release/src-rt-6.x.4708/linux/linux-2.6.36/net/ipv4/netfilter/nf_nat_proto_tcp.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #include <linux/types.h>
  10 #include <linux/init.h>
  11 #include <linux/ip.h>
  12 #include <linux/tcp.h>
  13
  14 #include <linux/netfilter.h>
  15 #include <linux/netfilter/nfnetlink_conntrack.h>
  16 #include <net/netfilter/nf_nat.h>
  17 #include <net/netfilter/nf_nat_rule.h>
  18 #include <net/netfilter/nf_nat_protocol.h>
  19 #include <net/netfilter/nf_nat_core.h>
  20
  21 static u_int16_t tcp_port_rover;
  22
  23 static void
  24 tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
  25                  const struct nf_nat_range *range,
  26                  enum nf_nat_manip_type maniptype,
  27                  const struct nf_conn *ct)
  28 {
  29         nf_nat_proto_unique_tuple(tuple, range, maniptype, ct, &tcp_port_rover);
  30 }
  31
  32 static bool
  33 tcp_manip_pkt(struct sk_buff *skb,
  34               unsigned int iphdroff,
  35               const struct nf_conntrack_tuple *tuple,
  36               enum nf_nat_manip_type maniptype)
  37 {
  38         const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
  39         struct tcphdr *hdr;
  40         unsigned int hdroff = iphdroff + iph->ihl*4;
  41         __be32 oldip, newip;
  42         __be16 *portptr, newport, oldport;
  43         int hdrsize = 8; /* TCP connection tracking guarantees this much */
  44
  45         /* this could be a inner header returned in icmp packet; in such
  46            cases we cannot update the checksum field since it is outside of
  47            the 8 bytes of transport layer headers we are guaranteed */
  48         if (skb->len >= hdroff + sizeof(struct tcphdr))
  49                 hdrsize = sizeof(struct tcphdr);
  50
  51         if (!skb_make_writable(skb, hdroff + hdrsize))
  52                 return false;
  53
  54         iph = (struct iphdr *)(skb->data + iphdroff);
  55         hdr = (struct tcphdr *)(skb->data + hdroff);
  56
  57         if (maniptype == IP_NAT_MANIP_SRC) {
  58                 /* Get rid of src ip and src pt */
  59                 oldip = iph->saddr;
  60                 newip = tuple->src.u3.ip;
  61                 newport = tuple->src.u.tcp.port;
  62                 portptr = &hdr->source;
  63         } else {
  64                 /* Get rid of dst ip and dst pt */
  65                 oldip = iph->daddr;
  66                 newip = tuple->dst.u3.ip;
  67                 newport = tuple->dst.u.tcp.port;
  68                 portptr = &hdr->dest;
  69         }
  70
  71         oldport = *portptr;
  72         *portptr = newport;
  73
  74         if (hdrsize < sizeof(*hdr))
  75                 return true;
  76
  77         inet_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
  78         inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
  79         return true;
  80 }
  81
  82 const struct nf_nat_protocol nf_nat_protocol_tcp = {
  83         .protonum               = IPPROTO_TCP,
  84         .me                     = THIS_MODULE,
  85         .manip_pkt              = tcp_manip_pkt,
  86         .in_range               = nf_nat_proto_in_range,
  87         .unique_tuple           = tcp_unique_tuple,
  88 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
  89         .range_to_nlattr        = nf_nat_proto_range_to_nlattr,
  90         .nlattr_to_range        = nf_nat_proto_nlattr_to_range,
  91 #endif
  92 };