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[PATCH/RFC] xen-blkback: set ring->xenblkd to NULL after kthread_stop()

Message ID 20210128090506.3174402-1-nobuhiro1.iwamatsu@toshiba.co.jp
State New
Headers show
Series [PATCH/RFC] xen-blkback: set ring->xenblkd to NULL after kthread_stop() | expand

Commit Message

Nobuhiro Iwamatsu Jan. 28, 2021, 9:05 a.m. UTC 
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>
[iwamatsu: change from ring to blkif]
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
---
 drivers/block/xen-blkback/xenbus.c | 1 +
 1 file changed, 1 insertion(+)
diff mbox series

Patch

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 823f3480ebd19e..f974ed7c33b5df 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -219,6 +219,7 @@  static int xen_blkif_disconnect(struct xen_blkif *blkif)
 
 	if (blkif->xenblkd) {
 		kthread_stop(blkif->xenblkd);
+		blkif->xenblkd = NULL;
 		wake_up(&blkif->shutdown_wq);
 	}