timesyncd mangles reported IPv6 address of NTP server

[bjh21]

systemd version the issue has been seen with

239-13

Used distribution

Debian testing

Expected behaviour you didn't see

timedatectl timesync-status should display IPv6 address of NTP server.

Unexpected behaviour you saw

timedatectl timesync-status displays an IPv6 address that isn't the address of the NTP server.

Steps to reproduce the problem

1: Configure timesyncd to use an IPv6-capable NTP server. For instance, in /etc/systemd/timesyncd.conf write:

[Time]
NTP=sntp.cam.ac.uk

2: Start or restart systemd-timesyncd:

wraith:~# systemctl restart systemd-timesyncd

3: Check that this has worked:

wraith:~# systemctl status systemd-timesyncd | grep Status
   Status: "Synchronized to time server [2001:630:212:8::123:20]:123 (sntp.cam.ac.uk)."

4: Ask timedatectl what it thinks the server IP address is:

wraith:~# timedatectl timesync-status | head -1
       Server: ::2001:630:212:8:0:0 (sntp.cam.ac.uk)
wraith:~# timedatectl show-timesync | grep ^ServerAddress=
ServerAddress=::2001:630:212:8:0:0

Note that the address shown by timedatectl is different from the one reported in the journal by systemd-timesyncd, but appears to be the correct one shifted right by 32 bits:

right: 2001:0630:0212:0008:0000:0000:0123:0020
wrong: 0000:0000:2001:0630:0212:0008:0000:0000

NB: I have only tested this against the Debian version of systemd: I haven't attempted to rebuild systemd from upstream sources. I originally reported the problem to Debian, but a Debian developer suggested that I should report it upstream.

[bjh21]

It looks like the problem is on the timesyncd side:

bjh21@fugloy:~ $ gdbus call --system --dest org.freedesktop.timesync1 --object-path /org/freedesktop/timesync1 --method org.freedesktop.DBus.Properties.Get org.freedesktop.timesync1.Manager ServerAddress
(<(10, [byte 0x00, 0x00, 0x00, 0x00, 0x20, 0x01, 0x06, 0x30, 0x02, 0x12, 0x00, 0x08, 0x00, 0x00, 0x00, 0x00])>,)

[poettering]

Fix waiting in #11186