USB: cdc-wdm: updating desc->length must be protected by spin_lock

wdm_in_callback() will also touch this field, so we cannot change it without locking

Cc: stable@vger.kernel.org
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

(cherry picked from commit c428b70c)
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

drivers/usb/class/cdc-wdm.c

@@ -518,7 +518,9 @@ static ssize_t wdm_read
 	for (i = 0; i < desc->length - cntr; i++)
 		desc->ubuf[i] = desc->ubuf[i + cntr];
 
+	spin_lock_irq(&desc->iuspin);
 	desc->length -= cntr;
+	spin_unlock_irq(&desc->iuspin);
 	/* in case we had outstanding data */
 	if (!desc->length)
 		clear_bit(WDM_READ, &desc->flags);