/*

 * tftp.c

 *

 * Copyright (C) 2009-11 - ipoque GmbH

 * Copyright (C) 2011-26 - ntop.org

 *

 * This file is part of nDPI, an open source deep packet inspection

 * library based on the OpenDPI and PACE technology by ipoque GmbH

 *

 * nDPI is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * nDPI 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 Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with nDPI.  If not, see <http://www.gnu.org/licenses/>.

 *

 */

#include "ndpi_protocol_ids.h"

#define NDPI_CURRENT_PROTO NDPI_PROTOCOL_TFTP

#include "ndpi_api.h"

#include "ndpi_private.h"

static void ndpi_int_tftp_add_connection(struct ndpi_detection_module_struct

           *ndpi_struct, struct ndpi_flow_struct *flow)

{

  ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_TFTP, NDPI_PROTOCOL_UNKNOWN, NDPI_CONFIDENCE_DPI);

}

static size_t tftp_dissect_szstr(struct ndpi_packet_struct const * const packet,

                                 size_t * const offset,

                                 char const ** const string_start)

{

  if (packet->payload_packet_len <= *offset)

  {

    return 0;

  }

  const union {

    uint8_t const * const as_ptr;

    char const * const as_str;

  } payload = { .as_ptr = packet->payload + *offset };

  size_t len = strnlen(payload.as_str, packet->payload_packet_len - *offset);

  if (len == 0 ||

      packet->payload_packet_len <= *offset + len ||

      payload.as_str[len] != '\0')

  {

    return 0;

  }

  if (string_start != NULL)

  {

    *string_start = payload.as_str;

  }

  *offset += len + 1;

  return len;

}

static int tftp_dissect_mode(struct ndpi_packet_struct const * const packet,

                             size_t * const offset)

{

  static char const * const valid_modes[] = {

    "netascii", "octet", "mail"

  };

  char const * string_start;

  size_t string_length = tftp_dissect_szstr(packet, offset, &string_start);

  size_t i;

  if (string_length == 0)

  {

    return 1;

  }

  for (i = 0; i < NDPI_ARRAY_LENGTH(valid_modes); ++i)

  {

    if (strncasecmp(string_start, valid_modes[i], string_length) == 0)

    {

      break;

    }

  }

  return i == NDPI_ARRAY_LENGTH(valid_modes);

}

static int tftp_dissect_options(struct ndpi_packet_struct const * const packet,

                                size_t * const offset)

{

  static char const * const valid_options[] = {

    "blksize", "tsize"

  };

  uint8_t options_used[NDPI_ARRAY_LENGTH(valid_options)] = {0, 0};

  size_t i;

  do {

    char const * string_start;

    size_t string_length = tftp_dissect_szstr(packet, offset, &string_start);

    if (string_length == 0 ||

        tftp_dissect_szstr(packet, offset, NULL) == 0 /* value, not interested */)

    {

      break;

    }

    for (i = 0; i < NDPI_ARRAY_LENGTH(valid_options); ++i)

    {

      if (strncasecmp(string_start, valid_options[i], string_length) == 0)

      {

        break;

      }

    }

    if (i == NDPI_ARRAY_LENGTH(valid_options) /* option not found in valid_options */ ||

        options_used[i] != 0 /* duplicate options are not allowed */)

    {

      break;

    }

    options_used[i] = 1;

  } while (1);

  return *offset != packet->payload_packet_len;

}

static void ndpi_search_tftp(struct ndpi_detection_module_struct *ndpi_struct,

           struct ndpi_flow_struct *flow)

{

  struct ndpi_packet_struct const * const packet = &ndpi_struct->packet;

  u_int16_t block_num;

  u_int16_t prev_num;

  NDPI_LOG_DBG(ndpi_struct, "search TFTP\n");

  if (packet->payload_packet_len < 4 /* min. header size */ ||

      get_u_int8_t(packet->payload, 0) != 0x00)

  {

    NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

    return;

  }

  /* parse TFTP opcode */

  switch (get_u_int8_t(packet->payload, 1))

  {

    case 0x01:

        /* Read request (RRQ) */

    case 0x02:

        /* Write request (WWQ) */

        if (packet->payload[packet->payload_packet_len - 1] != 0x00 /* last pdu element is a nul terminated string */)

        {

          NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

          return;

        }

        {

          size_t filename_len = 0;

          size_t offset = 2;

          char const * filename_start;

          filename_len = tftp_dissect_szstr(packet, &offset, &filename_start);

          /* Exclude the flow as TFPT if there was no filename and mode in the first two strings. */

          if (filename_len == 0 || ndpi_is_printable_buffer((uint8_t *)filename_start, filename_len) == 0)

          {

            NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

            return;

          }

          if (tftp_dissect_mode(packet, &offset) != 0)

          {

            NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

            return;

          }

          if (tftp_dissect_options(packet, &offset) != 0)

          {

            NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

            return;

          }

          /* Dissect RRQ/WWQ filename. */

          filename_len = ndpi_min(filename_len, sizeof(flow->protos.tftp.filename) - 1);

          memcpy(flow->protos.tftp.filename, filename_start, filename_len);

          flow->protos.tftp.filename[filename_len] = '\0';

          /* We have seen enough and do not need any more TFTP packets. */

          NDPI_LOG_INFO(ndpi_struct, "found tftp (RRQ/WWQ)\n");

          ndpi_int_tftp_add_connection(ndpi_struct, flow);

        }

        return;

    case 0x03:

        /* Data (DATA) */

        if (packet->payload_packet_len <= 4 /* min DATA header size */)

        {

          NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

          return;

        }

        /* First 2 bytes were opcode so next 16 bits are the block number.

         * This should increment every packet but give some leeway for midstream and packet loss. */

        block_num = ntohs(get_u_int16_t(packet->payload, 2));

        prev_num = flow->l4.udp.tftp_data_num;

        flow->l4.udp.tftp_data_num = block_num;

        if (!(block_num == prev_num + 1 || (prev_num != 0 && block_num == prev_num)))

        {

          return;

        }

        break;

    case 0x04:

        /* Acknowledgment (ACK) */

        if (packet->payload_packet_len != 4 /* ACK has a fixed packet size */)

        {

          NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

          return;

        }

        /* First 2 bytes were opcode so next 16 bits are the block number.

         * This should increment every packet but give some leeway for midstream and packet loss. */

        block_num = ntohs(get_u_int16_t(packet->payload, 2));

        prev_num = flow->l4.udp.tftp_ack_num;

        flow->l4.udp.tftp_ack_num = block_num;

        if (!(block_num == prev_num + 1 || (block_num == prev_num)))

        {

          return;

        }

        break;

    case 0x05:

        /* Error (ERROR) */

        if (packet->payload_packet_len < 5 ||

            packet->payload[packet->payload_packet_len - 1] != 0x00 ||

            packet->payload[2] != 0x00 || packet->payload[3] > 0x07)

        {

          NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

          return;

        }

        break;

    case 0x06:

        /* Option Acknowledgment (OACK) */

        {

          size_t offset = 2;

          if (tftp_dissect_options(packet, &offset) != 0)

          {

            NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

            return;

          }

        }

        /* We have seen enough and do not need any more TFTP packets. */

        NDPI_LOG_INFO(ndpi_struct, "found tftp (OACK)\n");

        ndpi_int_tftp_add_connection(ndpi_struct, flow);

        break;

    default:

        NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

        return;

  }

  if (flow->l4.udp.tftp_stage < 3)

  {

    NDPI_LOG_DBG2(ndpi_struct, "maybe tftp. need next packet\n");

    flow->l4.udp.tftp_stage++;

    return;

  }

  NDPI_LOG_INFO(ndpi_struct, "found tftp\n");

  ndpi_int_tftp_add_connection(ndpi_struct, flow);

}

void init_tftp_dissector(struct ndpi_detection_module_struct *ndpi_struct)

{

  ndpi_register_dissector("TFTP", ndpi_struct,

                     ndpi_search_tftp,

                     NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_UDP_WITH_PAYLOAD,

                     1, NDPI_PROTOCOL_TFTP);

}