From: Pawel Wieczorkiewicz wipawel@amazon.de
mainline inclusion from mainline-v5.11-rc1 commit 1c728719a4da6e654afb9cc047164755072ed7c9 category: bugfix bugzilla: NA CVE: CVE-2020-29569
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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: Yang Yingliang yangyingliang@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- 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 93896c992245..60594768057e 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -264,6 +264,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
if (ring->xenblkd) { kthread_stop(ring->xenblkd); + ring->xenblkd = NULL; wake_up(&ring->shutdown_wq); }