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From:   Kyungtae Kim <kt0755@gmail.com>
Date:   Tue, 8 Jan 2019 09:15:02 -0500
Message-ID: <CAEAjamuyjcxVNF5seJ0w0LQT0FSqvHYG30fzhe1s7UgVWzdaFg@mail.gmail.com>
Subject: Re: general protection fault in spk_ttyio_ldisc_close
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     William Hubbs <w.d.hubbs@gmail.com>,
        Christopher Brannon <chris@the-brannons.com>, kirk@reisers.ca,
        Samuel Thibault <samuel.thibault@ens-lyon.org>,
        Byoungyoung Lee <lifeasageek@gmail.com>,
        DaeRyong Jeong <threeearcat@gmail.com>,
        speakup@linux-speakup.org, devel@driverdev.osuosl.org,
        linux-kernel@vger.kernel.org, syzkaller@googlegroups.com
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On Tue, Jan 8, 2019 at 8:50 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jan 08, 2019 at 08:37:37AM -0500, Kyungtae Kim wrote:
> > We report a bug in linux-4.20: "general protection fault in
> > spk_ttyio_ldisc_close"
> >
> > kernel config: https://kt0755.github.io/etc/config_v4.20_stable
> > repro: https://kt0755.github.io/etc/repro.a670e.c
> >
> > This occurs when the function kfree is about to execute
> > (driver/staging/speakup/spk_ttyio.c:68).
> > Particularly, kfree takes the argument like speakup_tty->disc_data.
> > But speakup_tty is invalid, so the pointer dereference causes GPF.
> > At a glance, it seems that speakup_tty was deallocated somewhere ahead of kfree.
>
> How did you trigger this?  Did you shut down and close the device
> already somehow?  Do you have a real tty device that is driven by the
> device?
>
> thanks,
>
> greg k-h

For this crash, we did without real speakup tty device.
I'm currently trying to figure out how this actually happens.

Thanks,
Kyungtae Kim