netdev - Re: [PATCH bpf-next v2 05/17] inet: Run SK_LOOKUP BPF program on socket lookup

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Date:   Fri, 15 May 2020 08:07:42 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jakub Sitnicki <jakub@...udflare.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, dccp@...r.kernel.org,
        kernel-team@...udflare.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Gerrit Renker <gerrit@....abdn.ac.uk>,
        Jakub Kicinski <kuba@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Marek Majkowski <marek@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [PATCH bpf-next v2 05/17] inet: Run SK_LOOKUP BPF program on
 socket lookup

On Fri, May 15, 2020 at 02:28:30PM +0200, Jakub Sitnicki wrote:
> On Mon, May 11, 2020 at 10:44 PM CEST, Alexei Starovoitov wrote:
> > On Mon, May 11, 2020 at 08:52:06PM +0200, Jakub Sitnicki wrote:
> >> Run a BPF program before looking up a listening socket on the receive path.
> >> Program selects a listening socket to yield as result of socket lookup by
> >> calling bpf_sk_assign() helper and returning BPF_REDIRECT code.
> >>
> >> Alternatively, program can also fail the lookup by returning with BPF_DROP,
> >> or let the lookup continue as usual with BPF_OK on return.
> >>
> >> This lets the user match packets with listening sockets freely at the last
> >> possible point on the receive path, where we know that packets are destined
> >> for local delivery after undergoing policing, filtering, and routing.
> >>
> >> With BPF code selecting the socket, directing packets destined to an IP
> >> range or to a port range to a single socket becomes possible.
> >>
> >> Suggested-by: Marek Majkowski <marek@...udflare.com>
> >> Reviewed-by: Lorenz Bauer <lmb@...udflare.com>
> >> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> >> ---
> 
> [...]
> 
> > Also please switch to bpf_link way of attaching. All system wide attachments
> > should be visible and easily debuggable via 'bpftool link show'.
> > Currently we're converting tc and xdp hooks to bpf_link. This new hook
> > should have it from the beginning.
> 
> Just to clarify, I understood that bpf(BPF_PROG_ATTACH/DETACH) doesn't
> have to be supported for new hooks.

Yes. Not only no need. I don't think attach/detach fits.