Send packet via macvtap device

macvtap-test.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>

#include <arpa/inet.h>
#include <netinet/ether.h>
#include <netinet/ip.h>
#include <netinet/udp.h>

#include <net/if.h>
#include <netinet/in.h>

#define ETH_HDRLEN ETH_HLEN
#define IP4_HDRLEN (sizeof(struct iphdr))
#define UDP_HDRLEN (sizeof(struct udphdr))

#define HOST_IF "mvt1"
#define HOST_IP "10.0.1.54"
#define DEST_IP "179.32.32.11"
#define HOST_PORT 7000
#define DEST_PORT 8000

#define MAC_SRC { 0xbc, 0xae, 0xc5, 0x44, 0x3d, 0x46 }                                                                                     │···································
#define MAC_DST { 0x52, 0x54, 0x00, 0x26, 0xc1, 0x45 }

#define PAYLOAD "Hello World!\n"

void usage(char* proc)
{
  printf("usage: %s [vtap device]\n", proc);
}

size_t build_packet(uint8_t *pkt, size_t pkt_buf_len)
{
  // Sizes
  size_t hdr_len    = ETH_HDRLEN + IP4_HDRLEN + UDP_HDRLEN;
  uint16_t data_len = strlen(PAYLOAD);
  size_t pkt_len    = hdr_len + data_len;

  if (pkt_len > pkt_buf_len) {
    fprintf(stderr, "packet buffer too small! (%lu vs %lu)\n", pkt_len, pkt_buf_len);
    exit(EXIT_FAILURE);
  }

  // Packet
  struct ether_header *ethhdr = (struct ether_header *) pkt;
  struct iphdr  *iphdr  = (struct iphdr *) (pkt + ETH_HDRLEN);
  struct udphdr *udphdr = (struct udphdr *) (pkt + ETH_HDRLEN + IP4_HDRLEN);
  uint8_t *payload      = pkt + hdr_len;

  // Ethernet header
  uint8_t mac_dest[]   = MAC_DST;
  ethhdr->ether_dhost[0] = mac_dest[0];
  ethhdr->ether_dhost[1] = mac_dest[1];
  ethhdr->ether_dhost[2] = mac_dest[2];
  ethhdr->ether_dhost[3] = mac_dest[3];
  ethhdr->ether_dhost[4] = mac_dest[4];
  ethhdr->ether_dhost[5] = mac_dest[5];

  uint8_t mac_source[] = MAC_SRC;
  ethhdr->ether_shost[0] = mac_src[0];
  ethhdr->ether_shost[1] = mac_src[1];
  ethhdr->ether_shost[2] = mac_src[2];
  ethhdr->ether_shost[3] = mac_src[3];
  ethhdr->ether_shost[4] = mac_src[4];
  ethhdr->ether_shost[5] = mac_src[5];

  ethhdr->ether_type = htons(ETH_P_IP);

  // IPv4 header
  iphdr->version = 4;
  iphdr->ihl = 5;
  iphdr->tos = 0;
  iphdr->tot_len = htons(IP4_HDRLEN + UDP_HDRLEN + data_len);
  iphdr->id = htons(8318);
  iphdr->frag_off = 0;
  iphdr->ttl = 255;
  iphdr->protocol = IPPROTO_UDP;
  iphdr->check = 0;
  iphdr->saddr = inet_addr(HOST_IP);
  iphdr->daddr = inet_addr(DEST_IP);

  // IP Checksum
  iphdr->check = internet_checksum(pkt + ETH_HDRLEN, IP4_HDRLEN);

  // UDP header
  udphdr->source = htons(HOST_PORT);
  udphdr->dest = htons(DEST_PORT);
  udphdr->len = htons(UDP_HDRLEN + data_len);
  udphdr->check = 0;

  // Payload
  memcpy (payload, PAYLOAD, data_len);

  return pkt_len;
}

int tap_set_sndbuf(int fd)
{
  int sndbuf = 1024 * 1024;
  if (ioctl(fd, TUNSETSNDBUF, &sndbuf) < 0) {
    perror("ioctl(TUNSETSNDBUF)");
    return -1;
  }
  return 0;
}

int main(int argc, char* argv[])
{
  int err, vtap;
  uint8_t pkt[IP_MAXPACKET];
  size_t pkt_len;

  if (argc != 2) {
    usage(argv[0]);
    exit(EXIT_FAILURE);
  }

  // open ('/dev/tap3', ...);
  if ((vtap = open(argv[1], O_RDWR)) < 0) {
    perror("Failure to open vtap device");
    exit(EXIT_FAILURE);
  }
  
  if (tap_set_sndbuf(vtap) < 0) {
    exit(EXIT_FAILURE);
  }

  // Build packet
  pkt_len = build_packet(pkt, IP_MAXPACKET);
  if (pkt_len < 0) {
    perror("build_packet()");
    exit(EXIT_FAILURE);
  }

  // Send packet
  if ((err = write(vtap, pkt, pkt_len)) < 0) {
    perror("write()");
    printf("err: %d\n", errno);
    exit(EXIT_FAILURE);
  }

  return 0;
}