linux-kernel - Re: [PATCH] prctl: remove one-shot limitation for changing exe link

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Message-ID: <20160712172933.GE3661@uranus.lan>
Date:	Tue, 12 Jul 2016 20:29:33 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
	peterz@...radead.org, mingo@...hat.com, mhocko@...e.com,
	keescook@...omium.org, linux-kernel@...r.kernel.org,
	mguzik@...hat.com, bsegall@...gle.com, john.stultz@...aro.org,
	oleg@...hat.com, matthltc@...ibm.com, akpm@...ux-foundation.org,
	luto@...capital.net, vbabka@...e.cz, xemul@...tuozzo.com
Subject: Re: [PATCH] prctl: remove one-shot limitation for changing exe link

On Tue, Jul 12, 2016 at 11:52:09AM -0500, Eric W. Biederman wrote:
> >
> > Persistent exe-link doesn't guarantee anything if you have rights to ptrace
> > task and inject own code into (from security POV). So lets rip it out.
> >
> > Acked-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> 
> I believe the original concern was someone injecting a code into a
> process and playing silly buggers with the exe link.  Someone who does
> not have ptrace capability.

If you manage to inject code into a process, that's all, you're
compromised, preventing changing exe-link several times wont help
much I fear. Current limit -- one may change it once, Stas' patch
simply removes this limitation. The ability to change it only _once_
may be suitable for some kind of monitor daemon I guess but this
monitor should detect any change in exe-link state and notify
node's admin, otherwise it's simply useless.

> It is completely not ok to change this until someone goes back to the
> original conversation and looks at the original threat model, and
> refutes it.