linux-kernel - Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces

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Message-ID: <20110222195018.GA4000@outflux.net>
Date:	Tue, 22 Feb 2011 11:50:18 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Greg KH <gregkh@...e.de>, David Daney <ddaney@...iumnetworks.com>,
	linux-kernel@...r.kernel.org, Eugene Teo <eugeneteo@...nel.sg>,
	Ralph Campbell <infinipath@...gic.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, Matthew Wilcox <matthew@....cx>,
	James Morris <jmorris@...ei.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>,
	Nick Piggin <npiggin@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
	Ian Campbell <ian.campbell@...rix.com>,
	Jarkko Sakkinen <ext-jarkko.2.sakkinen@...ia.com>,
	Tejun Heo <tj@...nel.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging
 interfaces

On Tue, Feb 22, 2011 at 07:34:18PM +0000, Alan Cox wrote:
> > What system do you proposed to keep these "stupid mistakes" from
> > continuing to happen? If debugfs had already been mode 0700, we could have
> > avoided all of these CVEs, including the full-blown local root escalation.
> 
> And all sorts of features would have put themselves in sysfs instead and
> broken no doubt.
> 
> > The "no rules" approach to debugfs is not a good idea, IMO.
> 
> It's a debugging fs, it needs to be "no rules" other than the obvious
> "don't mount it on production systems"

Okay, so the debugfs is not supposed to be mounted on a production system.
This seems to be news to a lot of developers trying to use the interfaces
exposed there. It would be nice to say this more loudly.  Basically,
a normal system should not depend on anything in the debugfs. I can get
behind that.

> Or of course you could just chmod it 0700 in the distro !

I'm trying to, but that involves a race condition since I can't control it
during the mount (nor set the default mode like I was trying to with the
patchset). tmpfs allows "mode=", but debugfs does not...

-Kees

-- 
Kees Cook
Ubuntu Security Team
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