[lxc-users] is starting unprivileged containers as root as secure as running them as any other user?

[Serge Hallyn]

Quoting Carlos Alberto Lopez Perez (clopez at igalia.com):
> On 08/01/16 19:58, Serge Hallyn wrote:
> > Quoting Carlos Alberto Lopez Perez (clopez at igalia.com):
> >> Hi,
> >>
> >>
> >> Suppose that we create an unprivileged container as root (using the
> >> download template or manually converting it with uidmapshift).
> >>
> >> Such container config will contain (for example) the following maps:
> >>
> >> lxc.id_map = u 0 100000 65536
> >> lxc.id_map = g 0 100000 65536
> >>
> >> And root would be also allowed to use them:
> >>
> >> $ usermod --add-subuids 100000-165536 root
> >> $ usermod --add-subgids 100000-165536 root
> >>
> >>
> >> My question is....
> >>
> >> From a security point of view, does creating and starting an
> >> unprivileged container as root make any difference than doing it as any
> >> other user of the host?
> > 
> > Yes.
> > 
> > For example, if you'll then be running lxc-attach as root instead of as
> > an unpriv user, then any attacks from inside the container against lxc-attach
> > will attack the root user.
> > 
> 
> Is this the only difference from a security point of view?
> Suppose that I don't use lxc-attach, but lxc-console or login via ssh.

The monitor (look for "[lxc monitor]" in process listing) runs with your
uid.  So if there were a way for the container to make the lxc monitor
execute code, it would be privilege escalation.