From: Author Redacted Subject: [PATCH] xen-blkback: set ring->xenblkd to NULL after kthread_stop() When xen_blkif_disconnect() is called, the kernel thread behind the block interface is stopped by calling kthread_stop(ring->xenblkd). The ring->xenblkd thread pointer being non-NULL determines if the thread has been already stopped. Normally, the thread's function xen_blkif_schedule() sets the ring->xenblkd to NULL, when the thread's main loop ends. However, when the thread has not been started yet (i.e. wake_up_process() has not been called on it), the xen_blkif_schedule() function would not be called yet. In such case the kthread_stop() call returns -EINTR and the ring->xenblkd remains dangling. When this happens, any consecutive call to xen_blkif_disconnect (for example in frontend_changed() callback) leads to a kernel crash in kthread_stop() (e.g. NULL pointer dereference in exit_creds()). This is XSA-350. Reported-by: Olivier Benjamin Reported-by: Pawel Wieczorkiewicz Reviewed-by: Juergen Gross Signed-off-by: Pawel Wieczorkiewicz Fixes: a24fa22ce22a ("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread") Signed-off-by: Author Redacted Reviewed-by: Julien Grall Reviewed-by: Juergen Gross --- drivers/block/xen-blkback/xenbus.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index f5705569e2a7..f7b9b1f389fe 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -275,6 +275,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif) if (ring->xenblkd) { kthread_stop(ring->xenblkd); + ring->xenblkd = NULL; wake_up(&ring->shutdown_wq); } -- 2.17.1