linux-kernel - Re: Linux messages full of `random: get_random

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Message-ID: <20180502011111.m2jtl7tvdq3h3nhc@sultan-box>
Date:   Tue, 1 May 2018 18:11:11 -0700
From:   Sultan Alsawaf <sultanxda@...il.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        Justin Forbes <jmforbes@...uxtx.org>,
        Jeremy Cline <jeremy@...ine.org>, Pavel Machek <pavel@....cz>,
        LKML <linux-kernel@...r.kernel.org>, Jann Horn <jannh@...gle.com>
Subject: Re: Linux messages full of `random: get_random_u32 called from`

On Tue, May 01, 2018 at 08:56:04PM -0400, Theodore Y. Ts'o wrote:
> On Tue, May 01, 2018 at 05:43:17PM -0700, Sultan Alsawaf wrote:
> > 
> > I've attached what I think is a reasonable stopgap solution until this is
> > actually fixed. If you're willing to revert the CVE-2018-1108 patches
> > completely, then I don't think you'll mind using this patch in the meantime.
> 
> I would put it slightly differently; reverting the CVE-2018-1108
> patches is less dangerous than what you are proposing in your attached
> patch.
> 
> Again, I think the right answer is to fix userspace to not require
> cryptographic grade entropy during early system startup, and for
> people to *think* about what they are doing.  I've looked at the
> systemd's use of hmac in journal-authenticate, and as near as I can
> tell, there isn't any kind of explanation about why it was necessary,
> or what threat it was trying to protect against.
> 
> 						- Ted

Why is /dev/urandom so much more dangerous than /dev/random? The
more I search, the more I see that many sources consider /dev/urandom
to be cryptographically secure... and since I hold down a single key on
the keyboard to make my computer boot without any kernel workarounds,
I'm sure the NSA would eventually notice my predictable behavior and get
their hands on my Richard Stallman photos.

Fixing all the "broken" userspace instances of entropy usage during early
system startup is a tall order. What about barebone machines used as
remote servers? I feel like just "fixing userspace" isn't going to cover
all of the usecases that the CVE-2018-1108 patches broke.

Sultan