USB: adutux: fix use-after-free on release

BugLink: https://bugs.launchpad.net/bugs/1848780

commit 123a0f12 upstream.

The driver was accessing its struct usb_device in its release()
callback without holding a reference. This would lead to a
use-after-free whenever the device was disconnected while the character
device was still open.

Fixes: 66d4bc30 ("USB: adutux: remove custom debug macro")
Cc: stable <stable@vger.kernel.org>     # 3.12
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009153848.8664-2-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/usb/misc/adutux.c

@@ -152,6 +152,7 @@ static void adu_delete(struct adu_device *dev)
 	kfree(dev->read_buffer_secondary);
 	kfree(dev->interrupt_in_buffer);
 	kfree(dev->interrupt_out_buffer);
+	usb_put_dev(dev->udev);
 	kfree(dev);
 }
 
@@ -681,7 +682,7 @@ static int adu_probe(struct usb_interface *interface,
 
 	mutex_init(&dev->mtx);
 	spin_lock_init(&dev->buflock);
-	dev->udev = udev;
+	dev->udev = usb_get_dev(udev);
 	init_waitqueue_head(&dev->read_wait);
 	init_waitqueue_head(&dev->write_wait);