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

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Message-ID: <20141125215248.GA7958@redhat.com>
Date:	Tue, 25 Nov 2014 22:52:48 +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

Let me first apologize, I didn't actually read this series yet.

But I have to admit that so far I do not like this approach...
probably I am biased.

On 11/25, Ian Kent wrote:
>
> The call_usermodehelper() function executes all binaries in the
> global "init" root context. This doesn't allow a binary to be run
> within the callers namespace (aka. a container).

Please see below.

> Both containerized NFS client and NFS server need the ability to
> execute a binary within their container. To do this create a new
> nsproxy within the callers' context so it can be used for setup
> prior to calling do_execve() from the user mode helper thread
> runner.

and probably we also need this for coredump helpers, we want them
to be per-namespace.

> +static int umh_set_ns(struct subprocess_info *info, struct cred *new)
> +{
> +	struct nsproxy *ns = info->data;
> +
> +	mntns_setfs(ns->mnt_ns);

Firstly, it is not clear to me if we should use the caller's ->mnt_ns.
Let me remind about the coredump. The dumping task can cloned with
CLONE_NEWNS or it cam do unshare(NEWNS)... but OK, I do not understand
this enough.

> +	switch_task_namespaces(current, ns);

This doesn't look sane because this won't switch task_active_pid_ns().

And this reminds me another discussion, please look at
http://marc.info/?l=linux-kernel&m=138479570926192

Once again, this is just an idea to provoke more discussion. I am starting
to think that perhaps we need pid_ns->umh_helper (init by default). And
PR_SET_NS_UMH_HELPER.

Not sure.

Oleg.

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