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Date: Wed, 3 Sep 2008 17:02:15 -0500
From: "Serge E. Hallyn" <serue@us.ibm.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: ebiederm@xmission.com, akpm@linux-foundation.org, hch@infradead.org,
       viro@ZenIV.linux.org.uk, linux-fsdevel@vger.kernel.org,
       linux-kernel@vger.kernel.org
Subject: Re: unprivileged mounts git tree
Message-ID: <20080903220215.GA27705@us.ibm.com>
References: <E1JtiOX-0004Qg-1z@pomaz-ex.szeredi.hu> <20080807222751.GA28412@us.ibm.com> <m1prokgyje.fsf@frodo.ebiederm.org> <20080808002537.GA5364@us.ibm.com> <E1KXZpC-0008Ie-6w@pomaz-ex.szeredi.hu> <20080827153628.GA11242@us.ibm.com> <E1KYNMl-0000TG-Qs@pomaz-ex.szeredi.hu> <20080827184600.GA8069@us.ibm.com> <E1KaxLm-0006OD-K8@pomaz-ex.szeredi.hu>
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Quoting Miklos Szeredi (miklos@szeredi.hu):
> On Wed, 27 Aug 2008, Serge E. Hallyn wrote:
> > Ok, thanks.  I look forward to playing around with it when you publish
> > the resulting git tree  :)
> 
> A couple of centuries later...
> 
> ...here's the updated git tree:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git unprivileged-mounts
> 
> Changes since the previous version:
> 
>  - update to apply against latest git
>  - downgrade shared mounts to slave for unprivileged binds (if owners differ)
>  - don't allow unprivileged recursive binds
> 
> Serge, thanks again for testing and reviewing these patches!

Ooh.

You predicate the turning of shared mount to a slave mount on
!capable(CAP_SYS_ADMIN).  But in fact it's the mount by a privileged
user, turning the mount into a user mount, which you want to convert.
So my series of steps was:

	as root:
		(1) mount --bind /mnt /mnt
		(2) mount --make-rshared /mnt
		(3) /usr/src/mmount-0.3/mmount --bind -o user=hallyn /mnt \
			/home/hallyn/etc/mnt
	as hallyn:
		(4) mount --bind /usr /home/hallyn/etc/mnt/usr

You are turning mounts from shared->slave at step 4, but in fact we need
to do it at step 3, where we do have CAP_SYS_ADMIN.

-serge