xen-blkback: set ring->xenblkd to NULL after kthread_stop()
[upstream commit 1c728719a4da6e654afb9cc047164755072ed7c9]
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: <[email protected]> # 4.12
Fixes: a24fa22ce22a ("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread")
Reported-by: Olivier Benjamin <[email protected]>
Reported-by: Pawel Wieczorkiewicz <[email protected]>
Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Reviewed-by: Julien Grall <[email protected]>
Reviewed-by: Juergen Gross <[email protected]>
Signed-off-by: Juergen Gross <[email protected]>
1 file changed
