echo_dispatch.bpf.c

// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
/* Copyright (c) 2020 Cloudflare */
/*
 * BPF socket lookup program that dispatches connections destined to a
 * configured set of open ports, to the echo service socket.
 *
 * Program expects the echo service socket to be in the `echo_socket` BPF map.
 * Port is considered open when an entry for that port number exists in the
 * `echo_ports` BPF hashmap.
 *
 */

#include <linux/bpf.h>

#include <bpf/bpf_endian.h>
#include <bpf/bpf_helpers.h>

/* Declare BPF maps */

/* List of open echo service ports. Key is the port number. */
struct bpf_map_def SEC("maps") echo_ports = {
	.type		= BPF_MAP_TYPE_HASH,
	.max_entries	= 1024,
	.key_size	= sizeof(__u16),
	.value_size	= sizeof(__u8),
};

/* Echo server socket */
struct bpf_map_def SEC("maps") echo_socket = {
	.type		= BPF_MAP_TYPE_SOCKMAP,
	.max_entries	= 1,
	.key_size	= sizeof(__u32),
	.value_size	= sizeof(__u64),
};

/* Dispatcher program for the echo service */
SEC("sk_lookup/echo_dispatch")
int echo_dispatch(struct bpf_sk_lookup *ctx)
{
	const __u32 zero = 0;
	struct bpf_sock *sk;
	__u16 port;
	__u8 *open;
	long err;

	/* Is echo service enabled on packets destination port? */
	port = ctx->local_port;
	open = bpf_map_lookup_elem(&echo_ports, &port);
	if (!open)
		return SK_PASS;

	/* Get echo server socket */
	sk = bpf_map_lookup_elem(&echo_socket, &zero);
	if (!sk)
		return SK_DROP;

	/* Dispatch the packet to echo server socket */
	err = bpf_sk_assign(ctx, sk, 0);
	bpf_sk_release(sk);
	return err ? SK_DROP : SK_PASS;
}

SEC("license") const char __license[] = "Dual BSD/GPL";