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

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Message-ID: <20110222184726.GV4000@outflux.net>
Date:	Tue, 22 Feb 2011 10:47:26 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	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>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	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 10:32:19AM -0800, David Daney wrote:
> On 02/22/2011 10:16 AM, Kees Cook wrote:
> >Har har, I forgot --compose to "git send-email".
> >
> >Anyway, with the continuing deluge of bugs in the "debug" filesystem, I
> >would like to make that filesystem's root directory mode 0700 by default
> >since it's filled with crazy stuff that regular users do not need to see.
> >
> >Better to try to just close the door completely on all the stuff in there.
> >It is, after all, supposed to only be used for debugging, right?
> >
> 
> It depends if you consider use of ftrace and kprobes 'debugging'.
> In any event, you really have to be root to be able to manipulate
> them.
> 
> I can currently do 'cat /sys/kernel/debug/tracing/trace' as a normal
> user.  With your change I don't think it would be possible.  This is
> not something I often (ever) do, but it is a change.

Right, my thinking is that all the manipulations on this tree should be
root-only (non-root stuff shouldn't live in something named "debug"),
so we might as well lock it down a bit more so we can avoid all the CVEs[1]
being assigned for glitches in this tree.

-Kees

[1] http://seclists.org/oss-sec/2011/q1/229
    http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-4347
    etc

-- 
Kees Cook
Ubuntu Security Team
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