linux-kernel - Re: [PATCH 01/11] Security: Add hook to get full maclabel xattr name

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Date:	Fri, 29 Feb 2008 11:50:28 -0800
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	casey@...aufler-ca.com
Cc:	Christoph Hellwig <hch@...radead.org>,
	Dave Quigley <dpquigl@...ho.nsa.gov>,
	Stephen Smalley <sds@...ho.nsa.gov>, viro@....linux.org.uk,
	bfields@...ldses.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 01/11] Security: Add hook to get full maclabel xattr
	name

On Fri, 2008-02-29 at 10:52 -0800, Casey Schaufler wrote:
> So it sounds as if for an xattr protocol to be viable it would first
> require that xattr semantics be generally accepted (POSIX definition
> would suffice), that there be multiple implementations (Linux and Irix
> could suffice should Irix still be around when POSIX is done), and
> that there be a perceived need beyond that of the Lunitic Fringe
> Security Community.

The problem isn't that of supporting the naive user xattr model: we can
almost do that within the existing 'named attribute' model of NFSv4. The
problem is that of supporting the arbitrary "security metadata" that are
allowed to have side-effects on the system behaviour, and that we appear
to have thought was a good idea to overload onto the xattr interface.

In the case of maclabels, where the "side-effect" is to describe and
enable extra access control rules, then you have the potential for
setting people up with a major interoperability problem. Using a
dedicated interface for it instead of overloading a Linux-style xattr
interface allows you to limit the scope of the documentation problem
that you would otherwise have.

Trond

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