vnet: fix route cleanup and reconnect backoff (#5492)

pkg/plugin/visitor/virtual_net.go

@@ -48,6 +48,11 @@ type VirtualNetPlugin struct {
 	cancel context.CancelFunc
 }
 
+const (
+	virtualNetReconnectBaseDelay = 60 * time.Second
+	virtualNetReconnectMaxDelay  = 300 * time.Second
+)
+
 func NewVirtualNetPlugin(pluginCtx PluginContext, options v1.VisitorPluginOptions) (Plugin, error) {
 	opts := options.(*v1.VirtualNetVisitorPluginOptions)
 
@@ -152,8 +157,7 @@ func (p *VirtualNetPlugin) run() {
 					p.pluginCtx.Name, p.consecutiveErrors, closeErr)
 
 				// Exponential backoff: 60s, 120s, 240s, 300s (capped)
-				baseDelay := 60 * time.Second
-				reconnectDelay = min(baseDelay*time.Duration(1<<uint(p.consecutiveErrors-1)), 300*time.Second)
+				reconnectDelay = virtualNetReconnectDelay(p.consecutiveErrors)
 			} else {
 				// Reset consecutive errors on successful connection
 				if p.consecutiveErrors > 0 {
@@ -182,6 +186,18 @@ func (p *VirtualNetPlugin) run() {
 	}
 }
 
+// virtualNetReconnectDelay returns a bounded reconnect delay without allowing
+// the exponential shift to overflow for large consecutive error counts.
+func virtualNetReconnectDelay(consecutiveErrors int) time.Duration {
+	if consecutiveErrors <= 1 {
+		return virtualNetReconnectBaseDelay
+	}
+	if consecutiveErrors >= 4 {
+		return virtualNetReconnectMaxDelay
+	}
+	return virtualNetReconnectBaseDelay * time.Duration(1<<uint(consecutiveErrors-1))
+}
+
 // cleanupControllerConn closes the current controllerConn (if it exists) under lock.
 func (p *VirtualNetPlugin) cleanupControllerConn(xl *xlog.Logger) {
 	p.mu.Lock()
@@ -202,9 +218,12 @@ func (p *VirtualNetPlugin) Close() error {
 	// Signal the run loop goroutine to stop.
 	p.cancel()
 
-	// Unregister the route from the controller.
-	if p.pluginCtx.VnetController != nil {
-		p.pluginCtx.VnetController.UnregisterClientRoute(p.pluginCtx.Name)
+	// Unregister the route only if it is still owned by this plugin instance.
+	p.mu.Lock()
+	controllerConn := p.controllerConn
+	p.mu.Unlock()
+	if p.pluginCtx.VnetController != nil && controllerConn != nil &&
+		p.pluginCtx.VnetController.UnregisterClientRoute(p.pluginCtx.Name, controllerConn) {
 		xl.Infof("unregistered client route for visitor [%s]", p.pluginCtx.Name)
 	}
 

pkg/plugin/visitor/virtual_net_test.go

@@ -0,0 +1,47 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !frps
+
+package visitor
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestVirtualNetReconnectDelay verifies the documented exponential backoff and
+// ensures large error counts remain capped instead of overflowing to zero.
+func TestVirtualNetReconnectDelay(t *testing.T) {
+	tests := []struct {
+		name              string
+		consecutiveErrors int
+		want              time.Duration
+	}{
+		{name: "first error", consecutiveErrors: 1, want: 60 * time.Second},
+		{name: "second error", consecutiveErrors: 2, want: 120 * time.Second},
+		{name: "third error", consecutiveErrors: 3, want: 240 * time.Second},
+		{name: "fourth error", consecutiveErrors: 4, want: 300 * time.Second},
+		{name: "shift width boundary", consecutiveErrors: 64, want: 300 * time.Second},
+		{name: "observed retry storm", consecutiveErrors: 329769, want: 300 * time.Second},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, virtualNetReconnectDelay(tt.consecutiveErrors))
+		})
+	}
+}

pkg/vnet/controller.go

@@ -246,9 +246,9 @@ func (c *Controller) RegisterClientRoute(ctx context.Context, name string, route
 	go c.readLoopClient(ctx, conn)
 }
 
-// UnregisterClientRoute Remove client route from routing table
-func (c *Controller) UnregisterClientRoute(name string) {
-	c.clientRouter.delRoute(name)
+// UnregisterClientRoute removes a client route only when it is still owned by conn.
+func (c *Controller) UnregisterClientRoute(name string, conn io.Writer) bool {
+	return c.clientRouter.delRoute(name, conn)
 }
 
 // StartServerConnReadLoop starts the read loop for a server connection
@@ -304,10 +304,15 @@ func (r *clientRouter) findConn(dst net.IP) (io.Writer, error) {
 	return nil, fmt.Errorf("no route found for destination %s", dst)
 }
 
-func (r *clientRouter) delRoute(name string) {
+func (r *clientRouter) delRoute(name string, conn io.Writer) bool {
 	r.mu.Lock()
 	defer r.mu.Unlock()
+	re, ok := r.routes[name]
+	if !ok || re.conn != conn {
+		return false
+	}
 	delete(r.routes, name)
+	return true
 }
 
 func (r *clientRouter) removeConnRoute(conn io.Writer) {

pkg/vnet/controller_test.go

@@ -0,0 +1,57 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vnet
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	v1 "github.com/fatedier/frp/pkg/config/v1"
+)
+
+// TestClientRouterDeleteRouteRequiresMatchingConnection verifies that a stale
+// visitor cannot remove a replacement route registered under the same name.
+func TestClientRouterDeleteRouteRequiresMatchingConnection(t *testing.T) {
+	require := require.New(t)
+	controller := NewController(v1.VirtualNetConfig{})
+
+	_, route, err := net.ParseCIDR("10.1.0.1/32")
+	require.NoError(err)
+
+	oldConn, oldPeer := net.Pipe()
+	t.Cleanup(func() {
+		_ = oldConn.Close()
+		_ = oldPeer.Close()
+	})
+	replacementConn, replacementPeer := net.Pipe()
+	t.Cleanup(func() {
+		_ = replacementConn.Close()
+		_ = replacementPeer.Close()
+	})
+
+	controller.clientRouter.addRoute("vnet-visitor", []net.IPNet{*route}, oldConn)
+	controller.clientRouter.addRoute("vnet-visitor", []net.IPNet{*route}, replacementConn)
+
+	require.False(controller.UnregisterClientRoute("vnet-visitor", oldConn))
+	got, err := controller.clientRouter.findConn(net.ParseIP("10.1.0.1"))
+	require.NoError(err)
+	require.Same(replacementConn, got)
+
+	require.True(controller.UnregisterClientRoute("vnet-visitor", replacementConn))
+	_, err = controller.clientRouter.findConn(net.ParseIP("10.1.0.1"))
+	require.Error(err)
+}