0219-使用 TAP 来进行通信

环境

• Time 2022-11-20
• WSL-Ubuntu 22.04
• Rust 1.65.0
• pnet 0.31.0
• tun-tap 0.1.3

前言

说明

参考：https://docs.rs/pnet_packet/latest/pnet_packet/index.html
参考：https://www.kernel.org/doc/html/latest/networking/tuntap.html

目标

通过 TAP 来模拟二层设备，接收之前发送的 ARP 请求。

新增设备

root@jiangbo12490:~# ip tuntap add tap0 mode tap
root@jiangbo12490:~# ip addr add 172.24.51.244/24 dev tap0
root@jiangbo12490:~# ip link set up dev tap0
root@jiangbo12490:~# ip addr show tap0
20: tap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether ea:f3:f5:24:7a:dd brd ff:ff:ff:ff:ff:ff
    inet 172.24.51.244/24 scope global tap0
       valid_lft forever preferred_lft forever
    inet6 fe80::e8f3:f5ff:fe24:7add/64 scope link
       valid_lft forever preferred_lft forever

可以通过 ip tuntap add 命令新增 TUN/TAP 设备。

main

use std::net::IpAddr;

use pnet_datalink::{channel, Channel, MacAddr, NetworkInterface};
use pnet_packet::arp::{ArpHardwareTypes, ArpOperations, ArpPacket, MutableArpPacket};
use pnet_packet::ethernet::{EtherTypes, MutableEthernetPacket};
use pnet_packet::{MutablePacket, Packet};

fn main() {
    let interface = pnet_datalink::interfaces()
        .into_iter()
        .find(|iface| iface.name == "tap0")
        .unwrap();

    let channel = channel(&interface, Default::default());
    let (mut sender, mut reader) = match channel {
        Ok(Channel::Ethernet(tx, rx)) => (tx, rx),
        _ => panic!("Not a valid channel returned"),
    };

    let mut ethernet = init_ethernet(&interface);
    let mut arp = init_arp(interface);
    let mut ethernet = MutableEthernetPacket::new(&mut ethernet).unwrap();
    let mut arp = MutableArpPacket::new(&mut arp).unwrap();

    ethernet.set_payload(arp.packet_mut());
    sender.send_to(ethernet.packet(), None).unwrap().unwrap();

    println!("Sent ARP request");
    let buf = reader.next().unwrap();
    let arp = ArpPacket::new(&buf[MutableEthernetPacket::minimum_packet_size()..]).unwrap();
    println!("Target MAC address: {}", arp.get_sender_hw_addr());
}

地址解析协议还是使用之前的一篇的 ARP 请求。

Cargo.toml

[package]
edition = "2021"
name = "network"
version = "1.0.0"

[dependencies]
pnet_datalink = "0.31.0"
pnet_packet = "0.31.0"
tun-tap = "0.1.3"

控制 TAP

use tun_tap::{Iface, Mode};

fn main() -> std::io::Result<()> {
    let iface = Iface::without_packet_info("tap0", Mode::Tap)?;

    let mut buffer = vec![0; 1500];

    loop {
        let size = iface.recv(&mut buffer)?;
        println!("{:?}", &buffer[..size]);
    }
}

抓包结果

19:38:40.700686 ea:f3:f5:24:7a:dd > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 172.24.51.244 tell 172.24.51.244, length 28

程序输出

[255, 255, 255, 255, 255, 255, 234, 243, 245, 36, 122, 221, 8, 6, 0, 1, 8, 0, 6, 4, 0, 1, 234, 243, 245, 36, 122, 221, 172, 24, 51, 244, 0, 0, 0, 0, 0, 0, 172, 24, 51, 244]

程序收到发来的 ARP 请求，并且发送端阻塞了，因为并没有回消息。

总结

新增了 TAP 设备，可以接收链路层的网络包，并且接收到了发送的 ARP 请求。

附录