linux-kernel - Modifying an existing mount namespace where user_ns != mnt_ns->user

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Message-ID: <CAFLxGvxp+-gt+_dXiAR093psiySE_sD9MA-OdbNUK-AbXQn-pw@mail.gmail.com>
Date:	Sun, 28 Apr 2013 19:05:57 +0200
From:	richard -rw- weinberger <richard.weinberger@...il.com>
To:	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Modifying an existing mount namespace where user_ns != mnt_ns->user_ns

Hi!

If I create a process with CLONE_NEWNS|CLONE_NEWUSER set, how can I
modify the mount namespace later?

I thought I simply can run setns(/proc/<child>/ns/mnt) within my
privileged process which resists in the initial userns and then mount
whatever I want into the child's mount namespace.
But this fails because do_new_mount() uses current->nsproxy->mnt_ns->user_ns.

--
Thanks,
//richard
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