linux-kernel - Re: general protection fault in spk_ttyio_ldisc

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Date:   Tue, 8 Jan 2019 15:25:07 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kyungtae Kim <kt0755@...il.com>
Cc:     devel@...verdev.osuosl.org, kirk@...sers.ca,
        speakup@...ux-speakup.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com,
        Byoungyoung Lee <lifeasageek@...il.com>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        DaeRyong Jeong <threeearcat@...il.com>,
        Christopher Brannon <chris@...-brannons.com>
Subject: Re: general protection fault in spk_ttyio_ldisc_close

On Tue, Jan 08, 2019 at 09:15:02AM -0500, Kyungtae Kim wrote:
> On Tue, Jan 8, 2019 at 8:50 AM Greg KH <gregkh@...uxfoundation.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.

How did you bind a non-real speakup tty device to the driver?

> I'm currently trying to figure out how this actually happens.

That would be great to figure out :)

thanks,

greg k-h