This also relaxes the inode access modes a bit, in case they were set to
0600: we now set the "r" bit too, i.e. use 0644. This is beneficial
since it permits unpriv code to read the xattrs of the entrypoints
(which require read access). Note that in order to be able to connect()
to a socket inode you need write access, hence this shouldn't compromise
security in any way.
When systemd-imds is invoked as a Varlink service (via the new
systemd-imds-metrics.socket), it now acts as an io.systemd.Metrics
provider for systemd-report. It connects to systemd-imdsd over the
existing io.systemd.InstanceMetadata interface to acquire the real
data and re-exposes the detected cloud vendor plus the well-known
hostname, region, zone and public IPv4/IPv6 fields as metrics in the
io.systemd.InstanceMetadata.* namespace.
The metrics logic lives entirely on the client side
(imds-tool-metrics.c); systemd-imdsd is unchanged. Each metric is
acquired on demand with a blocking call to the daemon, benefiting from
its local cache. Fields that are unset or unsupported by the vendor are
simply omitted.
The metrics socket is statically enabled into sockets.target.wants/.
Lennart Poettering