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

1 files changed, 13 insertions, 24 deletions

diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index c32fe5c4f..87277fbd3 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -236,8 +236,8 @@ func (e *endpoint) prepareForWrite(to *tcpip.FullAddress) (retry bool, err *tcpi
 
 // Write writes data to the endpoint's peer. This method does not block
 // if the data cannot be written.
-func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
-	n, ch, err := e.write(p, opts)
+func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, *tcpip.Error) {
+	n, err := e.write(p, opts)
 	switch err {
 	case nil:
 		e.stats.PacketsSent.Increment()
@@ -247,8 +247,6 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		e.stats.WriteErrors.WriteClosed.Increment()
 	case tcpip.ErrInvalidEndpointState:
 		e.stats.WriteErrors.InvalidEndpointState.Increment()
-	case tcpip.ErrNoLinkAddress:
-		e.stats.SendErrors.NoLinkAddr.Increment()
 	case tcpip.ErrNoRoute, tcpip.ErrBroadcastDisabled, tcpip.ErrNetworkUnreachable:
 		// Errors indicating any problem with IP routing of the packet.
 		e.stats.SendErrors.NoRoute.Increment()
@@ -256,13 +254,13 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		// For all other errors when writing to the network layer.
 		e.stats.SendErrors.SendToNetworkFailed.Increment()
 	}
-	return n, ch, err
+	return n, err
 }
 
-func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
+func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, *tcpip.Error) {
 	// MSG_MORE is unimplemented. (This also means that MSG_EOR is a no-op.)
 	if opts.More {
-		return 0, nil, tcpip.ErrInvalidOptionValue
+		return 0, tcpip.ErrInvalidOptionValue
 	}
 
 	to := opts.To
@@ -272,14 +270,14 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 
 	// If we've shutdown with SHUT_WR we are in an invalid state for sending.
 	if e.shutdownFlags&tcpip.ShutdownWrite != 0 {
-		return 0, nil, tcpip.ErrClosedForSend
+		return 0, tcpip.ErrClosedForSend
 	}
 
 	// Prepare for write.
 	for {
 		retry, err := e.prepareForWrite(to)
 		if err != nil {
-			return 0, nil, err
+			return 0, err
 		}
 
 		if !retry {
@@ -294,7 +292,7 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		nicID := to.NIC
 		if e.BindNICID != 0 {
 			if nicID != 0 && nicID != e.BindNICID {
-				return 0, nil, tcpip.ErrNoRoute
+				return 0, tcpip.ErrNoRoute
 			}
 
 			nicID = e.BindNICID
@@ -302,31 +300,22 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 
 		dst, netProto, err := e.checkV4MappedLocked(*to)
 		if err != nil {
-			return 0, nil, err
+			return 0, err
 		}
 
 		// Find the endpoint.
 		r, err := e.stack.FindRoute(nicID, e.BindAddr, dst.Addr, netProto, false /* multicastLoop */)
 		if err != nil {
-			return 0, nil, err
+			return 0, err
 		}
 		defer r.Release()
 
 		route = r
 	}
 
-	if route.IsResolutionRequired() {
-		if ch, err := route.Resolve(nil); err != nil {
-			if err == tcpip.ErrWouldBlock {
-				return 0, ch, tcpip.ErrNoLinkAddress
-			}
-			return 0, nil, err
-		}
-	}
-
 	v, err := p.FullPayload()
 	if err != nil {
-		return 0, nil, err
+		return 0, err
 	}
 
 	switch e.NetProto {
@@ -338,10 +327,10 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 	}
 
 	if err != nil {
-		return 0, nil, err
+		return 0, err
 	}
 
-	return int64(len(v)), nil, nil
+	return int64(len(v)), nil
 }
 
 // SetSockOpt sets a socket option.