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

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Message-ID: <20091229163939.GA6984@us.ibm.com>
Date:	Tue, 29 Dec 2009 10:39:39 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Bryan Donlan <bdonlan@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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>,
	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: disablenetwork facility. (v4)

Quoting Bryan Donlan (bdonlan@...il.com):
> On Tue, Dec 29, 2009 at 10:11 AM, Serge E. Hallyn <serue@...ibm.com> wrote:
> > Eric, let me specifically point out a 'disable setuid-root'
> > problem on linux: root still owns most of the system even when
> > it's not privileged.  So does "disable setuid-root" mean
> > we don't allow exec of setuid-root binaries at all, or that
> > we don't setuid to root, or that we just don't raise privileges
> > for setuid-root?
> 
> I, for one, think it would be best to handle it exactly like the
> nosuid mount option - that is, pretend the file doesn't have any
> setuid bits set. There's no reason to deny execution; if the process
> would otherwise be able to execute it, it can also copy the file to
> make a non-suid version and execute that instead. And some programs
> can operate with reduced function without setuid. For example, screen
> comes to mind; it needs root to share screen sessions between multiple
> users, but can operate for a single user just fine without root, and
> indeed the latter is usually the default configuration.

That's fine with me, seems safe for a fully unprivileged program to
use, and would make sense to do through one of the securebits set
with prctl(PR_SET_SECUREBITS).

In addition, I assume we would also refuse to honor file capabilities?

-serge
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