linux-kernel - Re: [RFC 2/3] blktrace: fix debugfs use after free

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Message-ID: <20200406151907.GD11244@42.do-not-panic.com>
Date:   Mon, 6 Apr 2020 15:19:07 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Nicolai Stange <nstange@...e.de>
Cc:     Bart Van Assche <bvanassche@....org>,
        Eric Sandeen <sandeen@...deen.net>, axboe@...nel.dk,
        viro@...iv.linux.org.uk, gregkh@...uxfoundation.org,
        rostedt@...dmis.org, mingo@...hat.com, jack@...e.cz,
        ming.lei@...hat.com, mhocko@...e.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>,
        syzbot+603294af2d01acfdd6da@...kaller.appspotmail.com
Subject: Re: [RFC 2/3] blktrace: fix debugfs use after free

On Mon, Apr 06, 2020 at 11:18:13AM +0200, Nicolai Stange wrote:
> Bart Van Assche <bvanassche@....org> writes:

> So I'd suggest to drop patch [3/3] from this series and modify this
> patch [2/3] here to move the blk_q_debugfs_unregister(q) invocation from
> __blk_release_queue() to blk_unregister_queue() instead.

I'll take a stab.

> > Additionally, I think the following changes fix that problem by using
> > q->debugfs_dir in the blktrace code instead of debugfs_lookup():
> 
> That would fix the UAF, but !queue_is_mq() queues wouldn't get a debugfs
> directory created for them by blktrace anymore?

It would, it would just be done early on init as well, and it would now be
shared with the queue_is_mq() case.

  Luis