From: Pawel Wieczorkiewicz wipawel@amazon.de
commit 1c728719a4da6e654afb9cc047164755072ed7c9 upstream.
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: a24fa22ce22a ("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread") Reported-by: Olivier Benjamin oliben@amazon.com Reported-by: Pawel Wieczorkiewicz wipawel@amazon.de Signed-off-by: Pawel Wieczorkiewicz wipawel@amazon.de Reviewed-by: Julien Grall jgrall@amazon.com Reviewed-by: Juergen Gross jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/xen-blkback/xenbus.c | 1 + 1 file changed, 1 insertion(+)
--- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -256,6 +256,7 @@ static int xen_blkif_disconnect(struct x
if (ring->xenblkd) { kthread_stop(ring->xenblkd); + ring->xenblkd = NULL; wake_up(&ring->shutdown_wq); }