From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: IRQF_SAMPLE_RANDOM question... Date: Mon, 06 Apr 2009 20:30:59 -0400 Message-ID: <49DA9EC3.4060903@garzik.org> References: <200904061430.26276.rgetz@blackfin.uclinux.org> <1239044483.14392.55.camel@calx> <1239063404.14392.118.camel@calx> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Sven-Haegar Koch , Robin Getz , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Peterson To: Matt Mackall Return-path: In-Reply-To: <1239063404.14392.118.camel@calx> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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