netdev - Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in sock_is

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Date:   Sun, 29 Jul 2018 11:59:36 -0400
From:   Jeremy Cline <jcline@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] net: socket: Fix potential spectre v1 gadget in
 sock_is_registered

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@...hat.com>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Jeremy Cline <jcline@...hat.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.

Thanks for the review!