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From: Justin Forbes <jmforbes@linuxtx.org>
To: Jeremy Cline <jeremy@jcline.org>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>,
	Sultan Alsawaf <sultanxda@gmail.com>, Pavel Machek <pavel@ucw.cz>,
	LKML <linux-kernel@vger.kernel.org>, Jann Horn <jannh@google.com>
Subject: Re: Linux messages full of `random: get_random_u32 called from`
Date: Tue, 1 May 2018 06:52:47 -0500	[thread overview]
Message-ID: <CAFxkdAogN0S9vgQhKoO+Zpp07bXveDQYPLvwjULoTRv3Or83qQ@mail.gmail.com> (raw)
In-Reply-To: <01000163186628e6-3fe4abfc-eaaf-470c-90c8-2d8ad91db8f1-000000@email.amazonses.com>

On Mon, Apr 30, 2018 at 4:12 PM, Jeremy Cline <jeremy@jcline.org> wrote:
> On 04/29/2018 06:05 PM, Theodore Y. Ts'o wrote:
>> On Sun, Apr 29, 2018 at 01:20:33PM -0700, Sultan Alsawaf wrote:
>>> On Sun, Apr 29, 2018 at 08:41:01PM +0200, Pavel Machek wrote:
>>>> Umm. No. https://www.youtube.com/watch?v=xneBjc8z0DE
>>>
>>> Okay, but /dev/urandom isn't a solution to this problem because it isn't usable
>>> until crng init is complete, so it suffers from the same init lag as
>>> /dev/random.
>>
>> It's more accurate to say that using /dev/urandom is no worse than
>> before (from a few years ago).  There are, alas, plenty of
>> distributions and user space application programmers that basically
>> got lazy using /dev/urandom, and assumed that there would be plenty of
>> entropy during early system startup.
>>
>> When they switched over the getrandom(2), the most egregious examples
>> of this caused pain (and they got fixed), but due to a bug in
>> drivers/char/random.c, if getrandom(2) was called after the entropy
>> pool was "half initialized", it would not block, but proceed.
>>
>> Is that exploitable?  Well, Jann and I didn't find an _obvious_ way to
>> exploit the short coming, which is this wasn't treated like an
>> emergency situation ala the embarassing situation we had five years
>> ago[1].
>>
>> [1] https://factorable.net/paper.html
>>
>> However, it was enough to make us be uncomfortable, which is why I
>> pushed the changes that I did.  At least on the devices we had at
>> hand, using the distributions that we typically use, the impact seemed
>> minimal.  Unfortuantely, there is no way to know for sure without
>> rolling out change and seeing who screams.  In the ideal world,
>> software would not require cryptographic randomness immediately after
>> boot, before the user logs in.  And ***really***, as in [1], softwaret
>> should not be generating long-term public keys that are essential to
>> the security of the box a few seconds immediately after the device is
>> first unboxed and plugged in.i
>>
>> What would be useful is if people gave reports that listed exactly
>> what laptop and distributions they are using.  Just "a high spec x86
>> laptop" isn't terribly useful, because *my* brand-new Dell XPS 13
>> running Debian testing is working just fine.  The year, model, make,
>> and CPU type plus what distribution (and distro version number) you
>> are running is useful, so I can assess how wide spread the unhappiness
>> is going to be, and what mitigation steps make sense.
>
> Fedora has started seeing some bug reports on this for Fedora 27[0] and
> I've asked reporters to include their hardware details.
>
> [0] https://bugzilla.redhat.com/show_bug.cgi?id=1572944
>

We have also had reports that Fedora users are seeing this on Google
Compute Engine.

Justin

  reply	other threads:[~2018-05-01 11:52 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-26  4:11 Sultan Alsawaf
2018-04-26  5:00 ` Theodore Y. Ts'o
2018-04-26  5:05   ` Sultan Alsawaf
2018-04-26  7:32     ` Theodore Y. Ts'o
2018-04-26 15:17       ` Sultan Alsawaf
2018-04-26 19:25         ` Theodore Y. Ts'o
2018-04-26 20:22           ` Sultan Alsawaf
2018-04-26 20:47             ` Christian Brauner
2018-04-27  0:00               ` Theodore Y. Ts'o
2018-04-27 15:38                 ` Jason A. Donenfeld
2018-04-27 19:14                   ` Theodore Y. Ts'o
2018-04-26 23:56             ` Theodore Y. Ts'o
2018-04-27  5:20               ` Sultan Alsawaf
2018-04-27 20:10                 ` Theodore Y. Ts'o
2018-04-27 22:59                   ` Sultan Alsawaf
2018-04-29 14:32                   ` Pavel Machek
2018-04-29 17:05                     ` Sultan Alsawaf
2018-04-29 18:41                       ` Pavel Machek
2018-04-29 20:20                         ` Sultan Alsawaf
2018-04-29 21:18                           ` Pavel Machek
2018-04-29 21:34                             ` Sultan Alsawaf
2018-04-29 22:05                           ` Theodore Y. Ts'o
2018-04-29 22:26                             ` Sultan Alsawaf
2018-04-29 22:43                               ` Jason A. Donenfeld
2018-04-29 22:49                                 ` Sultan Alsawaf
2018-04-30  0:11                                   ` Theodore Y. Ts'o
2018-04-30  4:34                                     ` Sultan Alsawaf
2018-04-30 16:11                                       ` Theodore Y. Ts'o
2018-05-01 19:53                                         ` Pavel Machek
2018-04-29 22:43                             ` Pavel Machek
2018-04-30  0:32                             ` Laura Abbott
2018-04-30 21:12                             ` Jeremy Cline
2018-05-01 11:52                               ` Justin Forbes [this message]
2018-05-01 12:55                                 ` Theodore Y. Ts'o
2018-05-01 22:35                                   ` Justin Forbes
2018-05-02  0:02                                     ` Theodore Y. Ts'o
2018-05-02 12:09                                       ` Justin Forbes
2018-05-02 16:26                                         ` Theodore Y. Ts'o
2018-05-02 17:49                                           ` Laura Abbott
2018-05-02 22:25                                             ` Theodore Y. Ts'o
2018-05-03  6:19                                               ` Pavel Machek
2018-05-03 12:23                                               ` Justin Forbes
2018-05-02  0:43                                     ` Sultan Alsawaf
2018-05-02  0:56                                       ` Theodore Y. Ts'o
2018-05-02  1:11                                         ` Sultan Alsawaf
2018-04-29 18:30                   ` Sultan Alsawaf
2018-04-29 20:08                     ` Theodore Y. Ts'o
2018-05-18  1:27                   ` Trent Piepho
2018-05-18  2:32                     ` Theodore Y. Ts'o
2018-05-18 22:56                       ` Trent Piepho
2018-05-18 23:22                         ` Theodore Y. Ts'o
2018-05-21 18:39                           ` Trent Piepho
2018-04-29 14:29               ` Pavel Machek
  -- strict thread matches above, loose matches on Subject: below --
2018-04-24 11:48 Paul Menzel
2018-04-24 13:56 ` Theodore Y. Ts'o
2018-04-24 14:30   ` Paul Menzel
2018-04-24 15:49   ` Theodore Y. Ts'o
2018-04-24 15:56     ` Paul Menzel
2018-04-25  7:41       ` Theodore Y. Ts'o
2018-04-26  3:48         ` Paul Menzel
2018-04-29 14:22           ` Pavel Machek
2018-04-29 23:02   ` Dave Jones
2018-04-29 23:07     ` Dave Jones
2018-04-30  0:21       ` Theodore Y. Ts'o
2018-04-26  5:51 ` Pavel Machek

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