netdev - Re: [PATCH net 1/2] sock: make cookie generation global instead of per netns

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Date:   Thu, 8 Aug 2019 13:40:01 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        m@...bda.lt, Alexei Starovoitov <ast@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net 1/2] sock: make cookie generation global instead of
 per netns

On 8/8/19 1:37 PM, Eric Dumazet wrote:
> On Thu, Aug 8, 2019 at 1:09 PM Daniel Borkmann <daniel@...earbox.net> wrote:
>> On 8/8/19 12:45 PM, Eric Dumazet wrote:
>>> On Thu, Aug 8, 2019 at 11:50 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>>>
>>>> Socket cookie consumers must assume the value as opqaue in any case.
>>>> The cookie does not guarantee an always unique identifier since it
>>>> could wrap in fabricated corner cases where two sockets could end up
>>>> holding the same cookie,
>>>
>>> What do you mean by this ?
>>>
>>> Cookie is guaranteed to be unique, it is from a 64bit counter...
>>>
>>> There should be no collision.
>>
>> I meant the [theoretical] corner case where socket_1 has cookie X and
>> we'd create, trigger sock_gen_cookie() to increment, close socket in a
>> loop until we wrap and get another cookie X for socket_2; agree it's
>> impractical and for little gain anyway. So in practice there should be
>> no collision which is what I tried to say.
> 
> If a 64bit counter, updated by one unit at a time could overflow
> during the lifetime of a host,
> I would agree with you, but this can not happen, even if we succeed to
> make 1 billion
> locked increments per second (this would still need 584 years)
> 
> I would prefer not mentioning something that can not possibly happen
> in your changelog ;)

Yep fair enough, makes sense. I'll fix it :)