USB: iowarrior: fix use-after-free on disconnect

A recent fix addressing a deadlock on disconnect introduced a new bug
by moving the present flag out of the critical section protected by the
driver-data mutex. This could lead to a racing release() freeing the
driver data before disconnect() is done with it.

Due to insufficient locking a related use-after-free could be triggered
also before the above mentioned commit. Specifically, the driver needs
to hold the driver-data mutex also while checking the opened flag at
disconnect().

Fixes: c468a8aa79 ("usb: iowarrior: fix deadlock on disconnect")
Fixes: 946b960d13 ("USB: add driver for iowarrior devices.")
Cc: stable <stable@vger.kernel.org>	# 2.6.21
Reported-by: syzbot+0761012cebf7bdb38137@syzkaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191009104846.5925-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/iowarrior.c

@@ -866,8 +866,6 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	dev = usb_get_intfdata(interface);
 	mutex_lock(&iowarrior_open_disc_lock);
 	usb_set_intfdata(interface, NULL);
-	/* prevent device read, write and ioctl */
-	dev->present = 0;
 
 	minor = dev->minor;
 	mutex_unlock(&iowarrior_open_disc_lock);
@@ -878,8 +876,7 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 	mutex_lock(&dev->mutex);
 
 	/* prevent device read, write and ioctl */
-
-	mutex_unlock(&dev->mutex);
+	dev->present = 0;
 
 	if (dev->opened) {
 		/* There is a process that holds a filedescriptor to the device ,
@@ -889,8 +886,10 @@ static void iowarrior_disconnect(struct usb_interface *interface)
 		usb_kill_urb(dev->int_in_urb);
 		wake_up_interruptible(&dev->read_wait);
 		wake_up_interruptible(&dev->write_wait);
+		mutex_unlock(&dev->mutex);
 	} else {
 		/* no process is using the device, cleanup now */
+		mutex_unlock(&dev->mutex);
 		iowarrior_delete(dev);
 	}