linux-kernel - Re: [PATCH 4.16 163/196] random: fix crng

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Date:   Sat, 28 Apr 2018 09:59:25 -0500
From:   Dan Rue <dan.rue@...aro.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Jann Horn <jannh@...gle.com>, Theodore Tso <tytso@....edu>,
        Thierry Escande <thierry.escande@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>
Subject: Re: [PATCH 4.16 163/196] random: fix crng_ready() test

On Sat, Apr 28, 2018 at 08:00:03AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Apr 27, 2018 at 11:34:43AM -0500, Dan Rue wrote:
> > On Sun, Apr 22, 2018 at 03:53:03PM +0200, Greg Kroah-Hartman wrote:
> > > 4.16-stable review patch.  If anyone has any objections, please let me know.
> > > 
> > > ------------------
> > > 
> > > From: Theodore Ts'o <tytso@....edu>
> > > 
> > > commit 43838a23a05fbd13e47d750d3dfd77001536dd33 upstream.
> > > 
> > > The crng_init variable has three states:
> > > 
> > > 0: The CRNG is not initialized at all
> > > 1: The CRNG has a small amount of entropy, hopefully good enough for
> > >    early-boot, non-cryptographical use cases
> > > 2: The CRNG is fully initialized and we are sure it is safe for
> > >    cryptographic use cases.
> > > 
> > > The crng_ready() function should only return true once we are in the
> > > last state.  This addresses CVE-2018-1108.
> > > 
> > > Reported-by: Jann Horn <jannh@...gle.com>
> > > Fixes: e192be9d9a30 ("random: replace non-blocking pool...")
> > > Cc: stable@...nel.org # 4.8+
> > > Signed-off-by: Theodore Ts'o <tytso@....edu>
> > > Reviewed-by: Jann Horn <jannh@...gle.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > This patch has caused a regression on 4.16 using kselftest lib/printf.sh
> > - specifically, when it runs "/sbin/modprobe test_printf". This
> > regression has been detected on arm64 dragonboard 410c (not seen on
> > other arm64 or x86_64 devices).
> > 
> >     /sbin/modprobe test_printf
> >     [   22.725551] test_printf: hashing plain 'p' has unexpected format
> >     [   22.726031] test_printf: failed 1 out of 236 tests
> >     modprobe: ERROR: could not insert 'test_printf': Invalid argument
> > 
> > This problem has not been seen on 4.9 or 4.14 under the same
> > conditions.
> 
> Does 4.17-rc2 also fail like this?

No, but I did see it in v4.17-rc2-102-g3442097b765c, and it was fixed in
the subsequent build:

good: v4.17-rc2-64-g26ed24e429d8
bad: v4.17-rc2-102-g3442097b765c
good: v4.17-rc2-104-g69bfd470f462

I haven't investigated deeper though, and I do not see any changes to
random in those above revisions. This test passes on all the other
mainline builds, including v4.17-rc2.

> 
> You all are testing the -rc releases, right?  :)

We test every push to mainline and we test -next daily.

> 
> I think the random changes that will be in 4.17-rc3 should fix this, and
> if so, I'll suck them in here too.  But testing that would be good to
> see happen...

Waiting is fine with me.

Thanks,
Dan