Re: Sandbox thoughts

[Alexander Larsson <alexl redhat com>]

On fre, 2015-02-20 at 17:05 -0800, Andy Lutomirski wrote:
> On Fri, Feb 20, 2015 at 4:43 PM, Andy Lutomirski <luto amacapital net> wrote:
> > On Fri, Feb 20, 2015 at 4:31 PM, Eric W. Biederman
> > <ebiederm xmission com> wrote:
> > > Andy Lutomirski <luto amacapital net> writes:
> > >
> > > > On Thu, Feb 19, 2015 at 8:38 AM, Alexander Larsson <alexl redhat com> wrote:
> > > > > On Tue, 2015-02-17 at 13:23 -0800, Andy Lutomirski wrote:
> > > > >
> > > > > >  - setuid / privileged helper.  Why do you need a privileged helper?
> > > > > > You should be able to do all of this using user namespaces.  The
> > > > > > Sandstorm code linked above does exactly this.
> > > > >
> > > > > I tried this a bit, but i ran into two snags i don't understand.
> > > > >
> > > > > First of all, as uid/gid 1000 i can put "1000 1000 1"
> > > > > in /proc/self/uid_map from the child. However, i cannot put "1000 1000
> > > > > 1" into gid_map, as i get EPERM.
> > > > > I don't understand this, is this not supposed to work?
> > > >
> > > > You need newer manpages :-/  Try the attached variant.
> > >
> > > Yeah.  You need to disable setgroups for that to work.
> > >
> > > > > Secondly, i'm failing to mount another instance of devpts. It fails with
> > > > > EINVAL.
> > > >
> > > > Hmm.  Off the top of my head, there's no good reason that devpts with
> > > > the newinstance option couldn't be allowed in a userns.  Eric, any
> > > > thoughts here?  The patch would be straightforward.
> > >
> > > Looking at the code you have to have uid 0 and gid 0 mapped and you have
> > > to specify newinstance.  But devepts is mountable without being the
> > > global root user.'
> >
> > Wow, my grepping skills are nonexistent today.
> >
> > > The restriction of having uid 0 and gid 0 mapped is just that /dev/ptmx is
> > > and has alwasy been owned by root and so mknod_ptmx just won't let you
> > > create a device inode as with a uid or gid you can't map.
> >
> > All we'd have to do is to add ptmx_uid and ptmx_gid options, right?
> > I'll send a patch.
>
> With the patch I just sent out, the attached version of the test code works.

Hmm, i also want to have /sys readonly in the container. For things like
OpenGL to work (it needs to look at the pci tables to see what driver to
load). This seems to be problematic, I keep getting EPERM when i try to
mount my own copy of it.

I am able to do a bind mount of the system one, *if* i pass in MS_REC
(which is not necessarily what i want), but I then later fail when
trying to remount it read-only.

Any idea here?

-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Alexander Larsson                                            Red Hat, Inc 
       alexl redhat com            alexander larsson gmail com 
He's a globe-trotting hunchbacked filmmaker plagued by the memory of his 
family's brutal murder. She's a radical thirtysomething opera singer who 
dreams of becoming Elvis. They fight crime!