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Date: Tue, 9 Mar 2010 00:48:29 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Rik van Riel <riel@redhat.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Ingo Molnar <mingo@elte.hu>, James Morris <jmorris@namei.org>,
       linux-kernel@vger.kernel.org, Kyle McMartin <kyle@mcmartin.ca>,
       Alexander Viro <viro@ftp.linux.org.uk>
Subject: Re: Upstream first policy
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On Tue, Mar 09, 2010 at 12:15:54AM +0000, Al Viro wrote:
> 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.

BTW, if you actually look at apparmor (I'd suggest tomoyo, but I'm not _that_
sadistic), you'll see how seriously do they take pathname-based *anything*.
LSM hooks for namespace operations (you know, mount, umount) are lousy, but
they exist.  Not used by apparmor.