linux-kernel - Re: [PATCH v6] fs: allow protected cross-uid sticky symlinks

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Message-ID: <20100603184054.GA4714@outflux.net>
Date:	Thu, 3 Jun 2010 11:40:54 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Dave Young <hidave.darkstar@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	David Howells <dhowells@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tim Gardner <tim.gardner@...onical.com>,
	"Serge E. Hallyn" <serue@...ibm.com>
Subject: Re: [PATCH v6] fs: allow protected cross-uid sticky symlinks

On Thu, Jun 03, 2010 at 10:41:49AM +0100, Alan Cox wrote:
> > Past objections and rebuttals could be summarized as:
> 
> You've forgotten to update this with the list of the objections from your
> last few days postings.

I didn't think the recent discussions added anything thematically new.
"It changes how symlinks work" is a variation on "breaks POSIX", and
"should be done with per-user /tmp" is a variabtion on "userspace should
fix it".  I can certainly reword the commit log, though.

> You've forgotten to update it as suggested so its a security policy

It is a sysctl with a CONFIG, which is what Eric Paris was asking for.
I apologize if I missed something, but if there are further improvements
desired, I'm happy to add patches.

> Do you plan to post this daily until we get fed up of seeing it ?

I plan on getting this functionality into the kernel.  As such, whenever
I've been directed to improve it before it will be accepted, I will send
an updated version.  Having the lifecycle of this patch blocking on me
seems counter-productive and slightly rude.

At this point, I believe I've addressed the specific concerns that Al Viro,
Eric Paris, and a few others pointed out.  What else needs fixing?

Thanks,

-Kees

-- 
Kees Cook
Ubuntu Security Team
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