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 --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); }
Hi,
I forgot to write the kernel version. This is a patch for 4.4.y.
Best regards, Nobuhiro
On Thu, Jan 28, 2021 at 06:05:06PM +0900, Nobuhiro Iwamatsu wrote:
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 --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;2.30.0
linux-stable-mirror@lists.linaro.org
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Nobuhiro Iwamatsu