linux-kernel - Re: IRQF_SAMPLE

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Message-ID: <49DA9EC3.4060903@garzik.org>
Date:	Mon, 06 Apr 2009 20:30:59 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Matt Mackall <mpm@...enic.com>
CC:	Sven-Haegar Koch <haegar@...net.de>,
	Robin Getz <rgetz@...ckfin.uclinux.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Peterson <cpeterso@...terso.com>
Subject: Re: IRQF_SAMPLE_RANDOM question...

Matt Mackall wrote:
> On Tue, 2009-04-07 at 00:09 +0200, Sven-Haegar Koch wrote:
>> On Mon, 6 Apr 2009, Matt Mackall wrote:
>>
>>> On Mon, 2009-04-06 at 14:30 -0400, Robin Getz wrote:
>>>> We have lots of embedded headless systems (no keyboard/mouse, no soundcard, no 
>>>> video) systems with *no* sources of entropy - and people using SSL.
>>> I'd rather add a random_sample_network call somewhere reasonably central
>>> in the network stack. Then we can use the knowledge that the sample is
>>> network-connected in the random core to decide how to measure its
>>> entropy. The trouble with IRQF_SAMPLE_RANDOM is that many of its users
>>> are technically bogus as entropy sources in the current model.
>>>
>>> I'm eventually going to move the RNG away from the strict theoretical
>>> entropy accounting model to a more pragmatic one which will be much
>>> happier with iffy entropy sources, but that's a ways off.
>> Btw, perhaps not the perfect question in this thread:
>> But what should we use to keep servers running without a hardware rng 
>> available and without any external input besides the network?
>> After having ssh and openvpn die because of no random and having 
>> the machines like dead and unreachable for me I use "ln -sf 
>> /dev/urandom /dev/random", but that does not feel so good.
> 
> It's fine so long as you're not wearing a tinfoil hat. In fact, as
> the /dev/random maintainer, I'd recommend it.
> 
> Ted and I have recently been talking about revisiting the design
> of /dev/random to avoid these sorts of issues.


Two points...

- while I would welcome a more pragmatic entropy accounting model,

- it seems misplaced to _solely_ address network entropy problems 
(timer-based regularity, external visibility and access) within the 
devrandom machinery.

IRQF_SAMPLE_RANDOM in network drivers IMO just gives users a false sense 
of security about their entropy.

And more fundamentally, IRQF_SAMPLE_RANDOM should never be used on a 
non-random source.

	Jeff



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