netdev - Re: Removing skb_orphan() from ip_rcv

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Date:   Mon, 24 Jun 2019 20:26:34 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Joe Stringer <joe@...d.net.nz>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Florian Westphal <fw@...len.de>,
        netdev <netdev@...r.kernel.org>,
        john fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenz Bauer <lmb@...udflare.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: Removing skb_orphan() from ip_rcv_core()

On Mon, Jun 24, 2019 at 7:47 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On 2019-06-21 1:58 p.m., Joe Stringer wrote:
> > Hi folks, picking this up again..
> [..]
> > During LSFMM, it seemed like no-one knew quite why the skb_orphan() is
> > necessary in that path in the current version of the code, and that we
> > may be able to remove it. Florian, I know you weren't in the room for
> > that discussion, so raising it again now with a stack trace, Do you
> > have some sense what's going on here and whether there's a path
> > towards removing it from this path or allowing the skb->sk to be
> > retained during ip_rcv() in some conditions?
>
>
> Sorry - I havent followed the discussion but saw your email over
> the weekend and wanted to be at work to refresh my memory on some
> code. For maybe 2-3 years we have deployed the tproxy
> equivalent as a tc action on ingress (with no netfilter dependency).
>
> And, of course, we had to work around that specific code you are
> referring to - we didnt remove it. The tc action code increments
> the sk refcount and sets the tc index. The net core doesnt orphan
> the skb if a speacial tc index value is set (see attached patch)
>
> I never bothered up streaming the patch because the hack is a bit
> embarrassing (but worked ;->); and never posted the action code
> either because i thought this was just us that had this requirement.
> I am glad other people see the need for this feature. Is there effort
> to make this _not_ depend on iptables/netfilter? I am guessing if you
> want to do this from ebpf (tc or xdp) that is a requirement.
> Our need was with tcp at the time; so left udp dependency on netfilter
> alone.

I haven't got as far as UDP yet, but I didn't see any need for a
dependency on netfilter.