WIP: GRE

4 files changed, 57 insertions, 0 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
+}