On Fri, Mar 27, 2020 at 11:46 AM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> 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@xxxxxx>
Thanks for the reviews!
I've rolled in the current nits + acks into the branch below, pending
any further feedback. Alexei, happy to respin this on the mailinglist
at some point if that's easier for you.
https://github.com/joestringer/linux/tree/submit/bpf-sk-assign-v3+
