Re: [RFC PATCH 3/8] kmod - teach call_usermodehelper() to use a namespace

[Ian Kent <ikent@redhat.com>]

On Tue, 2015-02-10 at 17:55 +0100, Oleg Nesterov wrote:
> On 02/10, Ian Kent wrote:
> >
> > On Mon, 2015-02-09 at 17:03 +0100, Oleg Nesterov wrote:
> > >
> > > I understand. but I still can't understand why we can't implement something
> > > like
> > > 	enter_ns(struct nsproxy *p)
> > > 	{
> > > 		new_nsproxy = create_new_namespaces(...);
> > >
> > > 		p->mnt_ns->ns->ops->install(new_nsproxy, ...);
> > > 		p->pid_ns_for_children->ns->ops->install(new_nsproxy, ...);
> > > 		...
> > >
> > > 		switch_task_namespaces(new_nsproxy);
> > > 	}
> > >
> > > Why we should abuse fs/proc ?
> >
> > That sounds like a much better approach.
> > Your saying just take a reference to the nsproxy from the located
> > process and use it instead, right?
> 
> Yes,

I'm still not sure if this can be done (at least without surgery to the
namespace implementation) and I think I've been here before which is
what lead to the file_open_root() approach.

The difficulty is the second parameter to the install() call above, the
struct ns_common. In setns() it's obtained from the procfs file inode
and the file open is what's used to obtain each namespace type (in the
form of a struct ns_common) from a process context different from
current, current being the thread runner process.

I might still be able to work out a (viable) way to obtain the
appropriate ns_common struct in each case without a file open but it's
hard to see how.

Ian