netdev - Re: [PATCH 3/10] Fix leaking of kernel heap addresses in net/

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Date:	Thu, 11 Nov 2010 20:44:41 -0500
From:	Thomas Graf <tgraf@...radead.org>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Urs Thuermann <urs.thuermann@...kswagen.de>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	James Morris <jmorris@...ei.org>,
	Remi Denis-Courmont <remi.denis-courmont@...ia.com>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	Sridhar Samudrala <sri@...ibm.com>,
	Vlad Yasevich <vladislav.yasevich@...com>,
	Tejun Heo <tj@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Li Zefan <lizf@...fujitsu.com>, Joe Perches <joe@...ches.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Jamal Hadi Salim <hadi@...atatu.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Jiri Pirko <jpirko@...hat.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	Pavel Emelyanov <xemul@...nvz.org>,
	socketcan-core@...ts.berlios.de, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH 3/10] Fix leaking of kernel heap addresses in net/

On Thu, Nov 11, 2010 at 08:24:09PM -0500, Dan Rosenberg wrote:
> > If we really have to do this. At least don't duplicate all this code. Do
> > the check in the printf argument:
> > 
> > 	seq_printf(seq, "%4d: %08X:%04X %08X:%04X"
> > 		...
> > 		capable(CAP_NET_ADMIN) ? sp : 0,
> > 
> > I would even move the decision whether to expose kernel addresses or not
> > to a function so we can change behavior in one place.
> 
> I wrote it this way because the format specifier must also be changed,
> or the %p output will print "(null)", which cannot be parsed by
> userspace programs expecting "(nil)" or 0.  I could include another
> check inside the format specifier, but that seemed pretty ugly.  But
> then again, it's ugly either way.

Considering the amount of duplication you are about to do, you may
want to think about adding a new pointer format extension then. We
already have special '%p' modes for IPv6 addresse, MAC addresses and
various other pointer types. It wouldn't be hard to add one which
does not print (null).
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