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Subject: Re: RFC: introduce "K" flag for printf, similar to %pK
From: Joe Perches <joe@perches.com>
To: Kees Cook <kees.cook@canonical.com>
Cc: linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
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Date: Tue, 25 Jan 2011 09:41:13 -0800
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On Tue, 2011-01-25 at 09:28 -0800, Kees Cook wrote:
> On Mon, Jan 24, 2011 at 06:17:04PM -0800, Joe Perches wrote:
> > On Mon, 2011-01-24 at 18:03 -0800, Kees Cook wrote:
> > > In the interests of hiding kernel addresses from userspace (without
> > > messing with file permissions), I want to use %pK for /proc/kallsyms and
> > > /proc/modules, but this results in changing several %x's to %p's. The
> > > primary side-effects is that some legitimately "0" value things in
> > > /proc/kallsyms turn into "(null)".
> > 
> > Another option would be to allow '0' for
> > kernel pointers.
> 
> But then this changes the behavior of %p where (null) is expected. (i.e.
> when switching from %p to %pK.)

If you really want no change to any existing cases,
change it to "%pk" and a new case label.

> I'm personally fine with that, as I suspect anything parsing the output
> that can handle finding "(null)" will be fine with "0" too. But the other
> way around, not so much. :)

Maybe there's a case where somebody changed a kernel pointer
from %p to %pK that demands "(null)", but I can't think of one.

cheers, Joe