linux-kernel - Re: [PATCH] random: fix locking for crng_init in crng

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Message-ID: <YgSmDtA2hlrDBmrH@owl.dominikbrodowski.net>
Date:   Thu, 10 Feb 2022 06:43:42 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Theodore Ts'o <tytso@....edu>, LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH] random: fix locking for crng_init in crng_reseed()

Hi Jason,

Am Wed, Feb 09, 2022 at 10:39:17PM +0100 schrieb Jason A. Donenfeld:
> Thanks, applied. I changed complete_init to finalize_init, to match
> our naming scheme from earlier, and I moved
> invalidate_batched_entropy() to outside the lock and after
> crng_init=2, since now it uses atomics, and it should probably be
> ordered after crng_init = 2, so the new batch gets the new entropy.

Doesn't that mean that there is a small window where crng_init == 2, but
get_random_u64/get_random_u32 still returns old data, with potentially
insufficient entropy (as obtained at a time when crng_init was still < 2)?
That's why I moved invalidate_batched_entropy() under the lock.

But with your subsequent patch, it doesn't matter any more.

Thanks,
	Dominik