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, 7 insertions, 8 deletions

diff --git a/pkg/tcpip/link/fdbased/endpoint.go b/pkg/tcpip/link/fdbased/endpoint.go
index fc620c7d5..9f2084eae 100644
--- a/pkg/tcpip/link/fdbased/endpoint.go
+++ b/pkg/tcpip/link/fdbased/endpoint.go
@@ -410,7 +410,7 @@ func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.Net
 // currently writable, the packet is dropped.
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) *tcpip.Error {
 	if e.hdrSize > 0 {
-		e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress, protocol, pkt)
+		e.AddHeader(r.LocalLinkAddress, r.RemoteLinkAddress(), protocol, pkt)
 	}
 
 	var builder iovec.Builder
@@ -453,7 +453,7 @@ func (e *endpoint) sendBatch(batchFD int, batch []*stack.PacketBuffer) (int, *tc
 	mmsgHdrs := make([]rawfile.MMsgHdr, 0, len(batch))
 	for _, pkt := range batch {
 		if e.hdrSize > 0 {
-			e.AddHeader(pkt.EgressRoute.LocalLinkAddress, pkt.EgressRoute.RemoteLinkAddress, pkt.NetworkProtocolNumber, pkt)
+			e.AddHeader(pkt.EgressRoute.LocalLinkAddress, pkt.EgressRoute.RemoteLinkAddress(), pkt.NetworkProtocolNumber, pkt)
 		}
 
 		var vnetHdrBuf []byte
diff --git a/pkg/tcpip/link/fdbased/endpoint_test.go b/pkg/tcpip/link/fdbased/endpoint_test.go
index 709f829c8..ce4da7230 100644
--- a/pkg/tcpip/link/fdbased/endpoint_test.go
+++ b/pkg/tcpip/link/fdbased/endpoint_test.go
@@ -183,9 +183,8 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32, hash u
 	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: eth, GSOMaxSize: gsoMaxSize})
 	defer c.cleanup()
 
-	r := &stack.Route{
-		RemoteLinkAddress: raddr,
-	}
+	var r stack.Route
+	r.ResolveWith(raddr)
 
 	// Build payload.
 	payload := buffer.NewView(plen)
@@ -220,7 +219,7 @@ func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32, hash u
 			L3HdrLen:   header.IPv4MaximumHeaderSize,
 		}
 	}
-	if err := c.ep.WritePacket(r, gso, proto, pkt); err != nil {
+	if err := c.ep.WritePacket(&r, gso, proto, pkt); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}
 
@@ -325,9 +324,9 @@ func TestPreserveSrcAddress(t *testing.T) {
 
 	// Set LocalLinkAddress in route to the value of the bridged address.
 	r := &stack.Route{
-		RemoteLinkAddress: raddr,
-		LocalLinkAddress:  baddr,
+		LocalLinkAddress: baddr,
 	}
+	r.ResolveWith(raddr)
 
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 		// WritePacket panics given a prependable with anything less than