| Re: [chrony-users] Chrony vs. Linux RNG |
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On Wed, May 16, 2018 at 08:46:56AM +0200, Christian Ehrhardt wrote:
> On Wed, May 9, 2018 at 8:50 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx>
> wrote:
> > As I understand it, this affects quite a few applications and there is
> > still some upstream discussion related to the RNG fix. Maybe it will
> > sort itself out on the kernel side.
>
>
> You seem to track that already, do you have a few pointers to the Mailing
> list archives that cover the ongoing discussion that you could share?
I don't have any pointers. I just saw it mentioned in one of the bugs
that were filed for Fedora when the kernel was updated.
https://bugzilla.redhat.com/show_bug.cgi?id=1572944
> I Must admit I'm almost tempted to prefer implementing a fallback mechanism
> in general (who knows what else than the mentioned kernel changes will
> happen and make chrony hit that again).
> Is there any argument against implementing the fallback mechanism no matter
> what comes out on the kernel side of this discussion?
One is that chronyd's start would not be deterministic. If
/dev/urandom it's not available (e.g. in a chroot), or the access is
blocked by SELinux, AppArmor, etc, chronyd would sometimes fail to
start.
The other is that falling back to a more predictable PRNG will make it
a bit easier to spoof a server reply (i.e. guess the transmit
timestamp and the UDP port number). However, we still use /dev/urandom
when getrandom() is not available, so the worst supported case will
not change.
--
Miroslav Lichvar
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