linux-kernel - Re: [PATCH -mm 5/7] add user namespace

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Date:	Sat, 15 Jul 2006 17:29:25 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Kyle Moffett <mrmacman_g4@....com>,
	Dave Hansen <haveblue@...ibm.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Cedric Le Goater <clg@...ibm.com>,
	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	Kirill Korotaev <dev@...nvz.org>, Andrey Savochkin <saw@...ru>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Sam Vilain <sam.vilain@...alyst.net.nz>
Subject: Re: [PATCH -mm 5/7] add user namespace

Trond Myklebust <trond.myklebust@....uio.no> writes:

> On Sat, 2006-07-15 at 06:35 -0600, Eric W. Biederman wrote:
>> I hope the confusion has passed for Trond.  My impression was he
>> figured this was per process data so it didn't make sense any where
>> near a filesystem, and the superblock was the last place it should
>> be.
>
> You are still using the wrong abstraction. Data that is not global to
> the entire machine has absolutely _no_ place being put into the
> superblock. It doesn't matter if it is process-specific,
> container-specific or whatever-else-specific, it will still be vetoed.

Sure, I have no problem with only global data, and filesystem specific
data being in a super block.  In this case my impression is that the
data is at least arguably filesystem specific.  filesystem-specific
data is ok on the super block is it not?

> If your real problem is uid/gid mapping on top of generic filesystems,
> then have you looked into the *BSD solution of using a stackable
> filesystem (i.e. umapfs)?

I haven't and it sounds reasonable to look at.  As far as I know BSDs
don't have my specific problem.  uid mapping is simply a tool for
dealing with the problem, not the problem itself.  A stackable
filesystem is a reasonable alternative to using security keys to
do the mapping.

My real problem is that there is a good case for uids that are not
global to a machine.  The discussion is simply how do you cope with
that.

Now I do believe that there is a good case for uids being global to a
filesystem and all I was really talking about was a tag that marked
which parts of the entire system that used the same uids as the
filesystem.

Eric
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