esp-idf/examples/network/sta_to_eth/main/ethernet_iface.c

/*
 * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
 *
 * SPDX-License-Identifier: Unlicense OR CC0-1.0
 */
#include <string.h>
#include "esp_log.h"
#include "esp_netif.h"
#include "esp_event.h"
#include "wired_iface.h"
#include "dhcpserver/dhcpserver_options.h"
#include "esp_mac.h"
#include "ethernet_init.h"

/**
 *  Disable promiscuous mode on Ethernet interface by setting this macro to 0
 *  if disabled, we'd have to rewrite MAC addressed in frames with the actual Eth interface MAC address
 *  - this results in better throughput
 *  - might cause ARP conflicts if the PC is also connected to the same AP with another NIC
 */
#define ETH_BRIDGE_PROMISCUOUS  0

static const char *TAG = "example_wired_ethernet";
static esp_netif_t *s_netif = NULL;
static esp_eth_handle_t s_eth_handle = NULL;
static bool s_ethernet_is_connected = false;
static uint8_t s_eth_mac[6];
static wired_rx_cb_t s_rx_cb = NULL;
static wired_free_cb_t s_free_cb = NULL;

/**
 * @brief Event handler for Ethernet events
 */
void eth_event_handler(void *arg, esp_event_base_t event_base,
                       int32_t event_id, void *event_data)
{
    uint8_t mac_addr[6] = {0};
    /* we can get the ethernet driver handle from event data */
    esp_eth_handle_t eth_handle = *(esp_eth_handle_t *)event_data;

    switch (event_id) {
        case ETHERNET_EVENT_CONNECTED:
            esp_eth_ioctl(eth_handle, ETH_CMD_G_MAC_ADDR, mac_addr);
            ESP_LOGI(TAG, "Ethernet Link Up");
            ESP_LOGI(TAG, "Ethernet HW Addr %02x:%02x:%02x:%02x:%02x:%02x",
                     mac_addr[0], mac_addr[1], mac_addr[2], mac_addr[3], mac_addr[4], mac_addr[5]);
            s_ethernet_is_connected = true;
            break;
        case ETHERNET_EVENT_DISCONNECTED:
            ESP_LOGI(TAG, "Ethernet Link Down");
            s_ethernet_is_connected = false;
            break;
        case ETHERNET_EVENT_START:
            ESP_LOGI(TAG, "Ethernet Started");
            break;
        case ETHERNET_EVENT_STOP:
            ESP_LOGI(TAG, "Ethernet Stopped");
            break;
        default:
            ESP_LOGI(TAG, "Default Event");
            break;
    }
}

/**
 *  In this scenario of WiFi station to Ethernet bridge mode, we have this configuration
 *
 *   (ISP) router        ESP32               PC
 *      [ AP ] <->   [ sta -- eth ] <->  [ eth-NIC ]
 *
 *  From the PC's NIC perspective the L2 forwarding should be transparent and resemble this configuration:
 *
 *   (ISP) router                           PC
 *      [ AP ]       <---------->       [ virtual wifi-NIC ]
 *
 *  In order for the ESP32 to act as L2 bridge it needs to accept all frames on the interface
 *  - For Ethernet we just enable `PROMISCUOUS` mode
 *  - For Wifi we could also enable the promiscuous mode, but in that case we'd receive encoded frames
 *    from 802.11 and we'd have to decode it and process (using wpa-supplicant).
 *    The easier option (in this scenario of only one client -- eth-NIC) we could simply "pretend"
 *    that we have the HW mac address of eth-NIC and receive only ethernet frames for "us" from esp_wifi API
 *  (we could use the same technique for Ethernet and yield better throughput, see ETH_BRIDGE_PROMISCUOUS flag)
 *
 *  This API updates Ethernet frames to swap mac addresses of ESP32 interfaces with those of eth-NIC and AP.
 *  For that we'd have to parse initial DHCP packets (manually) to record the HW addresses of the AP and eth-NIC
 *  (note, that it is possible to simply spoof the MAC addresses, but that's not recommended technique)
 */
#define IP_V4 0x40
#define IP_PROTO_UDP 0x11
#define DHCP_PORT_IN 0x43
#define DHCP_PORT_OUT 0x44
#define DHCP_MACIG_COOKIE_OFFSET (8 + 236)
#define MIN_DHCP_PACKET_SIZE (285)
#define IP_HEADER_SIZE (20)
#define DHCP_DISCOVER 1
#define DHCP_OFFER 2
#define DHCP_COOKIE_WITH_PKT_TYPE(type) {0x63, 0x82, 0x53, 0x63, 0x35, 1, type};

void mac_spoof(mac_spoof_direction_t direction, uint8_t *buffer, uint16_t len, uint8_t own_mac[6])
{
    if (!s_ethernet_is_connected) {
        return;
    }
    static uint8_t eth_nic_mac[6] = {};
    static bool eth_nic_mac_found = false;
#if !ETH_BRIDGE_PROMISCUOUS
    static uint8_t ap_mac[6] = {};
    static bool ap_mac_found = false;
#endif
    uint8_t *dest_mac = buffer;
    uint8_t *src_mac = buffer + 6;
    uint8_t *eth_type = buffer + 12;
    if (eth_type[0] == 0x08) {      // support only IPv4
        // try to find NIC HW address (look for DHCP discovery packet)
        if (!eth_nic_mac_found && direction == FROM_WIRED && eth_type[1] == 0x00) {  // ETH IP4
            uint8_t *ip_header = eth_type + 2;
            if (len > MIN_DHCP_PACKET_SIZE && (ip_header[0] & 0xF0) == IP_V4 && ip_header[9] == IP_PROTO_UDP) {
                uint8_t *udp_header = ip_header + IP_HEADER_SIZE;
                const uint8_t dhcp_ports[] = {0, DHCP_PORT_OUT, 0, DHCP_PORT_IN};
                if (memcmp(udp_header, dhcp_ports, sizeof(dhcp_ports)) == 0) {
                    uint8_t *dhcp_magic = udp_header + DHCP_MACIG_COOKIE_OFFSET;
                    const uint8_t dhcp_type[] = DHCP_COOKIE_WITH_PKT_TYPE(DHCP_DISCOVER);
                    if (memcmp(dhcp_magic, dhcp_type, sizeof(dhcp_type)) == 0) {
                        eth_nic_mac_found = true;
                        memcpy(eth_nic_mac, src_mac, 6);
                    }
                }   // DHCP
            } // UDP/IP
#if !ETH_BRIDGE_PROMISCUOUS
            // try to find AP HW address (look for DHCP offer packet)
        } else if (!ap_mac_found && direction == TO_WIRED && eth_type[1] == 0x00) {  // ETH IP4
            uint8_t *ip_header = eth_type + 2;
            if (len > MIN_DHCP_PACKET_SIZE && (ip_header[0] & 0xF0) == IP_V4 && ip_header[9] == IP_PROTO_UDP) {
                uint8_t *udp_header = ip_header + IP_HEADER_SIZE;
                const uint8_t dhcp_ports[] = {0, DHCP_PORT_IN, 0, DHCP_PORT_OUT};
                if (memcmp(udp_header, dhcp_ports, sizeof(dhcp_ports)) == 0) {
                    uint8_t *dhcp_magic = udp_header + DHCP_MACIG_COOKIE_OFFSET;
                    const uint8_t dhcp_type[] = DHCP_COOKIE_WITH_PKT_TYPE(DHCP_OFFER);
                    if (memcmp(dhcp_magic, dhcp_type, sizeof(dhcp_type)) == 0) {
                        ap_mac_found = true;
                        memcpy(ap_mac, src_mac, 6);
                    }
                }   // DHCP
            } // UDP/IP
#endif // !ETH_BRIDGE_PROMISCUOUS
        }

        // swap addresses in ARP probes
        if (eth_type[1] == 0x06) { // ARP
            uint8_t *arp = eth_type + 2 + 8; // points to sender's HW address
            if (eth_nic_mac_found && direction == FROM_WIRED && memcmp(arp, eth_nic_mac, 6) == 0) {
                /* updates senders HW address to our wireless */
                memcpy(arp, own_mac, 6);
#if !ETH_BRIDGE_PROMISCUOUS
            } else if (ap_mac_found && direction == TO_WIRED && memcmp(arp, ap_mac, 6) == 0) {
                /* updates senders HW address to our wired */
                memcpy(arp, s_eth_mac, 6);
#endif // !ETH_BRIDGE_PROMISCUOUS
            }
        }
        // swap HW addresses in ETH frames
#if !ETH_BRIDGE_PROMISCUOUS
        if (ap_mac_found && direction == FROM_WIRED && memcmp(dest_mac, s_eth_mac, 6) == 0) {
            memcpy(dest_mac, ap_mac, 6);
        }
        if (ap_mac_found && direction == TO_WIRED && memcmp(src_mac, ap_mac, 6) == 0) {
            memcpy(src_mac, s_eth_mac, 6);
        }
#endif // !ETH_BRIDGE_PROMISCUOUS
        if (eth_nic_mac_found && direction == FROM_WIRED && memcmp(src_mac, eth_nic_mac, 6) == 0) {
            memcpy(src_mac, own_mac, 6);
        }
        if (eth_nic_mac_found && direction == TO_WIRED && memcmp(dest_mac, own_mac, 6) == 0) {
            memcpy(dest_mac, eth_nic_mac, 6);
        }
    }   // IP4 section of eth-type (0x08) both ETH-IP4 and ETHARP
}

static esp_err_t wired_recv(esp_eth_handle_t eth_handle, uint8_t *buffer, uint32_t len, void *priv)
{
    esp_err_t ret = s_rx_cb(buffer,len, buffer);
    free(buffer);
    return ret;
}

esp_err_t wired_bridge_init(wired_rx_cb_t rx_cb, wired_free_cb_t free_cb)
{
    uint8_t eth_port_cnt = 0;
    esp_eth_handle_t *eth_handles;
    ESP_ERROR_CHECK(example_eth_init(&eth_handles, &eth_port_cnt));

    // Check or multiple ethernet interface
    if (1 < eth_port_cnt) {
        ESP_LOGW(TAG, "Multiple Ethernet Interface detected: Only the first initialized interface is going to be used.");
    }
    s_eth_handle = eth_handles[0];
    free(eth_handles);
    ESP_ERROR_CHECK(esp_eth_update_input_path(s_eth_handle, wired_recv, NULL));
#if ETH_BRIDGE_PROMISCUOUS
    bool eth_promiscuous = true;
    ESP_ERROR_CHECK(esp_eth_ioctl(s_eth_handle, ETH_CMD_S_PROMISCUOUS, &eth_promiscuous));
#endif
    ESP_ERROR_CHECK(esp_eth_ioctl(s_eth_handle, ETH_CMD_G_MAC_ADDR, &s_eth_mac));
    ESP_ERROR_CHECK(esp_event_handler_register(ETH_EVENT, ESP_EVENT_ANY_ID, eth_event_handler, NULL));
    ESP_ERROR_CHECK(esp_eth_start(s_eth_handle));
    s_rx_cb = rx_cb;
    s_free_cb = free_cb;
    return ESP_OK;
}

esp_err_t wired_send(void *buffer, uint16_t len, void *buff_free_arg)
{
    if (s_ethernet_is_connected) {
        if (esp_eth_transmit(s_eth_handle, buffer, len) != ESP_OK) {
            ESP_LOGE(TAG, "Ethernet send packet failed");
            return ESP_FAIL;
        }
        if (s_free_cb) {
            s_free_cb(buff_free_arg, NULL);
        }
        return ESP_OK;
    }
    return ESP_ERR_INVALID_STATE;
}

/**
 *  In this scenario of configuring WiFi, we setup Ethernet to create a network and run DHCP server,
 *  so it could assign an IP address to the PC
 *
 *           ESP32               PC
 *      | <DHCP server>   eth | <->  [ eth-NIC ]
 *      | <HTTP server>       |
 *      | (wifi-provisioning) |
 *
 *  From the PC's NIC perspective the board acts as a separate network with it's own IP and MAC address
 *  (this network's MAC address is the native ESP32's Ethernet interface MAC)
 */
static void l2_free(void *h, void* buffer)
{
    free(buffer);
}

static esp_err_t netif_transmit (void *h, void *buffer, size_t len)
{
    if (wired_send(buffer, len, buffer) != ESP_OK) {
        ESP_LOGE(TAG, "Failed to send buffer to USB!");
    }
    return ESP_OK;
}

static esp_err_t netif_recv_callback(esp_eth_handle_t eth_handle, uint8_t *buffer, uint32_t len, void *priv)
{
    if (s_netif) {
        void *buf_copy = malloc(len);
        if (!buf_copy) {
            return ESP_ERR_NO_MEM;
        }
        memcpy(buf_copy, buffer, len);
        return esp_netif_receive(s_netif, buf_copy, len, NULL);
    }
    return ESP_OK;
}

esp_err_t wired_netif_init(void)
{
    uint8_t eth_port_cnt = 0;
    esp_eth_handle_t *eth_handles;
    ESP_ERROR_CHECK(example_eth_init(&eth_handles, &eth_port_cnt));

    // Check or multiple ethernet interface
    if (1 < eth_port_cnt) {
        ESP_LOGW(TAG, "Multiple Ethernet Interface detected: Only the first initialized interface is going to be used.");
    }
    s_eth_handle = eth_handles[0];
    free(eth_handles);
    ESP_ERROR_CHECK(esp_eth_update_input_path(s_eth_handle, netif_recv_callback, NULL));

    // 1) Derive the base config from the default AP (using DHCP server)
    esp_netif_inherent_config_t base_cfg = ESP_NETIF_INHERENT_DEFAULT_WIFI_AP();
    base_cfg.if_key = "wired";
    base_cfg.if_desc = "ethernet config device";
    // 2) Use static config for driver's config pointing only to static transmit and free functions
    esp_netif_driver_ifconfig_t driver_cfg = {
            .handle = (void*)1,     // will be replaced by the driver pointer only tinyusb_net supports ti
            .transmit = netif_transmit,
            .driver_free_rx_buffer = l2_free
    };

    // Config the esp-netif with:
    //   1) inherent config (behavioural settings of an interface)
    //   2) driver's config (connection to IO functions -- usb)
    //   3) stack config (using lwip IO functions -- derive from eth)
    esp_netif_config_t cfg = {
            .base = &base_cfg,
            .driver = &driver_cfg,
            // 3) use ethernet style of lwip netif settings
            .stack = ESP_NETIF_NETSTACK_DEFAULT_ETH
    };

    s_netif = esp_netif_new(&cfg);
    if (s_netif == NULL) {
        return ESP_FAIL;
    }

    uint8_t mac[6];
    ESP_ERROR_CHECK(esp_eth_ioctl(s_eth_handle, ETH_CMD_G_MAC_ADDR, &mac));
    esp_netif_set_mac(s_netif, mac);

    // set the minimum lease time
    uint32_t  lease_opt = 1;
    esp_netif_dhcps_option(s_netif, ESP_NETIF_OP_SET, IP_ADDRESS_LEASE_TIME, &lease_opt, sizeof(lease_opt));
    ESP_ERROR_CHECK(esp_event_handler_register(ETH_EVENT, ESP_EVENT_ANY_ID, eth_event_handler, NULL));
    ESP_ERROR_CHECK(esp_eth_start(s_eth_handle));

    // start the interface manually (as the driver has been started already)
    esp_netif_action_start(s_netif, 0, 0, 0);
    return ESP_OK;
}