linux-kernel - Re: unprivileged mounts git tree

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Message-ID: <20080903220215.GA27705@us.ibm.com>
Date:	Wed, 3 Sep 2008 17:02:15 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	ebiederm@...ssion.com, akpm@...ux-foundation.org,
	hch@...radead.org, viro@...IV.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: unprivileged mounts git tree

Quoting Miklos Szeredi (miklos@...redi.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
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