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

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Message-ID: <177491.29492.qm@web36613.mail.mud.yahoo.com>
Date:	Thu, 28 Feb 2008 17:04:39 -0800 (PST)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Dave Quigley <dpquigl@...ho.nsa.gov>,
	Christoph Hellwig <hch@...radead.org>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>, casey@...aufler-ca.com,
	viro@....linux.org.uk, trond.myklebust@....uio.no,
	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

--- Dave Quigley <dpquigl@...ho.nsa.gov> wrote:

> 
> ...
> 
> I can only speak for myself but honestly I've only seen Casey act
> confrontational to this idea from the beginning.

That is simply because I don't care for your design and implementation
choices, I think they're a bad way to go, I've suggested what I
think you should do, and I'm sorry that that comes off as
confrontational but that does not change what I see as flaws in
your approach. I understand what you're trying to do and I think
it's wrong.

> There is absolutely
> nothing in here that is SELinux specific, tecnically its not even MAC
> specific.

Then why are you putting "mac" in the interface name?

> I said from the beginning that this was perhaps not the best
> name and we are willing to change it.

If you read back in the thread, that is what I suggested you do.

> There is nothing in this hook that
> wasn't in LSM before. This is almost identical functionality to what
> Adrian removed in 2.6.24. The only difference between this and
> security_inode_getsuffix is that this returns security.suffix and that
> the name is different. I don't have a SMACK box to test it on but I'm
> 99% sure that if Casey tried to use SMACK with this patch set that he
> would have labeled nfs working with SMACK.

You're very possibly right. I am not argueing from what's right for
Smack, I am argueing from what's right for the LSM. Smack is a label
based MAC LSM, like SELinux. I would expect that it would be easy for
the NFS implementation to accomodate both.

> If it doesn't work with SMACK
> right now I'm willing to help him with that and even include it in the
> patch set. But spreading FUD about how we are including SELinux specific
> code in here is just that.

Sorry, but I'm not argueing that it's SELinux specific at this point.
I'm argueing that it's specific to single label stored in an xattr
based MAC systems (a set of which both SELinux and Smack are members)
and that it is file system specific to NFS. Any of these attributes
makes it questionable as an LSM interface.

As I said before, trying to be helpful, call it security_blob_name(),
and the upcoming Discretionary Time Lock module can return NULL,
indicating that it wants to share no blob name. Or call it
security_xattr_names() and DTL can return NULL and B&L+Biba can
return "security.Bell&LaPadula security.Biba", hoping that everyone
who uses the interface accepts the blank seperation as an indication
that there are multiple xattrs involved.

I am saying that security_maclabel() is a bad choice, and I think
that as an LSM (not MAC, not xattr, not NFS) interface it should
serve the LSM, making the LSM interface better first, and being
the specific interface that a particular file system finds
convenient second.

And before we go any further, I have personally been involved in
doing labeled NFS three times, and I know where the bodies are
buried. Your approach is fine for single label stored in xattr based
MAC systems. It does not generalize worth catfish whiskers, whereas
the two other schemes I've done do so flawlessly. I am critical of
this approach only because I know that y'all can do better.

Great. Now I owe the entire labeled NFS team beer.

Thank you.

Casey Schaufler
casey@...aufler-ca.com
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