Re: [PATCH net-next] net: init sk_cookie for inet socket

[Eric Dumazet]

On 04/23/2018 09:39 PM, Yafang Shao wrote:
> On Tue, Apr 24, 2018 at 12:09 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>>
>>
>> On 04/23/2018 08:58 AM, David Miller wrote:
>>> From: Yafang Shao <laoar.shao@xxxxxxxxx>
>>> Date: Sun, 22 Apr 2018 21:50:04 +0800
>>>
>>>> With sk_cookie we can identify a socket, that is very helpful for
>>>> traceing and statistic, i.e. tcp tracepiont and ebpf.
>>>> So we'd better init it by default for inet socket.
>>>> When using it, we just need call atomic64_read(&sk->sk_cookie).
>>>>
>>>> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
>>>
>>> Applied, thank you.
>>>
>>
>> This is adding yet another atomic_inc on a global cache line.
>>
> 
> That's a trade-off.
> 
>> Most applications do not need the cookie being ever set.
>>
>> The existing mechanism was fine. Set it on demand.
> 
> There are some drawback in the existing mechanism.
> - we have to set the net->cookie_gen and then sk->sk_cookie when we
> want to get the sk_cookie, that's a little expensive as well.

Same cost.

>   After that change, sock_gen_cookie() could be replaced by
> atomic64_read(&sk->sk_cookie) in most places.

Same cost than the helper.

> 
> - If the application want to get the sk_cookie, it must set it first.
>    What if the application don't have the permision to write?
>    Furthermore, maybe it is a security concern ?


Maybe ? Please elaborate.

Your patch destroys SYNFLOOD behavior.

I have spent months of work solving the SYNFLOOD behavior, your patch crushes it.

I am not that happy.

Please revert this patch.

Thank you.