linux-kernel - Re: Upstream first policy

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Date:	Mon, 8 Mar 2010 17:49:10 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
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 Tue, 9 Mar 2010, Al Viro wrote:
> 
> 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.

That's a good point, btw, and shows one conceptual difference between 
content-based and pathname-based rules.

For example, if you want to log any changes to "/etc/passwd" (which is 
something pretty reasonable to do at least conceptually), what about doing 
a bind mount on top of that file?

That bind mount doesn't actually change the underlying file in any way. It 
doesn't even really _access_ it. From a content standpoint of the 
filesystem that contains the file, it's a total no-op.

But from an attack standpoint, you don't actually care, because nobody 
cares about the inode that used to be the contents of "/etc/passwd": all 
anybody _really_ cares about is "could somebody change what happens to the 
_name_ '/etc/passwd'".

But yeah, it's easy to overlook namespace changes when the obvious 
operations are read/write/unlink/rename. And I'm not at all surprised that 
people do.

			Linus
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