linux-kernel - Re: [PATCH] drivers/net: remove network drivers' last few uses of IRQF_SAMPLE

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Message-ID: <20080518110306.GD9845@merlin.emma.line.org>
Date:	Sun, 18 May 2008 13:03:06 +0200
From:	Matthias Andree <matthias.andree@....de>
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/net: remove network drivers' last few uses of
	IRQF_SAMPLE_RANDOM

On Sat, 17 May 2008, Matt Mackall wrote:

> It certainly makes sense to sample network timing noise. It often does
> not make sense to assume that there's any entropy in those timing
> samples. For instance:
> 
> - our clock resolution may be low enough that an attacker can guess our
> samples (ie it's simply HZ, very common in embedded land)
> - the bus involved (ISA, peripheral bus, even slow PCI) may have the
> same issue
> - it may be heavily correlated with some other measurement (ie network
> vs disk samples on file servers)
> 
> We currently assume that IRQF_SAMPLE_RANDOM means 'this is a completely
> trusted unobservable entropy source' which is obviously wrong for
> network devices but is right for some other classes of device.

Without looking at code, should your summary should include
"independent of (as in non-correlated with) other sources" according to
your argument?

-- 
Matthias Andree
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