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 void
gre_unique_tuple(struct nf_conntrack_tuple * tuple,const struct nf_nat_ipv4_range * range,enum nf_nat_manip_type maniptype,const struct nf_conn * ct)41 gre_unique_tuple(struct nf_conntrack_tuple *tuple,
42 const struct nf_nat_ipv4_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;
54
55 if (maniptype == NF_NAT_MANIP_SRC)
56 keyptr = &tuple->src.u.gre.key;
57 else
58 keyptr = &tuple->dst.u.gre.key;
59
60 if (!(range->flags & NF_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; ; ++key) {
72 *keyptr = htons(min + key % range_size);
73 if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
74 return;
75 }
76
77 pr_debug("%p: no NAT mapping\n", ct);
78 return;
79 }
80
81 /* manipulate a GRE packet according to maniptype */
82 static bool
gre_manip_pkt(struct sk_buff * skb,unsigned int iphdroff,const struct nf_conntrack_tuple * tuple,enum nf_nat_manip_type maniptype)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 != NF_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 .manip_pkt = gre_manip_pkt,
123 .in_range = nf_nat_proto_in_range,
124 .unique_tuple = gre_unique_tuple,
125 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
126 .nlattr_to_range = nf_nat_proto_nlattr_to_range,
127 #endif
128 };
129
nf_nat_proto_gre_init(void)130 static int __init nf_nat_proto_gre_init(void)
131 {
132 return nf_nat_protocol_register(&gre);
133 }
134
nf_nat_proto_gre_fini(void)135 static void __exit nf_nat_proto_gre_fini(void)
136 {
137 nf_nat_protocol_unregister(&gre);
138 }
139
140 module_init(nf_nat_proto_gre_init);
141 module_exit(nf_nat_proto_gre_fini);
142
nf_nat_need_gre(void)143 void nf_nat_need_gre(void)
144 {
145 return;
146 }
147 EXPORT_SYMBOL_GPL(nf_nat_need_gre);
148