cse 2410 f13 wireshark

/* ber.c

 *

 * Basic Encoding Rules (BER) file reading

 *

 * $Id$

 *

 * 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 2

 * 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, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

 */

#include "config.h"

#include <errno.h>

#ifdef HAVE_SYS_STAT_H

#include <sys/stat.h>

#endif

#include "wtap-int.h"

#include "file_wrappers.h"

#include "buffer.h"

#include "ber.h"

#define BER_CLASS_UNI        0

#define BER_CLASS_APP        1

#define BER_CLASS_CON        2

#define BER_UNI_TAG_SEQ        16        /* SEQUENCE, SEQUENCE OF */

#define BER_UNI_TAG_SET        17        /* SET, SET OF */

static gboolean ber_read_file(wtap *wth, FILE_T fh, struct wtap_pkthdr *phdr,

                              Buffer *buf, int *err, gchar **err_info)

{

  gint64 file_size;

  int packet_size;

  if ((file_size = wtap_file_size(wth, err)) == -1)

    return FALSE;

  if (file_size > WTAP_MAX_PACKET_SIZE) {

    /*

     * Probably a corrupt capture file; don't blow up trying

     * to allocate space for an immensely-large packet.

     */

    *err = WTAP_ERR_BAD_FILE;

    *err_info = g_strdup_printf("ber: File has %" G_GINT64_MODIFIER "d-byte packet, bigger than maximum of %u",

                                file_size, WTAP_MAX_PACKET_SIZE);

    return FALSE;

  }

  packet_size = (int)file_size;

  phdr->presence_flags = 0; /* yes, we have no bananas^Wtime stamp */

  phdr->caplen = packet_size;

  phdr->len = packet_size;

  phdr->ts.secs = 0;

  phdr->ts.nsecs = 0;

  return wtap_read_packet_bytes(fh, buf, packet_size, err, err_info);

}

static gboolean ber_read(wtap *wth, int *err, gchar **err_info, gint64 *data_offset)

{

  gint64 offset;

  *err = 0;

  offset = file_tell(wth->fh);

  /* there is only ever one packet */

  if (offset != 0)

    return FALSE;

  *data_offset = offset;

  return ber_read_file(wth, wth->fh, &wth->phdr, wth->frame_buffer, err, err_info);

}

static gboolean ber_seek_read(wtap *wth, gint64 seek_off, struct wtap_pkthdr *phdr _U_,

                              Buffer *buf, int length _U_, int *err, gchar **err_info)

{

  /* there is only one packet */

  if(seek_off > 0) {

    *err = 0;

    return FALSE;

  }

  if (file_seek(wth->random_fh, seek_off, SEEK_SET, err) == -1)

    return FALSE;

  return ber_read_file(wth, wth->random_fh, phdr, buf, err, err_info);

}

int ber_open(wtap *wth, int *err, gchar **err_info)

{

#define BER_BYTES_TO_CHECK 8

  guint8 bytes[BER_BYTES_TO_CHECK];

  int bytes_read;

  guint8 ber_id;

  gint8 ber_class;

  gint8 ber_tag;

  gboolean ber_pc;

  guint8 oct, nlb = 0;

  int len = 0;

  gint64 file_size;

  int offset = 0, i;

  bytes_read = file_read(&bytes, BER_BYTES_TO_CHECK, wth->fh);

  if (bytes_read != BER_BYTES_TO_CHECK) {

    *err = file_error(wth->fh, err_info);

    if (*err != 0 && *err != WTAP_ERR_SHORT_READ)

      return -1;

    return 0;

  }

  ber_id = bytes[offset++];

  ber_class = (ber_id>>6) & 0x03;

  ber_pc = (ber_id>>5) & 0x01;

  ber_tag = ber_id & 0x1F;

  /* it must be constructed and either a SET or a SEQUENCE */

  /* or a CONTEXT less than 32 (arbitrary) */

  /* XXX: do we also want to allow APPLICATION */

  if(!(ber_pc &&

       (((ber_class == BER_CLASS_UNI) && ((ber_tag == BER_UNI_TAG_SET) || (ber_tag == BER_UNI_TAG_SEQ))) ||

        ((ber_class == BER_CLASS_CON) && (ber_tag < 32)))))

    return 0;

  /* now check the length */

  oct = bytes[offset++];

  if(oct != 0x80) {

    /* not indefinite length encoded */

    if(!(oct & 0x80))

      /* length fits into a single byte */

      len = oct;

    else {

      nlb = oct & 0x7F; /* number of length bytes */

      if((nlb > 0) && (nlb <= (BER_BYTES_TO_CHECK - 2))) {

        /* not indefinite length and we have read enough bytes to compute the length */

        i = nlb;

        while(i--) {

          oct = bytes[offset++];

          len = (len<<8) + oct;

        }

      }

    }

    len += (2 + nlb); /* add back Tag and Length bytes */

    file_size = wtap_file_size(wth, err);

    if(len != file_size) {

      return 0; /* not ASN.1 */

    }

  } else {

    /* Indefinite length encoded - assume it is BER */

  }

  /* seek back to the start of the file  */

  if (file_seek(wth->fh, 0, SEEK_SET, err) == -1)

    return -1;

  wth->file_type = WTAP_FILE_BER;

  wth->file_encap = WTAP_ENCAP_BER;

  wth->snapshot_length = 0;

  wth->subtype_read = ber_read;

  wth->subtype_seek_read = ber_seek_read;

  wth->tsprecision = WTAP_FILE_TSPREC_SEC;

  return 1;

}