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

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Message-ID: <CAG48ez3m1VBMHUBTP3yt4NFjFGv7qZCGJy3fUHvZWpM5mKQAog@mail.gmail.com>
Date:   Tue, 10 Jul 2018 13:34:59 -0700
From:   Jann Horn <jannh@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Samuel Thibault <samuel.thibault@...-lyon.org>,
        William Hubbs <w.d.hubbs@...il.com>,
        Christopher Brannon <chris@...-brannons.com>, kirk@...sers.ca,
        kernel list <linux-kernel@...r.kernel.org>,
        speakup@...ux-speakup.org, devel@...verdev.osuosl.org
Subject: Re: [PATCH] staging: speakup: fix wraparound in uaccess length check

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?