Commit 1c728719 authored by Pawel Wieczorkiewicz's avatar Pawel Wieczorkiewicz Committed by Juergen Gross

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.

Cc: <stable@vger.kernel.org> # 4.12
Fixes: a24fa22c ("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread")
Reported-by: default avatarOlivier Benjamin <oliben@amazon.com>
Reported-by: default avatarPawel Wieczorkiewicz <wipawel@amazon.de>
Signed-off-by: default avatarPawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: default avatarJulien Grall <jgrall@amazon.com>
Reviewed-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 9996bd49
......@@ -274,6 +274,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
if (ring->xenblkd) {
kthread_stop(ring->xenblkd);
ring->xenblkd = NULL;
wake_up(&ring->shutdown_wq);
}
......
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