linux-kernel - Re: [PATCH v24 00/12] /dev/random - a new approach with full SP800-90B compliance

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Message-ID: <5603724.uI2RiKDNrm@positron.chronox.de>
Date:   Tue, 12 Nov 2019 23:43:42 +0100
From:   Stephan Müller <smueller@...onox.de>
To:     Florian Weimer <fw@...eb.enyo.de>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>
Subject: Re: [PATCH v24 00/12] /dev/random - a new approach with full SP800-90B compliance

Am Dienstag, 12. November 2019, 14:23:10 CET schrieb Florian Weimer:

Hi Florian,

> * Stephan Müller:
> > * support deactivation of TRNG (i.e. blocking behavior of /dev/random)
> > 
> >   at compile time. If deactivated, /dev/random behaves like
> >   getrandom(2).
> 
> I don't quite understand this comment.  Doesn't getrandom with the
> GRND_RANDOM always behave like /dev/random?  Presumably, without the
> TRNG tap, the GRND_RANDOM flag for getrandom is ignored, and reading
> from /dev/random behaves like reading from /dev/urandom.

Absolutely. Apologies for the imprecision here. I will correct that.

The idea is that the constant blocking behavior of /dev/random and GRND_RANDOM 
is replaced with the blocking behavior of getrandom(2) without the GRND_RANDOM 
flag (i.e. the interface waits until the LRNG thinks it is completely seeded 
before it provides ulimited data).
> 
> Anyway, reading the accompanying PDF, this looks rather impressive:
> the userspace bootstrapping problem is gone (the issue where waiting
> for more entropy prevents the collection of more entropy), *and* we
> can still make the standards people happy.
> 
> (Replying from my other account due to mail issues, sorry.)


Ciao
Stephan