openvpn/tap-win32/macinfo.c

/*
 *  TAP-Win32/TAP-Win64 -- A kernel driver to provide virtual tap
 *                         device functionality on Windows.
 *
 *  This code was inspired by the CIPE-Win32 driver by Damion K. Wilson.
 *
 *  This source code is Copyright (C) 2002-2010 OpenVPN Technologies, Inc.,
 *  and is released under the GPL version 2 (see below).
 *
 *  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 (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "macinfo.h"

int
HexStringToDecimalInt (const int p_Character)
{
  int l_Value = 0;

  if (p_Character >= 'A' && p_Character <= 'F')
    l_Value = (p_Character - 'A') + 10;
  else if (p_Character >= 'a' && p_Character <= 'f')
    l_Value = (p_Character - 'a') + 10;
  else if (p_Character >= '0' && p_Character <= '9')
    l_Value = p_Character - '0';

  return l_Value;
}

BOOLEAN
ParseMAC (MACADDR dest, const char *src)
{
  int c;
  int mac_index = 0;
  BOOLEAN high_digit = FALSE;
  int delim_action = 1;

  MYASSERT (src);
  MYASSERT (dest);

  CLEAR_MAC (dest);

  while (c = *src++)
    {
      if (IsMacDelimiter (c))
	{
	  mac_index += delim_action;
	  high_digit = FALSE;
	  delim_action = 1;
	}
      else if (IsHexDigit (c))
	{
	  const int digit = HexStringToDecimalInt (c);
	  if (mac_index < sizeof (MACADDR))
	    {
	      if (!high_digit)
		{
		  dest[mac_index] = (char)(digit);
		  high_digit = TRUE;
		  delim_action = 1;
		}
	      else
		{
		  dest[mac_index] = (char)(dest[mac_index] * 16 + digit);
		  ++mac_index;
		  high_digit = FALSE;
		  delim_action = 0;
		}
	    }
	  else
	    return FALSE;
	}
      else
	return FALSE;
    }

  return (mac_index + delim_action) >= sizeof (MACADDR);
}

/*
 * Generate a MAC using the GUID in the adapter name.
 *
 * The mac is constructed as 00:FF:xx:xx:xx:xx where
 * the Xs are taken from the first 32 bits of the GUID in the
 * adapter name.  This is similar to the Linux 2.4 tap MAC
 * generator, except linux uses 32 random bits for the Xs.
 *
 * In general, this solution is reasonable for most
 * applications except for very large bridged TAP networks,
 * where the probability of address collisions becomes more
 * than infintesimal.
 *
 * Using the well-known "birthday paradox", on a 1000 node
 * network the probability of collision would be
 * 0.000116292153.  On a 10,000 node network, the probability
 * of collision would be 0.01157288998621678766.
 */

VOID GenerateRandomMac (MACADDR mac, const unsigned char *adapter_name)
{
  unsigned const char *cp = adapter_name;
  unsigned char c;
  unsigned int i = 2;
  unsigned int byte = 0;
  int brace = 0;
  int state = 0;

  CLEAR_MAC (mac);

  mac[0] = 0x00;
  mac[1] = 0xFF;

  while (c = *cp++)
    {
      if (i >= sizeof (MACADDR))
	break;
      if (c == '{')
	brace = 1;
      if (IsHexDigit (c) && brace)
	{
	  const unsigned int digit = HexStringToDecimalInt (c);
	  if (state)
	    {
	      byte <<= 4;
	      byte |= digit;
	      mac[i++] = (unsigned char) byte;
	      state = 0;
	    }
	  else
	    {
	      byte = digit;
	      state = 1;
	    }
	}
    }
}

VOID GenerateRelatedMAC (MACADDR dest, const MACADDR src, const int delta)
{
  COPY_MAC (dest, src);
  dest[2] += (UCHAR) delta;
}