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

[Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx>]

On 04/23/18 11:52, Holger Hoffstätte wrote:
> > I guess it could use a non-blocking read for the urandom device (or
> > getrandom() syscall) and fall back to random(), but I'm not sure if it
> > would be a good idea from the security point of view.
>
> I found in util.c that it *should* be using getrandom() already?
> Maybe the HAVE_GETRANDOM detection didn't work, but even then the
> urandom fallback should not be blocking either. I'll double-check the
> package script's autoconf log.

As I suspected..everything looking good:

$ebuild chrony-3.3.ebuild configure
 * chrony-3.3.tar.gz BLAKE2B SHA512 size ;-) ...                  [ ok ]
> > > Unpacking source...
> > > Unpacking chrony-3.3.tar.gz to /tmp/portage/net-misc/chrony-3.3/work
> > > Source unpacked in /tmp/portage/net-misc/chrony-3.3/work
> > > Preparing source in /tmp/portage/net-misc/chrony-3.3/work/chrony-3.3 ...
> > > Source prepared.
> > > Configuring source in /tmp/portage/net-misc/chrony-3.3/work/chrony-3.3 ...
 * ./configure --enable-scfilter --disable-pps --without-editline --docdir=/usr/share/doc/chrony-3.3 --chronysockdir=/run/chrony --mandir=/usr/share/man --prefix=/usr --sysconfdir=/etc/chrony --disable-sechash --without-nss --without-tomcrypt
Configuring for  Linux-x86_64
Checking for x86_64-pc-linux-gnu-gcc : Yes
Checking for 64-bit time_t : Yes
NTP time mapped to 1968-05-05T09:56:04Z/2104-06-11T16:24:20Z
Checking for math : No
Checking for math in -lm : Yes
Checking for <stdint.h> : Yes
Checking for <inttypes.h> : Yes
Checking for struct in_pktinfo : Yes
Checking for IPv6 support : Yes
Checking for struct in6_pktinfo : No
Checking for struct in6_pktinfo with _GNU_SOURCE : Yes
Checking for clock_gettime() : Yes
Checking for getaddrinfo() : Yes
Checking for pthread : Yes
Checking for arc4random_buf() : No
Checking for getrandom() : Yes
Checking for recvmmsg() : Yes
Checking for SW/HW timestamping : Yes
Checking for other timestamping options : Yes
Checking for libcap : Yes
Checking for seccomp : Yes
Checking for <linux/rtc.h> : Yes
Checking for <linux/ptp_clock.h> : Yes
Checking for sched_setscheduler() : Yes
Checking for mlockall() : Yes
Checking for readline : Yes
Features : +CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCFILTER -SIGND +ASYNCDNS +READLINE -SECHASH +IPV6 -DEBUG
Creating Makefile
Creating doc/Makefile
Creating test/unit/Makefile
> > > Source configured.

So it's probably indeed blocking in too-early getrandom() (thanks for
pointing that out!)and falling back to urandom with GRND_NONBLOCK could
work. Let me know if I can try any patches.

thanks,
Holger

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