Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 8 Jan 2019 14:50:20 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Kyungtae Kim <kt0755@gmail.com>
Cc:     w.d.hubbs@gmail.com, chris@the-brannons.com, kirk@reisers.ca,
        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
Subject: Re: general protection fault in spk_ttyio_ldisc_close
Message-ID: <20190108135020.GA10504@kroah.com>
References: <CAEAjamunJjFFJ8Yd-DQAv64MxYiiktsTUWex=boAOdc0+7h+uQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAEAjamunJjFFJ8Yd-DQAv64MxYiiktsTUWex=boAOdc0+7h+uQ@mail.gmail.com>
User-Agent: Mutt/1.11.1 (2018-12-01)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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