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

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Date:	Tue, 22 Feb 2011 11:14:54 -0800
From:	Greg KH <gregkh@...e.de>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	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 10:47:26AM -0800, Kees Cook wrote:
> 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.

The CVEs are for non-root writes to debugfs, same thing for sysfs.  It's
just stupid mistakes being made here, don't try to lock down the whole
filesystem for just a handfull of bugs.

So I really can't accept these patches, sorry.

thanks,

greg k-h
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