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

   1 /*
   2  * nf_nat_proto_gre.c
   3  *
   4  * NAT protocol helper module for GRE.
   5  *
   6  * GRE is a generic encapsulation protocol, which is generally not very
   7  * suited for NAT, as it has no protocol-specific part as port numbers.
   8  *
   9  * It has an optional key field, which may help us distinguishing two
  10  * connections between the same two hosts.
  11  *
  12  * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
  13  *
  14  * PPTP is built on top of a modified version of GRE, and has a mandatory
  15  * field called "CallID", which serves us for the same purpose as the key
  16  * field in plain GRE.
  17  *
  18  * Documentation about PPTP can be found in RFC 2637
  19  *
  20  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  21  *
  22  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  23  *
  24  */
  25
  26 #include <linux/module.h>
  27 #include <linux/skbuff.h>
  28 #include <linux/ip.h>
  29
  30 #include <net/netfilter/nf_nat.h>
  31 #include <net/netfilter/nf_nat_rule.h>
  32 #include <net/netfilter/nf_nat_protocol.h>
  33 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  34
  35 MODULE_LICENSE("GPL");
  36 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  37 MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
  38
  39 /* generate unique tuple ... */
  40 static void
  41 gre_unique_tuple(struct nf_conntrack_tuple *tuple,
  42                  const struct nf_nat_range *range,
  43                  enum nf_nat_manip_type maniptype,
  44                  const struct nf_conn *ct)
  45 {
  46         static u_int16_t key;
  47         __be16 *keyptr;
  48         unsigned int min, i, range_size;
  49
  50         /* If there is no master conntrack we are not PPTP,
  51            do not change tuples */
  52         if (!ct->master)
  53                 return;
  54
  55         if (maniptype == IP_NAT_MANIP_SRC)
  56                 keyptr = &tuple->src.u.gre.key;
  57         else
  58                 keyptr = &tuple->dst.u.gre.key;
  59
  60         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  61                 pr_debug("%p: NATing GRE PPTP\n", ct);
  62                 min = 1;
  63                 range_size = 0xffff;
  64         } else {
  65                 min = ntohs(range->min.gre.key);
  66                 range_size = ntohs(range->max.gre.key) - min + 1;
  67         }
  68
  69         pr_debug("min = %u, range_size = %u\n", min, range_size);
  70
  71         for (i = 0; ; ++key) {
  72                 *keyptr = htons(min + key % range_size);
  73                 if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
  74                         return;
  75         }
  76
  77         pr_debug("%p: no NAT mapping\n", ct);
  78         return;
  79 }
  80
  81 /* manipulate a GRE packet according to maniptype */
  82 static bool
  83 gre_manip_pkt(struct sk_buff *skb, unsigned int iphdroff,
  84               const struct nf_conntrack_tuple *tuple,
  85               enum nf_nat_manip_type maniptype)
  86 {
  87         const struct gre_hdr *greh;
  88         struct gre_hdr_pptp *pgreh;
  89         const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
  90         unsigned int hdroff = iphdroff + iph->ihl * 4;
  91
  92         /* pgreh includes two optional 32bit fields which are not required
  93          * to be there.  That's where the magic '8' comes from */
  94         if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
  95                 return false;
  96
  97         greh = (void *)skb->data + hdroff;
  98         pgreh = (struct gre_hdr_pptp *)greh;
  99
 100         /* we only have destination manip of a packet, since 'source key'
 101          * is not present in the packet itself */
 102         if (maniptype != IP_NAT_MANIP_DST)
 103                 return true;
 104         switch (greh->version) {
 105         case GRE_VERSION_1701:
 106                 /* We do not currently NAT any GREv0 packets.
 107                  * Try to behave like "nf_nat_proto_unknown" */
 108                 break;
 109         case GRE_VERSION_PPTP:
 110                 pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
 111                 pgreh->call_id = tuple->dst.u.gre.key;
 112                 break;
 113         default:
 114                 pr_debug("can't nat unknown GRE version\n");
 115                 return false;
 116         }
 117         return true;
 118 }
 119
 120 static const struct nf_nat_protocol gre = {
 121         .protonum               = IPPROTO_GRE,
 122         .me                     = THIS_MODULE,
 123         .manip_pkt              = gre_manip_pkt,
 124         .in_range               = nf_nat_proto_in_range,
 125         .unique_tuple           = gre_unique_tuple,
 126 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 127         .range_to_nlattr        = nf_nat_proto_range_to_nlattr,
 128         .nlattr_to_range        = nf_nat_proto_nlattr_to_range,
 129 #endif
 130 };
 131
 132 static int __init nf_nat_proto_gre_init(void)
 133 {
 134         return nf_nat_protocol_register(&gre);
 135 }
 136
 137 static void __exit nf_nat_proto_gre_fini(void)
 138 {
 139         nf_nat_protocol_unregister(&gre);
 140 }
 141
 142 module_init(nf_nat_proto_gre_init);
 143 module_exit(nf_nat_proto_gre_fini);
 144
 145 void nf_nat_need_gre(void)
 146 {
 147         return;
 148 }
 149 EXPORT_SYMBOL_GPL(nf_nat_need_gre);