linux-kernel - Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and introduce getrandom2()

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Message-ID: <20190920131309.GB16111@mit.edu>
Date:   Fri, 20 Sep 2019 09:13:09 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Ahmed S. Darwish" <darwish.07@...il.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        lkml <linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org,
        linux-man@...r.kernel.org
Subject: Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and
 introduce getrandom2()

On Thu, Sep 19, 2019 at 08:50:15AM -0700, Linus Torvalds wrote:
> .. btw, instead of bad workarounds for a theoretical attack, here's
> something that should add actual *practical* real value: use the time
> of day (whether from an RTC device, or from ntp) to add noise to the
> random pool.

Actally, we used to seed the pool from the RTC device --- that was the
case in the 3.4 kernel referenced by the Blackhat attack, and it
didn't stop the researchers.  In later kernels, we moved up when
rand_initialized() got called to before time_init(), so
init_std_data() was no longer seeding the pool from the RTC clock.

That being said, adding calls to add_device_randomness() to
do_settimeofday64() and timekeeping_inject_offset() is an obviously
good thing to do.  I'll prepare a separate patch for the random.git
tree to do that.

					- Ted