linux-kernel - Re: [syzbot] KASAN: use-after-free Read in kernfs_next_descendant

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Message-ID: <Y3QPLje5yYEZdPc6@slm.duckdns.org>
Date:   Tue, 15 Nov 2022 12:14:06 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Matthieu Castet <castet.matthieu@...e.fr>,
        Stanislaw Gruszka <stf_xl@...pl>, ming.lei@...hat.com,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+6bc35f3913193fe7f0d3@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in
 kernfs_next_descendant_post (2)

On Tue, Nov 15, 2022 at 11:35:10AM -0800, Luis Chamberlain wrote:
> request_firmware_nowait() is documented as requiring the caller to
> ensure to maintain the the reference count of @device during the
> lifetime of the call to request_firmware_nowait() and the callback.

My reading was that just holding the ref isn't enough. The code expects the
device to be not destroyed independent of the refcnt. I don't see how this
would be fixed by diddling with refcnt.

Thanks.

-- 
tejun