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Date:   Wed, 29 Apr 2020 12:19:54 -0700
From:   John Fastabend <>
To:     Jakub Sitnicki <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Joe Stringer <>,
        John Fastabend <>,
        Lorenz Bauer <>,
        Martin KaFai Lau <>
Subject: RE: [PATCH bpf-next 1/3] bpf: Allow bpf_map_lookup_elem for SOCKMAP

Jakub Sitnicki wrote:
> White-list map lookup for SOCKMAP/SOCKHASH from BPF. Lookup returns a
> pointer to a full socket and acquires a reference if necessary.
> To support it we need to extend the verifier to know that:
>  (1) register storing the lookup result holds a pointer to socket, if
>      lookup was done on SOCKMAP/SOCKHASH, and that
>  (2) map lookup on SOCKMAP/SOCKHASH is a reference acquiring operation,
>      which needs a corresponding reference release with bpf_sk_release.
> On sock_map side, lookup handlers exposed via bpf_map_ops now bump
> sk_refcnt if socket is reference counted. In turn, bpf_sk_select_reuseport,
> the only in-kernel user of SOCKMAP/SOCKHASH ops->map_lookup_elem, was
> updated to release the reference.
> Sockets fetched from a map can be used in the same way as ones returned by
> BPF socket lookup helpers, such as bpf_sk_lookup_tcp. In particular, they
> can be used with bpf_sk_assign to direct packets toward a socket on TC
> ingress path.
> Suggested-by: Lorenz Bauer <>
> Signed-off-by: Jakub Sitnicki <>
> ---

LGTM thanks!

Acked-by: John Fastabend <>

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