release/src-rt-6.x/linux/linux-2.6/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 #if 0
  40 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
  41                                        __FUNCTION__, ## args)
  42 #else
  43 #define DEBUGP(x, args...)
  44 #endif
  45
  46 /* is key in given range between min and max */
  47 static int
  48 gre_in_range(const struct nf_conntrack_tuple *tuple,
  49              enum nf_nat_manip_type maniptype,
  50              const union nf_conntrack_man_proto *min,
  51              const union nf_conntrack_man_proto *max)
  52 {
  53         __be16 key;
  54
  55         if (maniptype == IP_NAT_MANIP_SRC)
  56                 key = tuple->src.u.gre.key;
  57         else
  58                 key = tuple->dst.u.gre.key;
  59
  60         return ntohs(key) >= ntohs(min->gre.key) &&
  61                ntohs(key) <= ntohs(max->gre.key);
  62 }
  63
  64 /* generate unique tuple ... */
  65 static int
  66 gre_unique_tuple(struct nf_conntrack_tuple *tuple,
  67                  const struct nf_nat_range *range,
  68                  enum nf_nat_manip_type maniptype,
  69                  const struct nf_conn *conntrack)
  70 {
  71         static u_int16_t key;
  72         __be16 *keyptr;
  73         unsigned int min, i, range_size;
  74
  75         /* If there is no master conntrack we are not PPTP,
  76            do not change tuples */
  77         if (!conntrack->master)
  78                 return 0;
  79
  80         if (maniptype == IP_NAT_MANIP_SRC)
  81                 keyptr = &tuple->src.u.gre.key;
  82         else
  83                 keyptr = &tuple->dst.u.gre.key;
  84
  85         if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
  86                 DEBUGP("%p: NATing GRE PPTP\n", conntrack);
  87                 min = 1;
  88                 range_size = 0xffff;
  89         } else {
  90                 min = ntohs(range->min.gre.key);
  91                 range_size = ntohs(range->max.gre.key) - min + 1;
  92         }
  93
  94         DEBUGP("min = %u, range_size = %u\n", min, range_size);
  95
  96         for (i = 0; ; ++key) {
  97                 *keyptr = htons(min + key % range_size);
  98                 if (++i == range_size || !nf_nat_used_tuple(tuple, conntrack))
  99                         return 1;
 100         }
 101
 102         DEBUGP("%p: no NAT mapping\n", conntrack);
 103         return 0;
 104 }
 105
 106 /* manipulate a GRE packet according to maniptype */
 107 static int
 108 gre_manip_pkt(struct sk_buff *skb, unsigned int iphdroff,
 109               const struct nf_conntrack_tuple *tuple,
 110               enum nf_nat_manip_type maniptype)
 111 {
 112         struct gre_hdr *greh;
 113         struct gre_hdr_pptp *pgreh;
 114         struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
 115         unsigned int hdroff = iphdroff + iph->ihl * 4;
 116
 117         /* pgreh includes two optional 32bit fields which are not required
 118          * to be there.  That's where the magic '8' comes from */
 119         if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
 120                 return 0;
 121
 122         greh = (void *)skb->data + hdroff;
 123         pgreh = (struct gre_hdr_pptp *)greh;
 124
 125         /* we only have destination manip of a packet, since 'source key'
 126          * is not present in the packet itself */
 127         if (maniptype != IP_NAT_MANIP_DST)
 128                 return 1;
 129         switch (greh->version) {
 130         case GRE_VERSION_1701:
 131                 /* We do not currently NAT any GREv0 packets.
 132                  * Try to behave like "nf_nat_proto_unknown" */
 133                 break;
 134         case GRE_VERSION_PPTP:
 135                 DEBUGP("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
 136                 pgreh->call_id = tuple->dst.u.gre.key;
 137                 break;
 138         default:
 139                 DEBUGP("can't nat unknown GRE version\n");
 140                 return 0;
 141         }
 142         return 1;
 143 }
 144
 145 static struct nf_nat_protocol gre __read_mostly = {
 146         .name                   = "GRE",
 147         .protonum               = IPPROTO_GRE,
 148         .me                     = THIS_MODULE,
 149         .manip_pkt              = gre_manip_pkt,
 150         .in_range               = gre_in_range,
 151         .unique_tuple           = gre_unique_tuple,
 152 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 153         .range_to_nfattr        = nf_nat_port_range_to_nfattr,
 154         .nfattr_to_range        = nf_nat_port_nfattr_to_range,
 155 #endif
 156 };
 157
 158 int __init nf_nat_proto_gre_init(void)
 159 {
 160         return nf_nat_protocol_register(&gre);
 161 }
 162
 163 void __exit nf_nat_proto_gre_fini(void)
 164 {
 165         nf_nat_protocol_unregister(&gre);
 166 }
 167
 168 module_init(nf_nat_proto_gre_init);
 169 module_exit(nf_nat_proto_gre_fini);
 170
 171 void nf_nat_need_gre(void)
 172 {
 173         return;
 174 }
 175 EXPORT_SYMBOL_GPL(nf_nat_need_gre);