linux-kernel - Re: RFC: disablenetwork facility. (v4)

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Message-ID: <20091227163609.GD12645@heat>
Date:	Sun, 27 Dec 2009 11:36:10 -0500
From:	Michael Stone <michael@...top.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
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>,
	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>, Michael Stone <michael@...top.org>
Subject: Re: RFC: disablenetwork facility. (v4)

Serge Hallyn writes:
> Michael Stone writes:
>> The first reason why I'm not too worried is that anyone in a position to use
>> disablenetwork for nefarious purposes is also probably able to use ptrace(),
>> kill(), and/or LD_PRELOAD to similar ends.
> 
> How do you mean?  

I meant that, with the current interface, to set disablenetwork for pid P, you
have either be pid P or to have been one of P's ancestors. In either case, you
have lots of opportunity to mess with P's environment. 

> I thought that disabling network was a completely
> unprivileged operation?  And subsequently executing a setuid-root
> application won't reset the flag.

Correct and correct for the current patches.

>> The second reason why I'm not too worried is that I believe it to be
>> straightforward to use the pre-existing MAC frameworks to prevent individually
>> important processes from dropping networking privileges.
>>
>> Do you have a specific concern in mind not addressed by either of these
>> observations?
>
> Near as I can tell the worst one could do would be to prevent remote
> admins from getting useful audit messages, which could give you unlimited
> time to keep re-trying the server, on your quest to a brute-force attack
> of some sort, i.e. restarting the server with random passwords, and now
> no audit msg about the wrong password gets generated, so you're free to
> exhaust the space of valid passwords.
> 
> Not saying I'm all that worried about it - just something that came to
> mind.

I'll think about it further. Fortunately, there's no need to be hasty. :)

Michael
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