linux-kernel - Re: general protection fault in spk_ttyio_ldisc

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Message-ID: <20190108142609.3nraohfx6msxb4hm@function>
Date:   Tue, 8 Jan 2019 15:26:09 +0100
From:   Samuel Thibault <samuel.thibault@...-lyon.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Kyungtae Kim <kt0755@...il.com>, devel@...verdev.osuosl.org,
        kirk@...sers.ca, speakup@...ux-speakup.org,
        linux-kernel@...r.kernel.org, syzkaller@...glegroups.com,
        Byoungyoung Lee <lifeasageek@...il.com>,
        DaeRyong Jeong <threeearcat@...il.com>,
        Christopher Brannon <chris@...-brannons.com>
Subject: Re: general protection fault in spk_ttyio_ldisc_close

Greg KH, le mar. 08 janv. 2019 15:25:07 +0100, a ecrit:
> 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?

One can tell any device name to the driver and it will attempt to
communicate with it.

Samuel