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Linux/net/ipv4/netfilter/nf_nat_proto_gre.c

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  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 bool
 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 false;
 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; i < range_size; i++, key++) {
 72                 *keyptr = htons(min + key % range_size);
 73                 if (!nf_nat_used_tuple(tuple, ct))
 74                         return true;
 75         }
 76 
 77         pr_debug("%p: no NAT mapping\n", ct);
 78         return false;
 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);
150 

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