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

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Date:	Thu, 29 Sep 2011 22:44:16 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Josh Zimmerman <jzimmerm@...rew.cmu.edu>
Cc:	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.

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)

            Linus
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