Fixing Potential Double Free Issue (#517)

* Fix Potential Double Free

Co-authored-by: Daniel Henry-Mantilla <daniel.henry.mantilla@gmail.com>

notify/src/windows.rs

@@ -278,7 +278,7 @@ fn start_read(rd: &ReadData, event_handler: Arc<Mutex<dyn EventHandler>>, handle
     };
 
     unsafe {
-        let mut overlapped: Box<OVERLAPPED> = Box::new(mem::zeroed());
+        let mut overlapped = std::mem::ManuallyDrop::new(Box::new(mem::zeroed::<OVERLAPPED>()));
         // When using callback based async requests, we are allowed to use the hEvent member
         // for our own purposes
 
@@ -295,19 +295,18 @@ fn start_read(rd: &ReadData, event_handler: Arc<Mutex<dyn EventHandler>>, handle
             monitor_subdir,
             flags,
             &mut 0u32 as *mut u32, // not used for async reqs
-            &mut *overlapped as *mut OVERLAPPED,
+            (&mut **overlapped) as *mut OVERLAPPED,
             Some(handle_event),
         );
 
         if ret == 0 {
             // error reading. retransmute request memory to allow drop.
-            // allow overlapped to drop by omitting forget()
+            // Because of the error, ownership of the `overlapped` alloc was not passed
+            // over to `ReadDirectoryChangesW`.
+            // So we can claim ownership back.
+            let _overlapped_alloc = std::mem::ManuallyDrop::into_inner(overlapped);
             let request: Box<ReadDirectoryRequest> = mem::transmute(request_p);
-
             ReleaseSemaphore(request.data.complete_sem, 1, ptr::null_mut());
-        } else {
-            // read ok. forget overlapped to let the completion routine handle memory
-            mem::forget(overlapped);
         }
     }
 }