Re: [patch 0/8] unprivileged mount syscall

Miklos Szeredi
2007-04-15T20:39:40Z

> > > Agreed on desired behavior, but not on chroot sufficing. It actually
> > > sounds like you want exactly what was outlined in the OLS paper.
> > >
> > > Users still need to be in a different mounts namespace from the admin
> > > user so long as we consider the deluser and backup problems
> >
> > I don't think it matters, because /share/$USER duplicates a part or
> > the whole of the user's namespace.
> >
> > So backup would have to be taught about /share anyway, and deluser
> > operates on /home/$USER and not on /share/*, so there shouldn't be any
> > problem.
>
> In what I was thinking of, /share/$USER is bind mounted to
> ~$USER/share, so it would have to be done in a private namespace in
> order for deluser to not be tricked.

But /share/$USER is surely not bind mounted to ~$USER/share in the
_global_ namespace, is it? I can't see any sense in that.

> > There's actually very little difference between rbind+chroot, and
> > CLONE_NEWNS. In a private namespace:
> >
> > 1) when no more processes reference the namespace, the tree will be
> > disbanded
> >
> > 2) the mount tree won't be accessible from outside the namespace
>
> But it *can* be, if properly set up. That's part of the point of the
> example in the OLS paper. When a user logs in, sshd clones a new
> namespace, then bind-mounts /share/$USER into ~$USER/share. So assuming
> that /share/$USER was --make-shared'd, it and ~$USER are now in the
> same peer group, and any changes made by the user under ~$USER will
> be reflected back into /share/$USER.

I acknowledge, that it can be done. My point was that it can be done
more simply _without_ using CLONE_NS.

> > Wanting a persistent namespace contradicts 1).
>
> Not necessarily, see above.
>
> > Wanting a per-user (as opposed to per-session) namespace contradicts
> > 2). The namespace _has_ to be accessible from outside, so that a new
> > session can access/copy it.
>
> Again, I *think* you are wrong that private namespace contradicts this
> requirement.

I'm not saying there's any contradiction, I'm saying rbind+chroot is a
better fit.

I haven't yet heard a single reason why a per-session namespace with
parts shared per-user is better than just a per-user namespace.

Miklos