linux-kernel - Re: [PATCH] remove CONFIG_SECURITY_FILE

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Message-ID: <20091123231256.GB11570@us.ibm.com>
Date:	Mon, 23 Nov 2009 17:12:56 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	James Morris <jmorris@...ei.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Steve Grubb <sgrubb@...hat.com>,
	linux-security-module@...r.kernel.org,
	Kees Cook <kees.cook@...onical.com>,
	Andreas Gruenbacher <agruen@...e.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	George Wilson <gcwilson@...ibm.com>,
	KaiGai Kohei <kaigai@...gai.gr.jp>
Subject: Re: [PATCH] remove CONFIG_SECURITY_FILE_CAPABILITIES compile option

Quoting Randy Dunlap (randy.dunlap@...cle.com):
> Serge E. Hallyn wrote:
> > As far as I know, all distros currently ship kernels with default
> > CONFIG_SECURITY_FILE_CAPABILITIES=y.  Since having the option on
> > leaves a 'no_file_caps' option to boot without file capabilities,
> > the main reason to keep the option is that turning it off saves
> > you (on my s390x partition) 5k.  In particular, vmlinux sizes
> > came to:
> > 
> > without patch fscaps=n:		 	53598392
> > without patch fscaps=y:		 	53603406
> > with this patch applied:		53603342
> > 
> > with the security-next tree.
> > 
> > Against this we must weigh the fact that there is no simple way for
> > userspace to figure out whether file capabilities are supported,
> > while things like per-process securebits, capability bounding
> > sets, and adding bits to pI if CAP_SETPCAP is in pE are not supported
> > with SECURITY_FILE_CAPABILITIES=n, leaving a bit of a problem for
> > applications wanting to know whether they can use them and/or why
> > something failed.
> > 
> > It also adds another subtly different set of semantics which we must
> > maintain at the risk of severe security regressions.
> 
> Hi,
> 
> This is or is not the same security option that is referred to in
> (new:) http://bugzilla.kernel.org/show_bug.cgi?id=14675 ?

I don't know.  I would assume he meant 'CONFIG_SECURITY', but that
wouldn't make sense since it should make no difference if no specific
LSM is turned on.

I will subscribe to the bug so I can see his response.  If it is in
fact CONFIG_SECURITY_FILE_CAPABILITIES, then a binary which is setuid-root
may be installed with some file capabilities, but without enough caps
to do what it needs.

thanks,
-serge
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