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

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Date:   Thu, 8 Aug 2019 13:37:21 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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 ;)