linux-kernel - Re: [RFC] Should writes to /dev/urandom immediately affect reads?

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Date:   Wed, 20 Sep 2023 13:32:29 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        "Theodore Ts'o" <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [RFC] Should writes to /dev/urandom immediately affect reads?

On Wed, 20 Sept 2023 at 13:21, Eric Biggers <ebiggers@...nel.org> wrote:
>
> It seems that what you're claiming (in addition to the RNG always being
> initialized quickly on platforms that are "relevant", whatever that means) is
> that once the RNG is "initialized", there's no need to reseed it anymore.

No. You are literally putting words in my mouth that I at no point
even implied. You're making up an argument.

I *LITERALLY* am asking a very simple question: WHO DO YOU EVEN CARE
ABOUT THIS "IMMEDIATE" EFFECT.

Give me a real reason. Give me *any* reason.

Don't try to turn this into some other discussion. I'm asking WHY DOES
ANY OF THIS MATTER?

The immediacy has changed several times, as you yourself lined up. And
as far as I can tell, none of this matter in the least.

> The question is, given that, shouldn't the RNG also reseed right
> away when userspace explicitly adds something to it

I don't see that there is any "given" at all.

We do re-seed regularly. I'm not arguing against that.

I'm literally arguing against applying random changes without giving
any actual reason for them.

Which is why I'm asking "why do you care"? Give em a *reason*. Why
would a user space write matter at all?

It was why I also asked about entropy. Because *if* you argue that the
user-space write contains entropy, then that would be a reason.

You didn't.

You argue that the current behavior hasn't been the universal behavior. I agree.

But considering that we've switched behaviors apparently at least
three times, and at no point did it make any difference, my argument
is really that without a *REASON*, why would we switch behavior *four*
times?

Is it just "four changes is better than three"?

             Linus