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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 15 Sep 2019 12:08:31 -0700
Message-ID: <CAHk-=wgFrRCL3WP7vyuZ-92xyqb97ADc=JNyyVCucZ1Q9oh8TA@mail.gmail.com>
Subject: Re: [PATCH RFC v2] random: optionally block in getrandom(2) when the
 CRNG is uninitialized
To:     Willy Tarreau <w@1wt.eu>
Cc:     "Theodore Y. Ts'o" <tytso@mit.edu>,
        "Alexander E. Patrakov" <patrakov@gmail.com>,
        "Ahmed S. Darwish" <darwish.07@gmail.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Jan Kara <jack@suse.cz>, Ray Strode <rstrode@redhat.com>,
        William Jon McCann <mccann@jhu.edu>,
        zhangjs <zachary@baishancloud.com>, linux-ext4@vger.kernel.org,
        lkml <linux-kernel@vger.kernel.org>,
        Lennart Poettering <mzxreary@0pointer.de>
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On Sun, Sep 15, 2019 at 11:37 AM Willy Tarreau <w@1wt.eu> wrote:
>
> I also wanted to ask, are we going to enforce the same strategy on
> /dev/urandom ?

Right now the strategy for /dev/urandom is "print a one-line warning,
then do the read".

I don't see why we should change that. The whole point of urandom has
been that it doesn't block, and doesn't use up entropy.

It's the _blocking_ behavior that has always been problematic. It's
why almost nobody uses /dev/random in practice.

getrandom() looks like /dev/urandom in not using up entropy, but had
that blocking behavior of /dev/random that was problematic.

And exactly the same way it was problematic for /dev/random users, it
has now shown itself to be problematic for getrandom().

My suggested patch left the /dev/random blocking behavior, because
hopefully people *know* about the problems there.

And hopefully people understand that getrandom(GRND_RANDOM) has all
the same issues.

If you want that behavior, you can still use GRND_RANDOM or
/dev/random, but they are simply not acceptable for boot-time
schenarios. Never have been,

... exactly the way the "block forever" wasn't acceptable for getrandom().

                Linus