Do not resolve remote link address at transport layer

Link address resolution is performed at the link layer (if required) so
we can defer it from the transport layer. When link resolution is
required, packets will be queued and sent once link resolution
completes. If link resolution fails, the transport layer will receive a
control message indicating that the stack failed to route the packet.

tcpip.Endpoint.Write no longer returns a channel now that writes do not
wait for link resolution at the transport layer.

tcpip.ErrNoLinkAddress is no longer used so it is removed.

Removed calls to stack.Route.ResolveWith from the transport layer so
that link resolution is performed when a route is created in response
to an incoming packet (e.g. to complete TCP handshakes or send a RST).

Tests:
- integration_test.TestForwarding
- integration_test.TestTCPLinkResolutionFailure

Fixes #4458

RELNOTES: n/a
PiperOrigin-RevId: 351684158

2 files changed, 24 insertions, 22 deletions

diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index bbce1ef78..0ec0a0fef 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -645,29 +645,18 @@ func TestLinkResolution(t *testing.T) {
 		t.Fatalf("NewEndpoint(_) = (_, %s), want = (_, nil)", err)
 	}
 
-	for {
-		_, resCh, err := ep.Write(payload, tcpip.WriteOptions{To: &tcpip.FullAddress{NIC: nicID, Addr: lladdr1}})
-		if resCh != nil {
-			if err != tcpip.ErrNoLinkAddress {
-				t.Fatalf("ep.Write(_) = (_, <non-nil>, %s), want = (_, <non-nil>, tcpip.ErrNoLinkAddress)", err)
-			}
-			for _, args := range []routeArgs{
-				{src: c.linkEP0, dst: c.linkEP1, typ: header.ICMPv6NeighborSolicit, remoteLinkAddr: header.EthernetAddressFromMulticastIPv6Address(header.SolicitedNodeAddr(lladdr1))},
-				{src: c.linkEP1, dst: c.linkEP0, typ: header.ICMPv6NeighborAdvert},
-			} {
-				routeICMPv6Packet(t, args, func(t *testing.T, icmpv6 header.ICMPv6) {
-					if got, want := tcpip.Address(icmpv6[8:][:16]), lladdr1; got != want {
-						t.Errorf("%d: got target = %s, want = %s", icmpv6.Type(), got, want)
-					}
-				})
+	if _, err := ep.Write(payload, tcpip.WriteOptions{To: &tcpip.FullAddress{NIC: nicID, Addr: lladdr1}}); err != nil {
+		t.Fatalf("ep.Write(_): %s", err)
+	}
+	for _, args := range []routeArgs{
+		{src: c.linkEP0, dst: c.linkEP1, typ: header.ICMPv6NeighborSolicit, remoteLinkAddr: header.EthernetAddressFromMulticastIPv6Address(header.SolicitedNodeAddr(lladdr1))},
+		{src: c.linkEP1, dst: c.linkEP0, typ: header.ICMPv6NeighborAdvert},
+	} {
+		routeICMPv6Packet(t, args, func(t *testing.T, icmpv6 header.ICMPv6) {
+			if got, want := tcpip.Address(icmpv6[8:][:16]), lladdr1; got != want {
+				t.Errorf("%d: got target = %s, want = %s", icmpv6.Type(), got, want)
 			}
-			<-resCh
-			continue
-		}
-		if err != nil {
-			t.Fatalf("ep.Write(_) = (_, _, %s)", err)
-		}
-		break
+		})
 	}
 
 	for _, args := range []routeArgs{
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index f2018d073..2f82c3d5f 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -163,6 +163,7 @@ func getLabel(addr tcpip.Address) uint8 {
 	panic(fmt.Sprintf("should have a label for address = %s", addr))
 }
 
+var _ stack.LinkResolvableNetworkEndpoint = (*endpoint)(nil)
 var _ stack.GroupAddressableEndpoint = (*endpoint)(nil)
 var _ stack.AddressableEndpoint = (*endpoint)(nil)
 var _ stack.NetworkEndpoint = (*endpoint)(nil)
@@ -224,6 +225,18 @@ type OpaqueInterfaceIdentifierOptions struct {
 	SecretKey []byte
 }
 
+// HandleLinkResolutionFailure implements stack.LinkResolvableNetworkEndpoint.
+func (e *endpoint) HandleLinkResolutionFailure(pkt *stack.PacketBuffer) {
+	// handleControl expects the entire offending packet to be in the packet
+	// buffer's data field.
+	pkt = stack.NewPacketBuffer(stack.PacketBufferOptions{
+		Data: buffer.NewVectorisedView(pkt.Size(), pkt.Views()),
+	})
+	pkt.NICID = e.nic.ID()
+	pkt.NetworkProtocolNumber = ProtocolNumber
+	e.handleControl(stack.ControlAddressUnreachable, 0, pkt)
+}
+
 // onAddressAssignedLocked handles an address being assigned.
 //
 // Precondition: e.mu must be exclusively locked.