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

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Message-ID: <CAKD1Yr1GcK3XQpyx=p-EHWXHax_+-HXpHFT6uWZY_9ovv8V7mA@mail.gmail.com>
Date:   Tue, 13 Jun 2017 09:34:07 +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, hadi@...atatu.com
Subject: Re: [PATCH net-next 1/1] net: reflect mark on tcp syn ack packets

On Sun, Jun 11, 2017 at 8:58 PM, Jamal Hadi Salim <jhs@...atatu.com> wrote:
>> Maybe this should both be "inet_request_mark()"?
>>
>
> Challenge is making of a synack requires a new allocated skb;
> and sk is a listening socket - which should/has a mark of
> 0 meaning at ip_build_and_send_pkt() it overrides
> the value already set on the skb->mark.

As David says, the tcp_fwmark_accept sysctl is not really appropriate
for synack packets - what it does is ensure that when a connection is
accepted, sk->sk_mark is set to the mark of the incoming skb.

I think the correct behaviour here is to to honour the
ip_fwmark_reflect sysctl instead, and if it's enabled, make the synack
mark be the same as the the incoming syn mark.