From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH v6] fs: allow protected cross-uid sticky symlinks
Date: Mon, 7 Jun 2010 14:10:43 -0500
Message-ID: <20100607191043.GA8836@hallyn.com>
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Cc: Kees Cook <kees.cook@canonical.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Dave Young <hidave.darkstar@gmail.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Eric Paris <eparis@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	James Morris <jmorris@namei.org>, linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org,
	Randy Dunlap <rdunlap@xenotime.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jiri Kosina <jkosina@suse.cz>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	David Howells <dhowells@redhat.com>,
	Ingo Molnar <mingo@elte.hu>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Tim Gardner <tim.gardner@canonical.com>, tytso@mit.edu,
	Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Valdis.Kletnieks@vt.edu
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Quoting Valdis.Kletnieks@vt.edu (Valdis.Kletnieks@vt.edu):
> (Sorry for the late reply, didn't have time last few days to drink from the
> lkml firehose)
> 
> On Thu, 03 Jun 2010 14:00:51 PDT, Kees Cook said:
> > On Thu, Jun 03, 2010 at 01:02:48PM -0700, Eric W. Biederman wrote:
> > > Kees Cook <kees.cook@canonical.com> writes:
> > > > A long-standing class of security issues is the symlink-based
> > > > time-of-check-time-of-use race, most commonly seen in world-writable
> > > > directories like /tmp. The common method of exploitation of this flaw
> > > 
> > > Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
> > > 
> > > This approach to fix the problem to of /tmp looks to me like it
> > > will have the opposite effect.  I think this patch will encourage
> > > more badly written applications.
> > 
> > How to safely deal with /tmp has been well understood for well over
> > a decade.  I don't think this change would "encourage" poor code.
> 
> The fact that you're proposing this patch a decade after we "well understood"
> the problem should suggest that it *will* encourage poor code, as the same
> programmers who don't currently get it right (and are thus the targets of your
> patch) will quite likely just say "Oh, I saw a patch for that, I don't have to
> try to do it right..."

Come on, now, that's a leap, really...

I'm all for doing both this patch AND pushing for per-user /tmp.

-serge