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

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Date:	Thu, 13 Dec 2007 17:01:11 +0000
From:	David Howells <dhowells@...hat.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	dhowells@...hat.com, casey@...aufler-ca.com,
	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]

Stephen Smalley <sds@...ho.nsa.gov> wrote:

> They would correspond with the operations provided by the /dev/cachefiles
> interface, at the granularity you want to support distinctions to be made.

Can this be made simpler by the fact that /dev/cachefiles has its own unique
label (cachefiles_dev_t).

> Could just be a single 'setcontext' permission if that is all you want to
> control distinctly, or could be a permission per operation.

There is only one operation that makes sense to have a permission: "set
context and begin caching".

All the other operations on a file descriptor attached to /dev/cachfiles are
necessary for there to be a managed cache at all, and given that you've
managed to open /dev/cachefiles that's sufficient access for those, I think.

> If the latter, you don't really need a label for the object, and can
> just use the supplied context/secid as the object of the permission
> check, ala:
> 	rc = avc_has_perm(tsec->sid, secid, SECCLASS_CACHEFILES,
> CACHEFILES__SETCONTEXT);

Ummm.   I was under the impression that the target SID had to be a member of
target class.

David
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