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>

Author: ummakynes

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