netdev - Re: [bpf-next RFC 3/6] bpf: add bpf_tcp_gen

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Date:   Tue, 16 Jul 2019 17:27:02 -0700
From:   Petar Penkov <ppenkov.kernel@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        davem@...emloft.net, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [bpf-next RFC 3/6] bpf: add bpf_tcp_gen_syncookie helper

Thank you for the reviews!

On Tue, Jul 16, 2019 at 4:56 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> On Tue, 16 Jul 2019 at 08:59, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > > +             return -EINVAL;
> > > +
> > > +     if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
> > > +             return -EINVAL;
> > > +
> > > +     if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
> > > +             return -EINVAL;
> > > +
> > > +     if (!th->syn || th->ack || th->fin || th->rst)
> > > +             return -EINVAL;
> > > +
> > > +     switch (sk->sk_family) {
> >
> > This is strange, because a dual stack listener will have sk->sk_family set to AF_INET6.
> >
> > What really matters here is if the packet is IPv4 or IPv6.
> >
> > So you need to look at iph->version instead.
> >
> > Then look if the socket family allows this packet to be processed
> > (For example AF_INET6 sockets might prevent IPv4 packets, see sk->sk_ipv6only )

This makes a lot of sense, thanks Eric, will update!
>
> Does this apply for (the existing) tcp_check_syn_cookie as well?

I think we will probably have to update the check there, too.
>
> --
> Lorenz Bauer  |  Systems Engineer
> 6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
>
> www.cloudflare.com