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

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Message-ID: <2c0942db0712171012o613b2596x81f4a867e2b5c01@mail.gmail.com>
Date:	Mon, 17 Dec 2007 10:12:47 -0800
From:	"Ray Lee" <ray-lk@...rabbit.org>
To:	"Eric Dumazet" <dada1@...mosbay.com>
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 Dec 17, 2007 10:10 AM, Eric Dumazet <dada1@...mosbay.com> wrote:
> 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

Ah, my bad. One of these days I'll learn to not post before coffee.
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