tap-device-creator.cc

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2009 University of Washington
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <arpa/inet.h>
#include <unistd.h>
#include <stdint.h>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <cstring>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <net/if.h>
#include <linux/if_tun.h>
#include <net/route.h>
#include <netinet/in.h>

#include "creator-utils.h"

#define TAP_MAGIC 95549

//
// Lots of the following helper code taken from corresponding functions in src/node.
//
#define ASCII_DOT (0x2e)
#define ASCII_ZERO (0x30)
#define ASCII_a (0x41)
#define ASCII_z (0x5a)
#define ASCII_A (0x61)
#define ASCII_Z (0x7a)
#define ASCII_COLON (0x3a)
#define ASCII_ZERO (0x30)

using namespace ns3;

struct in6_ifreq {
  struct in6_addr ifr6_addr;      
  uint32_t        ifr6_prefixlen; 
  int32_t         ifr6_ifindex;   
};

char
AsciiToLowCase (char c)
{
  if (c >= ASCII_a && c <= ASCII_z)
    {
      return c;
    }
  else if (c >= ASCII_A && c <= ASCII_Z)
    {
      return c + (ASCII_a - ASCII_A);
    }
  else
    {
      return c;
    }
}

void
AsciiToMac48 (const char *str, uint8_t addr[6])
{
  int i = 0;
  while (*str != 0 && i < 6)
    {
      uint8_t byte = 0;
      while (*str != ASCII_COLON && *str != 0)
        {
          byte <<= 4;
          char low = AsciiToLowCase (*str);
          if (low >= ASCII_a)
            {
              byte |= low - ASCII_a + 10;
            }
          else
            {
              byte |= low - ASCII_ZERO;
            }
          str++;
        }
      addr[i] = byte;
      i++;
      if (*str == 0)
        {
          break;
        }
      str++;
    }
}

void
SetIpv4 (const char *deviceName, const char *ip, const char *netmask)
{
  struct ifreq ifr;
  struct sockaddr_in *sin;

  int sock = socket(AF_INET, SOCK_DGRAM, 0);

  //
  // Set the IP address of the new interface/device.
  //
  memset(&ifr,  0, sizeof(struct ifreq));
  strncpy(ifr.ifr_name, deviceName, IFNAMSIZ - 1);

  sin = (struct sockaddr_in*) &ifr.ifr_addr;
  inet_pton(AF_INET, ip, &sin->sin_addr);
  ifr.ifr_addr.sa_family = AF_INET;

  ABORT_IF (ioctl (sock, SIOCSIFADDR, &ifr) == -1, 
          "Could not set IP address", true);

  LOG ("Set device IP address to " << ip);

  //
  // Set the net mask of the new interface/device
  //
  memset(&ifr,  0, sizeof(struct ifreq));
  strncpy(ifr.ifr_name, deviceName, IFNAMSIZ - 1);

  sin = (struct sockaddr_in*) &ifr.ifr_netmask;
  inet_pton(AF_INET, netmask, &sin->sin_addr);
  ifr.ifr_addr.sa_family = AF_INET;

  ABORT_IF (ioctl (sock, SIOCSIFNETMASK, &ifr) == -1, 
          "Could not set net mask", true);

  LOG ("Set device Net Mask to " << netmask);
  close(sock);
}

void 
SetIpv6 (const char* deviceName, const char *ip, int netprefix)
{
  struct ifreq ifr;
  struct sockaddr_in6 sin;
  struct in6_ifreq ifr6;

  int sock = socket(AF_INET6, SOCK_DGRAM, 0);
  memset(&ifr,  0, sizeof(struct ifreq));
  strncpy(ifr.ifr_name, deviceName, IFNAMSIZ - 1);

  ABORT_IF (ioctl (sock, SIOGIFINDEX, &ifr) == -1, 
          "Could not get interface index", true);

  LOG ("Set device IP v6 address to " << ip);

  memset(&sin, 0, sizeof(struct sockaddr_in6));
  sin.sin6_family = AF_INET6;
  inet_pton(AF_INET6, ip, (void *) &sin.sin6_addr);
  
  memset(&ifr6, 0, sizeof(in6_ifreq));
  memcpy((char *) &ifr6.ifr6_addr, (char *) &sin.sin6_addr, sizeof(struct in6_addr));

  ifr6.ifr6_ifindex = ifr.ifr_ifindex;
  ifr6.ifr6_prefixlen = netprefix;

  //
  // Set the IP address of the new interface/device.
  //
  ABORT_IF (ioctl (sock, SIOCSIFADDR, &ifr6) == -1, 
          "Could not set IP v6 address", true);

  LOG ("Set device IP v6 address to " << ip);
  close (sock);

}

void 
SetMacAddress (int fd, const char* mac)
{
  struct ifreq ifr;
  memset(&ifr,  0, sizeof(struct ifreq));

  ifr.ifr_hwaddr.sa_family = 1; // this is ARPHRD_ETHER from if_arp.h
  AsciiToMac48 (mac, (uint8_t*)ifr.ifr_hwaddr.sa_data);
  ABORT_IF (ioctl (fd, SIOCSIFHWADDR, &ifr) == -1, "Could not set MAC address", true);
  LOG ("Set device MAC address to " << mac);
}

void
SetUp (char *deviceName)
{
  struct ifreq ifr;

  int sock = socket(AF_INET, SOCK_DGRAM, 0);

  memset(&ifr,  0, sizeof(struct ifreq));
  strncpy(ifr.ifr_name, deviceName, IFNAMSIZ - 1);

  ABORT_IF (ioctl (sock, SIOCGIFFLAGS, &ifr) == -1, 
          "Could not get flags for interface", true);
  ifr.ifr_flags |= IFF_UP | IFF_RUNNING;

  ABORT_IF (ioctl (sock, SIOCSIFFLAGS, &ifr) == -1, 
          "Could not bring interface up", true);

  LOG ("Device is up");
  close (sock);
}

int
CreateTap (char *deviceName, const char *mac, const int ifftap, const int iffpi,
        const char *ip4, const char *netmask, const char *ip6, const int netprefix)
{

  //
  // Creation and management of Tap devices is done via the tun device
  //
  int fd = open ("/dev/net/tun", O_RDWR);
  ABORT_IF (fd == -1, "Could not open /dev/net/tun", true);

  //
  // Set flags for device type and PI header.
  //
  struct ifreq ifr;

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

  ifr.ifr_flags = (ifftap ? IFF_TAP : IFF_TUN);
  if (!iffpi)
    {
       ifr.ifr_flags |= IFF_NO_PI;
    }

  //
  // If device name is not specified, the kernel chooses one.
  //
  if (*deviceName) 
    {
       strncpy(ifr.ifr_name, deviceName, IFNAMSIZ - 1);
    }

  
  ABORT_IF (ioctl (fd, TUNSETIFF, (void *) &ifr) == -1, 
          "Could not allocate tap device", true);

  LOG ("Allocated TAP device " << deviceName);

  //
  // Set the hardware (MAC) address of the new device
  //
  if (ifftap)
    {
      SetMacAddress(fd, mac);
    }

  //
  // Set the IP address and netmask of the new interface/device.
  //
  if (ip4)
    {
      SetIpv4(deviceName, ip4, netmask);
    }

  if (ip6)
    {
      SetIpv6(deviceName, ip6, netprefix);
    }

  //
  // Bring the interface up.
  //
  SetUp(deviceName);

  return fd;
}


int
main (int argc, char *argv[])
{
  int c;
  char *dev = NULL;
  char *ip4 = NULL;
  char *ip6 = NULL;
  char *mac = NULL;
  char *netmask = NULL;
  char *path = NULL;
  int tap = false;
  int pi = false;
  int prefix = -1;

  while ((c = getopt (argc, argv, "vd:i:m:n:I:P:thp:")) != -1)
    {
      switch (c)
        {
        case 'd':
          dev = optarg;           // name of the new tap device
          break;
        case 'i':
          ip4 = optarg;            // ip v4 address of the new device
          break;
        case 'I':
          ip6 = optarg;            // ip v6 address of the new device
          break;
        case 'm':
          mac = optarg;           // mac address of the new device
          break;
        case 'n':
          netmask = optarg;       // ip v4 net mask for the new device
          break;
        case 'P':
          prefix = atoi(optarg);         // ip v6 prefix for the new device
          break;
        case 't':
          tap = true;             // mode for the device (TAP or TUN)
          break;
        case 'h':
          pi = true;              // set the IFF_NO_PI flag
          break;
        case 'p':
          path = optarg;          // path back to the tap bridge
          break;
        case 'v':
          gVerbose = true;
          break;
        }
    }

  //
  // We have got to be able to coordinate the name of the tap device we are
  // going to create and or open with the device that an external Linux host
  // will use.  If this name is provided we use it.  If not we let the system
  // create the device for us.  This name is given in dev
  //
  LOG ("Provided Device Name is \"" << dev << "\"");

  //
  // We have got to be able to assign an IP address to the tap device we are
  // allocating.  This address is allocated in the simulation and assigned to
  // the tap bridge.  This address is given in ip.
  //
  ABORT_IF (ip4 == NULL && ip6 == NULL, "IP Address is a required argument", 0);
  if (ip4)
    {
      ABORT_IF (netmask == NULL, "Net mask is a required argument", 0);
      LOG ("Provided IP v4 Address is \"" << ip4 << "\"");
      LOG ("Provided IP v4 Net Mask is \"" << netmask << "\"");
    }
  if (ip6)
    {
      ABORT_IF (prefix == -1, "Prefix is a required argument", 0);
      LOG ("Provided IP v6 Address is \"" << ip6 << "\"");
      LOG ("Provided IP v6 Prefix is \"" << prefix << "\"");
    }

  //
  // We have got to be able to assign a Mac address to the tap device we are
  // allocating.  This address is allocated in the simulation and assigned to
  // the bridged device.  This allows packets addressed to the bridged device
  // to appear in the Linux host as if they were received there.
  //
  ABORT_IF (mac == NULL, "MAC Address is a required argument", 0);
  LOG ("Provided MAC Address is \"" << mac << "\"");

  //
  // We have got to know whether or not to create the TAP.
  //
  if (tap)
    {
      LOG ("Provided device Mode is TAP");
    }
  else
    {
      LOG ("Provided device Mode is TUN");
    }

  //
  // IFF_NO_PI flag.
  //
  if (pi)
    {
      LOG ("IFF_NO_PI flag set. Packet Information will be present in the traffic");
    }

  //
  // This program is spawned by a tap bridge running in a simulation.  It
  // wants to create a socket as described below.  We are going to do the
  // work here since we're running suid root.  Once we create the socket,
  // we have to send it back to the tap bridge.  We do that over a Unix
  // (local interprocess) socket.  The tap bridge created a socket to
  // listen for our response on, and it is expected to have encoded the address
  // information as a string and to have passed that string as an argument to
  // us.  We see it here as the "path" string.  We can't do anything useful
  // unless we have that string.
  //
  ABORT_IF (path == NULL, "path is a required argument", 0);
  LOG ("Provided path is \"" << path << "\"");

  //
  // The whole reason for all of the hoops we went through to call out to this
  // program will pay off here.  We created this program to run as suid root
  // in order to keep the main simulation program from having to be run with
  // root privileges.  We need root privileges to be able to futz with the
  // Tap device underlying all of this.  So all of these hoops are to allow
  // us to execute the following code:
  //
  LOG ("Creating Tap");
  int sock = CreateTap (dev, mac, tap, pi, ip4, netmask, ip6, prefix);
  ABORT_IF (sock == -1, "main(): Unable to create tap socket", 1);

  //
  // Send the socket back to the tap net device so it can go about its business
  //
  SendSocket (path, sock, TAP_MAGIC);

  return 0;
}