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   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/udp.h>
  13
  14 #include <linux/netfilter.h>
  15 #include <net/netfilter/nf_nat.h>
  16 #include <net/netfilter/nf_nat_core.h>
  17 #include <net/netfilter/nf_nat_rule.h>
  18 #include <net/netfilter/nf_nat_protocol.h>
  19
  20 static u_int16_t udp_port_rover;
  21
  22 static bool
  23 udp_unique_tuple(struct nf_conntrack_tuple *tuple,
  24                  const struct nf_nat_range *range,
  25                  enum nf_nat_manip_type maniptype,
  26                  const struct nf_conn *ct)
  27 {
  28         return nf_nat_proto_unique_tuple(tuple, range, maniptype, ct,
  29                                          &udp_port_rover);
  30 }
  31
  32 static bool
  33 udp_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 udphdr *hdr;
  40         unsigned int hdroff = iphdroff + iph->ihl*4;
  41         __be32 oldip, newip;
  42         __be16 *portptr, newport;
  43
  44         if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
  45                 return false;
  46
  47         iph = (struct iphdr *)(skb->data + iphdroff);
  48         hdr = (struct udphdr *)(skb->data + hdroff);
  49
  50         if (maniptype == IP_NAT_MANIP_SRC) {
  51                 /* Get rid of src ip and src pt */
  52                 oldip = iph->saddr;
  53                 newip = tuple->src.u3.ip;
  54                 newport = tuple->src.u.udp.port;
  55                 portptr = &hdr->source;
  56         } else {
  57                 /* Get rid of dst ip and dst pt */
  58                 oldip = iph->daddr;
  59                 newip = tuple->dst.u3.ip;
  60                 newport = tuple->dst.u.udp.port;
  61                 portptr = &hdr->dest;
  62         }
  63         if (hdr->check || skb->ip_summed == CHECKSUM_PARTIAL) {
  64                 inet_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
  65                 inet_proto_csum_replace2(&hdr->check, skb, *portptr, newport,
  66                                          0);
  67                 if (!hdr->check)
  68                         hdr->check = CSUM_MANGLED_0;
  69         }
  70         *portptr = newport;
  71         return true;
  72 }
  73
  74 const struct nf_nat_protocol nf_nat_protocol_udp = {
  75         .protonum               = IPPROTO_UDP,
  76         .me                     = THIS_MODULE,
  77         .manip_pkt              = udp_manip_pkt,
  78         .in_range               = nf_nat_proto_in_range,
  79         .unique_tuple           = udp_unique_tuple,
  80 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
  81         .range_to_nlattr        = nf_nat_proto_range_to_nlattr,
  82         .nlattr_to_range        = nf_nat_proto_nlattr_to_range,
  83 #endif
  84 };