4 * NAT protocol helper module for GRE.
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.
9 * It has an optional key field, which may help us distinguishing two
10 * connections between the same two hosts.
12 * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
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
18 * Documentation about PPTP can be found in RFC 2637
20 * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
22 * Development of this code funded by Astaro AG (http://www.astaro.com/)
26 #include <linux/module.h>
27 #include <linux/skbuff.h>
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>
35 MODULE_LICENSE("GPL");
36 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
37 MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
40 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
41 __FUNCTION__, ## args)
43 #define DEBUGP(x, args...)
46 /* is key in given range between min and max */
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)
55 if (maniptype == IP_NAT_MANIP_SRC)
56 key = tuple->src.u.gre.key;
58 key = tuple->dst.u.gre.key;
60 return ntohs(key) >= ntohs(min->gre.key) &&
61 ntohs(key) <= ntohs(max->gre.key);
64 /* generate unique tuple ... */
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)
73 unsigned int min, i, range_size;
75 /* If there is no master conntrack we are not PPTP,
76 do not change tuples */
77 if (!conntrack->master)
80 if (maniptype == IP_NAT_MANIP_SRC)
81 keyptr = &tuple->src.u.gre.key;
83 keyptr = &tuple->dst.u.gre.key;
85 if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
86 DEBUGP("%p: NATing GRE PPTP\n", conntrack);
90 min = ntohs(range->min.gre.key);
91 range_size = ntohs(range->max.gre.key) - min + 1;
94 DEBUGP("min = %u, range_size = %u\n", min, range_size);
96 for (i = 0; i < range_size; i++, key++) {
97 *keyptr = htons(min + key % range_size);
98 if (!nf_nat_used_tuple(tuple, conntrack))
102 DEBUGP("%p: no NAT mapping\n", conntrack);
106 /* manipulate a GRE packet according to maniptype */
108 gre_manip_pkt(struct sk_buff **pskb, unsigned int iphdroff,
109 const struct nf_conntrack_tuple *tuple,
110 enum nf_nat_manip_type maniptype)
112 struct gre_hdr *greh;
113 struct gre_hdr_pptp *pgreh;
114 struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
115 unsigned int hdroff = iphdroff + iph->ihl * 4;
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(pskb, hdroff + sizeof(*pgreh) - 8))
122 greh = (void *)(*pskb)->data + hdroff;
123 pgreh = (struct gre_hdr_pptp *)greh;
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)
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" */
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;
139 DEBUGP("can't nat unknown GRE version\n");
145 static struct nf_nat_protocol gre __read_mostly = {
147 .protonum = IPPROTO_GRE,
148 .manip_pkt = gre_manip_pkt,
149 .in_range = gre_in_range,
150 .unique_tuple = gre_unique_tuple,
151 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
152 .range_to_nfattr = nf_nat_port_range_to_nfattr,
153 .nfattr_to_range = nf_nat_port_nfattr_to_range,
157 int __init nf_nat_proto_gre_init(void)
159 return nf_nat_protocol_register(&gre);
162 void __exit nf_nat_proto_gre_fini(void)
164 nf_nat_protocol_unregister(&gre);
167 module_init(nf_nat_proto_gre_init);
168 module_exit(nf_nat_proto_gre_fini);
170 void nf_nat_need_gre(void)
174 EXPORT_SYMBOL_GPL(nf_nat_need_gre);