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Date: Wed, 26 Jan 2011 15:57:06 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <kees.cook@canonical.com>
Cc: linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
        Tejun Heo <tj@kernel.org>, Marcus Meissner <meissner@suse.de>,
        Jason Wessel <jason.wessel@windriver.com>,
        Eugene Teo <eugeneteo@kernel.org>, Joe Perches <joe@perches.com>,
        Bjorn Helgaas <bjorn.helgaas@hp.com>, Len Brown <len.brown@intel.com>,
        Changli Gao <xiaosuo@gmail.com>,
        Dan Rosenberg <drosenberg@vsecurity.com>
Subject: Re: [PATCH] use %pK for /proc/kallsyms and /proc/modules
Message-Id: <20110126155706.0188fe02.akpm@linux-foundation.org>
In-Reply-To: <20110125181058.GA25670@outflux.net>
References: <20110125181058.GA25670@outflux.net>
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On Tue, 25 Jan 2011 10:10:58 -0800
Kees Cook <kees.cook@canonical.com> wrote:

> Instead of messing with permissions on these files,

This implies that the patch alters permission handling, only it
doesn't.  But I worked it out!

> use %pK for kernel
> addresses to reduce potential information leaks that might be used to
> help target kernel privilege escalation exploits.
> 
> 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.)
> 
> Note that when compiling with -Wformat, these harmless warnings will
> be emitted, and can be ignored:
>   warning: '0' flag used with ___%p___ gnu_printf format

OK, so what applications did this patch just break?