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authorPawel Wieczorkiewicz <wipawel@amazon.de>2020-12-14 10:25:57 +0100
committerJuergen Gross <jgross@suse.com>2020-12-14 10:25:57 +0100
commit1c728719a4da6e654afb9cc047164755072ed7c9 (patch)
treeb0e7d2bf03ffd53abb72301f5e6b08e40ec88c65 /drivers/block
parent9996bd494794a2fe393e97e7a982388c6249aa76 (diff)
xen-blkback: set ring->xenblkd to NULL after kthread_stop()
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>
Diffstat (limited to 'drivers/block')
-rw-r--r--drivers/block/xen-blkback/xenbus.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 1d8b8d24496c..9860d4842f36 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -274,6 +274,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
if (ring->xenblkd) {
kthread_stop(ring->xenblkd);
+ ring->xenblkd = NULL;
wake_up(&ring->shutdown_wq);
}