linux-kernel - Re: disablenetwork (v5): Require CAP

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Message-ID: <20100118193004.GA17189@us.ibm.com>
Date:	Mon, 18 Jan 2010 13:30:04 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	"Andrew G. Morgan" <morgan@...nel.org>
Cc:	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>,
	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>, Al Viro <viro@...iv.linux.org.uk>,
	Kyle Moffett <kyle@...fetthome.net>
Subject: Re: disablenetwork (v5): Require CAP_SETPCAP to enable

Quoting Andrew G. Morgan (morgan@...nel.org):
> On Sat, Jan 16, 2010 at 8:48 PM, Michael Stone <michael@...top.org> wrote:
> > Andrew Morgan wrote:
> >>
> >> Please use CAP_NET_ADMIN for this feature (and add the corresponding
> >> comment in include/linux/capabilities.h).
> >
> > Sure.
> > However, to make sure I understand the purpose of the adjustment, would you
> > mind saying a word or two about what considerations cause you to recommend
> > CAP_NET_ADMIN instead of (or in addition to?) CAP_SETPCAP?
> 
> If you take a look at the capabilities.h file, you'll see that each of
> the capabilities is preceded by an explanation of what privilege it
> enables.
> 
> CAP_SETPCAP refers to privileged manipulation of capabilities
> (permission to violate the normal capability rules) and nothing to do
> with the network.
> 
> You are adding something akin to a per-process tree firewall setting -
> deny/enable network access to this process.

I think I originally suggested CAP_SETPCAP - because it's not deny network
access to this process, but deny network access to all child processes as
well, even if they are more privileged (through setuid-root or file caps).

CAP_NET_ADMIN is probably more straightforward, though.  Who's going to
think to add CAP_SETPCAP to a binary that is intended to drop network
perms, realistically...

> I think you'll agree that
> the CAP_NET_ADMIN description is a much better match for this.

I think it'll be more intuitive to most people so I agree.

-serge
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