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

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Date:   Sat, 7 Jul 2018 16:03:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Samuel Thibault <samuel.thibault@...-lyon.org>,
        Jann Horn <jannh@...gle.com>,
        William Hubbs <w.d.hubbs@...il.com>,
        Chris Brannon <chris@...-brannons.com>,
        Kirk Reiser <kirk@...sers.ca>, 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 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?

thanks,

greg k-h