[systemd-devel] [PATCH 1/2] Add detect_userns to detect uid/gid shifts

Lennart Poettering lennart at poettering.net
Fri Jan 9 07:05:09 PST 2015


On Fri, 09.01.15 01:16, Tom Gundersen (teg at jklm.no) wrote:

> On Fri, Jan 9, 2015 at 12:55 AM, St├ęphane Graber <stgraber at ubuntu.com> wrote:
> > I expect we'll run into some more problems when dealing with units that
> > start with their own view of /dev since mknod in a userns isn't allowed
> > but I haven't run into one of those yet so it's not very high on my list.
> >
> > Once that happens, I expect we can solve it either by again just
> > ignoring the failure or by catching the failure and falling back to
> > doing a bind-mount of the device in question from the parent /dev (which
> > works fine in a userns and is what we do today for nested containers
> > with LXC).
> 
> Ignoring the failure as in starting services with an empty /dev sounds
> like it won't work. Also, just using the parent dev despite explicitly
> being asked not to sounds dangerous (most of the time there won't be
> much interesting stuff in /dev in a container, but that is not
> guaranteed).

Well, I think it's OK to gracefully skip the extra namespacing
PrivateDevices=, PrivateTmp= and so on do if we lack the privs for
it. I mean, these options are for limiting attack surface to a
minimum. But if you run in a CAP_SYS_ADMIN-less or even userns-enabled
container, then your attack surfaces is kinda already smaller than
what PrivateDevices=, PrivateTmp= and so on would provide, hence we
should be OK.

Lennart

-- 
Lennart Poettering, Red Hat


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