10 files changed, 531 insertions, 2 deletions
diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
index 01240f5d0..20144ee85 100644
--- a/pkg/tcpip/header/BUILD
+++ b/pkg/tcpip/header/BUILD
@@ -8,6 +8,7 @@ go_library(
         "arp.go",
         "checksum.go",
         "eth.go",
+        "gre.go",
         "gue.go",
         "icmpv4.go",
         "icmpv6.go",
diff --git a/pkg/tcpip/header/arp.go b/pkg/tcpip/header/arp.go
index 83189676e..7cc0e2db9 100644
--- a/pkg/tcpip/header/arp.go
+++ b/pkg/tcpip/header/arp.go
@@ -41,6 +41,7 @@ const (
 	// https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#arp-parameters-2
 	ARPHardwareEther    ARPHardwareType = 1
 	ARPHardwareLoopback ARPHardwareType = 2
+	ARPHardwareIPGRE    ARPHardwareType = 3
 )
 
 // ARPOp is an ARP opcode.
diff --git a/pkg/tcpip/header/gre.go b/pkg/tcpip/header/gre.go
new file mode 100644
index 000000000..d4b1f200b
--- /dev/null
+++ b/pkg/tcpip/header/gre.go
@@ -0,0 +1,45 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+const (
+	greProtocolType = 2
+)
+
+// GRE represents a GRE header stored in a byte array.
+type GRE []byte
+
+const (
+	GREHeaderSize = 4
+
+	// GREProtocolNumber is GRE's transport protocol number.
+	GREProtocolNumber tcpip.TransportProtocolNumber = 47
+)
+
+func (b GRE) ProtocolType() tcpip.NetworkProtocolNumber {
+	proto := binary.BigEndian.Uint16(b[greProtocolType:])
+	return tcpip.NetworkProtocolNumber(proto)
+}
+
+// SetLength sets the "length" field of the udp header.
+func (b GRE) SetProtocolType(protocol tcpip.NetworkProtocolNumber) {
+	binary.BigEndian.PutUint16(b[greProtocolType:], uint16(protocol))
+}
diff --git a/pkg/tcpip/header/parse/parse.go b/pkg/tcpip/header/parse/parse.go
index 1c913b5e1..107665d9d 100644
--- a/pkg/tcpip/header/parse/parse.go
+++ b/pkg/tcpip/header/parse/parse.go
@@ -175,3 +175,13 @@ func TCP(pkt *stack.PacketBuffer) bool {
 	pkt.TransportProtocolNumber = header.TCPProtocolNumber
 	return ok
 }
+
+// GRE parses a GRE packet found in pkt.Data and populates pkt's transport
+// header with the GRE header.
+//
+// Returns true if the header was successfully parsed.
+func GRE(pkt *stack.PacketBuffer) bool {
+	_, ok := pkt.TransportHeader().Consume(header.GREHeaderSize)
+	pkt.TransportProtocolNumber = header.GREProtocolNumber
+	return ok
+}
diff --git a/pkg/tcpip/link/channel/channel.go b/pkg/tcpip/link/channel/channel.go
index 658557d62..fc6993722 100644
--- a/pkg/tcpip/link/channel/channel.go
+++ b/pkg/tcpip/link/channel/channel.go
@@ -136,6 +136,7 @@ type Endpoint struct {
 	linkAddr           tcpip.LinkAddress
 	LinkEPCapabilities stack.LinkEndpointCapabilities
 	SupportedGSOKind   stack.SupportedGSO
+	NMaxHeaderLength   uint16
 
 	// Outbound packet queue.
 	q *queue
@@ -229,8 +230,8 @@ func (e *Endpoint) SupportedGSO() stack.SupportedGSO {
 
 // MaxHeaderLength returns the maximum size of the link layer header. Given it
 // doesn't have a header, it just returns 0.
-func (*Endpoint) MaxHeaderLength() uint16 {
-	return 0
+func (e *Endpoint) MaxHeaderLength() uint16 {
+	return e.NMaxHeaderLength
 }
 
 // LinkAddress returns the link address of this endpoint.
diff --git a/pkg/tcpip/link/tunnel/BUILD b/pkg/tcpip/link/tunnel/BUILD
new file mode 100644
index 000000000..3b75b8ee3
--- /dev/null
+++ b/pkg/tcpip/link/tunnel/BUILD
@@ -0,0 +1,21 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "tunnel",
+    srcs = ["gre.go"],
+    visibility = ["//visibility:public"],
+    deps = [
+	"//pkg/tcpip",
+	"//pkg/tcpip/buffer",
+	"//pkg/tcpip/header",
+	"//pkg/tcpip/link/channel",
+	"//pkg/tcpip/network/ipv4",
+	"//pkg/tcpip/network/ipv6",
+	"//pkg/tcpip/stack",
+	"//pkg/tcpip/transport/gre",
+	"//pkg/tcpip/transport/raw",
+	"//pkg/waiter",
+    ],
+)
diff --git a/pkg/tcpip/link/tunnel/gre.go b/pkg/tcpip/link/tunnel/gre.go
new file mode 100644
index 000000000..ef2f9c4de
--- /dev/null
+++ b/pkg/tcpip/link/tunnel/gre.go
@@ -0,0 +1,250 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tunnel
+
+import (
+	"context"
+	"errors"
+	"log"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
+	"gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
+	"gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+	"gvisor.dev/gvisor/pkg/tcpip/transport/gre"
+	"gvisor.dev/gvisor/pkg/tcpip/transport/raw"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+var SIZE = 16
+
+type Endpoint struct {
+	channel.Endpoint
+	LocalAddr tcpip.Address
+	RemoteAddr tcpip.Address
+}
+
+type writer Endpoint
+
+func New(mtu uint32) *Endpoint {
+	var linkAddress tcpip.LinkAddress
+
+	ch := channel.New(SIZE, mtu, linkAddress)
+	return &Endpoint{
+		Endpoint: *ch,
+	}
+}
+
+func (e *Endpoint) GetChannel() *channel.Endpoint {
+	return &e.Endpoint
+}
+
+func (e *Endpoint) GetLocalAddress() tcpip.Address {
+	return e.LocalAddr
+}
+
+func (e *Endpoint) GetRemoteAddress() tcpip.Address {
+	return e.RemoteAddr
+}
+
+// Attach saves the stack network-layer dispatcher for use later when packets
+// are injected.
+func (e *Endpoint) Attach(dispatcher stack.NetworkDispatcher) {
+	log.Println("GRE: Attach")
+
+	e.Endpoint.Attach(dispatcher)
+}
+
+type GrePacketInfo struct {
+	pi *channel.PacketInfo
+}
+
+func (g GrePacketInfo) Len() int {
+	return g.pi.Pkt.Size()
+}
+
+func (g GrePacketInfo) Read(p []byte) (n int, err error){
+	pkt := g.pi.Pkt
+	size := pkt.Size()
+
+	if size > len(p) {
+		return 0, errors.New("Buffer too small")
+	}
+	vv := buffer.NewVectorisedView(size, pkt.Views())
+	pos := 0
+	for {
+		copied, err := vv.Read(p[pos:])
+		log.Printf("VectorisedView Read: %d %d %d %v", size, pos, copied, err)
+		if err != nil {
+			return 0, errors.New("&tcpip.ErrBadBuffer{}")
+		}
+		pos = pos + copied
+		if pos == size {
+			break
+		}
+	}
+
+	return pos, nil
+}
+
+func (g GrePacketInfo) Payload(size int) ([]byte, tcpip.Error){
+	log.Println("Payload")
+	return nil, &tcpip.ErrNotSupported{}
+}
+
+type GreHandlerInfo struct {
+	ChEp *channel.Endpoint
+	Raw tcpip.Endpoint
+	Raddr tcpip.FullAddress
+	Stack *stack.Stack
+	NIC tcpip.NICID
+}
+
+func (info *GreHandlerInfo) greHandler(req *gre.ForwarderRequest) {
+	pkt := req.Pkt
+	log.Println("greHandler: ", req.Pkt.Size(), req.Pkt.Views())
+	greHdr := header.GRE(pkt.TransportHeader().View())
+	proto := greHdr.ProtocolType()
+	pktData := pkt.Data()
+	views := pktData.Views()
+	size := pktData.Size()
+	data := buffer.NewVectorisedView(size, views)
+	newPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		Data: data,
+	})
+	log.Printf("greHandler proto: %d cloned: %v", proto, newPkt.Views())
+
+	info.ChEp.InjectInbound(proto, newPkt)
+}
+
+func ipAny(protocol tcpip.NetworkProtocolNumber) (tcpip.Address, tcpip.Error) {
+	switch protocol {
+	case header.IPv4ProtocolNumber:
+		return header.IPv4Any, nil
+	case header.IPv6ProtocolNumber:
+		return header.IPv6Any, nil
+	default:
+		log.Printf("Unsupported protocol %v", protocol)
+		return tcpip.Address([]byte{}), &tcpip.ErrNotSupported{}
+	}
+}
+
+func (info *GreHandlerInfo) greRead(ep *channel.Endpoint) {
+	for {
+		pi, err := ep.ReadContext(context.Background());
+		linkHdr := pi.Pkt.LinkHeader()
+		greHdr := header.GRE(linkHdr.Push(header.GREHeaderSize))
+		greHdr.SetProtocolType(pi.Proto)
+		log.Printf("greRead %d %v %v %v", pi.Proto, pi, err, greHdr)
+		opts := tcpip.WriteOptions{
+			//To: &info.Raddr
+		}
+		if info.Raddr.Addr == header.IPv4Any {
+			protocol := pi.Pkt.NetworkProtocolNumber
+			nw := pi.Pkt.Network()
+			addr := nw.DestinationAddress()
+			laddr, err := ipAny(protocol); if err != nil {
+				continue
+			}
+
+			err = info.Stack.GetLinkAddress(info.NIC, addr, laddr,  protocol, func (res stack.LinkResolutionResult) {
+
+				if res.Err != nil {
+					return
+				}
+
+				opts.To = &tcpip.FullAddress{
+					NIC: 0,
+					Addr: tcpip.Address(res.LinkAddress),
+				}
+			})
+			if err != nil {
+				continue
+			}
+		}
+		info.Raw.Write(GrePacketInfo{&pi}, opts)
+	}
+}
+
+func networkProtocolNumber(addr *tcpip.Address) tcpip.NetworkProtocolNumber {
+	if addr.To4() != "" {
+		return ipv4.ProtocolNumber
+	} else {
+		return ipv6.ProtocolNumber
+	}
+}
+
+// ARPHardwareType implements stack.LinkEndpoint.ARPHardwareType.
+func (*Endpoint) ARPHardwareType() header.ARPHardwareType {
+	return header.ARPHardwareIPGRE
+}
+
+func (e *Endpoint) Start(s *stack.Stack, nic tcpip.NICID, laddr, raddr *tcpip.Address) tcpip.Error {
+	proto := networkProtocolNumber(laddr)
+	if proto != networkProtocolNumber(raddr) {
+		return &tcpip.ErrBadAddress{}
+	}
+
+	// Create TCP endpoint.
+	var rawWq waiter.Queue
+	rawEp, tcperr := raw.NewEndpoint(s, proto, header.GREProtocolNumber, &rawWq)
+	if tcperr != nil {
+		return tcperr
+	}
+	log.Println("EP: %s", rawEp)
+
+	e.LocalAddr = *laddr
+	e.RemoteAddr = *raddr
+
+	fraddr := tcpip.FullAddress{NIC: 0, Addr: *raddr}
+	flAddr := tcpip.FullAddress{NIC: 0, Addr: *laddr}
+	tcperr = rawEp.Bind(flAddr)
+	if tcperr != nil {
+		return tcperr
+	}
+	log.Printf("Remote: %v %v", raddr, fraddr)
+
+	// Create GRE
+	// greEP := grelink.New(mtu - 24)
+	chEP := e.GetChannel()
+	// TODO detect IPv4/IPv6
+	e.NMaxHeaderLength = header.IPv6FixedHeaderSize + header.GREHeaderSize
+
+	greInfo := GreHandlerInfo{
+//		Ep: loEP,
+		ChEp: chEP,
+		Raw: rawEp,
+		Raddr: fraddr,
+		Stack: s,
+		NIC: nic,
+	}
+	greFwd := gre.NewForwarder(s, greInfo.greHandler)
+	s.SetTransportProtocolHandler(header.GREProtocolNumber, greFwd.HandlePacket)
+
+	go greInfo.greRead(chEP)
+
+	any, _ := ipAny(proto)
+	if fraddr.Addr != any {
+		tcperr = rawEp.Connect(fraddr)
+		if tcperr != nil {
+			return tcperr
+		}
+	}
+
+	return nil
+}
diff --git a/pkg/tcpip/transport/gre/BUILD b/pkg/tcpip/transport/gre/BUILD
new file mode 100644
index 000000000..a812c1000
--- /dev/null
+++ b/pkg/tcpip/transport/gre/BUILD
@@ -0,0 +1,18 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "gre",
+    srcs = ["forwarder.go", "protocol.go"],
+    visibility = ["//visibility:public"],
+    deps = [
+	"//pkg/tcpip",
+	"//pkg/tcpip/buffer",
+	"//pkg/tcpip/header",
+	"//pkg/tcpip/header/parse",
+	"//pkg/tcpip/stack",
+	"//pkg/tcpip/transport/raw",
+	"//pkg/waiter",
+    ],
+)
diff --git a/pkg/tcpip/transport/gre/forwarder.go b/pkg/tcpip/transport/gre/forwarder.go
new file mode 100644
index 000000000..83f63c844
--- /dev/null
+++ b/pkg/tcpip/transport/gre/forwarder.go
@@ -0,0 +1,67 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package gre
+
+import (
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+// Forwarder is a session request forwarder, which allows clients to decide
+// what to do with a session request, for example: ignore it, or process it.
+//
+// The canonical way of using it is to pass the Forwarder.HandlePacket function
+// to stack.SetTransportProtocolHandler.
+type Forwarder struct {
+	handler func(*ForwarderRequest)
+
+	stack *stack.Stack
+}
+
+// NewForwarder allocates and initializes a new forwarder.
+func NewForwarder(s *stack.Stack, handler func(*ForwarderRequest)) *Forwarder {
+	return &Forwarder{
+		stack:   s,
+		handler: handler,
+	}
+}
+
+// HandlePacket handles all packets.
+//
+// This function is expected to be passed as an argument to the
+// stack.SetTransportProtocolHandler function.
+func (f *Forwarder) HandlePacket(id stack.TransportEndpointID, pkt *stack.PacketBuffer) bool {
+	f.handler(&ForwarderRequest{
+		Stack: f.stack,
+		Id:    id,
+		Pkt:   pkt,
+	})
+
+	return true
+}
+
+// ForwarderRequest represents a session request received by the forwarder and
+// passed to the client. Clients may optionally create an endpoint to represent
+// it via CreateEndpoint.
+type ForwarderRequest struct {
+	Stack *stack.Stack
+	Id    stack.TransportEndpointID
+	Pkt   *stack.PacketBuffer
+}
+
+// ID returns the 4-tuple (src address, src port, dst address, dst port) that
+// represents the session request.
+func (r *ForwarderRequest) ID() stack.TransportEndpointID {
+	return r.Id
+}
diff --git a/pkg/tcpip/transport/gre/protocol.go b/pkg/tcpip/transport/gre/protocol.go
new file mode 100644
index 000000000..0a58cb73a
--- /dev/null
+++ b/pkg/tcpip/transport/gre/protocol.go
@@ -0,0 +1,115 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package gre contains the implementation of the GRE transport protocol.
+package gre
+
+import (
+	"log"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/header/parse"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+	"gvisor.dev/gvisor/pkg/tcpip/transport/raw"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+const (
+	// ProtocolNumber is the gre protocol number.
+	ProtocolNumber = header.GREProtocolNumber
+
+	// MinBufferSize is the smallest size of a receive or send buffer.
+	MinBufferSize = 4 << 10 // 4KiB bytes.
+
+	// DefaultSendBufferSize is the default size of the send buffer for
+	// an endpoint.
+	DefaultSendBufferSize = 32 << 10 // 32KiB
+
+	// DefaultReceiveBufferSize is the default size of the receive buffer
+	// for an endpoint.
+	DefaultReceiveBufferSize = 32 << 10 // 32KiB
+
+	// MaxBufferSize is the largest size a receive/send buffer can grow to.
+	MaxBufferSize = 4 << 20 // 4MiB
+)
+
+type protocol struct {
+	stack *stack.Stack
+}
+
+// Number returns the gre protocol number.
+func (*protocol) Number() tcpip.TransportProtocolNumber {
+	return ProtocolNumber
+}
+
+// NewEndpoint creates a new gre endpoint.
+func (p *protocol) NewEndpoint(netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, tcpip.Error) {
+	//	return newEndpoint(p.stack, netProto, waiterQueue), nil
+	return nil, &tcpip.ErrUnknownProtocolOption{}
+}
+
+// NewRawEndpoint creates a new raw GRE endpoint. It implements
+// stack.TransportProtocol.NewRawEndpoint.
+func (p *protocol) NewRawEndpoint(netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, tcpip.Error) {
+	return raw.NewEndpoint(p.stack, netProto, ProtocolNumber, waiterQueue)
+}
+
+// MinimumPacketSize returns the minimum valid gre packet size.
+func (*protocol) MinimumPacketSize() int {
+	// TODO ?
+	return header.GREHeaderSize
+}
+
+// ParsePorts returns the source and destination ports stored in the given gre
+// packet.
+func (*protocol) ParsePorts(v buffer.View) (src, dst uint16, err tcpip.Error) {
+	// h := header.GRE(v)
+	// return h.SourcePort(), h.DestinationPort(), nil
+	return 0, 0, nil
+}
+
+// HandleUnknownDestinationPacket handles packets that are targeted at this
+// protocol but don't match any existing endpoint.
+func (p *protocol) HandleUnknownDestinationPacket(id stack.TransportEndpointID, pkt *stack.PacketBuffer) stack.UnknownDestinationPacketDisposition {
+	log.Println("HandleUnknownDestinationPacket")
+	return stack.UnknownDestinationPacketHandled
+}
+
+// SetOption implements stack.TransportProtocol.SetOption.
+func (*protocol) SetOption(tcpip.SettableTransportProtocolOption) tcpip.Error {
+	return &tcpip.ErrUnknownProtocolOption{}
+}
+
+// Option implements stack.TransportProtocol.Option.
+func (*protocol) Option(tcpip.GettableTransportProtocolOption) tcpip.Error {
+	return &tcpip.ErrUnknownProtocolOption{}
+}
+
+// Close implements stack.TransportProtocol.Close.
+func (*protocol) Close() {}
+
+// Wait implements stack.TransportProtocol.Wait.
+func (*protocol) Wait() {}
+
+// Parse implements stack.TransportProtocol.Parse.
+func (*protocol) Parse(pkt *stack.PacketBuffer) bool {
+	return parse.GRE(pkt)
+}
+
+// NewProtocol returns a GRE transport protocol.
+func NewProtocol(s *stack.Stack) stack.TransportProtocol {
+	return &protocol{stack: s}
+}