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Date: Tue, 24 Jul 2012 08:37:21 -0400
From: David Schultz <das@FreeBSD.ORG>
To: Doug Barton <dougb@FreeBSD.ORG>
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References: <201207041951.q64JpPXu029310@svn.freebsd.org>
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Cc: src-committers@FreeBSD.ORG, Pawel Jakub Dawidek <pjd@FreeBSD.ORG>,
	svn-src-all@FreeBSD.ORG, svn-src-head@FreeBSD.ORG,
	Konstantin Belousov <kostikbel@gmail.com>,
	Andrey Chernov <ache@FreeBSD.ORG>, markm@FreeBSD.ORG
Subject: Re: svn commit: r238118 - head/lib/libc/gen
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On Wed, Jul 04, 2012, Doug Barton wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
> 
> On 07/04/2012 13:32, Andrey Chernov wrote:
> > 1) /dev/urandom may not exist in jails/sandboxes
> 
> That would be a pretty serious configuration error.

Yes -- but the scary part is that arc4random() is not fail-safe at
all.  If /dev/random isn't there, you just silently get
predictable "randomness".  If you needed that randomness for
cryptographic purposes you're out of luck; you might as well have
used rot13.  Using the sysctl doesn't fix the failure mode (in
fact, as I recall the sysctl dubiously never reports failure even
if there is no entropy), but there's a narrower set of
circumstances under which the sysctl can fail.