Re: pid ns feature request

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Andy Lutomirski (luto@amacapital.net):
> On Fri, Apr 25, 2014 at 12:37 PM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
> > Andy Lutomirski <luto@amacapital.net> writes:
> >
> >> Unless I'm missing some trick, it's currently rather painful to mount
> >> a namespace /proc.  You have to actually be in the pid namespace to
> >> mount the correct /proc instance, and you can't unmount the old /proc
> >> until you've mounted the new /proc.  This means that you have to fork
> >> into the new pid namespace before you can finish setting it up.
> >
> > Yes.  You have to be inside just about all namespaces before you can
> > finish setting them up.
> >
> > I don't know the context in which needed to be inside the pid namespace
> > is a burden.
> 
> I'm trying to sandbox myself.  I unshare everything, setup up new
> mounts, pivot_root, umount the old stuff, fork, and wait around for
> the child to finish.
> 
> This doesn't work: the parent can't mount the new /proc, and the child
> can't either because it's too late.

I'm probably not thinking it through enough...  But can't the parent, before
forking, do

	mkdir -p /childproc/proc
	mount --bind /childproc /childproc
	mount --make-rshared /childproc

then the child mounts its proc under /childproc/proc and have that show
up in the parent's tree?