linux-kernel - Re: [PATCH] staging: speakup: fix wraparound in uaccess length check

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Message-ID: <20180711092740.GA3972@kroah.com>
Date:   Wed, 11 Jul 2018 11:27:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     devel@...verdev.osuosl.org, kirk@...sers.ca,
        speakup@...ux-speakup.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Christopher Brannon <chris@...-brannons.com>
Subject: Re: [PATCH] staging: speakup: fix wraparound in uaccess length check

On Tue, Jul 10, 2018 at 01:34:59PM -0700, Jann Horn wrote:
> On Sat, Jul 7, 2018 at 7:03 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Sat, Jul 07, 2018 at 10:29:26AM +0200, Samuel Thibault wrote:
> > > Re,
> > >
> > > Could you review, test, and resubmit the patch below instead?
> > >
> > > Samuel
> > >
> > >
> > > If softsynthx_read() is called with `count < 3`, `count - 3` wraps, causing
> > > the loop to copy as much data as available to the provided buffer. If
> > > softsynthx_read() is invoked through sys_splice(), this causes an
> > > unbounded kernel write; but even when userspace just reads from it
> > > normally, a small size could cause userspace crashes.
> > >
> > > Fixes: 425e586cf95b ("speakup: add unicode variant of /dev/softsynth")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Samuel Thibault <samuel.thibault@...-lyon.org>
> >
> > You forgot a "reported-by:" line :(
> >
> > also, I already applied Jann's patch, so could you either just send the
> > fixup, or a revert/add of this patch once you all agree on the proper
> > solution here?
> 
> I think my patch was garbage (as both Samuel and Dan Carpenter's
> smatch warning pointed out) and should be reverted. Should I be
> sending the revert?

I'll just go drop it, thanks for letting me know.

greg k-h