfo;
 104         const struct ipt_entry *e = e_void;
 105
 106         if (einfo->operation & IPT_ECN_OP_MASK) {
 107                 printk(KERN_WARNING "ECN: unsupported ECN operation %x\n",
 108                         einfo->operation);
 109                 return false;
 110         }
 111         if (einfo->ip_ect & ~IPT_ECN_IP_MASK) {
 112                 printk(KERN_WARNING "ECN: new ECT codepoint %x out of mask\n",
 113                         einfo->ip_ect);
 114                 return false;
 115         }
 116         if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR))
 117             && (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 118                 printk(KERN_WARNING "ECN: cannot use TCP operations on a "
 119                        "non-tcp rule\n");
 120                 return false;
 121         }
 122         return true;
 123 }
 124
 125 static struct xt_target ecn_tg_reg __read_mostly = {
 126         .name           = "ECN",
 127         .family         = AF_INET,
 128         .target         = ecn_tg,
 129         .targetsize     = sizeof(struct ipt_ECN_info),
 130         .table          = "mangle",
 131         .checkentry     = ecn_tg_check,
 132         .me             = THIS_MODULE,
 133 };
 134
 135 static int __init ecn_tg_init(void)
 136 {
 137         return xt_register_target(&ecn_tg_reg);
 138 }
 139
 140 static void __exit ecn_tg_exit(void)
 141 {
 142         xt_unregister_target(&ecn_tg_reg);
 143 }
 144
 145 module_init(ecn_tg_init);
 146 module_exit(ecn_tg_exit);