Support sending with packet sockets

...through the loopback interface, only.

This change only supports sending on packet sockets through the loopback
interface as the loopback interface is the only interface used in packet
socket syscall tests - the other link endpoints are not excercised with
the existing test infrastructure.

Support for sending on packet sockets through the other interfaces will
be added as needed.

BUG: https://fxbug.dev/81592
PiperOrigin-RevId: 394368899

1 files changed, 16 insertions, 14 deletions

diff --git a/pkg/tcpip/link/loopback/loopback.go b/pkg/tcpip/link/loopback/loopback.go
index d7bbfa639..ca1f9c08d 100644
--- a/pkg/tcpip/link/loopback/loopback.go
+++ b/pkg/tcpip/link/loopback/loopback.go
@@ -76,19 +76,8 @@ func (*endpoint) Wait() {}
 
 // WritePacket implements stack.LinkEndpoint.WritePacket. It delivers outbound
 // packets to the network-layer dispatcher.
-func (e *endpoint) WritePacket(_ stack.RouteInfo, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
-	// Construct data as the unparsed portion for the loopback packet.
-	data := buffer.NewVectorisedView(pkt.Size(), pkt.Views())
-
-	// Because we're immediately turning around and writing the packet back
-	// to the rx path, we intentionally don't preserve the remote and local
-	// link addresses from the stack.Route we're passed.
-	newPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		Data: data,
-	})
-	e.dispatcher.DeliverNetworkPacket("" /* remote */, "" /* local */, protocol, newPkt)
-
-	return nil
+func (e *endpoint) WritePacket(_ stack.RouteInfo, _ tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) tcpip.Error {
+	return e.WriteRawPacket(pkt)
 }
 
 // WritePackets implements stack.LinkEndpoint.WritePackets.
@@ -105,4 +94,17 @@ func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.Net
 }
 
 // WriteRawPacket implements stack.LinkEndpoint.
-func (*endpoint) WriteRawPacket(*stack.PacketBuffer) tcpip.Error { return &tcpip.ErrNotSupported{} }
+func (e *endpoint) WriteRawPacket(pkt *stack.PacketBuffer) tcpip.Error {
+	// Construct data as the unparsed portion for the loopback packet.
+	data := buffer.NewVectorisedView(pkt.Size(), pkt.Views())
+
+	// Because we're immediately turning around and writing the packet back
+	// to the rx path, we intentionally don't preserve the remote and local
+	// link addresses from the stack.Route we're passed.
+	newPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		Data: data,
+	})
+	e.dispatcher.DeliverNetworkPacket("" /* remote */, "" /* local */, pkt.NetworkProtocolNumber, newPkt)
+
+	return nil
+}