Fix nil pointer exception when wrapping listener

lib/limiter/limiter.go

@@ -180,7 +180,7 @@ func (l *Limiter) StreamServerInterceptor(srv interface{}, serverStream grpc.Ser
 
 // WrapListener returns a [Listener] that wraps the provided listener
 // with one that limits connections
-func (l *Limiter) WrapListener(ln net.Listener) *Listener {
+func (l *Limiter) WrapListener(ln net.Listener) (*Listener, error) {
 	return NewListener(ln, l.ConnectionsLimiter)
 }
 

lib/limiter/limiter_test.go

@@ -407,7 +407,8 @@ func TestListener(t *testing.T) {
 			limiter, err := NewConnectionsLimiter(test.config)
 			require.NoError(t, err)
 
-			ln := NewListener(test.listener, limiter)
+			ln, err := NewListener(test.listener, limiter)
+			require.NoError(t, err)
 
 			// open connections without closing to enforce limits
 			conns := make([]net.Conn, 0, connLimit)

lib/limiter/listener.go

@@ -35,11 +35,15 @@ type Listener struct {
 // NewListener creates a [Listener] that enforces the limits of
 // the provided [ConnectionsLimiter] on the all connections accepted
 // by the provided [net.Listener].
-func NewListener(ln net.Listener, limiter *ConnectionsLimiter) *Listener {
+func NewListener(ln net.Listener, limiter *ConnectionsLimiter) (*Listener, error) {
+	if ln == nil {
+		return nil, trace.BadParameter("listener cannot be nil")
+	}
+
 	return &Listener{
 		Listener: ln,
 		limiter:  limiter,
-	}
+	}, nil
 }
 
 // Accept waits for and returns the next connection to the listener

lib/service/service.go

@@ -2849,7 +2849,12 @@ func (process *TeleportProcess) initSSH() error {
 			}()
 			defer mux.Close()
 
-			go s.Serve(limiter.WrapListener(mux.SSH()))
+			listener, err = limiter.WrapListener(mux.SSH())
+			if err != nil {
+				return trace.Wrap(err)
+			}
+
+			go s.Serve(listener)
 		} else {
 			// Start the SSH server. This kicks off updating labels and starting the
 			// heartbeat.
@@ -4118,14 +4123,19 @@ func (process *TeleportProcess) initProxyEndpoint(conn *Connector) error {
 			}
 		}
 
+		rtListener, err := reverseTunnelLimiter.WrapListener(listeners.reverseTunnel)
+		if err != nil {
+			return trace.Wrap(err)
+		}
+
 		tsrv, err = reversetunnel.NewServer(
 			reversetunnel.Config{
 				Context:               process.ExitContext(),
 				Component:             teleport.Component(teleport.ComponentProxy, process.id),
 				ID:                    process.Config.HostUUID,
 				ClusterName:           clusterName,
 				ClientTLS:             clientTLSConfig,
-				Listener:              reverseTunnelLimiter.WrapListener(listeners.reverseTunnel),
+				Listener:              rtListener,
 				GetHostSigners:        sshutils.StaticHostSigners(conn.ServerIdentity.KeySigner),
 				LocalAuthClient:       conn.Client,
 				LocalAccessPoint:      accessPoint,
@@ -4639,14 +4649,24 @@ func (process *TeleportProcess) initProxyEndpoint(conn *Connector) error {
 
 		// start ssh server
 		go func() {
-			if err := sshProxy.Serve(proxyLimiter.WrapListener(listeners.ssh)); err != nil && !utils.IsOKNetworkError(err) {
+			listener, err := proxyLimiter.WrapListener(listeners.ssh)
+			if err != nil {
+				logger.ErrorContext(process.ExitContext(), "Failed to set up SSH proxy server", "error", err)
+				return
+			}
+			if err := sshProxy.Serve(listener); err != nil && !utils.IsOKNetworkError(err) {
 				logger.ErrorContext(process.ExitContext(), "SSH proxy server terminated unexpectedly", "error", err)
 			}
 		}()
 
 		// start grpc server
 		go func() {
-			if err := sshGRPCServer.Serve(proxyLimiter.WrapListener(listeners.sshGRPC)); err != nil && !utils.IsOKNetworkError(err) && !errors.Is(err, grpc.ErrServerStopped) {
+			listener, err := proxyLimiter.WrapListener(listeners.sshGRPC)
+			if err != nil {
+				logger.ErrorContext(process.ExitContext(), "Failed to set up SSH proxy server", "error", err)
+				return
+			}
+			if err := sshGRPCServer.Serve(listener); err != nil && !utils.IsOKNetworkError(err) && !errors.Is(err, grpc.ErrServerStopped) {
 				logger.ErrorContext(process.ExitContext(), "SSH gRPC server terminated unexpectedly", "error", err)
 			}
 		}()

lib/sshutils/server.go

@@ -335,7 +335,12 @@ func (s *Server) Start() error {
 			return trace.ConvertSystemError(err)
 		}
 
-		if err := s.SetListener(s.limiter.WrapListener(listener)); err != nil {
+		listener, err = s.limiter.WrapListener(listener)
+		if err != nil {
+			return trace.Wrap(err)
+		}
+
+		if err := s.SetListener(listener); err != nil {
 			return trace.Wrap(err)
 		}
 	}