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path: root/src/transport/gnunet-helper-transport-wlan.c
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/*
   This file is part of GNUnet.
   (C) 2010, 2011 Christian Grothoff (and other contributing authors)
   Copyright (c) 2007, 2008, Andy Green <andy@warmcat.com>
   Copyright (C) 2009 Thomas d'Otreppe

   GNUnet 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, or (at your
   option) any later version.

   GNUnet 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 GNUnet; see the file COPYING.  If not, write to the
   Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.
*/
/**
 * @file src/transport/gnunet-helper-transport-wlan.c
 * @brief wlan layer two server; must run as root (SUID will do)
 *        This code will work under GNU/Linux only.
 * @author David Brodski
 *
 * This program serves as the mediator between the wlan interface and
 * gnunet
 */

/*-
 * we use our local copy of ieee80211_radiotap.h
 *
 * - since we can't support extensions we don't understand
 * - since linux does not include it in userspace headers
 *
 * Portions of this code were taken from the ieee80211_radiotap.h header,
 * which is
 *
 * Copyright (c) 2003, 2004 David Young.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of David Young may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY DAVID YOUNG ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL DAVID
 * YOUNG BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 */

/*
 * Modifications to fit into the linux IEEE 802.11 stack,
 * Mike Kershaw (dragorn@kismetwireless.net)
 */

/**
 * parts taken from aircrack-ng, parts changend.
 */
#define _GNU_SOURCE
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <netpacket/packet.h>
#include <linux/if_ether.h>
#include <linux/if.h>
#include <linux/wireless.h>
#include <netinet/in.h>
#include <linux/if_tun.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <fcntl.h>
#include <errno.h>
#include <dirent.h>
#include <sys/param.h>
#include <unistd.h>
#include <stdint.h>

#include "gnunet_protocols.h"
#include "plugin_transport_wlan.h"

#define ARPHRD_IEEE80211        801
#define ARPHRD_IEEE80211_PRISM  802
#define ARPHRD_IEEE80211_FULL   803

/**
 * size of 802.11 address
 */
#define IEEE80211_ADDR_LEN      6

/**
 * Maximum size of a message allowed in either direction.
 */
#define MAXLINE 4096


#define IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK 0x80000000


/* Name                                 Data type    Units
 * ----                                 ---------    -----
 *
 * IEEE80211_RADIOTAP_TSFT              __le64       microseconds
 *
 *      Value in microseconds of the MAC's 64-bit 802.11 Time
 *      Synchronization Function timer when the first bit of the
 *      MPDU arrived at the MAC. For received frames, only.
 *
 * IEEE80211_RADIOTAP_CHANNEL           2 x __le16   MHz, bitmap
 *
 *      Tx/Rx frequency in MHz, followed by flags (see below).
 *
 * IEEE80211_RADIOTAP_FHSS              __le16       see below
 *
 *      For frequency-hopping radios, the hop set (first byte)
 *      and pattern (second byte).
 *
 * IEEE80211_RADIOTAP_RATE              uint8_t           500kb/s
 *
 *      Tx/Rx data rate
 *
 * IEEE80211_RADIOTAP_DBM_ANTSIGNAL     s8           decibels from
 *                                                   one milliwatt (dBm)
 *
 *      RF signal power at the antenna, decibel difference from
 *      one milliwatt.
 *
 * IEEE80211_RADIOTAP_DBM_ANTNOISE      s8           decibels from
 *                                                   one milliwatt (dBm)
 *
 *      RF noise power at the antenna, decibel difference from one
 *      milliwatt.
 *
 * IEEE80211_RADIOTAP_DB_ANTSIGNAL      uint8_t           decibel (dB)
 *
 *      RF signal power at the antenna, decibel difference from an
 *      arbitrary, fixed reference.
 *
 * IEEE80211_RADIOTAP_DB_ANTNOISE       uint8_t           decibel (dB)
 *
 *      RF noise power at the antenna, decibel difference from an
 *      arbitrary, fixed reference point.
 *
 * IEEE80211_RADIOTAP_LOCK_QUALITY      __le16       unitless
 *
 *      Quality of Barker code lock. Unitless. Monotonically
 *      nondecreasing with "better" lock strength. Called "Signal
 *      Quality" in datasheets.  (Is there a standard way to measure
 *      this?)
 *
 * IEEE80211_RADIOTAP_TX_ATTENUATION    __le16       unitless
 *
 *      Transmit power expressed as unitless distance from max
 *      power set at factory calibration.  0 is max power.
 *      Monotonically nondecreasing with lower power levels.
 *
 * IEEE80211_RADIOTAP_DB_TX_ATTENUATION __le16       decibels (dB)
 *
 *      Transmit power expressed as decibel distance from max power
 *      set at factory calibration.  0 is max power.  Monotonically
 *      nondecreasing with lower power levels.
 *
 * IEEE80211_RADIOTAP_DBM_TX_POWER      s8           decibels from
 *                                                   one milliwatt (dBm)
 *
 *      Transmit power expressed as dBm (decibels from a 1 milliwatt
 *      reference). This is the absolute power level measured at
 *      the antenna port.
 *
 * IEEE80211_RADIOTAP_FLAGS             uint8_t           bitmap
 *
 *      Properties of transmitted and received frames. See flags
 *      defined below.
 *
 * IEEE80211_RADIOTAP_ANTENNA           uint8_t           antenna index
 *
 *      Unitless indication of the Rx/Tx antenna for this packet.
 *      The first antenna is antenna 0.
 *
 * IEEE80211_RADIOTAP_RX_FLAGS          __le16       bitmap
 *
 *     Properties of received frames. See flags defined below.
 *
 * IEEE80211_RADIOTAP_TX_FLAGS          __le16       bitmap
 *
 *     Properties of transmitted frames. See flags defined below.
 *
 * IEEE80211_RADIOTAP_RTS_RETRIES       uint8_t           data
 *
 *     Number of rts retries a transmitted frame used.
 *
 * IEEE80211_RADIOTAP_DATA_RETRIES      uint8_t           data
 *
 *     Number of unicast retries a transmitted frame used.
 *
 */
enum RadiotapType
{
  IEEE80211_RADIOTAP_TSFT = 0,
  IEEE80211_RADIOTAP_FLAGS = 1,
  IEEE80211_RADIOTAP_RATE = 2,
  IEEE80211_RADIOTAP_CHANNEL = 3,
  IEEE80211_RADIOTAP_FHSS = 4,
  IEEE80211_RADIOTAP_DBM_ANTSIGNAL = 5,
  IEEE80211_RADIOTAP_DBM_ANTNOISE = 6,
  IEEE80211_RADIOTAP_LOCK_QUALITY = 7,
  IEEE80211_RADIOTAP_TX_ATTENUATION = 8,
  IEEE80211_RADIOTAP_DB_TX_ATTENUATION = 9,
  IEEE80211_RADIOTAP_DBM_TX_POWER = 10,
  IEEE80211_RADIOTAP_ANTENNA = 11,
  IEEE80211_RADIOTAP_DB_ANTSIGNAL = 12,
  IEEE80211_RADIOTAP_DB_ANTNOISE = 13,
  IEEE80211_RADIOTAP_RX_FLAGS = 14,
  IEEE80211_RADIOTAP_TX_FLAGS = 15,
  IEEE80211_RADIOTAP_RTS_RETRIES = 16,
  IEEE80211_RADIOTAP_DATA_RETRIES = 17,
  IEEE80211_RADIOTAP_EXT = 31
};

/* For IEEE80211_RADIOTAP_FLAGS */
#define	IEEE80211_RADIOTAP_F_CFP	0x01    /* sent/received
                                                 * during CFP
                                                 */
#define	IEEE80211_RADIOTAP_F_SHORTPRE	0x02    /* sent/received
                                                 * with short
                                                 * preamble
                                                 */
#define	IEEE80211_RADIOTAP_F_WEP	0x04    /* sent/received
                                                 * with WEP encryption
                                                 */
#define	IEEE80211_RADIOTAP_F_FRAG	0x08    /* sent/received
                                                 * with fragmentation
                                                 */
#define	IEEE80211_RADIOTAP_F_FCS	0x10    /* frame includes FCS */
#define	IEEE80211_RADIOTAP_F_DATAPAD	0x20    /* frame has padding between
                                                 * 802.11 header and payload
                                                 * (to 32-bit boundary)
                                                 */
/* For IEEE80211_RADIOTAP_RX_FLAGS */
#define IEEE80211_RADIOTAP_F_RX_BADFCS	0x0001  /* frame failed crc check */

/* For IEEE80211_RADIOTAP_TX_FLAGS */
#define IEEE80211_RADIOTAP_F_TX_FAIL	0x0001  /* failed due to excessive
                                                 * retries */
#define IEEE80211_RADIOTAP_F_TX_CTS	0x0002  /* used cts 'protection' */
#define IEEE80211_RADIOTAP_F_TX_RTS	0x0004  /* used rts/cts handshake */
#define IEEE80211_RADIOTAP_F_TX_NOACK	0x0008  /* frame should not be ACKed */
#define IEEE80211_RADIOTAP_F_TX_NOSEQ	0x0010  /* sequence number handled
                                                 * by userspace */


/**
 * A generic radio capture format is desirable. There is one for
 * Linux, but it is neither rigidly defined (there were not even
 * units given for some fields) nor easily extensible.
 *
 * I suggest the following extensible radio capture format. It is
 * based on a bitmap indicating which fields are present.
 *
 * I am trying to describe precisely what the application programmer
 * should expect in the following, and for that reason I tell the
 * units and origin of each measurement (where it applies), or else I
 * use sufficiently weaselly language ("is a monotonically nondecreasing
 * function of...") that I cannot set false expectations for lawyerly
 * readers.
 *
 * The radio capture header precedes the 802.11 header.
 * All data in the header is little endian on all platforms.
 */
struct ieee80211_radiotap_header
{
  /**
   * Version 0. Only increases for drastic changes, introduction of
   * compatible new fields does not count.
   */
  uint8_t it_version;
  uint8_t it_pad;

  /**
   * length of the whole header in bytes, including it_version,
   * it_pad, it_len, and data fields.
   */
  uint16_t it_len;

  /**
   * A bitmap telling which fields are present. Set bit 31
   * (0x80000000) to extend the bitmap by another 32 bits.  Additional
   * extensions are made by setting bit 31.
   */
  uint32_t it_present;
};

/**
 *
 */
struct RadioTapheader
{
  /**
   *
   */
  struct ieee80211_radiotap_header header;

  /**
   *
   */
  uint8_t rate;

  /**
   *
   */
  uint8_t pad1;

  /**
   *
   */
  uint16_t txflags;
};


/**
 * IO buffer used for buffering data in transit (to wireless or to stdout).
 */
struct SendBuffer
{
  /**
   * How many bytes of data are stored in 'buf' for transmission right now?
   * Data always starts at offset 0 and extends to 'size'.
   */
  size_t size;

  /**
   * How many bytes that were stored in 'buf' did we already write to the
   * destination?  Always smaller than 'size'.
   */
  size_t pos;
  
  /**
   * Buffered data; twice the maximum allowed message size as we add some
   * headers.
   */
  char buf[MAXLINE * 2];
};

/**
 * Buffer for data read from stdin to be transmitted to the wirless card.
 */
static struct SendBuffer write_pout;

/**
 * Buffer for data read from the wireless card to be transmitted to stdout.
 */
static struct SendBuffer write_std;


GNUNET_NETWORK_STRUCT_BEGIN

/**
 * generic definitions for IEEE 802.11 frames
 */
struct ieee80211_frame
{
  uint8_t i_fc[2];
  uint8_t i_dur[2];
  uint8_t i_addr1[IEEE80211_ADDR_LEN];
  uint8_t i_addr2[IEEE80211_ADDR_LEN];
  uint8_t i_addr3[IEEE80211_ADDR_LEN];
  uint8_t i_seq[2];
  /* possibly followed by addr4[IEEE80211_ADDR_LEN]; */
  /* see below */
} GNUNET_PACKED;
GNUNET_NETWORK_STRUCT_END


/**
 * struct for storing the information of the hardware
 */
struct HardwareInfos
{

  /**
   * file descriptor for the raw socket
   */
  int fd_raw;

  /**
   * Which format has the header that we're getting when receiving packets?
   * Some  ARPHRD_IEEE80211_XXX-value.
   */
  int arptype_in;

  /**
   * Name of the interface, not necessarily 0-terminated (!).
   */
  char iface[IFNAMSIZ];

  /**
   * MAC address of our own WLAN interface.
   */
  struct GNUNET_TRANSPORT_WLAN_MacAddress pl_mac;
};


/**
 * struct ieee80211_radiotap_iterator - tracks walk through present radiotap arguments
 * in the radiotap header.
 */
struct ieee80211_radiotap_iterator
{
  /**
   * pointer to the radiotap header we are walking through
   */
  const struct ieee80211_radiotap_header *rtheader;

  /**
   * length of radiotap header in cpu byte ordering
   */
  size_t max_length;

  /**
   * IEEE80211_RADIOTAP_... index of current arg
   */
  unsigned int this_arg_index;

  /**
   * pointer to current radiotap arg
   */
  uint8_t *this_arg;

  /**
   * internal next argument index
   */
  unsigned int arg_index;

  /**
   * internal next argument pointer
   */
  uint8_t *arg;

  /**
   * internal pointer to next present uint32_t
   */
  uint32_t *next_bitmap;

  /**
   * internal shifter for curr uint32_t bitmap, b0 set == arg present
   */
  uint32_t bitmap_shifter;
};



/* specialized version of server_mst.c begins here */

#define ALIGN_FACTOR 8

/**
 * Smallest supported message.
 */
#define MIN_BUFFER_SIZE sizeof (struct GNUNET_MessageHeader)


/**
 * Functions with this signature are called whenever a
 * complete message is received by the tokenizer.
 *
 * @param cls closure
 * @param message the actual message
 */
typedef void (*MessageTokenizerCallback) (void *cls, 
					  const struct
					  GNUNET_MessageHeader *
					  message);

/**
 * Handle to a message stream tokenizer.
 */
struct MessageStreamTokenizer
{

  /**
   * Function to call on completed messages.
   */
  MessageTokenizerCallback cb;

  /**
   * Closure for cb.
   */
  void *cb_cls;

  /**
   * Size of the buffer (starting at 'hdr').
   */
  size_t curr_buf;

  /**
   * How many bytes in buffer have we already processed?
   */
  size_t off;

  /**
   * How many bytes in buffer are valid right now?
   */
  size_t pos;

  /**
   * Beginning of the buffer.  Typed like this to force alignment.
   */
  struct GNUNET_MessageHeader *hdr;

};



/**
 * Create a message stream tokenizer.
 *
 * @param cb function to call on completed messages
 * @param cb_cls closure for cb
 * @return handle to tokenizer
 */
static struct MessageStreamTokenizer *
mst_create (MessageTokenizerCallback cb,
	    void *cb_cls)
{
  struct MessageStreamTokenizer *ret;

  ret = malloc (sizeof (struct MessageStreamTokenizer));
  if (NULL == ret)
    exit (1);
  ret->hdr = malloc (MIN_BUFFER_SIZE);
  if (NULL == ret->hdr)
    exit (2);
  ret->curr_buf = MIN_BUFFER_SIZE;
  ret->cb = cb;
  ret->cb_cls = cb_cls;
  return ret;
}


/**
 * Add incoming data to the receive buffer and call the
 * callback for all complete messages.
 *
 * @param mst tokenizer to use
 * @param buf input data to add
 * @param size number of bytes in buf
 * @return GNUNET_OK if we are done processing (need more data)
 *         GNUNET_SYSERR if the data stream is corrupt
 */
static int
mst_receive (struct MessageStreamTokenizer *mst,
	     const char *buf, size_t size)
{
  const struct GNUNET_MessageHeader *hdr;
  size_t delta;
  uint16_t want;
  char *ibuf;
  int need_align;
  unsigned long offset;
  int ret;

  ret = GNUNET_OK;
  ibuf = (char *) mst->hdr;
  while (mst->pos > 0)
  {
do_align:
    if ((mst->curr_buf - mst->off < sizeof (struct GNUNET_MessageHeader)) ||
        (0 != (mst->off % ALIGN_FACTOR)))
    {
      /* need to align or need more space */
      mst->pos -= mst->off;
      memmove (ibuf, &ibuf[mst->off], mst->pos);
      mst->off = 0;
    }
    if (mst->pos - mst->off < sizeof (struct GNUNET_MessageHeader))
    {
      delta =
          GNUNET_MIN (sizeof (struct GNUNET_MessageHeader) -
                      (mst->pos - mst->off), size);
      memcpy (&ibuf[mst->pos], buf, delta);
      mst->pos += delta;
      buf += delta;
      size -= delta;
    }
    if (mst->pos - mst->off < sizeof (struct GNUNET_MessageHeader))
    {
      return GNUNET_OK;
    }
    hdr = (const struct GNUNET_MessageHeader *) &ibuf[mst->off];
    want = ntohs (hdr->size);
    if (want < sizeof (struct GNUNET_MessageHeader))
    {
      // GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
    if (mst->curr_buf - mst->off < want)
    {
      /* need more space */
      mst->pos -= mst->off;
      memmove (ibuf, &ibuf[mst->off], mst->pos);
      mst->off = 0;
    }
    if (want > mst->curr_buf)
    {
      mst->hdr = realloc (mst->hdr, want);
      if (NULL == mst->hdr)
	exit (3);
      ibuf = (char *) mst->hdr;
      mst->curr_buf = want;
    }
    hdr = (const struct GNUNET_MessageHeader *) &ibuf[mst->off];
    if (mst->pos - mst->off < want)
    {
      delta = GNUNET_MIN (want - (mst->pos - mst->off), size);
      memcpy (&ibuf[mst->pos], buf, delta);
      mst->pos += delta;
      buf += delta;
      size -= delta;
    }
    if (mst->pos - mst->off < want)
    {
      return GNUNET_OK;
    }
    mst->cb (mst->cb_cls, hdr);
    mst->off += want;
    if (mst->off == mst->pos)
    {
      /* reset to beginning of buffer, it's free right now! */
      mst->off = 0;
      mst->pos = 0;
    }
  }
  while (size > 0)
  {
    if (size < sizeof (struct GNUNET_MessageHeader))
      break;
    offset = (unsigned long) buf;
    need_align = (0 != offset % ALIGN_FACTOR) ? GNUNET_YES : GNUNET_NO;
    if (GNUNET_NO == need_align)
    {
      /* can try to do zero-copy and process directly from original buffer */
      hdr = (const struct GNUNET_MessageHeader *) buf;
      want = ntohs (hdr->size);
      if (want < sizeof (struct GNUNET_MessageHeader))
      {
        // GNUNET_break_op (0);
        mst->off = 0;
        return GNUNET_SYSERR;
      }
      if (size < want)
        break;                  /* or not, buffer incomplete, so copy to private buffer... */
      mst->cb (mst->cb_cls, hdr);
      buf += want;
      size -= want;
    }
    else
    {
      /* need to copy to private buffer to align;
       * yes, we go a bit more spagetti than usual here */
      goto do_align;
    }
  }
  if (size > 0)
  {
    if (size + mst->pos > mst->curr_buf)
    {
      mst->hdr = realloc (mst->hdr, size + mst->pos);
      if (NULL == mst->hdr)
	exit (4);
      ibuf = (char *) mst->hdr;
      mst->curr_buf = size + mst->pos;
    }
    // GNUNET_assert (mst->pos + size <= mst->curr_buf);
    memcpy (&ibuf[mst->pos], buf, size);
    mst->pos += size;
  }
  return ret;
}


/**
 * Destroys a tokenizer.
 *
 * @param mst tokenizer to destroy
 */
static void
mst_destroy (struct MessageStreamTokenizer *mst)
{
  free (mst->hdr);
  free (mst);
}

/* end of server_mst.c copy */




/**
 * Radiotap header iteration
 *
 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
 * then loop calling __ieee80211_radiotap_iterator_next()... it returns -1
 * if there are no more args in the header, or the next argument type index
 * that is present.  The iterator's this_arg member points to the start of the
 * argument associated with the current argument index that is present,
 * which can be found in the iterator's this_arg_index member.  This arg
 * index corresponds to the IEEE80211_RADIOTAP_... defines.
 *
 * @param iterator iterator to initialize
 * @param radiotap_header message to parse
 * @param max_length number of valid bytes in radiotap_header
 * @return 0 on success, -1 on error
 */
static int
ieee80211_radiotap_iterator_init (struct ieee80211_radiotap_iterator *iterator,
                                  const struct ieee80211_radiotap_header
                                  *radiotap_header, 
				  size_t max_length)
{
  if ( (iterator == NULL) ||
       (radiotap_header == NULL) )
    return -1;

  /* Linux only supports version 0 radiotap format */
  if (0 != radiotap_header->it_version)
    return -1;

  /* sanity check for allowed length and radiotap length field */
  if ( (max_length < sizeof (struct ieee80211_radiotap_header)) ||
       (max_length < (GNUNET_le16toh (radiotap_header->it_len))) )
    return -1;

  iterator->rtheader = radiotap_header;
  iterator->max_length = GNUNET_le16toh (radiotap_header->it_len);
  iterator->arg_index = 0;
  iterator->bitmap_shifter = GNUNET_le32toh (radiotap_header->it_present);
  iterator->arg =
      ((uint8_t *) radiotap_header) + sizeof (struct ieee80211_radiotap_header);
  iterator->this_arg = 0;

  /* find payload start allowing for extended bitmap(s) */
  if ((iterator->bitmap_shifter & IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK))
  {
    while (GNUNET_le32toh (*((uint32_t *) iterator->arg)) &
           IEEE80211_RADIOTAP_PRESENT_EXTEND_MASK)
    {
      iterator->arg += sizeof (uint32_t);

      /*
       * check for insanity where the present bitmaps
       * keep claiming to extend up to or even beyond the
       * stated radiotap header length
       */
      if (iterator->arg - ((uint8_t*) iterator->rtheader) > iterator->max_length)
        return -1;
    }
    iterator->arg += sizeof (uint32_t);
    /*
     * no need to check again for blowing past stated radiotap
     * header length, becuase ieee80211_radiotap_iterator_next
     * checks it before it is dereferenced
     */
  }
  /* we are all initialized happily */
  return 0;
}


/**
 * @brief ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 *
 * This function returns the next radiotap arg index (IEEE80211_RADIOTAP_...)
 * and sets iterator->this_arg to point to the payload for the arg.  It takes
 * care of alignment handling and extended present fields.  interator->this_arg
 * can be changed by the caller.  The args pointed to are in little-endian
 * format.
 *
 * @param iterator: radiotap_iterator to move to next arg (if any)
 *
 * @return next present arg index on success or -1 if no more or error
 */
static int
ieee80211_radiotap_iterator_next (struct ieee80211_radiotap_iterator *iterator)
{

  /*
   * small length lookup table for all radiotap types we heard of
   * starting from b0 in the bitmap, so we can walk the payload
   * area of the radiotap header
   *
   * There is a requirement to pad args, so that args
   * of a given length must begin at a boundary of that length
   * -- but note that compound args are allowed (eg, 2 x uint16_t
   * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
   * a reliable indicator of alignment requirement.
   *
   * upper nybble: content alignment for arg
   * lower nybble: content length for arg
   */

  static const uint8_t rt_sizes[] = {
    [IEEE80211_RADIOTAP_TSFT] = 0x88,
    [IEEE80211_RADIOTAP_FLAGS] = 0x11,
    [IEEE80211_RADIOTAP_RATE] = 0x11,
    [IEEE80211_RADIOTAP_CHANNEL] = 0x24,
    [IEEE80211_RADIOTAP_FHSS] = 0x22,
    [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
    [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
    [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
    [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
    [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
    [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
    [IEEE80211_RADIOTAP_ANTENNA] = 0x11,
    [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
    [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11,
    [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22,
    [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22,
    [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11,
    [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11
        /*
         * add more here as they are defined in
         * include/net/ieee80211_radiotap.h
         */
  };

  /*
   * for every radiotap entry we can at
   * least skip (by knowing the length)...
   */

  while (iterator->arg_index < sizeof (rt_sizes))
  {
    int hit = 0;

    if (!(iterator->bitmap_shifter & 1))
      goto next_entry;          /* arg not present */

    /*
     * arg is present, account for alignment padding
     *  8-bit args can be at any alignment
     * 16-bit args must start on 16-bit boundary
     * 32-bit args must start on 32-bit boundary
     * 64-bit args must start on 64-bit boundary
     *
     * note that total arg size can differ from alignment of
     * elements inside arg, so we use upper nybble of length
     * table to base alignment on
     *
     * also note: these alignments are ** relative to the
     * start of the radiotap header **.  There is no guarantee
     * that the radiotap header itself is aligned on any
     * kind of boundary.
     */

    if ((((void *) iterator->arg) -
         ((void *) iterator->rtheader)) & ((rt_sizes[iterator->arg_index] >> 4)
                                           - 1))
      iterator->arg_index +=
          (rt_sizes[iterator->arg_index] >> 4) -
          ((((void *) iterator->arg) -
            ((void *) iterator->rtheader)) & ((rt_sizes[iterator->arg_index] >>
                                               4) - 1));

    /*
     * this is what we will return to user, but we need to
     * move on first so next call has something fresh to test
     */

    iterator->this_arg_index = iterator->arg_index;
    iterator->this_arg = iterator->arg;
    hit = 1;

    /* internally move on the size of this arg */

    iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;

    /*
     * check for insanity where we are given a bitmap that
     * claims to have more arg content than the length of the
     * radiotap section.  We will normally end up equalling this
     * max_length on the last arg, never exceeding it.
     */

    if ((((void *) iterator->arg) - ((void *) iterator->rtheader)) >
        iterator->max_length)
      return -1;

next_entry:

    iterator->arg_index++;
    if (((iterator->arg_index & 31) == 0))
    {
      /* completed current uint32_t bitmap */
      if (iterator->bitmap_shifter & 1)
      {
        /* b31 was set, there is more */
        /* move to next uint32_t bitmap */
        iterator->bitmap_shifter = GNUNET_le32toh (*iterator->next_bitmap);
        iterator->next_bitmap++;
      }
      else
      {
        /* no more bitmaps: end */
        iterator->arg_index = sizeof (rt_sizes);
      }
    }
    else
    {                           /* just try the next bit */
      iterator->bitmap_shifter >>= 1;
    }

    /* if we found a valid arg earlier, return it now */

    if (hit)
      return iterator->this_arg_index;

  }

  /* we don't know how to handle any more args, we're done */
  return -1;
}


/**
 * Return the channel from the frequency (in Mhz)
 * @param frequency of the channel
 * @return number of the channel
 */
static int
get_channel_from_frequency (int frequency)
{
  if (frequency >= 2412 && frequency <= 2472)
    return (frequency - 2407) / 5;
  if (frequency == 2484)
    return 14;
  if (frequency >= 5000 && frequency <= 6100)
    return (frequency - 5000) / 5;
  return -1;
}


/**
 * function to calculate the crc, the start of the calculation
 *
 * @param buf buffer to calc the crc
 * @param len len of the buffer
 * @return crc sum
 */
static unsigned long
calc_crc_osdep (const unsigned char *buf, size_t len)
{
  static const unsigned long int crc_tbl_osdep[256] = {
    0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F,
    0xE963A535, 0x9E6495A3,
    0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD,
    0xE7B82D07, 0x90BF1D91,
    0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB,
    0xF4D4B551, 0x83D385C7,
    0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
    0xFA0F3D63, 0x8D080DF5,
    0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447,
    0xD20D85FD, 0xA50AB56B,
    0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75,
    0xDCD60DCF, 0xABD13D59,
    0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423,
    0xCFBA9599, 0xB8BDA50F,
    0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11,
    0xC1611DAB, 0xB6662D3D,
    0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F,
    0x9FBFE4A5, 0xE8B8D433,
    0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D,
    0x91646C97, 0xE6635C01,
    0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B,
    0x8208F4C1, 0xF50FC457,
    0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49,
    0x8CD37CF3, 0xFBD44C65,
    0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7,
    0xA4D1C46D, 0xD3D6F4FB,
    0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5,
    0xAA0A4C5F, 0xDD0D7CC9,
    0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3,
    0xB966D409, 0xCE61E49F,
    0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81,
    0xB7BD5C3B, 0xC0BA6CAD,
    0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF,
    0x04DB2615, 0x73DC1683,
    0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D,
    0x0A00AE27, 0x7D079EB1,
    0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
    0x196C3671, 0x6E6B06E7,
    0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9,
    0x17B7BE43, 0x60B08ED5,
    0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767,
    0x3FB506DD, 0x48B2364B,
    0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55,
    0x316E8EEF, 0x4669BE79,
    0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703,
    0x220216B9, 0x5505262F,
    0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31,
    0x2CD99E8B, 0x5BDEAE1D,
    0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F,
    0x72076785, 0x05005713,
    0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D,
    0x7CDCEFB7, 0x0BDBDF21,
    0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B,
    0x6FB077E1, 0x18B74777,
    0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69,
    0x616BFFD3, 0x166CCF45,
    0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7,
    0x4969474D, 0x3E6E77DB,
    0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5,
    0x47B2CF7F, 0x30B5FFE9,
    0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693,
    0x54DE5729, 0x23D967BF,
    0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1,
    0x5A05DF1B, 0x2D02EF8D
  };

  unsigned long crc = 0xFFFFFFFF;

  for (; len > 0; len--, buf++)
    crc = crc_tbl_osdep[(crc ^ *buf) & 0xFF] ^ (crc >> 8);
  return (~crc);
}


/**
 * Function to calculate and check crc of the wlan packet
 *
 * @param buf buffer of the packet, with len + 4 bytes of data,
 *            the last 4 bytes being the checksum
 * @param len length of the payload in data
 * @return 0 on success (checksum matches), 1 on error
 */
static int
check_crc_buf_osdep (const unsigned char *buf, size_t len)
{
  unsigned long crc;

  crc = calc_crc_osdep (buf, len);
  buf += len;
  if (((crc) & 0xFF) == buf[0] && ((crc >> 8) & 0xFF) == buf[1] &&
      ((crc >> 16) & 0xFF) == buf[2] && ((crc >> 24) & 0xFF) == buf[3])
    return 0;
  return 1;     
}


/**
 * Get the channel used by our WLAN interface.
 *
 * @param dev pointer to the dev struct of the card
 * @return channel number, -1 on error
 */
static int
linux_get_channel (const struct HardwareInfos *dev)
{
  struct iwreq wrq;
  int fd;
  int frequency;
  int chan;

  memset (&wrq, 0, sizeof (struct iwreq));
  strncpy (wrq.ifr_name, dev->iface, IFNAMSIZ);
  fd = dev->fd_raw;
  if (0 > ioctl (fd, SIOCGIWFREQ, &wrq))
    return -1;

  frequency = wrq.u.freq.m;
  if (100000000 < frequency)
    frequency /= 100000;
  else if (1000000 < frequency)
    frequency /= 1000;
  if (1000 < frequency)
    chan = get_channel_from_frequency (frequency);
  else
    chan = frequency;
  return chan;
}


/**
 * function to read from a wlan card
 * @param dev pointer to the struct of the wlan card
 * @param buf buffer to read to
 * @param buf_size size of the buffer
 * @param ri radiotap_rx info
 * @return size read from the buffer
 */
static ssize_t
linux_read (struct HardwareInfos *dev, unsigned char *buf, size_t buf_size,
            struct Radiotap_rx *ri)
{
  unsigned char tmpbuf[buf_size];
  ssize_t caplen;
  int n, got_signal, got_noise, got_channel, fcs_removed;

  n = got_signal = got_noise = got_channel = fcs_removed = 0;

  caplen = read (dev->fd_raw, tmpbuf, buf_size);
  if (0 > caplen)
  {
    if (EAGAIN == errno)
      return 0;
    fprintf (stderr, "Failed to read from RAW socket: %s\n", strerror (errno));
    return -1;
  }

  memset (buf, 0, buf_size);
  memset (ri, 0, sizeof (*ri));

  switch (dev->arptype_in)
  {
  case ARPHRD_IEEE80211_PRISM:
  {
    /* skip the prism header */
    if (tmpbuf[7] == 0x40)
    {
      /* prism54 uses a different format */
      ri->ri_power = tmpbuf[0x33];
      ri->ri_noise = *(unsigned int *) (tmpbuf + 0x33 + 12);
      ri->ri_rate = (*(unsigned int *) (tmpbuf + 0x33 + 24)) * 500000;
      got_signal = 1;
      got_noise = 1;
      n = 0x40;
    }
    else
    {
      ri->ri_mactime = *(uint64_t *) (tmpbuf + 0x5C - 48);
      ri->ri_channel = *(unsigned int *) (tmpbuf + 0x5C - 36);
      ri->ri_power = *(unsigned int *) (tmpbuf + 0x5C);
      ri->ri_noise = *(unsigned int *) (tmpbuf + 0x5C + 12);
      ri->ri_rate = (*(unsigned int *) (tmpbuf + 0x5C + 24)) * 500000;
      got_channel = 1;
      got_signal = 1;
      got_noise = 1;
      n = *(int *) (tmpbuf + 4);
    }

    if ( (n < 8) || (n >= caplen) )
      return 0;
  }
    break;

  case ARPHRD_IEEE80211_FULL:
  {
    struct ieee80211_radiotap_iterator iterator;
    struct ieee80211_radiotap_header *rthdr;

    rthdr = (struct ieee80211_radiotap_header *) tmpbuf;

    if (0 != ieee80211_radiotap_iterator_init (&iterator, rthdr, caplen))
      return 0;

    /* go through the radiotap arguments we have been given
     * by the driver
     */

    while (ieee80211_radiotap_iterator_next (&iterator) >= 0)
    {

      switch (iterator.this_arg_index)
      {

      case IEEE80211_RADIOTAP_TSFT:
        ri->ri_mactime = GNUNET_le64toh (*((uint64_t *) iterator.this_arg));
        break;

      case IEEE80211_RADIOTAP_DBM_ANTSIGNAL:
        if (!got_signal)
        {
          if (*iterator.this_arg < 127)
            ri->ri_power = *iterator.this_arg;
          else
            ri->ri_power = *iterator.this_arg - 255;

          got_signal = 1;
        }
        break;

      case IEEE80211_RADIOTAP_DB_ANTSIGNAL:
        if (!got_signal)
        {
          if (*iterator.this_arg < 127)
            ri->ri_power = *iterator.this_arg;
          else
            ri->ri_power = *iterator.this_arg - 255;

          got_signal = 1;
        }
        break;

      case IEEE80211_RADIOTAP_DBM_ANTNOISE:
        if (!got_noise)
        {
          if (*iterator.this_arg < 127)
            ri->ri_noise = *iterator.this_arg;
          else
            ri->ri_noise = *iterator.this_arg - 255;

          got_noise = 1;
        }
        break;

      case IEEE80211_RADIOTAP_DB_ANTNOISE:
        if (!got_noise)
        {
          if (*iterator.this_arg < 127)
            ri->ri_noise = *iterator.this_arg;
          else
            ri->ri_noise = *iterator.this_arg - 255;

          got_noise = 1;
        }
        break;

      case IEEE80211_RADIOTAP_ANTENNA:
        ri->ri_antenna = *iterator.this_arg;
        break;

      case IEEE80211_RADIOTAP_CHANNEL:
        ri->ri_channel = *iterator.this_arg;
        got_channel = 1;
        break;

      case IEEE80211_RADIOTAP_RATE:
        ri->ri_rate = (*iterator.this_arg) * 500000;
        break;

      case IEEE80211_RADIOTAP_FLAGS:
        /* is the CRC visible at the end?
         * remove
         */
        if (*iterator.this_arg & IEEE80211_RADIOTAP_F_FCS)
        {
          fcs_removed = 1;
          caplen -= 4;
        }

        if (*iterator.this_arg & IEEE80211_RADIOTAP_F_RX_BADFCS)
          return (0);

        break;
      }
    }
    n = GNUNET_le16toh (rthdr->it_len);
    if (n <= 0 || n >= caplen)
      return 0;
  }
    break;
  case ARPHRD_IEEE80211:
    /* do nothing? */
    break;
  default:
    errno = ENOTSUP;
    return -1;
  }

  caplen -= n;

  //detect fcs at the end, even if the flag wasn't set and remove it
  if ((0 == fcs_removed) && (0 == check_crc_buf_osdep (tmpbuf + n, caplen - 4)))
  {
    caplen -= 4;
  }
  memcpy (buf, tmpbuf + n, caplen);
  if (!got_channel)
    ri->ri_channel = linux_get_channel (dev);

  return caplen;
}


/**
 * Open the wireless network interface for reading/writing.
 *
 * @param dev pointer to the device struct
 * @return 0 on success
 */
static int
open_device_raw (struct HardwareInfos *dev)
{
  struct ifreq ifr;
  struct iwreq wrq;
  struct packet_mreq mr;
  struct sockaddr_ll sll;

  /* find the interface index */
  memset (&ifr, 0, sizeof (ifr));
  strncpy (ifr.ifr_name, dev->iface, IFNAMSIZ);
  if (-1 == ioctl (dev->fd_raw, SIOCGIFINDEX, &ifr))
  {
    fprintf (stderr, "ioctl(SIOCGIFINDEX) on interface `%.*s' failed: %s\n",
             IFNAMSIZ, dev->iface, strerror (errno));
    return 1;
  }

  /* lookup the hardware type */
  memset (&sll, 0, sizeof (sll));
  sll.sll_family = AF_PACKET;
  sll.sll_ifindex = ifr.ifr_ifindex;
  sll.sll_protocol = htons (ETH_P_ALL);
  if (-1 == ioctl (dev->fd_raw, SIOCGIFHWADDR, &ifr))
  {
    fprintf (stderr, "ioctl(SIOCGIFHWADDR) on interface `%.*s' failed: %s\n",
             IFNAMSIZ, dev->iface, strerror (errno));
    return 1;
  }

  /* lookup iw mode */
  memset (&wrq, 0, sizeof (struct iwreq));
  strncpy (wrq.ifr_name, dev->iface, IFNAMSIZ);
  if (-1 == ioctl (dev->fd_raw, SIOCGIWMODE, &wrq))
  {
    /* most probably not supported (ie for rtap ipw interface) *
     * so just assume its correctly set...                     */
    wrq.u.mode = IW_MODE_MONITOR;
  }

  if (((ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211) &&
       (ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211_PRISM) &&
       (ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211_FULL)) ||
      (wrq.u.mode != IW_MODE_MONITOR))
  {
    fprintf (stderr, "Error: interface `%.*s' is not in monitor mode\n",
             IFNAMSIZ, dev->iface);
    return 1;
  }

  /* Is interface st to up, broadcast & running ? */
  if ((ifr.ifr_flags | IFF_UP | IFF_BROADCAST | IFF_RUNNING) != ifr.ifr_flags)
  {
    /* Bring interface up */
    ifr.ifr_flags |= IFF_UP | IFF_BROADCAST | IFF_RUNNING;

    if (-1 == ioctl (dev->fd_raw, SIOCSIFFLAGS, &ifr))
    {
      fprintf (stderr, "ioctl(SIOCSIFFLAGS) on interface `%.*s' failed: %s\n",
               IFNAMSIZ, dev->iface, strerror (errno));
      return 1;
    }
  }

  /* bind the raw socket to the interface */
  if (-1 == bind (dev->fd_raw, (struct sockaddr *) &sll, sizeof (sll)))
  {
    fprintf (stderr, "Failed to bind interface `%.*s': %s\n", IFNAMSIZ,
             dev->iface, strerror (errno));
    return 1;
  }

  /* lookup the hardware type */
  if (-1 == ioctl (dev->fd_raw, SIOCGIFHWADDR, &ifr))
  {
    fprintf (stderr, "ioctl(SIOCGIFHWADDR) on interface `%.*s' failed: %s\n",
             IFNAMSIZ, dev->iface, strerror (errno));
    return 1;
  }

  memcpy (&dev->pl_mac, ifr.ifr_hwaddr.sa_data, MAC_ADDR_SIZE);
  dev->arptype_in = ifr.ifr_hwaddr.sa_family;
  if ((ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211) &&
      (ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211_PRISM) &&
      (ifr.ifr_hwaddr.sa_family != ARPHRD_IEEE80211_FULL))
  {
    fprintf (stderr, "Unsupported hardware link type %d on interface `%.*s'\n",
             ifr.ifr_hwaddr.sa_family, IFNAMSIZ, dev->iface);
    return 1;
  }

  /* enable promiscuous mode */
  memset (&mr, 0, sizeof (mr));
  mr.mr_ifindex = sll.sll_ifindex;
  mr.mr_type = PACKET_MR_PROMISC;
  if (0 !=
      setsockopt (dev->fd_raw, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mr,
                  sizeof (mr)))
  {
    fprintf (stderr, "Failed to enable promiscuous mode on interface `%.*s'\n",
             IFNAMSIZ, dev->iface);
    return 1;
  }

  return 0;
}


/**
 * Test if the given interface name really corresponds to a wireless
 * device.
 *
 * @param iface name of the interface
 * @return 0 on success, 1 on error
 */
static int
test_wlan_interface (const char *iface)
{
  char strbuf[512];
  struct stat sbuf;
  int ret;

  /* mac80211 stack detection */
  ret =
      snprintf (strbuf, sizeof (strbuf), "/sys/class/net/%s/phy80211/subsystem",
                iface);
  if ((ret < 0) || (ret >= sizeof (strbuf)) || (0 != stat (strbuf, &sbuf)))
  {
    fprintf (stderr, "Did not find 802.11 interface `%s'. Exiting.\n", iface);
    return 1;
  }
  return 0;
}


/**
 * Function to test incoming packets mac for being our own.
 *
 * @param uint8_taIeeeHeader buffer of the packet
 * @param dev the Hardware_Infos struct
 * @return 0 if mac belongs to us, 1 if mac is for another target
 */
static int
mac_test (const struct ieee80211_frame *uint8_taIeeeHeader,
          const struct HardwareInfos *dev)
{
  if (0 != memcmp (uint8_taIeeeHeader->i_addr3, &mac_bssid_gnunet, MAC_ADDR_SIZE))
    return 1;
  if (0 == memcmp (uint8_taIeeeHeader->i_addr1, &dev->pl_mac, MAC_ADDR_SIZE))
    return 0;
  if (0 == memcmp (uint8_taIeeeHeader->i_addr1, &bc_all_mac, MAC_ADDR_SIZE))
    return 0;
  return 1;
}


/**
 * function to set the wlan header to make attacks more difficult
 * @param uint8_taIeeeHeader pointer to the header of the packet
 * @param dev pointer to the Hardware_Infos struct
 */
static void
mac_set (struct ieee80211_frame *uint8_taIeeeHeader,
         const struct HardwareInfos *dev)
{
  uint8_taIeeeHeader->i_fc[0] = 0x08;
  uint8_taIeeeHeader->i_fc[1] = 0x00;
  memcpy (uint8_taIeeeHeader->i_addr2, &dev->pl_mac, MAC_ADDR_SIZE);
  memcpy (uint8_taIeeeHeader->i_addr3, &mac_bssid_gnunet, MAC_ADDR_SIZE);
}


/**
 * function to process the data from the stdin
 * @param cls pointer to the device struct
 * @param hdr pointer to the start of the packet
 */
static void
stdin_send_hw (void *cls, const struct GNUNET_MessageHeader *hdr)
{
  struct HardwareInfos *dev = cls;
  struct Radiotap_Send *header = (struct Radiotap_Send *) &hdr[1];
  struct ieee80211_frame *wlanheader;
  size_t sendsize;
  struct RadioTapheader rtheader;

  rtheader.header.it_version = 0; /* radiotap version */
  rtheader.header.it_len = GNUNET_htole16 (0x0c); /* radiotap header length */
  rtheader.header.it_present = GNUNET_le16toh (0x00008004); /* our bitmap */
  rtheader.rate = 0x00;
  rtheader.pad1 = 0x00;
  rtheader.txflags =
      GNUNET_htole16 (IEEE80211_RADIOTAP_F_TX_NOACK | IEEE80211_RADIOTAP_F_TX_NOSEQ);

  sendsize = ntohs (hdr->size);
  if (sendsize <
      sizeof (struct Radiotap_Send) + sizeof (struct GNUNET_MessageHeader))
  {
    fprintf (stderr, "Function stdin_send_hw: malformed packet (too small)\n");
    exit (1);
  }
  sendsize -=
      sizeof (struct Radiotap_Send) + sizeof (struct GNUNET_MessageHeader);

  if (MAXLINE < sendsize)
  {
    fprintf (stderr, "Function stdin_send_hw: Packet too big for buffer\n");
    exit (1);
  }
  if (GNUNET_MESSAGE_TYPE_WLAN_HELPER_DATA != ntohs (hdr->type))
  {
    fprintf (stderr, "Function stdin_send_hw: wrong packet type\n");
    exit (1);
  }

  rtheader.header.it_len = GNUNET_htole16 (sizeof (rtheader));
  rtheader.rate = header->rate;
  memcpy (write_pout.buf, &rtheader, sizeof (rtheader));
  memcpy (write_pout.buf + sizeof (rtheader), &header[1], sendsize);
  /* payload contains MAC address, but we don't trust it, so we'll
   * overwrite it with OUR MAC address again to prevent mischief */
  wlanheader = (struct ieee80211_frame *) (write_pout.buf + sizeof (rtheader));
  mac_set (wlanheader, dev);
  write_pout.size = sendsize + sizeof (rtheader);
}


/**
 * Main function of the helper.  This code accesses a WLAN interface
 * in monitoring mode (layer 2) and then forwards traffic in both
 * directions between the WLAN interface and stdin/stdout of this
 * process.  Error messages are written to stdout.
 *
 * @param argc number of arguments, must be 2
 * @param argv arguments only argument is the name of the interface (i.e. 'mon0')
 * @return 0 on success (never happens, as we don't return unless aborted), 1 on error
 */
int
main (int argc, char *argv[])
{
  struct HardwareInfos dev;
  char readbuf[MAXLINE];
  int maxfd;
  fd_set rfds;
  fd_set wfds;
  int stdin_open;
  struct MessageStreamTokenizer *stdin_mst;
  int raw_eno;

  memset (&dev, 0, sizeof (dev));
  dev.fd_raw = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL));
  raw_eno = errno; /* remember for later */

  /* drop privs */
  {
    uid_t uid = getuid ();
#ifdef HAVE_SETRESUID
    if (0 != setresuid (uid, uid, uid))
    {
      fprintf (stderr, "Failed to setresuid: %s\n", strerror (errno));
      if (-1 != dev.fd_raw)
	(void) close (dev.fd_raw);
      return 1;
    }
#else
    if (0 != (setuid (uid) | seteuid (uid)))
    {
      fprintf (stderr, "Failed to setuid: %s\n", strerror (errno));
      if (-1 != dev.fd_raw)
	(void) close (dev.fd_raw);
      return 1;
    }
  }
#endif

  /* now that we've dropped root rights, we can do error checking */
  if (2 != argc)
  {
    fprintf (stderr,
             "You must specify the name of the interface as the first and only argument to this program.\n");
    if (-1 != dev.fd_raw)
      (void) close (dev.fd_raw);
    return 1;
  }

  if (-1 == dev.fd_raw)
  {
    fprintf (stderr, "Failed to create raw socket: %s\n", strerror (raw_eno));
    return 1;
  }
  if (dev.fd_raw >= FD_SETSIZE)
  {
    fprintf (stderr, "File descriptor too large for select (%d > %d)\n",
             dev.fd_raw, FD_SETSIZE);
    (void) close (dev.fd_raw);
    return 1;
  }
  if (0 != test_wlan_interface (argv[1]))
  {
    (void) close (dev.fd_raw);
    return 1;
  }
  strncpy (dev.iface, argv[1], IFNAMSIZ);
  if (0 != open_device_raw (&dev))
  {
    (void) close (dev.fd_raw);
    return 1;
  }

  /* send MAC address of the WLAN interface to STDOUT first */
  {
    struct GNUNET_TRANSPORT_WLAN_HelperControlMessage macmsg;

    macmsg.hdr.size = htons (sizeof (macmsg));
    macmsg.hdr.type = htons (GNUNET_MESSAGE_TYPE_WLAN_HELPER_CONTROL);
    memcpy (&macmsg.mac, &dev.pl_mac, sizeof (struct GNUNET_TRANSPORT_WLAN_MacAddress));
    memcpy (write_std.buf, &macmsg, sizeof (macmsg));
    write_std.size = sizeof (macmsg);
  }  

  stdin_mst = mst_create (&stdin_send_hw, &dev);  
  stdin_open = 1;
  while (1)
  {
    maxfd = -1;
    FD_ZERO (&rfds);
    if ((0 == write_pout.size) && (1 == stdin_open))
    {
      FD_SET (STDIN_FILENO, &rfds);
      maxfd = MAX (maxfd, STDIN_FILENO);
    }
    if (0 == write_std.size)
    {
      FD_SET (dev.fd_raw, &rfds);
      maxfd = MAX (maxfd, dev.fd_raw);
    }
    FD_ZERO (&wfds);
    if (0 < write_std.size)
    {
      FD_SET (STDOUT_FILENO, &wfds);
      maxfd = MAX (maxfd, STDOUT_FILENO);
    }
    if (0 < write_pout.size)
    {
      FD_SET (dev.fd_raw, &wfds);
      maxfd = MAX (maxfd, dev.fd_raw);
    }
    {
      int retval = select (maxfd + 1, &rfds, &wfds, NULL, NULL);
      if ((-1 == retval) && (EINTR == errno))
	continue;
      if (0 > retval)
      {
	fprintf (stderr, "select failed: %s\n", strerror (errno));
	break;
      }
    }
    if (FD_ISSET (STDOUT_FILENO, &wfds))
    {
      ssize_t ret =
          write (STDOUT_FILENO, write_std.buf + write_std.pos,
                 write_std.size - write_std.pos);
      if (0 > ret)
      {
        fprintf (stderr, "Failed to write to STDOUT: %s\n", strerror (errno));
        break;
      }
      write_std.pos += ret;
      if (write_std.pos == write_std.size)
      {
        write_std.pos = 0;
        write_std.size = 0;
      }
    }
    if (FD_ISSET (dev.fd_raw, &wfds))
    {
      ssize_t ret =
	write (dev.fd_raw, write_pout.buf + write_std.pos, 
	       write_pout.size - write_pout.pos);
      if (0 > ret)
      {
        fprintf (stderr, "Failed to write to WLAN device: %s\n",
                 strerror (errno));
        break;
      }
      write_pout.pos += ret;
      if ((write_pout.pos != write_pout.size) && (0 != ret))
      {
        /* we should not get partial sends with packet-oriented devices... */
        fprintf (stderr, "Write error, partial send: %u/%u\n",
                 (unsigned int) write_pout.pos,
		 (unsigned int) write_pout.size);
        break;
      }
      if (write_pout.pos == write_pout.size)
      {
        write_pout.pos = 0;
        write_pout.size = 0;
      }
    }

    if (FD_ISSET (STDIN_FILENO, &rfds))
    {
      ssize_t ret = 
	read (STDIN_FILENO, readbuf, sizeof (readbuf));
      if (0 > ret)
      {
        fprintf (stderr, "Read error from STDIN: %s\n", strerror (errno));
        break;
      }
      if (0 == ret)
      {
        /* stop reading... */
        stdin_open = 0;
      }
      mst_receive (stdin_mst, readbuf, ret);
    }

    if (FD_ISSET (dev.fd_raw, &rfds))
    {
      struct GNUNET_MessageHeader *header;
      struct Radiotap_rx *rxinfo;
      struct ieee80211_frame *datastart;
      ssize_t ret;

      header = (struct GNUNET_MessageHeader *) write_std.buf;
      rxinfo = (struct Radiotap_rx *) &header[1];
      datastart = (struct ieee80211_frame *) &rxinfo[1];
      ret =
          linux_read (&dev, (unsigned char *) datastart,
                      sizeof (write_std.buf) - sizeof (struct Radiotap_rx) -
                      sizeof (struct GNUNET_MessageHeader), rxinfo);
      if (0 > ret)
      {
        fprintf (stderr, "Read error from raw socket: %s\n", strerror (errno));
        break;
      }
      if ((0 < ret) && (0 == mac_test (datastart, &dev)))
      {
        write_std.size =
            ret + sizeof (struct GNUNET_MessageHeader) +
            sizeof (struct Radiotap_rx);
        header->size = htons (write_std.size);
        header->type = htons (GNUNET_MESSAGE_TYPE_WLAN_HELPER_DATA);
      }
    }

  }
  /* Error handling, try to clean up a bit at least */
  mst_destroy (stdin_mst);
  (void) close (dev.fd_raw);
  return 1;                     /* we never exit 'normally' */
}

/* end of gnunet-helper-transport-wlan.c */