netdev - Re: [PATCH net-next 1/1] net: reflect mark on tcp syn ack packets

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Message-ID: <CAKD1Yr1uGL-OPUJ76D=md8kCT0psreew20Em=BokHWEYdP9xOg@mail.gmail.com>
Date:   Tue, 13 Jun 2017 22:58:24 +0900
From:   Lorenzo Colitti <lorenzo@...gle.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        mrv@...atatu.com, Jamal Hadi Salim <hadi@...atatu.com>
Subject: Re: [PATCH net-next 1/1] net: reflect mark on tcp syn ack packets

On Sat, Jun 10, 2017 at 10:31 PM, Jamal Hadi Salim <jhs@...atatu.com> wrote:
>         skb->priority = sk->sk_priority;
> -       skb->mark = sk->sk_mark;
> +       if (!skb->mark)
> +               skb->mark = sk->sk_mark;

It looks a bit iffy to take sk->sk_mark only if skb->mark is zero
instead of relying on the callers to tell this function what they
want. I think the patch is correct, but it might be better to fix the
other callers (dccp_make_response and dccp_ctl_make_reset) to set
skb->mark to what they want. Either way.

>         tcp_ecn_make_synack(req, th);
>         th->source = htons(ireq->ir_num);
>         th->dest = ireq->ir_rmt_port;
> +       if (sock_net(sk)->ipv4.sysctl_tcp_fwmark_accept)
> +               skb->mark = ireq->ir_mark;

I think checking the sysctl here is unnecessary. It seems to me that
ir_mark already takes that into account. Its semantics (see
inet_request_mark) are:

- If listen socket has a nonzero mark, use that
- Else if sysctl_tcp_fwmark_accept is set and inbound SYN packet has
mark, use that
- Else zero.

which is what you want.

Other than that,

Reviewed-By: Lorenzo Colitti <lorenzo@...gle.com>

Please disregard my earlier comment about fwmark_reflect - I didn't
notice that the code sets ir_mark based on tcp_fwmark_accept, and
doesn't look at fwmark_reflect at all.