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

[Kees Cook <kees.cook@canonical.com>]

Hi David,

On Tue, May 24, 2011 at 03:58:01AM -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.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