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KFunc bpf_skb_get_fou_encap

v6.4

Get FOU (Foo over UDP) encap parameters

Definition

This function allows for reading encap metadata from a packet received on an ipip device in collect-metadata mode.

Parameters

skb_ctx: Pointer to ctx (__sk_buff) in TC program. Cannot be NULL

encap: Pointer to a struct bpf_fou_encap storing UDP source and destination port. Cannot be NULL

Returns

0 on success, a negative error code on failure

int bpf_skb_get_fou_encap(struct __sk_buff *skb_ctx, struct bpf_fou_encap *encap)

Usage

On the ingress path bpf_skb_get_fou_encap can be used to read UDP source and destination ports from the receiver's point of view and allows for packet multiplexing across different destination ports within a single BPF program and ipip device.

Program types

The following program types can make use of this kfunc:

Example

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2016 VMware
 * Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */

SEC("tc")
int ipip_gue_set_tunnel(struct __sk_buff *skb)
{
    struct bpf_tunnel_key key = {};
    struct bpf_fou_encap encap = {};
    void *data = (void *)(long)skb->data;
    struct iphdr *iph = data;
    void *data_end = (void *)(long)skb->data_end;
    int ret;

    if (data + sizeof(*iph) > data_end) {
        log_err(1);
        return TC_ACT_SHOT;
    }

    key.tunnel_ttl = 64;
    if (iph->protocol == IPPROTO_ICMP)
        key.remote_ipv4 = 0xac100164; /* 172.16.1.100 */

    ret = bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    encap.sport = 0;
    encap.dport = bpf_htons(5555);

    ret = bpf_skb_set_fou_encap(skb, &encap, FOU_BPF_ENCAP_GUE);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    return TC_ACT_OK;
}

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2016 VMware
 * Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */

SEC("tc")
int ipip_encap_get_tunnel(struct __sk_buff *skb)
{
    int ret;
    struct bpf_tunnel_key key = {};
    struct bpf_fou_encap encap = {};

    ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    ret = bpf_skb_get_fou_encap(skb, &encap);
    if (ret < 0) {
        log_err(ret);
        return TC_ACT_SHOT;
    }

    if (bpf_ntohs(encap.dport) != 5555)
        return TC_ACT_SHOT;

    bpf_printk("%d remote ip 0x%x, sport %d, dport %d\n", ret,
           key.remote_ipv4, bpf_ntohs(encap.sport),
           bpf_ntohs(encap.dport));
    return TC_ACT_OK;
}