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/)
24 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
28 #include <linux/module.h>
29 #include <linux/skbuff.h>
32 #include <net/netfilter/nf_nat.h>
33 #include <net/netfilter/nf_nat_l4proto.h>
34 #include <linux/netfilter/nf_conntrack_proto_gre.h>
36 MODULE_LICENSE("GPL");
37 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
38 MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
40 /* generate unique tuple ... */
42 gre_unique_tuple(const struct nf_nat_l3proto
*l3proto
,
43 struct nf_conntrack_tuple
*tuple
,
44 const struct nf_nat_range
*range
,
45 enum nf_nat_manip_type maniptype
,
46 const struct nf_conn
*ct
)
50 unsigned int min
, i
, range_size
;
52 /* If there is no master conntrack we are not PPTP,
53 do not change tuples */
57 if (maniptype
== NF_NAT_MANIP_SRC
)
58 keyptr
= &tuple
->src
.u
.gre
.key
;
60 keyptr
= &tuple
->dst
.u
.gre
.key
;
62 if (!(range
->flags
& NF_NAT_RANGE_PROTO_SPECIFIED
)) {
63 pr_debug("%p: NATing GRE PPTP\n", ct
);
67 min
= ntohs(range
->min_proto
.gre
.key
);
68 range_size
= ntohs(range
->max_proto
.gre
.key
) - min
+ 1;
71 pr_debug("min = %u, range_size = %u\n", min
, range_size
);
73 for (i
= 0; ; ++key
) {
74 *keyptr
= htons(min
+ key
% range_size
);
75 if (++i
== range_size
|| !nf_nat_used_tuple(tuple
, ct
))
79 pr_debug("%p: no NAT mapping\n", ct
);
83 /* manipulate a GRE packet according to maniptype */
85 gre_manip_pkt(struct sk_buff
*skb
,
86 const struct nf_nat_l3proto
*l3proto
,
87 unsigned int iphdroff
, unsigned int hdroff
,
88 const struct nf_conntrack_tuple
*tuple
,
89 enum nf_nat_manip_type maniptype
)
91 const struct gre_hdr
*greh
;
92 struct gre_hdr_pptp
*pgreh
;
94 /* pgreh includes two optional 32bit fields which are not required
95 * to be there. That's where the magic '8' comes from */
96 if (!skb_make_writable(skb
, hdroff
+ sizeof(*pgreh
) - 8))
99 greh
= (void *)skb
->data
+ hdroff
;
100 pgreh
= (struct gre_hdr_pptp
*)greh
;
102 /* we only have destination manip of a packet, since 'source key'
103 * is not present in the packet itself */
104 if (maniptype
!= NF_NAT_MANIP_DST
)
106 switch (greh
->version
) {
107 case GRE_VERSION_1701
:
108 /* We do not currently NAT any GREv0 packets.
109 * Try to behave like "nf_nat_proto_unknown" */
111 case GRE_VERSION_PPTP
:
112 pr_debug("call_id -> 0x%04x\n", ntohs(tuple
->dst
.u
.gre
.key
));
113 pgreh
->call_id
= tuple
->dst
.u
.gre
.key
;
116 pr_debug("can't nat unknown GRE version\n");
122 static const struct nf_nat_l4proto gre
= {
123 .l4proto
= IPPROTO_GRE
,
124 .manip_pkt
= gre_manip_pkt
,
125 .in_range
= nf_nat_l4proto_in_range
,
126 .unique_tuple
= gre_unique_tuple
,
127 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
128 .nlattr_to_range
= nf_nat_l4proto_nlattr_to_range
,
132 static int __init
nf_nat_proto_gre_init(void)
134 return nf_nat_l4proto_register(NFPROTO_IPV4
, &gre
);
137 static void __exit
nf_nat_proto_gre_fini(void)
139 nf_nat_l4proto_unregister(NFPROTO_IPV4
, &gre
);
142 module_init(nf_nat_proto_gre_init
);
143 module_exit(nf_nat_proto_gre_fini
);
145 void nf_nat_need_gre(void)
149 EXPORT_SYMBOL_GPL(nf_nat_need_gre
);