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/export.h>
  12 #include <linux/ip.h>
  13 #include <linux/tcp.h>
  14
  15 #include <linux/netfilter.h>
  16 #include <linux/netfilter/nfnetlink_conntrack.h>
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_rule.h>
  19 #include <net/netfilter/nf_nat_protocol.h>
  20 #include <net/netfilter/nf_nat_core.h>
  21
  22 static u_int16_t tcp_port_rover;
  23
  24 static void
  25 tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
  26                  const struct nf_nat_range *range,
  27                  enum nf_nat_manip_type maniptype,
  28                  const struct nf_conn *ct)
  29 {
  30         nf_nat_proto_unique_tuple(tuple, range, maniptype, ct, &tcp_port_rover);
  31 }
  32
  33 static bool
  34 tcp_manip_pkt(struct sk_buff *skb,
  35               unsigned int iphdroff,
  36               const struct nf_conntrack_tuple *tuple,
  37               enum nf_nat_manip_type maniptype)
  38 {
  39         const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
  40         struct tcphdr *hdr;
  41         unsigned int hdroff = iphdroff + iph->ihl*4;
  42         __be32 oldip, newip;
  43         __be16 *portptr, newport, oldport;
  44         int hdrsize = 8; /* TCP connection tracking guarantees this much */
  45
  46         /* this could be a inner header returned in icmp packet; in such
  47            cases we cannot update the checksum field since it is outside of
  48            the 8 bytes of transport layer headers we are guaranteed */
  49         if (skb->len >= hdroff + sizeof(struct tcphdr))
  50                 hdrsize = sizeof(struct tcphdr);
  51
  52         if (!skb_make_writable(skb, hdroff + hdrsize))
  53                 return false;
  54
  55         iph = (struct iphdr *)(skb->data + iphdroff);
  56         hdr = (struct tcphdr *)(skb->data + hdroff);
  57
  58         if (maniptype == IP_NAT_MANIP_SRC) {
  59                 /* Get rid of src ip and src pt */
  60                 oldip = iph->saddr;
  61                 newip = tuple->src.u3.ip;
  62                 newport = tuple->src.u.tcp.port;
  63                 portptr = &hdr->source;
  64         } else {
  65                 /* Get rid of dst ip and dst pt */
  66                 oldip = iph->daddr;
  67                 newip = tuple->dst.u3.ip;
  68                 newport = tuple->dst.u.tcp.port;
  69                 portptr = &hdr->dest;
  70         }
  71
  72         oldport = *portptr;
  73         *portptr = newport;
  74
  75         if (hdrsize < sizeof(*hdr))
  76                 return true;
  77
  78         inet_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
  79         inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
  80         return true;
  81 }
  82
  83 const struct nf_nat_protocol nf_nat_protocol_tcp = {
  84         .protonum               = IPPROTO_TCP,
  85         .me                     = THIS_MODULE,
  86         .manip_pkt              = tcp_manip_pkt,
  87         .in_range               = nf_nat_proto_in_range,
  88         .unique_tuple           = tcp_unique_tuple,
  89 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
  90         .range_to_nlattr        = nf_nat_proto_range_to_nlattr,
  91         .nlattr_to_range        = nf_nat_proto_nlattr_to_range,
  92 #endif
  93 };