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 /* is key in given range between min and max */
  40 static int
  41 gre_in_range(const struct nf_conntrack_tuple *tuple,
  42              enum nf_nat_manip_type maniptype,
  43              const union nf_conntrack_man_proto *min,
  44              const union nf_conntrack_man_proto *max)
  45 {
  46         __be16 key;
  47
  48         if (maniptype == IP_NAT_MANIP_SRC)
  49                 key = tuple->src.u.gre.key;
  50         else
  51                 key = tuple->dst.u.gre.key;
  52
  53         return ntohs(key) >= ntohs(min->gre.key) &&
  54                ntohs(key) <= ntohs(max->gre.key);
  55 }
  56
  57 /* generate unique tuple ... */
  58 static int
  59 gre_unique_tuple(struct nf_conntrack_tuple *tuple,
  60                  const struct nf_nat_range *range,
  61                  enum nf_nat_manip_type maniptype,
  62                  const struct nf_conn *ct)
  63 {
  64         static u_int16_t key;
  65         __be16 *keyptr;
  66         unsigned int min, i, range_size;
  67
  68         /* If there is no master conntrack we are not PPTP,
  69            do not change tuples */
  70         if (!ct->master)
  71                 return 0;
  72
  73         if (maniptype == IP_NAT_MANIP_SRC)
  74                 keyptr = &tuple->src.u.gre.key;
  75         else
  76                 keyptr = &tuple->dst.u.gre.key;
  77
  78         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  79                 pr_debug("%p: NATing GRE PPTP\n", ct);
  80                 min = 1;
  81                 range_size = 0xffff;
  82         } else {
  83                 min = ntohs(range->min.gre.key);
  84                 range_size = ntohs(range->max.gre.key) - min + 1;
  85         }
  86
  87         pr_debug("min = %u, range_size = %u\n", min, range_size);
  88
  89         for (i = 0; i < range_size; i++, key++) {
  90                 *keyptr = htons(min + key % range_size);
  91                 if (!nf_nat_used_tuple(tuple, ct))
  92                         return 1;
  93         }
  94
  95         pr_debug("%p: no NAT mapping\n", ct);
  96         return 0;
  97 }
  98
  99 /* manipulate a GRE packet according to maniptype */
 100 static int
 101 gre_manip_pkt(struct sk_buff *skb, unsigned int iphdroff,
 102               const struct nf_conntrack_tuple *tuple,
 103               enum nf_nat_manip_type maniptype)
 104 {
 105         struct gre_hdr *greh;
 106         struct gre_hdr_pptp *pgreh;
 107         const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
 108         unsigned int hdroff = iphdroff + iph->ihl * 4;
 109
 110         /* pgreh includes two optional 32bit fields which are not required
 111          * to be there.  That's where the magic '8' comes from */
 112         if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
 113                 return 0;
 114
 115         greh = (void *)skb->data + hdroff;
 116         pgreh = (struct gre_hdr_pptp *)greh;
 117
 118         /* we only have destination manip of a packet, since 'source key'
 119          * is not present in the packet itself */
 120         if (maniptype != IP_NAT_MANIP_DST)
 121                 return 1;
 122         switch (greh->version) {
 123         case GRE_VERSION_1701:
 124                 /* We do not currently NAT any GREv0 packets.
 125                  * Try to behave like "nf_nat_proto_unknown" */
 126                 break;
 127         case GRE_VERSION_PPTP:
 128                 pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
 129                 pgreh->call_id = tuple->dst.u.gre.key;
 130                 break;
 131         default:
 132                 pr_debug("can't nat unknown GRE version\n");
 133                 return 0;
 134         }
 135         return 1;
 136 }
 137
 138 static const struct nf_nat_protocol gre = {
 139         .name                   = "GRE",
 140         .protonum               = IPPROTO_GRE,
 141         .me                     = THIS_MODULE,
 142         .manip_pkt              = gre_manip_pkt,
 143         .in_range               = gre_in_range,
 144         .unique_tuple           = gre_unique_tuple,
 145 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 146         .range_to_nlattr        = nf_nat_port_range_to_nlattr,
 147         .nlattr_to_range        = nf_nat_port_nlattr_to_range,
 148 #endif
 149 };
 150
 151 static int __init nf_nat_proto_gre_init(void)
 152 {
 153         return nf_nat_protocol_register(&gre);
 154 }
 155
 156 static void __exit nf_nat_proto_gre_fini(void)
 157 {
 158         nf_nat_protocol_unregister(&gre);
 159 }
 160
 161 module_init(nf_nat_proto_gre_init);
 162 module_exit(nf_nat_proto_gre_fini);
 163
 164 void nf_nat_need_gre(void)
 165 {
 166         return;
 167 }
 168 EXPORT_SYMBOL_GPL(nf_nat_need_gre);