linux-kernel - Re: Signed divides vs shifts (Re: [Security] /dev/urandom uses uninit bytes, leaks user data)

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Message-Id: <20071217191017.117c61ff.dada1@cosmosbay.com>
Date:	Mon, 17 Dec 2007 19:10:17 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"Ray Lee" <ray-lk@...rabbit.org>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Herbert Xu" <herbert@...dor.apana.org.au>,
	"John Reiser" <jreiser@...wagon.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>, security@...nel.org,
	tytso@....edu,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	mpm@...enic.com, linux-sparse@...r.kernel.org
Subject: Re: Signed divides vs shifts (Re: [Security] /dev/urandom uses
 uninit bytes, leaks user data)

On Mon, 17 Dec 2007 10:05:35 -0800
"Ray Lee" <ray-lk@...rabbit.org> wrote:

> On Dec 17, 2007 9:55 AM, Eric Dumazet <dada1@...mosbay.com> wrote:
> > -               mid = (last - first) / 2 + first;
> > +       while (low <= high) {
> > +               mid = (low + high) / 2;
> 
> I think you just introduced a bug. Think about what happens if
> low=high=MAX_LONG/2 + 1.
> 

Fortunatly this is not possible :)

Hint : sizeof(struct exception_table_entry) is >= 8

so high is garanteed to be <= MAX_LONG/8

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