linux-kernel - Re: Detecting if you are running in a container

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Message-ID: <20111012190452.GA23845@fieldses.org>
Date:	Wed, 12 Oct 2011 15:04:52 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Kyle Moffett <kyle@...fetthome.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Theodore Tso <tytso@....edu>,
	Matt Helsley <matthltc@...ibm.com>,
	Lennart Poettering <mzxreary@...inter.de>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, harald@...hat.com, david@...ar.dk,
	greg@...ah.com, Linux Containers <containers@...ts.osdl.org>,
	Linux Containers <lxc-devel@...ts.sourceforge.net>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	Paul Menage <paul@...lmenage.org>
Subject: Re: Detecting if you are running in a container

On Wed, Oct 12, 2011 at 02:25:04PM -0400, Kyle Moffett wrote:
> On Wed, Oct 12, 2011 at 13:57, J. Bruce Fields <bfields@...ldses.org> wrote:
> > On Tue, Oct 11, 2011 at 02:16:24PM -0700, Eric W. Biederman wrote:
> >> Where all of this winds up interesting in the field of oncoming kernel
> >> work is that uids are persistent and are stored in file systems.  So
> >> once we have all of the permission checks in the kernel tweaked to care
> >> about user namespaces we next look at the filesystems.   The easy
> >> initial implementation is going to be just associating a user namespace
> >> with a super block.  But farther out being able to store uids from
> >> different user namespaces on the same filesystem becomes an interesting
> >> problem.
> >
> > Yipes.  Why would anyone want to do that?
> 
> Consider an NFS file server providing collaborative access to multiple
> independently managed domains (EG: several different universities),
> each with their own LDAP userid database and Kerberos services.
> 
> The common server is in its own realm and allows cross-realm
> authentication to the other university realms, using the origin realm
> to decide what namespace to map each user into.
> 
> If you are just doing read-only operations then you don't need any
> kind of namespace persistence on the NFS server's storage.  On the
> other hand, if you want to allow users to collaborate and create ACLs
> then you need something dramatically more involved.

Yeah, OK, I suppose I'd imagined mapping into the server's id space
somehow for that case, but I suppose this would be cleaner.  Still,
seems like a big pain....

> On the wire, the kerberos server would simply identify each NFSv4 ACL
> entry with a particular realm ID, but in the backend it would need
> some filesystem-level disambiguation (possibly the recently-proposed
> RichACL features?)

That doesn't help with owner and group.

--b.
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