linux-kernel - Re: Linux 3.6

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Message-ID: <20121004160354.GA19347@elliptictech.com>
Date:	Thu, 4 Oct 2012 12:03:54 -0400
From:	Nick Bowler <nbowler@...iptictech.com>
To:	Kees Cook <kees@...flux.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.6

On 2012-10-04 08:49 -0700, Kees Cook wrote:
> On Thu, Oct 04, 2012 at 09:35:04AM -0400, Nick Bowler wrote:
> > On 2012-10-03 13:54 -0700, Linus Torvalds wrote:
> > > On Wed, Oct 3, 2012 at 1:49 PM, Kees Cook <kees@...flux.net> wrote:
> > > > I think the benefits of this being on by default outweigh glitches
> > > > like this. Based on Nick's email, it looks like a directory tree of his
> > > > own creation.
> > > 
> > > I agree that *one* report like this doesn't necessarily mean that we
> > > need to turn it off, if Nick is happy to just fix up his script and
> > > it's all local.
> > > 
> > > However, I suspect we'll see more. And once that happens, we're not
> > > going to keep a default that breaks peoples old scripts, and we're
> > > going to have to rely on distributions (or users) explicitly setting
> > > it.
> > 
> > Yes, it is a directory of my own creation, intended as a place for users
> > (read: me) to stick stuff on the local disk as opposed to on NFS.  It's
> > pretty trivial for me to fixup everything to not need this symlink
> > anymore (and I suspect it is the only offender); I just created the
> > symlink in the first place so that I wouldn't have to change anything
> > else.
> > 
> > (While on /this/ machine I created the directory, I have used shared lab
> > machines with a similar setup).
> > 
> > The thing that bothers me most about all this is that it's basically
> > impossible to see why things are failing without digging through the git
> > tree or posting to the mailing list (or recalling earlier mailing list
> > discussions about the restriction, as I vaguely do now).  You just
> > suddenly get "permission denied" errors when all the permissions
> > involved look fine.  As far as I know, the owner, group and mode of
> > symlinks have always been completely meaningless.  Upgrade to 3.6, and
> > they're suddenly meaningful in extremely non-obvious ways.
> 
> FWIW, there should have been an audit message about it in dmesg.

There were zero messages in the kernel log.

  # dmesg -C
  # cd /tmp
  # mkdir testdir
  # ln -s testdir testlink
  # chown -h nobody testlink
  # cd testlink
  cd: permission denied: testlink
  # dmesg
  (no output)

Cheers,
-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

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