linux-kernel - Re: [RFC][PATCH 0/2] Correct behavior for listxattr and 'trusted' xattrs

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Date:	Wed, 03 Mar 2010 08:02:58 -0500
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	James Morris <jmorris@...ei.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>,
	Joel Becker <joel.becker@...cle.com>,
	Mark Fasheh <mfasheh@...e.com>, Alex Elder <aelder@....com>,
	Chris Mason <chris.mason@...cle.com>,
	a.gruenbacher@...puter.org
Subject: Re: [RFC][PATCH 0/2] Correct behavior for listxattr and 'trusted'
 xattrs

On Tue, 2010-03-02 at 19:01 +1100, James Morris wrote:
> I noticed that there are differences in the behavior of listxattr(2) for 
> xattrs in the trusted namespace.
> 
> Some filesystems, such as ext[234], require CAP_SYS_ADMIN for this, i.e. 
> trusted xattr names are hidden from unprivileged users.
> 
> I audited the kernel for users of the trusted xattr namespace, and found 
> the following filesystems not checking for CAP_SYS_ADMIN:
> 
>   - jffs2
>   - ocfs2
>   - btrfs
>   - xfs
> 
> I've created patches for jffs2 (tested) and ocfs2 (not tested) to add the 
> check -- see following emails. btrfs and xfs have custom listxattr 
> operations and will need a bit more work to fix.
> 
> I'm not sure what the initial intention was for the behavior, although 
> given that several major filesystems are have been fielded with the 
> CAP_SYS_ADMIN check, it seems most prudent to make this the standard 
> behavior for all filesystems, in case any users are depending on it.
> 
> Thoughts?

Should it be using has_capability_noaudit() rather than capable() so
that merely calling listxattr() on a file that happens to have trusted
xattrs does not set PF_SUPERPRIV on the task and does not trigger an
audit message?

-- 
Stephen Smalley
National Security Agency

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