From: "David Schwartz" <davids@webmaster.com>
To: "Theodore Tso" <tytso@mit.edu>, <jreiser@bitwagon.com>
Cc: "Matt Mackall" <mpm@selenic.com>, <linux-kernel@vger.kernel.org>,
       <security@kernel.org>
Subject: RE: /dev/urandom uses uninit bytes, leaks user data
Date: Mon, 17 Dec 2007 12:59:04 -0800
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> The bottom line:  At a cost of at most three unpredictable branches
> (whether to clear the bytes in the last word with indices congruent
> to 1, 2, or 3 modulo 4), then the code can reduce the risk from something
> small but positive, to zero.  This is very inexpensive insurance.

> John Reiser, jreiser@BitWagon.com

Even if you're right, the change isn't free. You've simply presented
evidence of one non-zero benefit of it. You've given no ability to assess
the size of this benefit and no way to figure if it exceeds the cost. There
is also a non-zero *security* cost to this change.

DS


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