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