linux-kernel - Re: [PATCH 12/19] CacheFiles: Permit a process's create SID to be overridden

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Date:	Mon, 20 Nov 2006 14:56:15 -0500
From:	Karl MacMillan <kmacmillan@...talrootkit.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
CC:	James Morris <jmorris@...ei.org>,
	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...l.org>,
	Andrew Morton <akpm@...l.org>, trond.myklebust@....uio.no,
	selinux@...ho.nsa.gov, linux-kernel@...r.kernel.org,
	aviro@...hat.com, steved@...hat.com
Subject: Re: [PATCH 12/19] CacheFiles: Permit a process's create SID to be
 overridden

Stephen Smalley wrote:
> On Tue, 2006-11-14 at 16:19 -0500, James Morris wrote:
>> On Tue, 14 Nov 2006, David Howells wrote:
>>
>>> +static u32 selinux_set_fscreate_secid(u32 secid)
>>> +{
>>> +	struct task_security_struct *tsec = current->security;
>>> +	u32 oldsid = tsec->create_sid;
>>> +
>>> +	tsec->create_sid = secid;
>>> +	return oldsid;
>>> +}
>> The ability to set this needs to be mediated via MAC policy.
>>
>> See selinux_setprocattr()
> 
> That's different - selinux_set_fscreate_secid() is for internal use by a
> kernel module that wishes to temporarily assume a particular fscreate
> SID, whereas selinux_setprocattr() handles userspace writes
> to /proc/self/attr nodes.  Imposing a permission check here makes no
> sense.
> 

Since that discussion last week I have been thinking about this and I 
have to say I agree with Steve. This should be a kernel only mechanism 
for impersonating another SID - controlling the setting of process 
attributes shouldn't be restricted as this will only lead to 
inconsistencies in those attributes.

Karl
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