linux-kernel - Re: general protection fault in spk_ttyio_ldisc

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Message-ID: <20190108135020.GA10504@kroah.com>
Date:   Tue, 8 Jan 2019 14:50:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kyungtae Kim <kt0755@...il.com>
Cc:     w.d.hubbs@...il.com, chris@...-brannons.com, kirk@...sers.ca,
        samuel.thibault@...-lyon.org,
        Byoungyoung Lee <lifeasageek@...il.com>,
        DaeRyong Jeong <threeearcat@...il.com>,
        speakup@...ux-speakup.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, syzkaller@...glegroups.com
Subject: Re: general protection fault in spk_ttyio_ldisc_close

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