linux-kernel - Re: /dev/urandom uses uninit bytes, leaks user data

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Message-ID: <20071215163010.GS19691@waste.org>
Date:	Sat, 15 Dec 2007 10:30:10 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	John Reiser <jreiser@...Wagon.com>, akpm@...ux-foundation.org,
	tytso@....edu, linux-kernel@...r.kernel.org
Subject: Re: /dev/urandom uses uninit bytes, leaks user data

On Sat, Dec 15, 2007 at 03:13:19PM +0800, Herbert Xu wrote:
> John Reiser <jreiser@...wagon.com> wrote:
> >
> > If speed matters that much, then please recoup 33 cycles on x86
> > by using shifts instead of three divides, such as (gcc 4.1.2):
> > 
> >                add_entropy_words(r, tmp, (bytes + 3) / 4);
> > 
> > 0x8140689 <xfer_secondary_pool+206>:    lea    0x3(%esi),%eax
> > 0x814068c <xfer_secondary_pool+209>:    mov    $0x4,%dl
> > 0x814068e <xfer_secondary_pool+211>:    mov    %edx,%edi
> > 0x8140690 <xfer_secondary_pool+213>:    cltd
> > 0x8140691 <xfer_secondary_pool+214>:    idiv   %edi
> 
> There ought to be a warning about this sort of thing.

Indeed. Seems it would be better to adjust the types appropriately.
Anyway, this is no longer relevant to security@.

-- 
Mathematics is the supreme nostalgia of our time.
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