[PATCH 4.4 11/56] staging: gdm724x: gdm_mux: fix use-after-free on module unload

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

commit b58f45c8fc301fe83ee28cad3e64686c19e78f1c upstream.

Make sure to deregister the USB driver before releasing the tty driver
to avoid use-after-free in the USB disconnect callback where the tty
devices are deregistered.

Fixes: 61e121047645 ("staging: gdm7240: adding LTE USB driver")
Cc: Won Kang <wkang77@xxxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/staging/gdm724x/gdm_mux.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/staging/gdm724x/gdm_mux.c
+++ b/drivers/staging/gdm724x/gdm_mux.c
@@ -670,14 +670,14 @@ static int __init gdm_usb_mux_init(void)
 
 static void __exit gdm_usb_mux_exit(void)
 {
-	unregister_lte_tty_driver();
-
 	if (mux_rx_wq) {
 		flush_workqueue(mux_rx_wq);
 		destroy_workqueue(mux_rx_wq);
 	}
 
 	usb_deregister(&gdm_mux_driver);
+	unregister_lte_tty_driver();
+
 }
 
 module_init(gdm_usb_mux_init);