linux-kernel - Re: [Patch 1/2] selinux: ajust rules for ATTR

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Date:	Mon, 17 Aug 2009 15:56:21 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Amerigo Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	esandeen@...hat.com, eteo@...hat.com, eparis@...hat.com,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk
Subject: Re: [Patch 1/2] selinux: ajust rules for ATTR_FORCE

On Tue, 2009-08-18 at 04:46 +0900, OGAWA Hirofumi wrote:
> Stephen Smalley <sds@...ho.nsa.gov> writes:
> 
> >> [I'm still not sure what selinux want to do. normally inode_permission()
> >> should check truncate() permission, and this FILE__SIZE checks something
> >> again...? And we want to check FILE__WRITE for ATTR_[AMC]TIME?]
> >
> > Explicit setting of mode, owner, group, or timestamps is to be checked
> > by the setattr permission, while implicit setting of timestamps or size
> > is mediated by the write permission.
> 
> E.g. mode change has implicit ATTR_CTIME change. So it meant, we should
> check the both of FILE__SETATTR and FILE__WRITE?

No, just setattr.

> > ATTR_FORCE is supposed to suppress permission checking altogether, and
> > shouldn't be mixed with multiple attribute changes if some should be
> > subject to permission checks while others should not.
> 
> I disagree. In fact, ATTR_FORCE is just used for ATTR_KILL_S[UG]ID, and
> notify_change() is disallowing the mixed ATTR_MODE and ATTR_KILL_*. I
> think it should be enough.

Ok, then we just need to adjust selinux_inode_setattr to understand that
ATTR_FORCE only means to bypass checking on ATTR_MODE.

> If ATTR_FORCE is confusable, I think we can just add new ATTR_FORCE_MODE
> or ATTR_FORCE_KILL, and replace with current ATTR_FORCE. I'm ok either
> way.  But, with this change, ATTR_FORCE has no users.

-- 
Stephen Smalley
National Security Agency

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