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; ; ++key
) {
97 *keyptr
= htons(min
+ key
% range_size
);
98 if (++i
== range_size
|| !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
*skb
, 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
*)(skb
->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(skb
, hdroff
+ sizeof(*pgreh
) - 8))
122 greh
= (void *)skb
->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
,
149 .manip_pkt
= gre_manip_pkt
,
150 .in_range
= gre_in_range
,
151 .unique_tuple
= gre_unique_tuple
,
152 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
153 .range_to_nfattr
= nf_nat_port_range_to_nfattr
,
154 .nfattr_to_range
= nf_nat_port_nfattr_to_range
,
158 int __init
nf_nat_proto_gre_init(void)
160 return nf_nat_protocol_register(&gre
);
163 void __exit
nf_nat_proto_gre_fini(void)
165 nf_nat_protocol_unregister(&gre
);
168 module_init(nf_nat_proto_gre_init
);
169 module_exit(nf_nat_proto_gre_fini
);
171 void nf_nat_need_gre(void)
175 EXPORT_SYMBOL_GPL(nf_nat_need_gre
);