On Thu, Sep 27, 2018 at 04:26:54PM -0700, Joe Stringer wrote:
> This patch adds new BPF helper functions, bpf_sk_lookup_tcp() and
> bpf_sk_lookup_udp() which allows BPF programs to find out if there is a
> socket listening on this host, and returns a socket pointer which the
> BPF program can then access to determine, for instance, whether to
> forward or drop traffic. bpf_sk_lookup_xxx() may take a reference on the
> socket, so when a BPF program makes use of this function, it must
> subsequently pass the returned pointer into the newly added sk_release()
> to return the reference.
>
> By way of example, the following pseudocode would filter inbound
> connections at XDP if there is no corresponding service listening for
> the traffic:
>
> struct bpf_sock_tuple tuple;
> struct bpf_sock_ops *sk;
>
> populate_tuple(ctx, &tuple); // Extract the 5tuple from the packet
> sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof tuple, netns, 0);
> if (!sk) {
> // Couldn't find a socket listening for this traffic. Drop.
> return TC_ACT_SHOT;
> }
> bpf_sk_release(sk);
> return TC_ACT_OK;
>
> Signed-off-by: Joe Stringer <j...@wand.net.nz>
> ---
> v2: Rework 'struct bpf_sock_tuple' to allow passing a packet pointer
> Limit netns_id field to 32 bits
> Fix compile error with CONFIG_IPV6 enabled
> Allow direct packet access from helper
>
> v3: Fix release of caller_net when netns is not specified.
> Use skb->sk to find caller net when skb->dev is unavailable.
> Remove flags argument to sk_release()
> Define the semantics of the new helpers more clearly.
Acked-by: Alexei Starovoitov <a...@kernel.org>
