linux-kernel - Re: [PATCH 4/5] nsfs: add ioctl to get a parent namespace

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Date:	Sun, 24 Jul 2016 00:07:24 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	linux-api@...r.kernel.org, containers@...ts.linux-foundation.org,
	Alexander Viro <viro@...iv.linux.org.uk>, criu@...nvz.org,
	linux-fsdevel@...r.kernel.org,
	"Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 4/5] nsfs: add ioctl to get a parent namespace

Andrey Vagin <avagin@...nvz.org> writes:

> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index 3529a03..a63adfb 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -388,12 +388,38 @@ static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
>  	return 0;
>  }
>  
> +static struct ns_common *pidns_get_parent(struct ns_common *ns)
> +{
> +	struct pid_namespace *active = task_active_pid_ns(current);
> +	struct pid_namespace *pid_ns, *p;
> +
> +	pid_ns = to_pid_ns(ns);
> +	if (pid_ns == &init_pid_ns) {
> +		if (capable(CAP_SYS_ADMIN))
> +			return ERR_PTR(-ENOENT);
> +		return ERR_PTR(-EPERM);
> +	}
> +
> +	pid_ns = p = pid_ns->parent;
> +
> +	for (;;) {
> +		if (p == active)
> +			break;
> +		if (p == &init_pid_ns)
> +			return ERR_PTR(-EPERM);
> +		p = p->parent;
> +	}

Similarly to the user namespace issue the permission check here needs to
be:
	if (!ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)
		return ERR_PTR(-EPERM);
> +
> +	return &get_pid_ns(pid_ns)->ns;
> +}
> +
>  const struct proc_ns_operations pidns_operations = {
>  	.name		= "pid",
>  	.type		= CLONE_NEWPID,
>  	.get		= pidns_get,
>  	.put		= pidns_put,
>  	.install	= pidns_install,
> +	.get_parent	= pidns_get_parent,
>  };
>  

Eric