On Thu, Feb 28, 2019 at 10:07:35AM -0500, Sasha Levin wrote:

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[ Upstream commit 36991ca68db9dd43bac7f3519f080ee3939263ef ]

If debugfs were to return a non-NULL error for a debugfs call, using
that pointer later in debugfs_create_files() would crash.

Fix that by properly checking the pointer before referencing it.

Reported-by: Michal Hocko <mhocko@kernel.org>
Reported-and-tested-by: syzbot+b382ba6a802a3d242790@syzkaller.appspotmail.com
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-mq-debugfs.c | 3 +++
 1 file changed, 3 insertions(+)

As the commit this "fixes" should not be backported, no need for this
patch in any stable kernel either.  Please drop from all queues.

thanks,

greg k-h