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/*
* nf_nat_proto_gre.c
*
* NAT protocol helper module for GRE.
*
* GRE is a generic encapsulation protocol, which is generally not very
* suited for NAT, as it has no protocol-specific part as port numbers.
*
* It has an optional key field, which may help us distinguishing two
* connections between the same two hosts.
*
* GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
*
* PPTP is built on top of a modified version of GRE, and has a mandatory
* field called "CallID", which serves us for the same purpose as the key
* field in plain GRE.
*
* Documentation about PPTP can be found in RFC 2637
*
* (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
*
* Development of this code funded by Astaro AG (http://www.astaro.com/)
*
* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
*
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_l4proto.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
MODULE_DESCRIPTION("Netfilter NAT protocol helper module for GRE");
/* manipulate a GRE packet according to maniptype */
static bool
gre_manip_pkt(struct sk_buff *skb,
const struct nf_nat_l3proto *l3proto,
unsigned int iphdroff, unsigned int hdroff,
const struct nf_conntrack_tuple *tuple,
enum nf_nat_manip_type maniptype)
{
const struct gre_base_hdr *greh;
struct pptp_gre_header *pgreh;
/* pgreh includes two optional 32bit fields which are not required
* to be there. That's where the magic '8' comes from */
if (!skb_make_writable(skb, hdroff + sizeof(*pgreh) - 8))
return false;
greh = (void *)skb->data + hdroff;
pgreh = (struct pptp_gre_header *)greh;
/* we only have destination manip of a packet, since 'source key'
* is not present in the packet itself */
if (maniptype != NF_NAT_MANIP_DST)
return true;
switch (greh->flags & GRE_VERSION) {
case GRE_VERSION_0:
/* We do not currently NAT any GREv0 packets.
* Try to behave like "nf_nat_proto_unknown" */
break;
case GRE_VERSION_1:
pr_debug("call_id -> 0x%04x\n", ntohs(tuple->dst.u.gre.key));
pgreh->call_id = tuple->dst.u.gre.key;
break;
default:
pr_debug("can't nat unknown GRE version\n");
return false;
}
return true;
}
static const struct nf_nat_l4proto gre = {
.l4proto = IPPROTO_GRE,
.manip_pkt = gre_manip_pkt,
.in_range = nf_nat_l4proto_in_range,
#if IS_ENABLED(CONFIG_NF_CT_NETLINK)
.nlattr_to_range = nf_nat_l4proto_nlattr_to_range,
#endif
};
static int __init nf_nat_proto_gre_init(void)
{
return nf_nat_l4proto_register(NFPROTO_IPV4, &gre);
}
static void __exit nf_nat_proto_gre_fini(void)
{
nf_nat_l4proto_unregister(NFPROTO_IPV4, &gre);
}
module_init(nf_nat_proto_gre_init);
module_exit(nf_nat_proto_gre_fini);
void nf_nat_need_gre(void)
{
return;
}
EXPORT_SYMBOL_GPL(nf_nat_need_gre);
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