linux-kernel - Re: [RFC PATCH 3/4] kmod - add call_usermodehelper

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Message-ID: <20141127013022.GA3476@redhat.com>
Date:	Thu, 27 Nov 2014 02:30:22 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ian Kent <ikent@...hat.com>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	David Howells <dhowells@...hat.com>,
	Benjamin Coddington <bcodding@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH 3/4] kmod - add call_usermodehelper_ns() helper

I didn't have time to follow this thread today, will try tomorrow.
Perhaps this was already answered...

On 11/26, Ian Kent wrote:
>
> On Tue, 2014-11-25 at 22:52 +0100, Oleg Nesterov wrote:
> >
> > and probably we also need this for coredump helpers, we want them
> > to be per-namespace.
>
> To save me some time could you point me to some of the related code
> please. I don't normally play in that area.

See call_usermodehelper_*() in do_coredump(). This has the same problems
(and just in case, of course other problems, starting from the fact that
core_pattern is global). We need the right root to find the binary, etc.

> > > +	switch_task_namespaces(current, ns);
> >
> > This doesn't look sane because this won't switch task_active_pid_ns().
>
> I wondered about that too but I didn't design the open()/setns()

No, I don't think we should use setns() in this case...

> > And otoh. If we actually want to use the caller's mnt_ns/namespaces we
> > could simply fork/reparent a child which will do execve ?
>
> Are you saying that the user space program should be modified to do
> this?

No, no, I meant that the kernel could do this (yes, not that trivial)
on behalf of the caller's process.

Oleg.

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