[UWP] BugReport: Deadlock in VpnChannel.StartExistingTransports() in Windows 10 2004?

Question

I am developing a UWP VPN application and I recently noticed that after a successful connection, no data was sent through the tunnel. While debugging, I noticed that the call to StartExistingTransports() never returned.

This started after I upgraded my development machine to Windows 10 2004 (it was working fine in the previous version: 1903) and it happens every time.

I do not see any errors but the thread is stuck.

I have created a new solution with only the bare minimum in order to test and the same happens. I can not attach the whole solution but here are the main classes.

MainPage.xaml.cs:

    public sealed partial class MainPage : Page
    {
        private readonly VpnManagementAgent vpnManagementAgent = new VpnManagementAgent();

        public MainPage()
        {
            this.InitializeComponent();
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            const string profileName = "profileName";
            var profile = await this.GetProfileByNameAsync(profileName);
            if (profile != null)
            {
                // We can't update the IP/URI in the profile so deletes it instead
                var deleteProfileStatus = await this.vpnManagementAgent.DeleteProfileAsync(profile);
                if (deleteProfileStatus != 0)
                {
                    throw new InvalidOperationException($"Could not delete VPN profile. Error code: {deleteProfileStatus}.");
                }
            }


            profile = new VpnPlugInProfile
            {
                ServerUris = { new Uri("https://10.1.2.3") },
                ProfileName = profileName,
                AlwaysOn = false,
                VpnPluginPackageFamilyName = Package.Current.Id.FamilyName
            };

            var addProfileStatus = await this.vpnManagementAgent.AddProfileFromObjectAsync(profile);
            if (addProfileStatus != 0)
            {
                throw new InvalidOperationException($"Could not create VPN profile. Error code: {addProfileStatus}.");
            }

            Debug.WriteLine($"Connecting profile name: {profile.ProfileName}");
            var errorCode = await this.vpnManagementAgent.ConnectProfileAsync(profile);
            Debug.WriteLine($"Connecting attempt resulted in error code: {errorCode}");

        }

        private async Task<VpnPlugInProfile> GetProfileByNameAsync(string profileName)
        {
            var profiles = await this.vpnManagementAgent.GetProfilesAsync();
            foreach (var p in profiles)
            {
                if (p is VpnPlugInProfile profile &&
                    profile.VpnPluginPackageFamilyName.Equals(Package.Current.Id.FamilyName) &&
                    profile.ProfileName.Equals(profileName))
                {
                    return profile;
                }
            }

            return null;
        }

    }

VpnBackgroundTask.cs:

    public sealed class VpnBackgroundTask : IBackgroundTask
    {
        private static SslVpnPlugin vpnPlugin;

        private BackgroundTaskDeferral serviceDeferral;

        /// <inheritdoc />
        public void Run(IBackgroundTaskInstance taskInstance)
        {
            //Take a service deferral so the service isn't terminated
            this.serviceDeferral = taskInstance.GetDeferral();

            if (VpnBackgroundTask.vpnPlugin == null)
            {
                VpnBackgroundTask.vpnPlugin = new SslVpnPlugin();
                taskInstance.Canceled += this.OnTaskCanceled;
            }

            VpnChannel.ProcessEventAsync(VpnBackgroundTask.vpnPlugin, taskInstance.TriggerDetails);
        }

        private void OnTaskCanceled(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason)
        {
            if (this.serviceDeferral != null)
            {
                //Complete the service deferral
                this.serviceDeferral.Complete();
                this.serviceDeferral = null;
            }
        }
    }

SslVpnPlugin.cs

    public sealed class SslVpnPlugin : IVpnPlugIn
    {
        StreamSocket Socket = new StreamSocket();

        public void Connect(VpnChannel channel)
        {
            try
            {
                channel.AssociateTransport(this.Socket, null);

                var myAddress = new List<HostName>
                {
                    new HostName("192.168.80.100")
                };

                var myRoute = new VpnRouteAssignment();
                myRoute.Ipv4InclusionRoutes.Add(new VpnRoute(new HostName("192.168.80.0"), 24));

                Debug.WriteLine("Calling channel.StartExistingTransports()");
                // This call will block
                channel.StartExistingTransports(myAddress,
                    null,
                    null,
                    myRoute,
                    null,
                    1472,
                    1500,
                    false);
                Debug.WriteLine("channel.StartExistingTransports() returned");

            }
            catch (Exception e)
            {
                Debug.WriteLine(e);
                throw;
            }

            Debug.WriteLine("Connected");
        }

        public void Disconnect(VpnChannel channel)
        {
            throw new System.NotImplementedException();
        }

        public void GetKeepAlivePayload(VpnChannel channel, out VpnPacketBuffer keepAlivePacket)
        {
            throw new System.NotImplementedException();
        }

        public void Encapsulate(VpnChannel channel, VpnPacketBufferList packets, VpnPacketBufferList encapulatedPackets)
        {
            throw new System.NotImplementedException();
        }

        public void Decapsulate(VpnChannel channel, VpnPacketBuffer encapBuffer, VpnPacketBufferList decapsulatedPackets,
            VpnPacketBufferList controlPacketsToSend)
        {
            throw new System.NotImplementedException();
        }
    }

Answer 1

Hello,

Welcome to Microsoft Q&A!

Currently, Microsoft Q&A supports the products listed over here: supported topics (more to be added later on).

I'm sorry to say that currently, we could offer limited help with VPN. For VPN issues, Tt needs more professional support. I suggest that you might need to open a support ticket for this. Please contact our paid phone support at MS Support. You will get 1:1 support on that. Please kindly note that your support ticket will be free if it is Microsoft's issue.

Thank you.

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