auxdisplay: ht16k33: fix potential user-after-free on module unload

ojeda · ojeda · commit 69ef9bc54715 · 2019-02-15T19:48:39.000+01:00
On module unload/remove, we need to ensure that work does not run after we have freed resources. Concretely, cancel_delayed_work() may return while the callback function is still running. From kernel/workqueue.c: The work callback function may still be running on return, unless it returns true and the work doesn't re-arm itself. Explicitly flush or use cancel_delayed_work_sync() to wait on it. Link: https://lore.kernel.org/lkml/20190204220952.30761-1-TheSven73@googlemail.com/ Reported-by: Sven Van Asbroeck <thesven73@gmail.com> Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> Reviewed-by: Sven Van Asbroeck <TheSven73@gmail.com> Acked-by: Robin van der Gracht <robin@protonic.nl> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
diff --git a/drivers/auxdisplay/ht16k33.c b/drivers/auxdisplay/ht16k33.c
@@ -509,7 +509,7 @@ static int ht16k33_remove(struct i2c_client *client)
 	struct ht16k33_priv *priv = i2c_get_clientdata(client);
 	struct ht16k33_fbdev *fbdev = &priv->fbdev;
 
-	cancel_delayed_work(&fbdev->work);
+	cancel_delayed_work_sync(&fbdev->work);
 	unregister_framebuffer(fbdev->info);
 	framebuffer_release(fbdev->info);
 	free_page((unsigned long) fbdev->buffer);
