tuntap_linux.c

/**
 * (C) 2007-18 - ntop.org and contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not see see <http://www.gnu.org/licenses/>
 *
 */

#include "n2n.h"

#ifdef __linux__

#include <net/if_arp.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>

/* ********************************** */

static int setup_ifname(int fd, const char *ifname, const char *ipaddr,
          const char *netmask, uint8_t *mac, int mtu) {
  struct ifreq ifr;

  memset(&ifr, 0, sizeof(ifr));

  strncpy(ifr.ifr_name, ifname, IFNAMSIZ);
  ifr.ifr_name[IFNAMSIZ-1] = '\0';

  ifr.ifr_hwaddr.sa_family = ARPHRD_ETHER;
  memcpy(ifr.ifr_hwaddr.sa_data, mac, 6);

  if(ioctl(fd, SIOCSIFHWADDR, &ifr) == -1) {
    traceEvent(TRACE_ERROR, "ioctl(SIOCSIFHWADDR) failed [%d]: %s", errno, strerror(errno));
    return(-1);
  }

  ifr.ifr_addr.sa_family = AF_INET;

  /* Interface Address */
  inet_pton(AF_INET, ipaddr, &((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr);
  if(ioctl(fd, SIOCSIFADDR, &ifr) == -1) {
    traceEvent(TRACE_ERROR, "ioctl(SIOCSIFADDR) failed [%d]: %s", errno, strerror(errno));
    return(-2);
  }

  /* Netmask */
  if(netmask && (((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr.s_addr != 0)) {
    inet_pton(AF_INET, netmask, &((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr);
    if(ioctl(fd, SIOCSIFNETMASK, &ifr) == -1) {
      traceEvent(TRACE_ERROR, "ioctl(SIOCSIFNETMASK, %s) failed [%d]: %s", netmask, errno, strerror(errno));
      return(-3);
    }
  }

  /* MTU */
  ifr.ifr_mtu = mtu;
  if(ioctl(fd, SIOCSIFMTU, &ifr) == -1) {
    traceEvent(TRACE_ERROR, "ioctl(SIOCSIFMTU) failed [%d]: %s", errno, strerror(errno));
    return(-4);
  }

  /* Set up and running */
  if(ioctl(fd, SIOCGIFFLAGS, &ifr) == -1) {
    traceEvent(TRACE_ERROR, "ioctl(SIOCGIFFLAGS) failed [%d]: %s", errno, strerror(errno));
    return(-5);
  }

  ifr.ifr_flags |= (IFF_UP | IFF_RUNNING);

  if(ioctl(fd, SIOCSIFFLAGS, &ifr) == -1) {
    traceEvent(TRACE_ERROR, "ioctl(SIOCSIFFLAGS) failed [%d]: %s", errno, strerror(errno));
    return(-6);
  }

  return(0);
}

/* ********************************** */

/** @brief  Open and configure the TAP device for packet read/write.
 *
 *  This routine creates the interface via the tuntap driver and then
 *  configures it.
 *
 *  @param device      - [inout] a device info holder object
 *  @param dev         - user-defined name for the new iface, 
 *                       if NULL system will assign a name
 *  @param device_ip   - address of iface
 *  @param device_mask - netmask for device_ip
 *  @param mtu         - MTU for device_ip
 *
 *  @return - negative value on error
 *          - non-negative file-descriptor on success
 */
int tuntap_open(tuntap_dev *device, 
                char *dev, /* user-definable interface name, eg. edge0 */
                const char *address_mode, /* static or dhcp */
                char *device_ip, 
                char *device_mask,
                const char * device_mac,
		int mtu) {
  char *tuntap_device = "/dev/net/tun";
  int ioctl_fd;
  struct ifreq ifr;
  int rc;
  int nl_fd;
  char nl_buf[8192]; /* >= 8192 to avoid truncation, see "man 7 netlink" */
  struct iovec iov;
  struct sockaddr_nl sa;
  int up_and_running = 0;
  struct msghdr msg;

  device->fd = open(tuntap_device, O_RDWR);
  if(device->fd < 0) {
    traceEvent(TRACE_ERROR, "tuntap open() error: %s[%d]. Is the tun kernel module loaded?\n", strerror(errno), errno);
    return -1;
  }

  memset(&ifr, 0, sizeof(ifr));
  ifr.ifr_flags = IFF_TAP|IFF_NO_PI; /* Want a TAP device for layer 2 frames. */
  strncpy(ifr.ifr_name, dev, IFNAMSIZ-1);
  ifr.ifr_name[IFNAMSIZ-1] = '\0';
  rc = ioctl(device->fd, TUNSETIFF, (void *)&ifr);

  if(rc < 0) {
    traceEvent(TRACE_ERROR, "tuntap ioctl(TUNSETIFF, IFF_TAP) error: %s[%d]\n", strerror(errno), rc);
    close(device->fd);
    return -1;
  }

  /* Store the device name for later reuse */
  strncpy(device->dev_name, ifr.ifr_name, MIN(IFNAMSIZ, N2N_IFNAMSIZ) );

  if(device_mac && device_mac[0]) {
    /* Use the user-provided MAC */
    str2mac(device->mac_addr, device_mac);
  } else {
    /* Set an explicit random MAC to know the exact MAC in use. Manually
     * reading the MAC address is not safe as it may change internally
     * also after the TAP interface UP status has been notified. */
    int i;

    for(i = 0; i < 6; i++)
      device->mac_addr[i] = rand();

    device->mac_addr[0] &= ~0x01; /* Clear multicast bit */
    device->mac_addr[0] |= 0x02;  /* Set locally-assigned bit */
  }

  /* Initialize Netlink socket */
  if((nl_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) == -1) {
    traceEvent(TRACE_ERROR, "netlink socket creation failed [%d]: %s", errno, strerror(errno));
    return -1;
  }

  iov.iov_base = nl_buf;
  iov.iov_len = sizeof(nl_buf);

  memset(&sa, 0, sizeof(sa));
  sa.nl_family = PF_NETLINK;
  sa.nl_groups = RTMGRP_LINK;
  sa.nl_pid = getpid();

  msg.msg_name = &sa;
  msg.msg_namelen = sizeof(sa);
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;

  /* Subscribe to interface events */
  if(bind(nl_fd, (struct sockaddr*)&sa, sizeof(sa)) == -1) {
    traceEvent(TRACE_ERROR, "netlink socket bind failed [%d]: %s", errno, strerror(errno));
    return -1;
  }

  if((ioctl_fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0) {
    traceEvent(TRACE_ERROR, "socket creation failed [%d]: %s", errno, strerror(errno));
    close(nl_fd);
    return -1;
  }

  if(setup_ifname(ioctl_fd, device->dev_name, device_ip, device_mask, device->mac_addr, mtu) < 0) {
    close(nl_fd);
    close(ioctl_fd);
    close(device->fd);
    return -1;
  }

  close(ioctl_fd);

  /* Wait for the up and running notification */
  traceEvent(TRACE_INFO, "Waiting for TAP interface to be up and running...");

  while(!up_and_running) {
    ssize_t len = recvmsg(nl_fd, &msg, 0);
    struct nlmsghdr *nh;

    for(nh = (struct nlmsghdr *)nl_buf; NLMSG_OK(nh, len); nh = NLMSG_NEXT(nh, len)) {
      if(nh->nlmsg_type == NLMSG_ERROR) {
        traceEvent(TRACE_DEBUG, "nh->nlmsg_type == NLMSG_ERROR");
        break;
      }

      if(nh->nlmsg_type == NLMSG_DONE)
        break;

      if(nh->nlmsg_type == NETLINK_GENERIC) {
        struct ifinfomsg *ifi = NLMSG_DATA(nh);

        /* NOTE: skipping interface name check, assuming it's our TAP */
        if((ifi->ifi_flags & IFF_UP) && (ifi->ifi_flags & IFF_RUNNING)) {
          up_and_running = 1;
          traceEvent(TRACE_INFO, "Interface is up and running");
          break;
        }
      }
    }
  }

  close(nl_fd);

  device->ip_addr = inet_addr(device_ip);
  device->device_mask = inet_addr(device_mask);
  return(device->fd);
}

/* *************************************************** */

int tuntap_read(struct tuntap_dev *tuntap, unsigned char *buf, int len) {
  return(read(tuntap->fd, buf, len));
}

/* *************************************************** */

int tuntap_write(struct tuntap_dev *tuntap, unsigned char *buf, int len) {
  return(write(tuntap->fd, buf, len));
}

/* *************************************************** */

void tuntap_close(struct tuntap_dev *tuntap) {
  close(tuntap->fd);
}

/* *************************************************** */

/* Fill out the ip_addr value from the interface. Called to pick up dynamic
 * address changes. */
void tuntap_get_address(struct tuntap_dev *tuntap) {
  struct ifreq ifr;
  int fd;

  if((fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0) {
    traceEvent(TRACE_ERROR, "socket creation failed [%d]: %s", errno, strerror(errno));
    return;
  }

  ifr.ifr_addr.sa_family = AF_INET;
  strncpy(ifr.ifr_name, tuntap->dev_name, IFNAMSIZ);
  ifr.ifr_name[IFNAMSIZ-1] = '\0';

  if(ioctl(fd, SIOCGIFADDR, &ifr) != -1)
    tuntap->ip_addr = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr;

  close(fd);
}

#endif /* #ifdef __linux__ */