linux-kernel - Re: [PATCH 2/2] random: spread out jitter callback to different CPUs

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Message-ID: <Yz/VU/FhdgspxFdh@linutronix.de>
Date:   Fri, 7 Oct 2022 09:29:23 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Sultan Alsawaf <sultan@...neltoast.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH 2/2] random: spread out jitter callback to different CPUs

On 2022-10-06 09:39:46 [-0700], Sultan Alsawaf wrote:
> Hi Sebastian,
Hi Sultan,

> But since a timer is marked as not-pending prior to when it runs, add_timer_on()
> can't detect if the timer is actively running; the above BUG_ON() won't be
> tripped. So the UaF scenario I forsee is that doing this:
>     add_timer_on(timer, 0);
>     // timer is actively running on CPU0, timer is no longer pending
>     add_timer_on(timer, 1); // changes timer base, won't wait for timer to stop
>     del_timer_sync(timer); // only checks CPU1 timer base for the running timer

/me taking notes.

> Sultan

Sebastian