Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces [LWN.net]

From:		Greg KH <gregkh-AT-suse.de>
To:		Kees Cook <kees.cook-AT-canonical.com>
Subject:		Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces
Date:		Tue, 22 Feb 2011 11:14:54 -0800
Message-ID:		<20110222191454.GB9991@suse.de>
Cc:		David Daney <ddaney-AT-caviumnetworks.com>, linux-kernel-AT-vger.kernel.org, Eugene Teo <eugeneteo-AT-kernel.sg>, Ralph Campbell <infinipath-AT-qlogic.com>, Roland Dreier <roland-AT-kernel.org>, Sean Hefty <sean.hefty-AT-intel.com>, Hal Rosenstock <hal.rosenstock-AT-gmail.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge-AT-citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk-AT-oracle.com>, Alexander Viro <viro-AT-zeniv.linux.org.uk>, Miklos Szeredi <miklos-AT-szeredi.hu>, "J. Bruce Fields" <bfields-AT-fieldses.org>, Neil Brown <neilb-AT-suse.de>, Matthew Wilcox <matthew-AT-wil.cx>, James Morris <jmorris-AT-namei.org>, Stephen Smalley <sds-AT-tycho.nsa.gov>, Eric Paris <eparis-AT-parisplace.org>, Nick Piggin <npiggin-AT-kernel.dk>, Arnd Bergmann <arnd-AT-arndb.de>, Ian Campbell <ian.campbell-AT-citrix.com>, Jarkko Sakkinen <ext-jarkko.2.sakkinen-AT-nokia.com>, Tejun Heo <tj-AT-kernel.org>, Casey Schaufler <casey-AT-schaufler-ca.com>
Archive-link:		Article, Thread

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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