Comment 0 for bug 1879231

I've been working on snapping an app (shairport-sync) that uses Avahi. Currently on startup it's logging the following in the system logs, and is not showing up in avahi-browse:

type=USER_AVC msg=audit(1589774287.950:1675435): pid=1759 uid=102 auid=4294967295 ses=4294967295 msg='apparmor="DENIED" operation="dbus_method_call" bus="system" path="/" interface="org.freedesktop.DBus.Peer" member="Ping" mask="send" name="org.freedesktop.Avahi" pid=3965241 label="snap.shairport-sync.shairport-sync" peer_pid=2184133 peer_label="avahi-daemon" exe="/usr/bin/dbus-daemon" sauid=102 hostname=? addr=? terminal=?'

I see the following in avahi_observe.go:

        dbus (receive)
            bus=system
            path=/
            interface=org.freedesktop.DBus.Peer
            member=Ping
            peer=(label=###PLUG_SECURITY_TAGS###),

Other rules seem to be of this form:

            peer=(name=org.freedesktop.Avahi,label=###SLOT_SECURITY_TAGS###),

and as you can see above the denied message has name="org.freedesktop.Avahi".

As an experiment I reinstalled my snap in devmode and got the following:

type=USER_AVC msg=audit(1589775249.321:1676149): pid=1759 uid=102 auid=4294967295 ses=4294967295 msg='apparmor="ALLOWED" operation="dbus_method_call" bus="system" path="/" interface="org.freedesktop.DBus.Peer" member="Ping" mask="send" name="org.freedesktop.Avahi" pid=3988011 label="snap.shairport-sync.shairport-sync" peer_pid=2184133 peer_label="avahi-daemon" exe="/usr/bin/dbus-daemon" sauid=102 hostname=? addr=? terminal=?'

followed by lots of other happy-looking messages, e.g.:

type=USER_AVC msg=audit(1589775249.321:1676150): pid=1759 uid=102 auid=4294967295 ses=4294967295 msg='apparmor="ALLOWED" operation="dbus_method_call" bus="system" path="/" interface="org.freedesktop.Avahi.Server" member="GetAPIVersion" mask="send" name="org.freedesktop.Avahi" pid=3988011 label="snap.shairport-sync.shairport-sync" peer_pid=2184133 peer_label="avahi-daemon" exe="/usr/bin/dbus-daemon" sauid=102 hostname=? addr=? terminal=?'

and my machine appeared in avahi-browse and was visible to my other mDNS devices.

Given all this I suspect the rule for Ping above is too restrictive and should be loosened to allow the denied message above.

For reference, here's the full devmode trace: https://pastebin.canonical.com/p/PmMNQF3S3g/