/* Copyright (c) 2011 Ethan Blanton */
/*
 * To compile this program, execute:
 *
 *     gcc -o tuncreate tuncreate.c
 *
 * To create a tun device, execute it as:
 *
 *     tuncreate <device> <user>
 *
 * Where <device> is the network device name to be created, and <user>
 * is a non-root username which should have access to the device.  For
 * example, to create a tun device tun0 which may be manipulated by
 * user elb:
 *
 *      tuncreate tun0 elb
 */

#include <stdio.h>
#include <fcntl.h>
#include <string.h>

#include <sys/types.h>
#include <pwd.h>

#include <sys/ioctl.h>
#include <net/if.h>
#include <linux/if_tun.h>

int main(int argc, char *argv[])
{
    struct ifreq ifr;
    struct passwd *pwent;
    int fd;

    if (argc != 3) {
        fprintf(stderr, "usage: %s <device> <user>\n", argv[0]);
        return -1;
    }

    if ((pwent = getpwnam(argv[2])) == NULL) {
        perror("Could not find user");
        return -1;
    }

    if ((fd = open("/dev/net/tun", O_RDWR)) < 0) {
        perror("Could not open tun control device");
        return -1;
    }

    memset(&ifr, 0, sizeof(ifr));
    ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
    strncpy(ifr.ifr_name, argv[1], IFNAMSIZ);

    if (ioctl(fd, TUNSETIFF, (void *)&ifr) < 0) {
        perror("Could not configure device");
        return -1;
    }
    if (ioctl(fd, TUNSETPERSIST, 1) < 0) {
        perror("Could not set device persistent");
        return -1;
    }
    if (ioctl(fd, TUNSETOWNER, pwent->pw_uid) < 0) {
        perror("Could not set device owner");
        return -1;
    }

    return 0;
}