Some grep implementations detect binary data and return success without
matching whole line. This might be an issue for the DHCPv6 NTP FQDN
check. The GNU grep in the C locale seems to check only for the NUL
character, which cannot be passed in an environment variable, but other
implementations might behave differently and there doesn't seem to be a
portable way to force matching the whole line.
Instead of the grep command, check for invalid characters by comparing
the length of the input passed through "tr -d -c".
Latest NetworkManager code provides NTP servers from the DHCPv6 NTP
option (RFC 5908) in the DHCP6_DHCP6_NTP_SERVERS variable to dispatcher
scripts.
Check for invalid characters (which can come from the FQDN suboption)
and include the servers in the interface-specific sources file.
Add new NM dispatcher script for NTP servers given by DHCP through
NetworkManager in a similar way to how distributions have done in
11-dhclient, e.g. [1]. New NTP servers are written as entries to a
file per-interface in /var/run/chrony-dhcp, which is re-read by
chronyd upon executing `chronyc reload sources`.
This provides a way for NTP server configuration to be carried over
from NetworkManager DHCP events to chrony, for DHCP clients other
than dhclient. Part of fixing integration where the NetworkManager
internal client is used, e.g [2].
Paths to the chronyc executable and sources directory are set in
variables, which may be overwritten by downstream packages, but
should work for distributions for the most part.
[1] https://src.fedoraproject.org/rpms/dhcp/blob/master/f/11-dhclient
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1800901
