Re: [PATCHv3 bpf-next 0/5] Add bpf_sk_assign eBPF helper

[Martin KaFai Lau <kafai@fb.com>]

On Thu, Mar 26, 2020 at 09:25:51PM -0700, 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
> 
> This series is laid out as follows:
> * Patch 1 extends the eBPF API to add sk_assign() and defines a new
>   socket free function to allow the later paths to understand when the
>   socket associated with the skb should be kept through receive.
> * Patches 2-3 optimize the receive path to avoid taking a reference on
>   listener sockets during receive.
> * Patches 4-5 extends the selftests with examples of the new
>   functionality and validation of correct behaviour.
> 
> Changes since v2:
> * Add selftests for UDP socket redirection
> * Drop the early demux optimization patch (defer for more testing)
> * Fix check for orphaning after TC act return
> * Tidy up the tests to clean up properly and be less noisy.
> 
> Changes since v1:
> * Replace the metadata_dst approach with using the skb->destructor to
>   determine whether the socket has been prefetched. This is much
>   simpler.
> * Avoid taking a reference on listener sockets during receive
> * Restrict assigning sockets across namespaces
> * Restrict assigning SO_REUSEPORT sockets
> * Fix cookie usage for socket dst check
> * Rebase the tests against test_progs infrastructure
> * Tidy up commit messages
lgtm.

Acked-by: Martin KaFai Lau <kafai@fb.com>