Date: Thu, 4 Oct 2012 12:03:54 -0400
From: Nick Bowler <nbowler@elliptictech.com>
To: Kees Cook <kees@outflux.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux 3.6
Message-ID: <20121004160354.GA19347@elliptictech.com>
References: <CA+55aFw1Y5_HtfXh+-OEQ2KGpW0N18kA4O3R7=cv29_CaF+3UQ@mail.gmail.com>
 <20121003194614.GA2893@elliptictech.com>
 <20121003200515.GZ9092@outflux.net>
 <CA+55aFwgF1O_DzF0bqGO06n2kxNGE=f5BQsvZF_+q9o0pFPeGw@mail.gmail.com>
 <20121003204141.GB6026@thunk.org>
 <20121003204919.GA9092@outflux.net>
 <CA+55aFwXLXfAHHBEYYiz_4qjxWUpENECCZwFN_1gq+e48f+3Sw@mail.gmail.com>
 <20121004133504.GA5599@elliptictech.com>
 <20121004154919.GE9092@outflux.net>
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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@outflux.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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