linux-kernel - Re: Upstream first policy

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Message-ID: <20100309001554.GP30031@ZenIV.linux.org.uk>
Date:	Tue, 9 Mar 2010 00:15:54 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>, James Morris <jmorris@...ei.org>,
	linux-kernel@...r.kernel.org, Kyle McMartin <kyle@...artin.ca>,
	Alexander Viro <viro@....linux.org.uk>
Subject: Re: Upstream first policy

On Mon, Mar 08, 2010 at 03:37:38PM -0800, Linus Torvalds wrote:

> Of course, you can make /etc unwritable, and that is indeed the 
> traditional UNIX model of handling namespace security: by just 
> implementing it as "content security" of the directory.
> 
> The sgid and sticky bits can be used to further try to make it more 
> fine-grained (exactly becuase it is _not_ sufficient to say "you can't 
> read or write this directory" on a whole-directory basis), and obviously 
> SELinux has extensions of its own too.

But that's not what the apparmor et.al. are doing.  If you want (and that's
not obviously a good thing) fine-grained access control for directory
entries, it would at least make some sense.  Prohibitively pricy, probably,
but that's a separate story.  But they are *NOT* protecting /foo/bar directory
entry when you want to protect /foo/bar/baz/barf; it doesn't go up towards
root.

And if you *do* protect each ancestor and try to keep granularity, you'll
end up with complexity from hell.
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