linux-kernel - Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

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Date:	Mon, 11 Jan 2010 09:58:52 +1100 (EST)
From:	James Morris <jmorris@...ei.org>
To:	Michael Stone <michael@...top.org>
cc:	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>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Bryan Donlan <bdonlan@...il.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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>,
	"Serge E. Hallyn" <serue@...ibm.com>, Pavel Machek <pavel@....cz>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

On Sun, 10 Jan 2010, Michael Stone wrote:

> 
> Pavel's position is that disablenetwork is likely to permit some attacker
> somewhere to deny network access to some setuid app some day in a way that
> violates some security policy.
> 
> He has mentioned specific concern over scenarios like:
> 
>   Alice configures PAM auth to 'fail open' by checking login credentials
>   against a restrictive LDAP server and, if the server is unavailable, against
>   a very permissive files database.
> 
>   Alice updates her kernel to a version with disablenetwork.
> 
>   Mallory calls disablenetwork, calls su -, and vanquishes all.
> 
> My position is that better isolation facilities like disablenetwork will
> prevent far more grievous security faults than they (theoretically) cause.
> 
> What is your perspective on the matter?

Unexpected failure modes for privileged apps using security interfaces has 
already proven to be a problem (e.g. the sendmail capabilities bug), so it 
seems prudent to try and mitigate that as well. I don't think we need to 
look at this as an either-or situation -- it seems we can do both, and get 
something useful in its own right from the mitigation.


-- 
James Morris
<jmorris@...ei.org>
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