utun demo in macos

macos-utun.c

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/sys_domain.h>
#include <sys/kern_control.h>
#include <net/if_utun.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <stdlib.h> // exit, etc.

// Simple User-Tunneling Proof of Concept - extends listing 17-15 in book
// Compiles for both iOS and OS X..

int tun(char name[20]) {
	struct sockaddr_ctl sc;
	struct ctl_info ctlInfo;
	int fd;

	memset(&ctlInfo, 0, sizeof(ctlInfo));
	if (strlcpy(ctlInfo.ctl_name, UTUN_CONTROL_NAME, sizeof(ctlInfo.ctl_name)) >=
	    sizeof(ctlInfo.ctl_name)) {
		fprintf(stderr,"UTUN_CONTROL_NAME too long");
		return -1;
	}
	fd = socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL);
 	
	if (fd == -1) {
		perror ("socket(SYSPROTO_CONTROL)");
		return -1;
	}
	if (ioctl(fd, CTLIOCGINFO, &ctlInfo) == -1) {
		perror ("ioctl(CTLIOCGINFO)");
		close(fd);
		return -1;
	}

	sc.sc_id = ctlInfo.ctl_id;
	sc.sc_len = sizeof(sc);
	sc.sc_family = AF_SYSTEM;
	sc.ss_sysaddr = AF_SYS_CONTROL;
	sc.sc_unit = 0;	/* create now interface, in this example... */
	
	// If the connect is successful, a tun%d device will be created, where "%d"
 	// is our unit number -1

	if (connect(fd, (struct sockaddr *)&sc, sizeof(sc)) == -1) {
		perror ("connect(AF_SYS_CONTROL)");
		close(fd);
		return -1;
	}

    char ifname[20] = { 0 };
    socklen_t ifname_len = sizeof(ifname);
    getsockopt(fd, SYSPROTO_CONTROL, UTUN_OPT_IFNAME, ifname, &ifname_len);
	strncpy(name, ifname, ifname_len);

	return fd;
}

int 
main (int argc, char **argv)
{
  char name[20] = { 0 };
  int utunfd = tun (name);

  if (utunfd == -1) {
    fprintf(stderr,"Unable to establish UTUN descriptor - aborting\n");
    exit(1);
  }

  fprintf(stderr,"Utun interface is up.. Configure IPv4 using \"ifconfig %s _ipA_ _ipB_\"\n", name);
  fprintf(stderr,"                       Configure IPv6 using \"ifconfig %s inet6 _ip6_\"\n", name);
  fprintf(stderr,"Then (e.g.) ping _ipB_ (IPv6 will automatically generate ND messages)\n");

  // PoC - Just dump the packets...
  for (;;) {
		unsigned char 	c[1500];
		int     len;
		int	i;

		len = read (utunfd,c, 1500);

		// First 4 bytes of read data are the AF: 2 for AF_INET, 1E for AF_INET6, etc..
		for (i = 4; i< len; i++) {
		   printf ("%02x ", c[i]);
		   if ( (i-4)%16 ==15) printf("\n");
		}
		printf ("\n");
	}

   return(0);
}