linux-kernel - Re: [RFC][PATCH] Unprivileged: Disable acquisition of privileges

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Date:	Tue, 29 Dec 2009 23:57:50 -0500
From:	Bryan Donlan <bdonlan@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Benny Amorsen <benny+usenet@...rsen.dk>,
	Michael Stone <michael@...top.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, David Lang <david@...g.hm>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	James Morris <jmorris@...ei.org>,
	Bernie Innocenti <bernie@...ewiz.org>,
	Mark Seaborn <mrs@...hic-beasts.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Samir Bellabes <sam@...ack.fr>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Pavel Machek <pavel@....cz>, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC][PATCH] Unprivileged: Disable acquisition of privileges

On Tue, Dec 29, 2009 at 11:33 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Bryan Donlan <bdonlan@...il.com> writes:
>
>> Is this sufficient for other security models such as selinux or
>> TOMOYO? Can processes in these models gain privileges through means
>> not restricted here?
>
> The LSM is primarily about returning -EPERM more often.
> Except for the prctl and the capability hooks I am not aware
> of anywhere a LSM can increase a processes capabilities.

I'm more concerned about a case where a privilege that the LSM
currently denies is lifted by execing some executable - this is still
an increase in privilege, even though the LSM only adds additional
restrictions. That is:

1) Initial state: LSM denies access to /somefile (although normal
POSIX permissions would permit access)
2) Disable capability-gaining
3) Disable network access with proposed API
4) Exec some application, which is labeled in a way that permits
access to /somefile
5) Application fails to access the network, then does something to /somefile

I'm not entirely sure if step 4) can happen in any of the currently
existing LSMs - if it's not possible to gain privileges in them via a
suid-like mechanism, this isn't a problem, but it's something that
needs to be checked for.
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