Index: /trunk/src/VBox/HostDrivers/Support/SUPDrv.c
===================================================================
--- /trunk/src/VBox/HostDrivers/Support/SUPDrv.c	(revision 38074)
+++ /trunk/src/VBox/HostDrivers/Support/SUPDrv.c	(revision 38075)
@@ -974,5 +974,7 @@
      * We check the two prereqs after doing this only to allow the compiler to optimize things better.
      */
-    if (RT_LIKELY(pSession->pVM && pDevExt->pfnVMMR0EntryFast))
+    if (RT_LIKELY(   RT_VALID_PTR(pSession) 
+                  && pSession->pVM 
+                  && pDevExt->pfnVMMR0EntryFast))
     {
         switch (uIOCtl)
@@ -1046,4 +1048,10 @@
         OSDBGPRINT(("vboxdrv: Bad ioctl request header; cbIn=%#lx cbOut=%#lx fFlags=%#lx\n",
                     (long)pReqHdr->cbIn, (long)pReqHdr->cbOut, (long)pReqHdr->fFlags));
+        VBOXDRV_SUPDRV_IOCTL_RETURN(pSession, uIOCtl, pReqHdr, VERR_INVALID_PARAMETER, VINF_SUCCESS);
+        return VERR_INVALID_PARAMETER;
+    }
+    if (RT_UNLIKELY(!RT_VALID_PTR(pSession)))
+    {
+        OSDBGPRINT(("vboxdrv: Invalid pSession valud %p (ioctl=%p)\n", pSession, (void *)uIOCtl));
         VBOXDRV_SUPDRV_IOCTL_RETURN(pSession, uIOCtl, pReqHdr, VERR_INVALID_PARAMETER, VINF_SUCCESS);
         return VERR_INVALID_PARAMETER;
Index: /trunk/src/VBox/HostDrivers/Support/win/SUPDrv-win.cpp
===================================================================
--- /trunk/src/VBox/HostDrivers/Support/win/SUPDrv-win.cpp	(revision 38074)
+++ /trunk/src/VBox/HostDrivers/Support/win/SUPDrv-win.cpp	(revision 38075)
@@ -75,4 +75,5 @@
 static void     _stdcall   VBoxDrvNtUnload(PDRIVER_OBJECT pDrvObj);
 static NTSTATUS _stdcall   VBoxDrvNtCreate(PDEVICE_OBJECT pDevObj, PIRP pIrp);
+static NTSTATUS _stdcall   VBoxDrvNtCleanup(PDEVICE_OBJECT pDevObj, PIRP pIrp);
 static NTSTATUS _stdcall   VBoxDrvNtClose(PDEVICE_OBJECT pDevObj, PIRP pIrp);
 static NTSTATUS _stdcall   VBoxDrvNtDeviceControl(PDEVICE_OBJECT pDevObj, PIRP pIrp);
@@ -138,9 +139,8 @@
                     pDrvObj->DriverUnload                                   = VBoxDrvNtUnload;
                     pDrvObj->MajorFunction[IRP_MJ_CREATE]                   = VBoxDrvNtCreate;
+                    pDrvObj->MajorFunction[IRP_MJ_CLEANUP]                  = VBoxDrvNtCleanup;
                     pDrvObj->MajorFunction[IRP_MJ_CLOSE]                    = VBoxDrvNtClose;
                     pDrvObj->MajorFunction[IRP_MJ_DEVICE_CONTROL]           = VBoxDrvNtDeviceControl;
-//#if 0 /** @todo test IDC on windows. */
                     pDrvObj->MajorFunction[IRP_MJ_INTERNAL_DEVICE_CONTROL]  = VBoxDrvNtInternalDeviceControl;
-//#endif
                     pDrvObj->MajorFunction[IRP_MJ_READ]                     = VBoxDrvNtNotSupportedStub;
                     pDrvObj->MajorFunction[IRP_MJ_WRITE]                    = VBoxDrvNtNotSupportedStub;
@@ -272,18 +272,51 @@
 
 /**
- * Close file entry point.
+ * Clean up file handle entry point.
  *
  * @param   pDevObj     Device object.
  * @param   pIrp        Request packet.
  */
+NTSTATUS _stdcall VBoxDrvNtCleanup(PDEVICE_OBJECT pDevObj, PIRP pIrp)
+{
+    PSUPDRVDEVEXT       pDevExt  = (PSUPDRVDEVEXT)pDevObj->DeviceExtension;
+    PIO_STACK_LOCATION  pStack   = IoGetCurrentIrpStackLocation(pIrp);
+    PFILE_OBJECT        pFileObj = pStack->FileObject;
+    PSUPDRVSESSION      pSession = (PSUPDRVSESSION)pFileObj->FsContext;
+
+    Log(("VBoxDrvNtCleanup: pDevExt=%p pFileObj=%p pSession=%p\n", pDevExt, pFileObj, pSession));
+    if (pSession)
+    {
+        supdrvCloseSession(pDevExt, (PSUPDRVSESSION)pFileObj->FsContext);
+        pFileObj->FsContext = NULL;
+    }
+
+    pIrp->IoStatus.Information = 0;
+    pIrp->IoStatus.Status = STATUS_SUCCESS;
+    IoCompleteRequest(pIrp, IO_NO_INCREMENT);
+
+    return STATUS_SUCCESS;
+}
+
+
+/**
+ * Close file entry point.
+ *
+ * @param   pDevObj     Device object.
+ * @param   pIrp        Request packet.
+ */
 NTSTATUS _stdcall VBoxDrvNtClose(PDEVICE_OBJECT pDevObj, PIRP pIrp)
 {
-    PSUPDRVDEVEXT       pDevExt = (PSUPDRVDEVEXT)pDevObj->DeviceExtension;
-    PIO_STACK_LOCATION  pStack = IoGetCurrentIrpStackLocation(pIrp);
+    PSUPDRVDEVEXT       pDevExt  = (PSUPDRVDEVEXT)pDevObj->DeviceExtension;
+    PIO_STACK_LOCATION  pStack   = IoGetCurrentIrpStackLocation(pIrp);
     PFILE_OBJECT        pFileObj = pStack->FileObject;
-    Log(("VBoxDrvNtClose: pDevExt=%p pFileObj=%p pSession=%p\n",
-         pDevExt, pFileObj, pFileObj->FsContext));
-    supdrvCloseSession(pDevExt, (PSUPDRVSESSION)pFileObj->FsContext);
-    pFileObj->FsContext = NULL;
+    PSUPDRVSESSION      pSession = (PSUPDRVSESSION)pFileObj->FsContext;
+
+    Log(("VBoxDrvNtClose: pDevExt=%p pFileObj=%p pSession=%p\n", pDevExt, pFileObj, pSession));
+    if (pSession)
+    {
+        supdrvCloseSession(pDevExt, (PSUPDRVSESSION)pFileObj->FsContext);
+        pFileObj->FsContext = NULL;
+    }
+
     pIrp->IoStatus.Information = 0;
     pIrp->IoStatus.Status = STATUS_SUCCESS;
@@ -446,6 +479,4 @@
           pIrp->AssociatedIrp.SystemBuffer, pStack->Parameters.DeviceIoControl.InputBufferLength,
           pStack->Parameters.DeviceIoControl.OutputBufferLength, pSession));
-
-/** @todo IDC on NT: figure when to create the session and that stuff... */
 
     /* Verify that it's a buffered CTL. */