Subject: Re: [PATCH 3/7] SLIM main patch
From: David Safford <safford@watson.ibm.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Serge E Hallyn <sergeh@us.ibm.com>, kjhall@us.ibm.com,
       Benjamin LaHaise <bcrl@kvack.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       LSM ML <linux-security-module@vger.kernel.org>,
       David Safford <safford@us.ibm.com>, Mimi Zohar <zohar@us.ibm.com>
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Date: Thu, 24 Aug 2006 13:34:09 -0400
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On Thu, 2006-08-24 at 18:05 +0100, Alan Cox wrote:
> It is a matter of the timing and the device. You need to do revocation
> at the device level because your security state change must occur after
> the devices have all been dealt with. This is why I said you need the
> core of revoke() to do this.

In a typical system, most applications are started at the correct level,
and we don't have to demote/promote them. In those cases where demotion
or promotion are needed, only a small number actually already have
access that needs to be revoked. Of those, most involve shmem, which
I believe we are revoking safely, as we don't have the same problems
with drivers and incomplete I/O. In the remaining cases, where we really
can't revoke safely, we could simply not allow the requested access, and
not demote/promote the process.

I think this would give us a useful balance of allowing "safe" demotion
or promotions, while not requiring general revocation. Does this sound
like a reasonable approach?

dave

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