gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)

This is an initial implementation of a netdev driver for GTP datapath
(GTP-U) v0 and v1, according to the GSM TS 09.60 and 3GPP TS 29.060
standards. This tunneling protocol is used to prevent subscribers from
accessing mobile carrier core network infrastructure.

This implementation requires a GGSN userspace daemon that implements the
signaling protocol (GTP-C), such as OpenGGSN [1]. This userspace daemon
updates the PDP context database that represents active subscriber
sessions through a genetlink interface.

For more context on this tunneling protocol, you can check the slides
that were presented during the NetDev 1.1 [2].

Only IPv4 is supported at this time.

[1] http://git.osmocom.org/openggsn/
[2] http://www.netdevconf.org/1.1/proceedings/slides/schultz-welte-osmocom-gtp.pdf

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -192,6 +192,23 @@ config GENEVE
 	  To compile this driver as a module, choose M here: the module
 	  will be called geneve.
 
+config GTP
+	tristate "GPRS Tunneling Protocol datapath (GTP-U)"
+	depends on INET && NET_UDP_TUNNEL
+	select NET_IP_TUNNEL
+	---help---
+	  This allows one to create gtp virtual interfaces that provide
+	  the GPRS Tunneling Protocol datapath (GTP-U). This tunneling protocol
+	  is used to prevent subscribers from accessing mobile carrier core
+	  network infrastructure. This driver requires a userspace software that
+	  implements the signaling protocol (GTP-C) to update its PDP context
+	  base, such as OpenGGSN <http://git.osmocom.org/openggsn/). This
+	  tunneling protocol is implemented according to the GSM TS 09.60 and
+	  3GPP TS 29.060 standards.
+
+	  To compile this drivers as a module, choose M here: the module
+	  wil be called gtp.
+
 config MACSEC
 	tristate "IEEE 802.1AE MAC-level encryption (MACsec)"
 	select CRYPTO

drivers/net/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_VETH) += veth.o
 obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
 obj-$(CONFIG_VXLAN) += vxlan.o
 obj-$(CONFIG_GENEVE) += geneve.o
+obj-$(CONFIG_GTP) += gtp.o
 obj-$(CONFIG_NLMON) += nlmon.o
 obj-$(CONFIG_NET_VRF) += vrf.o
 

include/net/gtp.h

@@ -0,0 +1,34 @@
+#ifndef _GTP_H_
+#define _GTP_H
+
+/* General GTP protocol related definitions. */
+
+#define GTP0_PORT	3386
+#define GTP1U_PORT	2152
+
+#define GTP_TPDU	255
+
+struct gtp0_header {	/* According to GSM TS 09.60. */
+	__u8	flags;
+	__u8	type;
+	__be16	length;
+	__be16	seq;
+	__be16	flow;
+	__u8	number;
+	__u8	spare[3];
+	__be64	tid;
+} __attribute__ ((packed));
+
+struct gtp1_header {	/* According to 3GPP TS 29.060. */
+	__u8	flags;
+	__u8	type;
+	__be16	length;
+	__be32	tid;
+} __attribute__ ((packed));
+
+#define GTP1_F_NPDU	0x01
+#define GTP1_F_SEQ	0x02
+#define GTP1_F_EXTHDR	0x04
+#define GTP1_F_MASK	0x07
+
+#endif

include/uapi/linux/Kbuild

@@ -141,6 +141,7 @@ header-y += gfs2_ondisk.h
 header-y += gigaset_dev.h
 header-y += gpio.h
 header-y += gsmmux.h
+header-y += gtp.h
 header-y += hdlcdrv.h
 header-y += hdlc.h
 header-y += hdreg.h

include/uapi/linux/gtp.h

@@ -0,0 +1,33 @@
+#ifndef _UAPI_LINUX_GTP_H_
+#define _UAPI_LINUX_GTP_H__
+
+enum gtp_genl_cmds {
+	GTP_CMD_NEWPDP,
+	GTP_CMD_DELPDP,
+	GTP_CMD_GETPDP,
+
+	GTP_CMD_MAX,
+};
+
+enum gtp_version {
+	GTP_V0 = 0,
+	GTP_V1,
+};
+
+enum gtp_attrs {
+	GTPA_UNSPEC = 0,
+	GTPA_LINK,
+	GTPA_VERSION,
+	GTPA_TID,	/* for GTPv0 only */
+	GTPA_SGSN_ADDRESS,
+	GTPA_MS_ADDRESS,
+	GTPA_FLOW,
+	GTPA_NET_NS_FD,
+	GTPA_I_TEI,	/* for GTPv1 only */
+	GTPA_O_TEI,	/* for GTPv1 only */
+	GTPA_PAD,
+	__GTPA_MAX,
+};
+#define GTPA_MAX (__GTPA_MAX + 1)
+
+#endif /* _UAPI_LINUX_GTP_H_ */

include/uapi/linux/if_link.h

@@ -529,6 +529,16 @@ enum {
 };
 #define IFLA_PPP_MAX (__IFLA_PPP_MAX - 1)
 
+/* GTP section */
+enum {
+	IFLA_GTP_UNSPEC,
+	IFLA_GTP_FD0,
+	IFLA_GTP_FD1,
+	IFLA_GTP_PDP_HASHSIZE,
+	__IFLA_GTP_MAX,
+};
+#define IFLA_GTP_MAX (__IFLA_GTP_MAX - 1)
+
 /* Bonding section */
 
 enum {

include/uapi/linux/udp.h

@@ -36,6 +36,7 @@ struct udphdr {
 #define UDP_ENCAP_ESPINUDP_NON_IKE	1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
 #define UDP_ENCAP_ESPINUDP	2 /* draft-ietf-ipsec-udp-encaps-06 */
 #define UDP_ENCAP_L2TPINUDP	3 /* rfc2661 */
-
+#define UDP_ENCAP_GTP0		4 /* GSM TS 09.60 */
+#define UDP_ENCAP_GTP1U		5 /* 3GPP TS 29.060 */
 
 #endif /* _UAPI_LINUX_UDP_H */