To talk to ovsdb, we use the unix socket at
/var/run/openvswitch/db.sock. But that socket is owned by another user
and NetworkManager would need dac_override capability to open it.
We want to drop dac_override, but we still need to talk to ovsdb. Add a
GetFD() method to nm-sudo.
We still first try to open the socket directly. Maybe it just works.
Note that SELinux may block passing file descriptors from nm-sudo. If it
doesn't work for you, test with SELinux permissive mode and wait for an
SELinux update.
NetworkManager runs as root and has lots of capabilities.
We want to reduce the attach surface by dropping capabilities,
but there is a genuine need to do certain things.
For example, we currently require dac_override capability, to open
the unix socket of ovsdb. Most users wouldn't use OVS, so we should
find a way to not require that dac_override capability. The solution
is to have a separate, D-Bus activate service (nm-sudo), which
has the capability to open and provide the file descriptor.
For authentication, we only rely on D-Bus. We watch the name owner
of NetworkManager, and only accept requests from that service. We trust
D-Bus to get it right a request from that name owner is really coming
from NetworkManager. If we couldn't trust that, how could PolicyKit
or any authentication via D-Bus work? For testing, the user can set
NM_SUDO_NO_AUTH_FOR_TESTING=1.
https://bugzilla.redhat.com/show_bug.cgi?id=1921826
