Date: Tue, 22 Feb 2011 12:37:04 -0800
From: Greg KH <gregkh@suse.de>
To: Kees Cook <kees.cook@canonical.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
        David Daney <ddaney@caviumnetworks.com>, linux-kernel@vger.kernel.org,
        Eugene Teo <eugeneteo@kernel.sg>,
        Ralph Campbell <infinipath@qlogic.com>,
        Roland Dreier <roland@kernel.org>, Sean Hefty <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
        "J. Bruce Fields" <bfields@fieldses.org>, Neil Brown <neilb@suse.de>,
        Matthew Wilcox <matthew@wil.cx>, James Morris <jmorris@namei.org>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Eric Paris <eparis@parisplace.org>, Nick Piggin <npiggin@kernel.dk>,
        Arnd Bergmann <arnd@arndb.de>, Ian Campbell <ian.campbell@citrix.com>,
        Jarkko Sakkinen <ext-jarkko.2.sakkinen@nokia.com>,
        Tejun Heo <tj@kernel.org>, Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging
 interfaces
Message-ID: <20110222203704.GA7224@suse.de>
References: <1298398198-18482-2-git-send-email-kees.cook@canonical.com>
 <20110222181613.GU4000@outflux.net>
 <4D640133.9020901@caviumnetworks.com>
 <20110222184726.GV4000@outflux.net>
 <20110222191454.GB9991@suse.de>
 <20110222192532.GY4000@outflux.net>
 <20110222193418.773ccd4b@lxorguk.ukuu.org.uk>
 <20110222195018.GA4000@outflux.net>
 <20110222201610.GA29787@suse.de>
 <20110222202856.GE4000@outflux.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110222202856.GE4000@outflux.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2914
Lines: 63

On Tue, Feb 22, 2011 at 12:28:56PM -0800, Kees Cook wrote:
> On Tue, Feb 22, 2011 at 12:16:10PM -0800, Greg KH wrote:
> > On Tue, Feb 22, 2011 at 11:50:18AM -0800, Kees Cook wrote:
> > > 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.
> > 
> > No, not true at all, the "enterprise" distros all mount debugfs for good
> > reason on their systems.
> 
> What reasons are those? Or better yet, why do you and Alan Cox disagree on
> this point?

These distros have made the decision to support the perf interface,
which lives in debugfs, for their customers.  I'm not saying that I
disagree with Alan about this, just pointing out the reality of the
situation here.

> > > 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.
> > 
> > Again, not true.  Mostly all due to the perf interface, fix that to move
> > out of debugfs (patches have been proposed) and this problem will go
> > away.
> 
> You can't have "no rules" and "all distros mount debugfs for good reason".
> This is asking for (even more) trouble. If there is something universally
> useful in debugfs (I do not count perf as universally useful -- my parents
> do not use perf), then why is it living in a filesystem with no rules
> (where "no rules" seems to also include "don't break interfaces").

Again, "don't break interfaces" is just me saying "don't break the
interfaces I have created in debugfs as they are to be used by all
users."  Don't take that as a set-in-stone rule of debugfs at all, it
isn't.

Again, you are trying to exclude a whole range of useful and valid files
from being used, when there was only a very very very small percentage
created incorrectly.  They have now been fixed, and we have the
infrastructure to prevent future ones from being created as well, so I
don't see the issue here anymore.

thanks,

greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/