linux-kernel - Re: Why does reading from /dev/urandom deplete entropy so much?

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Message-ID: <20071204223345.GJ19691@waste.org>
Date:	Tue, 4 Dec 2007 16:33:46 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Mike McGrath <mmcgrath@...hat.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Theodore Tso <tytso@....edu>,
	Ray Lee <ray@...rabbit.org>, Adrian Bunk <bunk@...nel.org>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Why does reading from /dev/urandom deplete entropy so much?

On Tue, Dec 04, 2007 at 04:23:12PM -0600, Mike McGrath wrote:
> Matt Mackall wrote:
> >On Tue, Dec 04, 2007 at 03:18:27PM -0600, Mike McGrath wrote:
> >  
> >>Matt Mackall wrote:
> >>    
> >>>which would have been in v2.6.22-rc4 through the normal CVE process.
> >>>The only other bits in there are wall time and utsname, so systems
> >>>with no CMOS clock would behave repeatably. Can we find out what
> >>>kernels are affected?
> >>>
> >>> 
> >>>      
> >>We can but it will likely take a few weeks to get a good sampling. UUID 
> >>is unique in the db so when someone checks in with the same UUID, the 
> >>old one gets overwritten.
> >>    
> >
> >We can probably assume that for whatever reason the two things with
> >duplicate UUID had the same seed. If not, we've got -much- bigger
> >problems.
> >  
> 
> Ok, I think I see whats going on here. I have some further investigation 
> to do but it seems that the way our Live CD installer works is causing 
> these issues. I'm going to try to grab some live CD's and hardware to 
> confirm but at this point it seems thats whats going on.

Alright, keep me posted. We probably need a scheme to make the initial
seed more robust regardless of what you find out.

-- 
Mathematics is the supreme nostalgia of our time.
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