linux-kernel - Re: [PATCH 08/28] SECURITY: Allow kernel services to override LSM settings for task actions [try #2]

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Date:	Wed, 12 Dec 2007 22:29:55 +0000
From:	David Howells <dhowells@...hat.com>
To:	casey@...aufler-ca.com
Cc:	dhowells@...hat.com, Stephen Smalley <sds@...ho.nsa.gov>,
	Karl MacMillan <kmacmill@...hat.com>, viro@....linux.org.uk,
	hch@...radead.org, Trond.Myklebust@...app.com,
	linux-kernel@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 08/28] SECURITY: Allow kernel services to override LSM settings for task actions [try #2]

Casey Schaufler <casey@...aufler-ca.com> wrote:

> Yes, but we're talking about writing the configuration information
> to the kernel, not actually making any access checks with it. I
> think. What I think we're talking about (and please correct me David
> if I've stepped into the wrong theatre) is getting the magic
> secctx that cachefiles will use instead of the secctx that the task
> would have otherwise. I don't think we're talking about recomputing
> it on every access, I think David is looking for the blunderbuss
> secctx that he can use any time he needs one.

Indeed.

The way I do it is:

 (1) The daemon opens /dev/cachefiles to being an instance of a cache.

 (2) The daemon negotiates a security context for the module to use.

 (3) The security context is place in a task_security structure.

 (4) This task_security struct is attached temporarily to task->act_as each
     time any task attempts to access the cache through the module.

 (5) The task_security struct is discarded when the file descriptor that was
     created in (1) is closed and the cache is withdrawn at the same time.

David
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