linux-kernel - Re: [PATCH] kernel/groups.c: Minor bugfix for overflow in binary search

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Message-ID: <CAOJsxLEzFKHkxSUh7jwQRmudtYzBRLFo3VdJpVjNOEgSCh3ehg@mail.gmail.com>
Date:	Fri, 30 Sep 2011 09:59:41 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Josh Zimmerman <jzimmerm@...rew.cmu.edu>,
	akpm@...ux-foundation.org, serge.hallyn@...onical.com,
	ebiederm@...ssion.com, dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/groups.c: Minor bugfix for overflow in binary search

On Thu, Sep 29, 2011 at 9:39 PM, Josh Zimmerman <jzimmerm@...rew.cmu.edu> wrote:
>> Fixed possible unsigned int overflow bug. (2 + 2^(32) - 1)/2 results in overflow; 2 + (2^(32)-1-2)/2 does not.

On Fri, Sep 30, 2011 at 8:44 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> We can't have that many groups anyway, so the overflow is pretty theoretical.
>
> The max should be NGROUPS_MAX, afaik (65536) and other places have
> lower limits (ie sunrpc/nfs). And if some place doesn't limit it
> correctly, we have bigger problems than this (the whole allocation and
> CPU use issues)

The code site could be converted to lib/bsearch.c::bsearch(), AFAICT. That'd
take care of the theoretical overflow too.

                        Pekka
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