linux-kernel - Re: [PATCH 1/4] kernel: add a helper to get an owning user namespace for a namespace

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Message-ID: <20160831025605.GA21788@mail.hallyn.com>
Date:   Tue, 30 Aug 2016 21:56:05 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Andrei Vagin <avagin@...nvz.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        containers@...ts.linux-foundation.org,
        Serge Hallyn <serge.hallyn@...onical.com>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/4] kernel: add a helper to get an owning user namespace
 for a namespace

On Fri, Aug 26, 2016 at 04:08:08PM -0700, Andrei Vagin wrote:
> +struct ns_common *ns_get_owner(struct ns_common *ns)
> +{
> +	struct user_namespace *my_user_ns = current_user_ns();
> +	struct user_namespace *owner, *p;
> +
> +	/* See if the owner is in the current user namespace */
> +	owner = p = ns->ops->get_owner(ns);
> +	for (;;) {
> +		if (!p)
> +			return ERR_PTR(-EPERM);
> +		if (p == my_user_ns)
> +			break;
> +		p = p->parent;
> +	}
> +
> +	return &get_user_ns(owner)->ns;

get_user_ns() bumps the owner's refcount.  I don't see where
this is being dropped, especially when ns_ioctl() uses it in
the next patch.