netdev - Re: [RFC] Socket termination for policy enforcement and load-balancing

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Date:   Sun, 4 Sep 2022 11:14:30 -0700
From:   Aditi Ghag <aditivghag@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>
Subject: Re: [RFC] Socket termination for policy enforcement and load-balancing

On Wed, Aug 31, 2022 at 4:02 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Wed, Aug 31, 2022 at 09:37:41AM -0700, Aditi Ghag wrote:
> > - Use BPF (sockets) iterator to identify sockets connected to a
> > deleted backend. The BPF (sockets) iterator is network namespace aware
> > so we'll either need to enter every possible container network
> > namespace to identify the affected connections, or adapt the iterator
> > to be without netns checks [3]. This was discussed with my colleague
> > Daniel Borkmann based on the feedback he shared from the LSFMMBPF
> > conference discussions.
> Being able to iterate all sockets across different netns will
> be useful.
>
> It should be doable to ignore the netns check.  For udp, a quick
> thought is to have another iter target. eg. "udp_all_netns".
> From the sk, the bpf prog should be able to learn the netns and
> the bpf prog can filter the netns by itself.
>
> The TCP side is going to have an 'optional' per netns ehash table [0] soon,
> not lhash2 (listening hash) though.  Ideally, the same bpf
> all-netns iter interface should work similarly for both udp and
> tcp case.  Thus, both should be considered and work at the same time.
>
> For udp, something more useful than plain udp_abort() could potentially
> be done.  eg. directly connect to another backend (by bpf kfunc?).
> There may be some details in socket locking...etc but should
> be doable and the bpf-iter program could be sleepable also.

This won't be effective for connected udp though, will it? Interesting thought
around using bpf kfunc!

> fwiw, we are iterating the tcp socket to retire some older
> bpf-tcp-cc (congestion control) on the long-lived connections
> by bpf_setsockopt(TCP_CONGESTION).
>
> Also, potentially, instead of iterating all,
> a more selective case can be done by
> bpf_prog_test_run()+bpf_sk_lookup_*()+udp_abort().

Can you elaborate more on the more selective iterator approach?

On a similar note, are there better ways as alternatives to the
sockets iterator approach.
Since we have BPF programs executed on cgroup BPF hooks (e.g.,
connect), we already know what client
sockets are connected to a backend. Can we somehow store these socket
pointers in a regular BPF map, and
when a backend is deleted, use a regular map iterator to invoke
sock_destroy() for these sockets? Does anyone have
experience using the "typed pointer support in BPF maps" APIs [0]?

[0] https://lwn.net/ml/bpf/20220424214901.2743946-1-memxor@gmail.com/