linux-kernel - Re: [PATCH] random: opportunistically initialize on /dev/urandom reads

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Message-ID: <CAHk-=wjFSsa7ZTFOiDCpZbwQsCKdAo3KFetSpGCjusqjjcb2XA@mail.gmail.com>
Date:   Tue, 5 Apr 2022 10:37:05 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH] random: opportunistically initialize on /dev/urandom reads

On Tue, Apr 5, 2022 at 7:10 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Practically speaking, this means that at least on x86, /dev/urandom
> becomes safe. Probably other architectures with working cycle counters
> will also become safe. And architectures with slow or broken cycle
> counters at least won't be affected at all by this change.

I think this is a good change, as it's a bit pointless to warn about
uninitialized random data if we can just initialize it.

I do wonder if it wouldn't be better to perhaps move this all into
wait_for_random_bytes(), though, and add an argument to that function
for "no delay".

Because I think we should at the same time also add a warning to
wait_for_random_bytes() for the "uhhhuh, it timed out".

Right now wait_for_random_bytes() returns an error that most people
then just ignore. Including drivers/net/wireguard/cookie.c.

So instead of returning an error that nobody can do much about, how
about we move the warning code into wait_for_random_bytes()?

And make that urandom_read() call the same wait_for_random_bytes()
that random_read() calls, just with GRND_NONBLOCK as an argument?

Not a big deal. Your patch is fine by me too.

                    Linus