netdev - Re: Network isolation with RLIMIT

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Message-ID: <3e8340490912171153s56e966d6lb76041fefc52e735@mail.gmail.com>
Date:	Thu, 17 Dec 2009 14:53:00 -0500
From:	Bryan Donlan <bdonlan@...il.com>
To:	Bernie Innocenti <bernie@...ewiz.org>
Cc:	Mark Seaborn <mrs@...hic-beasts.com>,
	Michael Stone <michael@...top.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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>,
	Rémi Denis-Courmont <rdenis@...phalempin.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	James Morris <jmorris@...ei.org>,
	Linux Containers <containers@...ts.osdl.org>
Subject: Re: Network isolation with RLIMIT_NETWORK, cont'd.

On Thu, Dec 17, 2009 at 2:35 PM, Bernie Innocenti <bernie@...ewiz.org> wrote:
> On Thu, 2009-12-17 at 13:24 -0500, Bryan Donlan wrote:
>> Can this be done using openat() and friends currently? It would seem
>> the natural way to implement this; open /proc/(pid)/root, then
>> openat() things from there (or even chdir to it and see the mounts
>> that it sees from there...)
>
> Yeah, but /proc/<pid>/root is just a symlink. It's correct for chroots,
> but I doubt it can be meaningful for per-process namespaces.

The files in /proc/<pid>/fs are 'just symlinks', but opening them can
provide access to objects (eg, deleted files) not accessible through
the normal filesystem namespace. I see no reason, API-wise, why
/proc/<pid>/root couldn't be extended similarly - but I've not looked
at the namespaces implementation, so maybe there's some reason it'd be
difficult to implement...
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