Re: [chrony-users] Chrony vs. Linux RNG

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Sun, Apr 22, 2018 at 04:25:40PM -0700, Bill Unruh wrote:
> It def. should not do that. t sounds likesomething is using /dev/random
> instead of /dev/urandom. Nothing should use /dev/random.
> (chrony does not seem to). urandon should NOT block. I f they have altered the
> kernel so it does, that is a bug.

chronyd uses the getrandom() system call if it is available, in a mode
that can block.

According to the random(4) man page, reading from /dev/urandom never
blocks and always returns some data, but the getrandom() system call
either blocks or fails if not allowed to block when the PRNG isn't
initialized yet.

So, chronyd could fall back to reading from /dev/urandom if the
getrandom() call failed (setting the flag to not block).

-- 
Miroslav Lichvar

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