linux-kernel - Re: [PATCH v2] random: tie batched entropy generation to base

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Message-ID: <CAHmME9pcFkPysTHHUCiPwqO0rv-i8X4nzNvomaSnyxbx3nauig@mail.gmail.com>
Date:   Mon, 21 Feb 2022 15:35:44 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v2] random: tie batched entropy generation to base_crng generation

On Mon, Feb 21, 2022 at 5:13 AM Eric Biggers <ebiggers@...nel.org> wrote:
> > @@ -455,7 +453,7 @@ static size_t crng_fast_load(const void *cp, size_t len)
> >               src++; crng_init_cnt++; len--; ret++;
> >       }
> >       if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
> > -             invalidate_batched_entropy();
> > +             ++base_crng.generation;
> >               crng_init = 1;
> >       }
>
> This is an existing issue, but why doesn't crng_slow_load() do this too?

Because it's called by add_device_randomness(), which is mostly
ingesting static bytes, akin to what you get by running `dmidecode`
and such. The idea is that this is something that's good to mix, but
bad to credit. I think there was a CVE a few years back about this,
precipitating the change.

Jason