Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is_registered

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Sun, Jul 29, 2018 at 11:59:36AM -0400, Jeremy Cline wrote:
> On 07/29/2018 09:59 AM, Josh Poimboeuf wrote:
> > On Fri, Jul 27, 2018 at 10:43:02PM +0000, Jeremy Cline wrote:
> >> 'family' can be a user-controlled value, so sanitize it after the bounds
> >> check to avoid speculative out-of-bounds access.
> >>
> >> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Jeremy Cline <jcline@redhat.com>
> >> ---
> >>  net/socket.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/net/socket.c b/net/socket.c
> >> index f15d5cbb3ba4..608e29ae6baf 100644
> >> --- a/net/socket.c
> >> +++ b/net/socket.c
> >> @@ -2672,7 +2672,8 @@ EXPORT_SYMBOL(sock_unregister);
> >>  
> >>  bool sock_is_registered(int family)
> >>  {
> >> -	return family < NPROTO && rcu_access_pointer(net_families[family]);
> >> +	return family < NPROTO &&
> >> +		rcu_access_pointer(net_families[array_index_nospec(family, NPROTO)]);
> >>  }
> >>  
> >>  static int __init sock_init(void)
> > 
> > This is another one where I think it would be better to do the nospec
> > clamp higher up the call chain.  The untrusted 'family' value comes from
> > __sock_diag_cmd():
> > 
> > __sock_diag_cmd
> >   sock_load_diag_module
> >     sock_is_registered
> > 
> > That function has a bounds check, and also uses the value in some other
> > array accesses:
> > 
> > 	if (req->sdiag_family >= AF_MAX)
> > 		return -EINVAL;
> > 
> > 	if (sock_diag_handlers[req->sdiag_family] == NULL)
> > 		sock_load_diag_module(req->sdiag_family, 0);
> > 
> > 	mutex_lock(&sock_diag_table_mutex);
> > 	hndl = sock_diag_handlers[req->sdiag_family];
> > 	...
> > 
> > So I think clamping 'req->sdiag_family' right after the bounds check
> > would be the way to go.
> > 
> 
> Indeed, the clamp there would cover this clamp. I had a scheme that I
> quickly fix all the gadgets in functions with local comparisons, but
> clearly that's going to result in call chains with multiple clamps.
> 
> I can fix this in a follow-up with a clamp here, or respin this patch
> set, whatever is easier for David.

Hi Jeremy,

Just checking up on this... since this patch was merged, will you be
doing a followup patch?

-- 
Josh