net/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/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_l3proto.h>
  18 #include <net/netfilter/nf_nat_l4proto.h>
  19 #include <net/netfilter/nf_nat_core.h>
  20
  21 static u16 tcp_port_rover;
  22
  23 static void
  24 tcp_unique_tuple(const struct nf_nat_l3proto *l3proto,
  25                  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_l4proto_unique_tuple(l3proto, tuple, range, maniptype, ct,
  31                                     &tcp_port_rover);
  32 }
  33
  34 static bool
  35 tcp_manip_pkt(struct sk_buff *skb,
  36               const struct nf_nat_l3proto *l3proto,
  37               unsigned int iphdroff, unsigned int hdroff,
  38               const struct nf_conntrack_tuple *tuple,
  39               enum nf_nat_manip_type maniptype)
  40 {
  41         struct tcphdr *hdr;
  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         hdr = (struct tcphdr *)(skb->data + hdroff);
  55
  56         if (maniptype == NF_NAT_MANIP_SRC) {
  57                 /* Get rid of src port */
  58                 newport = tuple->src.u.tcp.port;
  59                 portptr = &hdr->source;
  60         } else {
  61                 /* Get rid of dst port */
  62                 newport = tuple->dst.u.tcp.port;
  63                 portptr = &hdr->dest;
  64         }
  65
  66         oldport = *portptr;
  67         *portptr = newport;
  68
  69         if (hdrsize < sizeof(*hdr))
  70                 return true;
  71
  72         l3proto->csum_update(skb, iphdroff, &hdr->check, tuple, maniptype);
  73         inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, false);
  74         return true;
  75 }
  76
  77 const struct nf_nat_l4proto nf_nat_l4proto_tcp = {
  78         .l4proto                = IPPROTO_TCP,
  79         .manip_pkt              = tcp_manip_pkt,
  80         .in_range               = nf_nat_l4proto_in_range,
  81         .unique_tuple           = tcp_unique_tuple,
  82 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
  83         .nlattr_to_range        = nf_nat_l4proto_nlattr_to_range,
  84 #endif
  85 };