gstfsd, the root service on each compute that rewrites a shut-off VM's
/etc/shadow and authorized_keys, did what any client on its port asked.
Now it needs GSTFSD_KEY (64 hexadecimal characters, in the unit's
/etc/default/webvirt-gstfsd) and does not start without it. Each
connection gets a new challenge; the panel signs its request for it
with HMAC-SHA256 and gstfsd checks the signature before any change, so
a request recorded on one connection is refused on another. gstfsd
signs its reply for the same challenge and the panel's nonce, and the
panel accepts only that reply.
Each compute has a gstfsd key, the host's GSTFSD_KEY: the compute forms
and the API take it and never show it, and an empty value on an edit
keeps it. The bootstrap script makes the key file once, readable by
root only; the README shows how to make it and where the panel takes
it. The traffic is still not encrypted: a remote panel's port stays
open to the panel's address only.
The compute bootstrap installs gstfsd and webvirt-gstfsd.service in one
helper and no longer installs or restarts supervisor; the README's
compute step does the same, a remote panel's bind goes into a drop-in,
and a compute moving from supervisor removes its gstfsd program.
gstfsd only listens on loopback unless GSTFSD_BIND_HOST and
GSTFSD_ALLOW_REMOTE=1 are set; add commented environment lines for both
service definitions. gstfsd.conf now ends with a newline, which matters
because dev/libvirt-bootstrap.sh appends it to /etc/supervisor.conf.
