1 files changed, 149 insertions, 0 deletions
diff --git a/net/ipv4/netfilter/nf_nat_proto_gre.c b/net/ipv4/netfilter/nf_nat_proto_gre.c
new file mode 100644
index 00000000..bc8d83a3
--- /dev/null
+++ b/net/ipv4/netfilter/nf_nat_proto_gre.c
@@ -0,0 +1,149 @@
+/*
+ * 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/)
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+
+#include <net/netfilter/nf_nat.h>
+#include <net/netfilter/nf_nat_rule.h>
+#include <net/netfilter/nf_nat_protocol.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");
+
+/* generate unique tuple ... */
+static void
+gre_unique_tuple(struct nf_conntrack_tuple *tuple,
+		 const struct nf_nat_range *range,
+		 enum nf_nat_manip_type maniptype,
+		 const struct nf_conn *ct)
+{
+	static u_int16_t key;
+	__be16 *keyptr;
+	unsigned int min, i, range_size;
+
+	/* If there is no master conntrack we are not PPTP,
+	   do not change tuples */
+	if (!ct->master)
+		return;
+
+	if (maniptype == IP_NAT_MANIP_SRC)
+		keyptr = &tuple->src.u.gre.key;
+	else
+		keyptr = &tuple->dst.u.gre.key;
+
+	if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
+		pr_debug("%p: NATing GRE PPTP\n", ct);
+		min = 1;
+		range_size = 0xffff;
+	} else {
+		min = ntohs(range->min.gre.key);
+		range_size = ntohs(range->max.gre.key) - min + 1;
+	}
+
+	pr_debug("min = %u, range_size = %u\n", min, range_size);
+
+	for (i = 0; ; ++key) {
+		*keyptr = htons(min + key % range_size);
+		if (++i == range_size || !nf_nat_used_tuple(tuple, ct))
+			return;
+	}
+
+	pr_debug("%p: no NAT mapping\n", ct);
+	return;
+}
+
+/* manipulate a GRE packet according to maniptype */
+static bool
+gre_manip_pkt(struct sk_buff *skb, unsigned int iphdroff,
+	      const struct nf_conntrack_tuple *tuple,
+	      enum nf_nat_manip_type maniptype)
+{
+	const struct gre_hdr *greh;
+	struct gre_hdr_pptp *pgreh;
+	const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
+	unsigned int hdroff = iphdroff + iph->ihl * 4;
+
+	/* 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 gre_hdr_pptp *)greh;
+
+	/* we only have destination manip of a packet, since 'source key'
+	 * is not present in the packet itself */
+	if (maniptype != IP_NAT_MANIP_DST)
+		return true;
+	switch (greh->version) {
+	case GRE_VERSION_1701:
+		/* We do not currently NAT any GREv0 packets.
+		 * Try to behave like "nf_nat_proto_unknown" */
+		break;
+	case GRE_VERSION_PPTP:
+		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_protocol gre = {
+	.protonum		= IPPROTO_GRE,
+	.me			= THIS_MODULE,
+	.manip_pkt		= gre_manip_pkt,
+	.in_range		= nf_nat_proto_in_range,
+	.unique_tuple		= gre_unique_tuple,
+#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
+	.range_to_nlattr	= nf_nat_proto_range_to_nlattr,
+	.nlattr_to_range	= nf_nat_proto_nlattr_to_range,
+#endif
+};
+
+static int __init nf_nat_proto_gre_init(void)
+{
+	return nf_nat_protocol_register(&gre);
+}
+
+static void __exit nf_nat_proto_gre_fini(void)
+{
+	nf_nat_protocol_unregister(&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);