linux-kernel - Re: [PATCH v2] fbdev: Detect integer underflow at "struct fbcon_ops"->clear

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Message-ID: <adfa8720-c411-dfe6-6b0f-7591dd95396c@i-love.sakura.ne.jp>
Date:   Thu, 16 Jul 2020 00:29:00 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        George Kennedy <george.kennedy@...cle.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot <syzbot+e5fd3e65515b48c02a30@...kaller.appspotmail.com>
Subject: Re: [PATCH v2] fbdev: Detect integer underflow at "struct
 fbcon_ops"->clear_margins.

On 2020/07/16 0:12, Dan Carpenter wrote:
> I've complained about integer overflows in fbdev for a long time...
> 
> What I'd like to see is something like the following maybe.  I don't
> know how to get the vc_data in fbmem.c so it doesn't include your checks
> for negative.

Yes. Like I said "Thus, I consider that we need more sanity/constraints checks." at
https://lore.kernel.org/lkml/b1e7dd6a-fc22-bba8-0abb-d3e779329bce@i-love.sakura.ne.jp/ ,
we want basic checks. That's a task for fbdev people who should be familiar with
necessary constraints.

Anyway, my two patches are small and low cost; can we apply these patches regardless
of basic checks?