/* ber.c

 *

 * Basic Encoding Rules (BER) file reading

 *

 * SPDX-License-Identifier: GPL-2.0-or-later

 */

#include "config.h"

#include "ber.h"

#include "wtap_module.h"

#include "file_wrappers.h"

#include <wsutil/buffer.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 int ber_file_type_subtype = -1;

void register_ber(void);

static bool ber_full_file_read(wtap *wth, wtap_rec *rec,

                                   int *err, char **err_info,

                                   int64_t *data_offset)

{

  if (!wtap_full_file_read(wth, rec, err, err_info, data_offset))

    return false;

  /* Pass the file name. */

  rec->rec_header.packet_header.pseudo_header.ber.pathname = wth->pathname;

  return true;

}

static bool ber_full_file_seek_read(wtap *wth, int64_t seek_off, wtap_rec *rec,

                                        int *err, char **err_info)

{

  if (!wtap_full_file_seek_read(wth, seek_off, rec, err, err_info))

    return false;

  /* Pass the file name. */

  rec->rec_header.packet_header.pseudo_header.ber.pathname = wth->pathname;

  return true;

}

wtap_open_return_val ber_open(wtap *wth, int *err, char **err_info)

{

#define BER_BYTES_TO_CHECK 8

  uint8_t bytes[BER_BYTES_TO_CHECK];

  uint8_t ber_id;

  uint8_t ber_class;

  uint8_t ber_tag;

  bool ber_pc;

  uint8_t oct, ntb = 0, nlb = 0;

  int64_t len = 0;

  int64_t file_size;

  size_t offset = 0;

  if (!wtap_read_bytes(wth->fh, &bytes, BER_BYTES_TO_CHECK, err, err_info)) {

    if (*err != WTAP_ERR_SHORT_READ)

      return WTAP_OPEN_ERROR;

    return WTAP_OPEN_NOT_MINE;

  }

  ber_id = bytes[offset++];

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

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

  ber_tag = ber_id & 0x1F;

  if (ber_tag == 0x1F) {

    ber_tag = bytes[offset++];

    ntb = 1; /* number of tag bytes */

  }

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

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

  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_class == BER_CLASS_APP)) && (ber_tag < 0xFF)))))

    return WTAP_OPEN_NOT_MINE;

  /* 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) {

        if (nlb + offset >= sizeof(bytes)) {

            /* This limits us to 1 or 256 TiB, depending on tag length. */

            return WTAP_OPEN_NOT_MINE;

        }

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

        for(int i = 0; i < nlb; i++) {

          oct = bytes[offset++];

          if (ckd_mul(&len, len, 256)) {

            /* Can't happen, unless we increase BER_BYTES_TO_CHECK */

            return WTAP_OPEN_NOT_MINE;

          }

          len += oct;

        }

      }

    }

    /* add back Tag and Length bytes */

    if (ckd_add(&len, len, 2 + ntb + nlb)) {

      return WTAP_OPEN_NOT_MINE;

    }

    file_size = wtap_file_size(wth, err);

    if(len != file_size) {

      return WTAP_OPEN_NOT_MINE; /* 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 WTAP_OPEN_ERROR;

  wth->file_type_subtype = ber_file_type_subtype;

  wth->file_encap = WTAP_ENCAP_BER;

  wth->snapshot_length = 0;

  wth->subtype_read = ber_full_file_read;

  wth->subtype_seek_read = ber_full_file_seek_read;

  wth->file_tsprec = WTAP_TSPREC_SEC;

  return WTAP_OPEN_MINE;

}

static const struct supported_block_type ber_blocks_supported[] = {

  /*

   * These are file formats that we dissect, so we provide only one

   * "packet" with the file's contents, and don't support any

   * options.

   */

  { WTAP_BLOCK_PACKET, ONE_BLOCK_SUPPORTED, NO_OPTIONS_SUPPORTED }

};

static const struct file_type_subtype_info ber_info = {

  "ASN.1 Basic Encoding Rules", "ber", NULL, NULL,

  false, BLOCKS_SUPPORTED(ber_blocks_supported),

  NULL, NULL, NULL

};

void register_ber(void)

{

  ber_file_type_subtype = wtap_register_file_type_subtype(&ber_info);

  /*

   * Register name for backwards compatibility with the

   * wtap_filetypes table in Lua.

   */

  wtap_register_backwards_compatibility_lua_name("BER", ber_file_type_subtype);

}

/*

 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html

 *

 * Local Variables:

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 * End:

 *

 * vi: set shiftwidth=2 tabstop=8 expandtab:

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 */