net/ipv4/netfilter/ip_nat_proto_gre.c

   1 /*
   2  * ip_nat_proto_gre.c - Version 2.0
   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/ip.h>
  28 #include <linux/netfilter_ipv4/ip_nat.h>
  29 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  30 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  31 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  32
  33 MODULE_LICENSE("GPL");
  34 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  35 MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
  36
  37 #if 0
  38 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
  39                                        __FUNCTION__, ## args)
  40 #else
  41 #define DEBUGP(x, args...)
  42 #endif
  43
  44 /* is key in given range between min and max */
  45 static int
  46 gre_in_range(const struct ip_conntrack_tuple *tuple,
  47              enum ip_nat_manip_type maniptype,
  48              const union ip_conntrack_manip_proto *min,
  49              const union ip_conntrack_manip_proto *max)
  50 {
  51         __be16 key;
  52
  53         if (maniptype == IP_NAT_MANIP_SRC)
  54                 key = tuple->src.u.gre.key;
  55         else
  56                 key = tuple->dst.u.gre.key;
  57
  58         return ntohs(key) >= ntohs(min->gre.key)
  59                 && ntohs(key) <= ntohs(max->gre.key);
  60 }
  61
  62 /* generate unique tuple ... */
  63 static int
  64 gre_unique_tuple(struct ip_conntrack_tuple *tuple,
  65                  const struct ip_nat_range *range,
  66                  enum ip_nat_manip_type maniptype,
  67                  const struct ip_conntrack *conntrack)
  68 {
  69         static u_int16_t key;
  70         __be16 *keyptr;
  71         unsigned int min, i, range_size;
  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                 DEBUGP("%p: NATing GRE PPTP\n", conntrack);
  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         DEBUGP("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 (!ip_nat_used_tuple(tuple, conntrack))
  92                         return 1;
  93         }
  94
  95         DEBUGP("%p: no NAT mapping\n", conntrack);
  96
  97         return 0;
  98 }
  99
 100 /* manipulate a GRE packet according to maniptype */
 101 static int
 102 gre_manip_pkt(struct sk_buff **pskb,
 103               unsigned int iphdroff,
 104               const struct ip_conntrack_tuple *tuple,
 105               enum ip_nat_manip_type maniptype)
 106 {
 107         struct gre_hdr *greh;
 108         struct gre_hdr_pptp *pgreh;
 109         struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
 110         unsigned int hdroff = iphdroff + iph->ihl*4;
 111
 112         /* pgreh includes two optional 32bit fields which are not required
 113          * to be there.  That's where the magic '8' comes from */
 114         if (!skb_make_writable(pskb, hdroff + sizeof(*pgreh)-8))
 115                 return 0;
 116
 117         greh = (void *)(*pskb)->data + hdroff;
 118         pgreh = (struct gre_hdr_pptp *) greh;
 119
 120         /* we only have destination manip of a packet, since 'source key'
 121          * is not present in the packet itself */
 122         if (maniptype == IP_NAT_MANIP_DST) {
 123                 /* key manipulation is always dest */
 124                 switch (greh->version) {
 125                 case 0:
 126                         if (!greh->key) {
 127                                 DEBUGP("can't nat GRE w/o key\n");
 128                                 break;
 129                         }
 130                         if (greh->csum) {
 131                                 /* FIXME: Never tested this code... */
 132                                 nf_proto_csum_replace4(gre_csum(greh), *pskb,
 133                                                         *(gre_key(greh)),
 134                                                         tuple->dst.u.gre.key, 0);
 135                         }
 136                         *(gre_key(greh)) = tuple->dst.u.gre.key;
 137                         break;
 138                 case GRE_VERSION_PPTP:
 139                         DEBUGP("call_id -> 0x%04x\n",
 140                                 ntohs(tuple->dst.u.gre.key));
 141                         pgreh->call_id = tuple->dst.u.gre.key;
 142                         break;
 143                 default:
 144                         DEBUGP("can't nat unknown GRE version\n");
 145                         return 0;
 146                         break;
 147                 }
 148         }
 149         return 1;
 150 }
 151
 152 /* nat helper struct */
 153 static struct ip_nat_protocol gre = {
 154         .name           = "GRE",
 155         .protonum       = IPPROTO_GRE,
 156         .manip_pkt      = gre_manip_pkt,
 157         .in_range       = gre_in_range,
 158         .unique_tuple   = gre_unique_tuple,
 159 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 160     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 161         .range_to_nfattr        = ip_nat_port_range_to_nfattr,
 162         .nfattr_to_range        = ip_nat_port_nfattr_to_range,
 163 #endif
 164 };
 165
 166 int __init ip_nat_proto_gre_init(void)
 167 {
 168         return ip_nat_protocol_register(&gre);
 169 }
 170
 171 void __exit ip_nat_proto_gre_fini(void)
 172 {
 173         ip_nat_protocol_unregister(&gre);
 174 }