linux-kernel - Re: [PATCH] use %pK for /proc/kallsyms and /proc/modules

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Message-ID: <20110127013019.GJ4981@outflux.net>
Date:	Wed, 26 Jan 2011 17:30:19 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>, Marcus Meissner <meissner@...e.de>,
	Jason Wessel <jason.wessel@...driver.com>,
	Eugene Teo <eugeneteo@...nel.org>,
	Joe Perches <joe@...ches.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Len Brown <len.brown@...el.com>,
	Changli Gao <xiaosuo@...il.com>,
	Dan Rosenberg <drosenberg@...curity.com>
Subject: Re: [PATCH] use %pK for /proc/kallsyms and /proc/modules

On Wed, Jan 26, 2011 at 04:46:50PM -0800, Andrew Morton wrote:
> On Wed, 26 Jan 2011 16:29:36 -0800
> Kees Cook <kees.cook@...onical.com> wrote:
> 
> > > > Note that this changes %x to %p, so some legitimately 0 values in
> > > > /proc/kallsyms would have changed from 00000000 to "(null)". To avoid
> > > > this, "(null)" is not used when using the "K" format. Anything parsing
> > > > such addresses should have no problem with this change. (Thanks to Joe
> > > > Perches for the suggestion.)
> > > 
> > > OK, so what applications did this patch just break?
> > 
> > I'm not aware of any breakage as a result of this yet.
> 
> There will be some - there always are :( But users will only see
> problems if they've set kptr_restrict.

If something can parse "null", "00000001" through "99999999", and _not_
"00000000", I will happily giggle at them. :)

> 
> Which they shall do.  How come we defaulted kptr_restrict to "true"?

Because that's the correct value! :) Unprivileged userspace doesn't need to
see kernel addresses by default, that's for CAP_SYSLOG.

-Kees

-- 
Kees Cook
Ubuntu Security Team
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