linux-kernel - Re: [PATCH 4.9 75/95] random: set up the NUMA crng instances after the CRNG is fully initialized

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Date:   Mon, 23 Apr 2018 09:21:48 +0200
From:   Salvatore Bonaccorso <carnil@...ian.org>
To:     Ben Hutchings <ben@...adent.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Theodore Tso <tytso@....edu>
Cc:     stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        stable@...nel.org
Subject: Re: [PATCH 4.9 75/95] random: set up the NUMA crng instances after
 the CRNG is fully initialized

Hi

On Sun, Apr 22, 2018 at 11:28:52PM +0100, Ben Hutchings wrote:
> On Sun, 2018-04-22 at 15:53 +0200, Greg Kroah-Hartman wrote:
> > 4.9-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Theodore Ts'o <tytso@....edu>
> > 
> > commit 8ef35c866f8862df074a49a93b0309725812dea8 upstream.
> > 
> > Until the primary_crng is fully initialized, don't initialize the NUMA
> > crng nodes.  Otherwise users of /dev/urandom on NUMA systems before
> > the CRNG is fully initialized can get very bad quality randomness.  Of
> > course everyone should move to getrandom(2) where this won't be an
> > issue, but there's a lot of legacy code out there.  This related to
> > CVE-2018-1108.
> > 
> > Reported-by: Jann Horn <jannh@...gle.com>
> > Fixes: 1e7f583af67b ("random: make /dev/urandom scalable for silly...")
> > Cc: stable@...nel.org # 4.8+
> > Signed-off-by: Theodore Ts'o <tytso@....edu>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> In 4.9 (and probably older branches too) this leads to a deadlock:
> 
> crng_reseed(primary_crng, ...) takes primary_crng.lock
> -> numa_rcng_init()
>    -> crng_initialize()
>       -> get_random_bytes()
>          -> extract_crng()
>             -> _extract_crng(primary_crng, ...) tries to take primary_crng.lock
> 
> I think this can be fixed by backporting commit 4a072c71f49b
> "random: silence compiler warnings and fix race" but I'm not sure
> whether that depends on other changes.

That is, the following test patch on top of the 4.9-stable review
queue seem to resolve the issue. The commit message of the original
commit 4a072c71f49b0a0e495ea13423bdb850da73c58c would though not match
anymore.

Regards,
Salvatore

View attachment "random-silence-compiler-warnings-and-fix-race.patch" of type "text/x-diff" (2442 bytes)