| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.14 235/242] xen-blkback: set ring->xenblkd to NULL after kthread_stop() | Date | Mon, 28 Dec 2020 13:50:40 +0100 |
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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 @@ -263,6 +263,7 @@ static int xen_blkif_disconnect(struct x if (ring->xenblkd) { kthread_stop(ring->xenblkd); + ring->xenblkd = NULL; wake_up(&ring->shutdown_wq); }
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