linux-kernel - Re: drop SECURITY_FILE

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Message-ID: <20091110172335.GI5129@outflux.net>
Date:	Tue, 10 Nov 2009 09:23:35 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Andrew Morgan <morgan@...nel.org>,
	Steve Grubb <sgrubb@...hat.com>,
	Andreas Gruenbacher <agruen@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	George Wilson <gcwilson@...ibm.com>
Subject: Re: drop SECURITY_FILE_CAPABILITIES?

Hi,

On Tue, Nov 10, 2009 at 08:07:39AM -0600, Serge E. Hallyn wrote:
> Just a probe to see what people think.  I've seen two cases
> in about the last month where software was confounded by
> an assumption that prctl(PR_CAPBSET_DROP, CAP_SOMETHING)
> would succeed if privileged, but not handling the fact
> that SECURITY_FILE_CAPABILITIES=n means you can't do that.
> 
> Are we at the point yet where we feel we can get rid of
> the SECURITY_FILE_CAPABILITIES=n case?

It seems to me that the process caps bounding set (and file caps) are the
way forward and retaining the =n option is nonsense, especially since caps
are an integral part of the kernel.

> Does anyone know of cases where CONFIG_SECURITY_FILE_CAPABILITIES=n
> is still perceived as useful?

Building a kernel that willfully ignores fscaps?  I don't see the point.
It saves only a few bytes of code, AFAICT, and if it needs to be disabled
for some reason, the kernel boot option "no_file_caps" can be set.

At the very least it should default to "y" and/or have its help updated to
include the list of things it enables.

-Kees

-- 
Kees Cook
Ubuntu Security Team
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