Make `stack.Route` thread safe

Currently we rely on the user to take the lock on the endpoint that owns the
route, in order to modify it safely. We can instead move
`Route.RemoteLinkAddress` under `Route`'s mutex, and allow non-locking and
thread-safe access to other fields of `Route`.

PiperOrigin-RevId: 345461586

2 files changed, 13 insertions, 18 deletions

diff --git a/pkg/tcpip/link/sharedmem/sharedmem.go b/pkg/tcpip/link/sharedmem/sharedmem.go
index a1e7018c8..5660418fa 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem.go
@@ -204,7 +204,7 @@ func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.Net
 // WritePacket writes outbound packets to the file descriptor. If it is not
 // currently writable, the packet is dropped.
 func (e *endpoint) WritePacket(r *stack.Route, _ *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
-	e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress, protocol, pkt)
+	e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress(), protocol, pkt)
 
 	views := pkt.Views()
 	// Transmit the packet.
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_test.go b/pkg/tcpip/link/sharedmem/sharedmem_test.go
index 22d5c97f1..7131392cc 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_test.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_test.go
@@ -260,9 +260,8 @@ func TestSimpleSend(t *testing.T) {
 	defer c.cleanup()
 
 	// Prepare route.
-	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-	}
+	var r stack.Route
+	r.ResolveWith(remoteLinkAddr)
 
 	for iters := 1000; iters > 0; iters-- {
 		func() {
@@ -342,9 +341,9 @@ func TestPreserveSrcAddressInSend(t *testing.T) {
 	newLocalLinkAddress := tcpip.LinkAddress(strings.Repeat("0xFE", 6))
 	// Set both remote and local link address in route.
 	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-		LocalLinkAddress:  newLocalLinkAddress,
+		LocalLinkAddress: newLocalLinkAddress,
 	}
+	r.ResolveWith(remoteLinkAddr)
 
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 		// WritePacket panics given a prependable with anything less than
@@ -395,9 +394,8 @@ func TestFillTxQueue(t *testing.T) {
 	defer c.cleanup()
 
 	// Prepare to send a packet.
-	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-	}
+	var r stack.Route
+	r.ResolveWith(remoteLinkAddr)
 
 	buf := buffer.NewView(100)
 
@@ -444,9 +442,8 @@ func TestFillTxQueueAfterBadCompletion(t *testing.T) {
 	c.txq.rx.Flush()
 
 	// Prepare to send a packet.
-	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-	}
+	var r stack.Route
+	r.ResolveWith(remoteLinkAddr)
 
 	buf := buffer.NewView(100)
 
@@ -509,9 +506,8 @@ func TestFillTxMemory(t *testing.T) {
 	defer c.cleanup()
 
 	// Prepare to send a packet.
-	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-	}
+	var r stack.Route
+	r.ResolveWith(remoteLinkAddr)
 
 	buf := buffer.NewView(100)
 
@@ -557,9 +553,8 @@ func TestFillTxMemoryWithMultiBuffer(t *testing.T) {
 	defer c.cleanup()
 
 	// Prepare to send a packet.
-	r := stack.Route{
-		RemoteLinkAddress: remoteLinkAddr,
-	}
+	var r stack.Route
+	r.ResolveWith(remoteLinkAddr)
 
 	buf := buffer.NewView(100)