linux-kernel - Re: [PATCH 1/2] random: avoid init'ing twice in credit race

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Message-ID: <Yn35bNS6RlElAGYh@owl.dominikbrodowski.net>
Date:   Fri, 13 May 2022 08:23:40 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] random: avoid init'ing twice in credit race

Am Mon, May 09, 2022 at 02:14:08PM +0200 schrieb Jason A. Donenfeld:
> Since all changes of crng_init now go through credit_init_bits(), we can
> fix a long standing race in which two concurrent callers of
> credit_init_bits() have the new bit count >= some threshold, but are
> doing so with crng_init as a lower threshold, checked outside of a lock,
> resulting in crng_reseed() or similar being called twice.

Sidenote: crng_reseed() did manage quite fine if called twice in short
order.

> In order to fix this, we can use the original cmpxchg value of the bit
> count, and only change crng_init when the bit count transitions from
> below a threshold to meeting the threshold.
> 
> Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>

	Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>

Thanks,
	Dominik