linux-kernel - Re: unprivileged mounts git tree

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Message-ID: <20080903215443.GA25072@us.ibm.com>
Date:	Wed, 3 Sep 2008 16:54:43 -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!

Well I see where a shared mount *should* be turned into a slave mount
when bind-mounted as a user mount, but it doesn't seem to be happening.
In particular, after doing a user mount of /mnt onto
/home/hallyn/etc/mnt, /proc/self/mountinfo ends in:

22 13 3:1 /mnt /mnt rw shared:1 - ext3 /dev/root
rw,errors=continue,user_xattr,acl,data=ordered
23 13 3:1 /mnt /root/mnt rw shared:1 - ext3 /dev/root
rw,errors=continue,user_xattr,acl,data=ordered
24 13 3:1 /mnt /home/hallyn/etc/mnt rw,user=500 shared:1 - ext3
/dev/root rw,errors=continue,user_xattr,acl,data=ordered

I assume this means that /mnt and /home/hallyn/etc/mnt are peers
in peergroup 1?

And indeed if hallyn does mount --bind /usr /home/hallyn/etc/mnt/usr,
then /mnt/usr shows the contents of /usr.

I see that in do_loopback() you are adding CL_SLAVE|CL_MAKE_SHARED to
flags so I don't get what is going on.  Still looking through the code.

-serge
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