linux-kernel - Re: [PATCH] fs: make dumpable=2 only write to a pipe

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Date:	Thu, 21 Jun 2012 15:03:42 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Alan Cox <alan@...ux.intel.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Doug Ledford <dledford@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Joe Korty <joe.korty@...r.com>, linux-doc@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: make dumpable=2 only write to a pipe

On Thu, Jun 21, 2012 at 2:18 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> On Thu, 21 Jun 2012 12:43:19 -0700
> Kees Cook <keescook@...omium.org> wrote:
>
>> When the suid_dumpable sysctl is set to "2", and there is no
>> core dump pipe defined in the core_pattern sysctl, a local user
>> can cause core files to be written to root-writable directories,
>> potentially with user-controlled content. This means an admin
>> can unknowningly reintroduce a variation of CVE-2006-2451 (see
>> abf75a5033d4da7b8a7e92321d74021d1fcfb502).
>
> Its intended to work the way it does. It's also ABI. I think pipe-only is
> a really good idea. Likewise I accept with the pipe feature nowdays there
> is a good case to kill off case 2.
>
> However I don't think magically turning one into the other is sensible,
> in fact its *stupid* IMHO because it's asking systems to get unexpected
> behaviour.
>
> I would much rather see case 2 either left as is, or set to return
> -EINVAL (or similar) and a new case 3 for pipe only.

If mode 2 switches to -EINVAL, setuid dumps won't be written to disk,
and won't go to pipes. If mode 2 switches to pipe-only, only disk
dumps go missing. Either change seems like a break from the prior
behavior, but the latter seems the least disruptive to me.

I'm happy to go the -EINVAL route and add mode 3 (which will just be
mode 2 renamed) if that really is more acceptable.

-Kees

-- 
Kees Cook
Chrome OS Security
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