netdev - Re: [PATCHv3 bpf-next 0/5] Add bpf_sk

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Date:   Fri, 27 Mar 2020 10:13:51 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Joe Stringer <joe@...d.net.nz>, bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org,
        eric.dumazet@...il.com, lmb@...udflare.com, kafai@...com,
        Roman Mashak <mrv@...atatu.com>
Subject: Re: [PATCHv3 bpf-next 0/5] Add bpf_sk_assign eBPF helper

On 2020-03-27 12:25 a.m., Joe Stringer wrote:
> Introduce a new helper that allows assigning a previously-found socket
> to the skb as the packet is received towards the stack, to cause the
> stack to guide the packet towards that socket subject to local routing
> configuration. The intention is to support TProxy use cases more
> directly from eBPF programs attached at TC ingress, to simplify and
> streamline Linux stack configuration in scale environments with Cilium.
> 
> Normally in ip{,6}_rcv_core(), the skb will be orphaned, dropping any
> existing socket reference associated with the skb. Existing tproxy
> implementations in netfilter get around this restriction by running the
> tproxy logic after ip_rcv_core() in the PREROUTING table. However, this
> is not an option for TC-based logic (including eBPF programs attached at
> TC ingress).
> 
> This series introduces the BPF helper bpf_sk_assign() to associate the
> socket with the skb on the ingress path as the packet is passed up the
> stack. The initial patch in the series simply takes a reference on the
> socket to ensure safety, but later patches relax this for listen
> sockets.
> 
> To ensure delivery to the relevant socket, we still consult the routing
> table, for full examples of how to configure see the tests in patch #5;
> the simplest form of the route would look like this:
> 
>    $ ip route add local default dev lo
> 

Trying to understand so if we can port our tc action (and upstream),
we would need to replicate:

  bpf_sk_assign() - invoked everytime we succeed finding the sk
  bpf_sk_release() - invoked everytime we are done processing the sk

Anything else i missed?

cheers,
jamal