linux-kernel - Re: [PATCH v4] fs: make dumpable=2 only write to a pipe

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Date:	Sat, 23 Jun 2012 23:46:50 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>, Rob Landley <rob@...dley.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Doug Ledford <dledford@...hat.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Joe Korty <joe.korty@...r.com>, linux-doc@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	James Morris <james.l.morris@...cle.com>
Subject: Re: [PATCH v4] fs: make dumpable=2 only write to a pipe

On Sat, Jun 23, 2012 at 4:21 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> 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, allowing local users to gain
>> root privileges.
>
> Is there a security exploit possible if a path is defined in the
> core_pattern?
>
> From the description of the problem so far I don't think there is.
> Requiring a program when a simple path will do seems excessive.

Having a fully qualified path would be sufficient, yes. Looking at how
%e and %E are handled, I'm satisfied (for example, no additional "/"
characters can be injected via argv0). In this case, then, I'll adjust
this to require either a pipe or a fully qualified core_pattern (i.e.
core_pattern must start with "!" or "/" for mode 2). How does that
sound?

-Kees

-- 
Kees Cook
Chrome OS Security
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