netstack: use a proper network protocol to set gso.L3HdrLen

It is possible to create a listening socket which will accept
IPv4 and IPv6 connections. In this case, we set IPv6ProtocolNumber
for all accepted endpoints, even if they handle IPv4 connections.

This means that we can't use endpoint.netProto to set gso.L3HdrLen.

PiperOrigin-RevId: 244227948
Change-Id: I5e1863596cb9f3d216febacdb7dc75651882eef1

2 files changed, 16 insertions, 3 deletions

diff --git a/pkg/tcpip/link/channel/channel.go b/pkg/tcpip/link/channel/channel.go
index 8c0d11288..f7501a1bc 100644
--- a/pkg/tcpip/link/channel/channel.go
+++ b/pkg/tcpip/link/channel/channel.go
@@ -28,6 +28,7 @@ type PacketInfo struct {
 	Header  buffer.View
 	Payload buffer.View
 	Proto   tcpip.NetworkProtocolNumber
+	GSO     *stack.GSO
 }
 
 // Endpoint is link layer endpoint that stores outbound packets in a channel
@@ -36,6 +37,7 @@ type Endpoint struct {
 	dispatcher stack.NetworkDispatcher
 	mtu        uint32
 	linkAddr   tcpip.LinkAddress
+	GSO        bool
 
 	// C is where outbound packets are queued.
 	C chan PacketInfo
@@ -93,8 +95,17 @@ func (e *Endpoint) MTU() uint32 {
 }
 
 // Capabilities implements stack.LinkEndpoint.Capabilities.
-func (*Endpoint) Capabilities() stack.LinkEndpointCapabilities {
-	return 0
+func (e *Endpoint) Capabilities() stack.LinkEndpointCapabilities {
+	caps := stack.LinkEndpointCapabilities(0)
+	if e.GSO {
+		caps |= stack.CapabilityGSO
+	}
+	return caps
+}
+
+// GSOMaxSize returns the maximum GSO packet size.
+func (*Endpoint) GSOMaxSize() uint32 {
+	return 1 << 15
 }
 
 // MaxHeaderLength returns the maximum size of the link layer header. Given it
@@ -109,11 +120,12 @@ func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
 }
 
 // WritePacket stores outbound packets into the channel.
-func (e *Endpoint) WritePacket(_ *stack.Route, _ *stack.GSO, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
+func (e *Endpoint) WritePacket(_ *stack.Route, gso *stack.GSO, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
 	p := PacketInfo{
 		Header:  hdr.View(),
 		Proto:   protocol,
 		Payload: payload.ToView(),
+		GSO:     gso,
 	}
 
 	select {
diff --git a/pkg/tcpip/link/fdbased/endpoint_test.go b/pkg/tcpip/link/fdbased/endpoint_test.go
index 5a06c6387..c8b037d57 100644
--- a/pkg/tcpip/link/fdbased/endpoint_test.go
+++ b/pkg/tcpip/link/fdbased/endpoint_test.go
@@ -166,6 +166,7 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32) {
 			CsumOffset: csumOffset,
 			MSS:        gsoMSS,
 			MaxSize:    gsoMaxSize,
+			L3HdrLen:   header.IPv4MaximumHeaderSize,
 		}
 	}
 	if err := c.ep.WritePacket(r, gso, hdr, payload.ToVectorisedView(), proto); err != nil {