netdev - Re: [patch 1/1] net: convert %p usage to %pK

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Message-ID: <20110525232921.GD19633@outflux.net>
Date:	Wed, 25 May 2011 16:29:21 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, joe@...ches.com, mingo@...e.hu,
	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	drosenberg@...curity.com, a.p.zijlstra@...llo.nl,
	eparis@...isplace.org, eugeneteo@...nel.org, jmorris@...ei.org,
	tgraf@...radead.org
Subject: Re: [patch 1/1] net: convert %p usage to %pK

Hi David,

On Tue, May 24, 2011 at 03:58:01AM -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Tue, 24 May 2011 09:45:01 +0200
> 
> > Le mardi 24 mai 2011 à 00:35 -0700, Joe Perches a écrit :
> > 
> >> I think it's be better without the casts
> >> using the standard kernel.h macros.
> >> 
> >> 	void *ptr;
> >> 
> >> 	ptr = maybe_hide_ptr(sk);
> >> 	r->id.idiag_cookie[0] = lower_32_bits(ptr);
> >> 	r->id.idiag_cookie[1] = upper_32_bits(ptr);
> >> 
> > 
> > I am not sure I want to patch lower_32_bits() and upper_32_bits() for
> > this.
> > 
> > They dont work on pointers, but on "numbers", according to kerneldoc
> > Andrew wrote years ago. gcc agrees :
> > 
> > net/ipv4/inet_diag.c: In function ‘inet_csk_diag_fill’:
> > net/ipv4/inet_diag.c:119: warning: cast from pointer to integer of different size
> > net/ipv4/inet_diag.c:120: error: invalid operands to binary >>
> > make[1]: *** [net/ipv4/inet_diag.o] Error 1
> 
> Also you can't do this, the "cookie" is used by the kernel future
> lookups to find sockets.
> 
> The kernel pointer is part of the API, so sorry you can't "hide"
> kernel pointers in this case without really breaking user visible
> things.

But this is precisely what we're trying to control with kptr_restrict.
Setting kptr_restrict will make inet_diag (and some details of similar
things in /proc) meaningless. Based on the name, "diag" isn't going to be
used in normal operation, and kptr_restrict is 0 by default, so only system
owners interested in this will enable it and effectively disable inet_diag.

It seems like everything that fills idiag_cookie needs to be adjusted, not
just the one instance, too:

$ fgrep 'idiag_cookie[0] = ' net/ipv4/inet_diag.c
	r->id.idiag_cookie[0] = (u32)(unsigned long)sk;
	r->id.idiag_cookie[0] = (u32)(unsigned long)tw;
	r->id.idiag_cookie[0] = (u32)(unsigned long)req;

-Kees

-- 
Kees Cook
Ubuntu Security Team
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