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

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Message-ID: <20100111120131.GB1697@atrey.karlin.mff.cuni.cz>
Date:	Mon, 11 Jan 2010 13:01:31 +0100
From:	Pavel Machek <pavel@....cz>
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>,
	James Morris <jmorris@...ei.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Bernie Innocenti <bernie@...ewiz.org>,
	Mark Seaborn <mrs@...hic-beasts.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Am?rico 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>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

Hi!

> >You can trivialy make disablenetwork disable setuid exec, too. That
> >will introduce better isolation facilities, but not introduce any new
> >security problems.
> >
> >For some reason, you don't want to do the obviously right thing.
> 
> I don't want to do it because it's not "obviously right" to me: I *have* 
> setuid
> programs that I want to be able to raise privileges when network-disabled.
> I *don't have* any setuid programs that will be harmed by disablenetwork.

Well, I do not have any desire to use disablenetwork, but I do not
want my users to use it and DoS sendmail.

> Examples of software that I want to be able to gain privileges normally 
> include:

You'll have to make sure those are not accessed from the
disablenetworked parts, I'd say. Pre-existing unix domain socket
should be the way to go.

>   rainbow, which requires privilege in order to add new accounts to the 
>   system
>   and in order to call setuid() but which does not require networking
>   privileges.
> 
>   qmail-queue, which uses setuid to deliver mail that it reads from fd 0 to
>   local users
> 
>   and other old favorites like mount, fusermount, X, and, presumably, any 
>   audio
>   software that wants to go realtime.

mount certainly wants network access for NFS.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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