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

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Message-ID: <e4ceaa56-0550-b560-751d-7288a4c1b850@redhat.com>
Date:   Mon, 13 Aug 2018 20:03:20 +0100
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 08/13/2018 06:16 PM, Josh Poimboeuf wrote:
> 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@...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.
> 
> Hi Jeremy,
> 
> Just checking up on this... since this patch was merged, will you be
> doing a followup patch?
> 

Yes, apologies, I've been traveling. I'll have a patch tomorrow.