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Date: Tue, 22 Feb 2011 11:50:18 -0800
From: Kees Cook <kees.cook@canonical.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg KH <gregkh@suse.de>, David Daney <ddaney@caviumnetworks.com>,
        linux-kernel@vger.kernel.org, Eugene Teo <eugeneteo@kernel.sg>,
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Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging
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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