[NTOSKRNL] Implement IoGetFileObjectFilterContext()

ntoskrnl/include/internal/io.h

@@ -96,6 +96,7 @@
 typedef struct _FILE_OBJECT_EXTENSION
 {
     PDEVICE_OBJECT TopDeviceObjectHint;
+    PVOID FilterContext;
 
 } FILE_OBJECT_EXTENSION, *PFILE_OBJECT_EXTENSION;
 

ntoskrnl/io/iomgr/file.c

@@ -2443,9 +2443,10 @@ IoGetFileObjectFilterContext(IN PFILE_OBJECT FileObject)
 {
     if (FileObject->Flags & FO_FILE_OBJECT_HAS_EXTENSION)
     {
-        UNIMPLEMENTED;
-        /* FIXME: return NULL for the moment ~ */
-        return NULL;
+        PFILE_OBJECT_EXTENSION FileObjectExtension;
+
+        FileObjectExtension = FileObject->FileObjectExtension;
+        return FileObjectExtension->FilterContext;
     }
 
     return NULL;