/*

 * telnet.c

 *

 * Copyright (C) 2011-25 - ntop.org

 * Copyright (C) 2009-11 - ipoque GmbH

 *

 * 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_TELNET

#include "ndpi_api.h"

#include "ndpi_private.h"

/* #define TELNET_DEBUG 1 */

/* ************************************************************************ */

static int search_telnet_again(struct ndpi_detection_module_struct *ndpi_struct,

             struct ndpi_flow_struct *flow) {

  struct ndpi_packet_struct *packet = &ndpi_struct->packet;

  int i;

#ifdef TELNET_DEBUG

  printf("==> %s() [%.*s][direction: %u]\n", __FUNCTION__, packet->payload_packet_len,

   packet->payload, packet->packet_direction);

#endif

  if((packet->payload == NULL)

     || (packet->payload_packet_len == 0)

     || (packet->payload[0] == 0xFF))

    return(1);

  if(flow->protos.telnet.username_detected) {

    if((!flow->protos.telnet.password_found)

  && (packet->payload_packet_len > 9)) {

      if(strncasecmp((char*)packet->payload, "password:", 9) == 0) {

  flow->protos.telnet.password_found = 1;

      }

      return(1);

    }

    if(packet->payload[0] == '\r' || packet->payload[0] == '\n') {

      if(!flow->protos.telnet.password_found)

  return(1);

      flow->protos.telnet.password_detected = 1;

      ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS, "Found password");

      flow->protos.telnet.password[flow->protos.telnet.character_id] = '\0';

      return(0);

    }

    if(packet->packet_direction == 0) /* client -> server */ {

      for(i=0; i<packet->payload_packet_len; i++) {

  if(flow->protos.telnet.character_id < (sizeof(flow->protos.telnet.password)-1))

    flow->protos.telnet.password[flow->protos.telnet.character_id++] = packet->payload[i];

      }

    }

    return(1);

  }

  if((!flow->protos.telnet.username_found)

     && (packet->payload_packet_len > 6)) {

    if(strncasecmp((char*)packet->payload, "login:", 6) == 0) {

      flow->protos.telnet.username_found = 1;

    }

    return(1);

  }

  if(packet->payload[0] == '\r' || packet->payload[0] == '\n') {

    char buf[64];

    flow->protos.telnet.username_detected = 1;

    flow->protos.telnet.username[flow->protos.telnet.character_id] = '\0';

    flow->protos.telnet.character_id = 0;

    snprintf(buf, sizeof(buf), "Found Telnet username (%s)",

       flow->protos.telnet.username);

    ndpi_set_risk(ndpi_struct, flow, NDPI_CLEAR_TEXT_CREDENTIALS, buf);

    return(1);

  }

  for(i=0; i<packet->payload_packet_len; i++) {

    if(packet->packet_direction == 0) /* client -> server */ {

      if(flow->protos.telnet.character_id < (sizeof(flow->protos.telnet.username)-1))

      {

        if (i>=packet->payload_packet_len-2 &&

            (packet->payload[i] == '\r' || packet->payload[i] == '\n'))

        {

          continue;

        }

        else if (ndpi_isprint(packet->payload[i]) == 0)

        {

          flow->protos.telnet.username[flow->protos.telnet.character_id++] = '?';

        } else {

          flow->protos.telnet.username[flow->protos.telnet.character_id++] = packet->payload[i];

        }

      }

    }

  }

  /* Possibly more processing */

  return(1);

}

/* ************************************************************************ */

static void ndpi_int_telnet_add_connection(struct ndpi_detection_module_struct

             *ndpi_struct, struct ndpi_flow_struct *flow) {

  flow->max_extra_packets_to_check = 64;

  flow->extra_packets_func = search_telnet_again;

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

}

/* ************************************************************************ */

#if !defined(WIN32)

static inline

#elif defined(MINGW_GCC)

__mingw_forceinline static

#else

__forceinline static

#endif

u_int8_t search_iac(struct ndpi_detection_module_struct *ndpi_struct) {

  struct ndpi_packet_struct *packet = &ndpi_struct->packet;

  u_int16_t a;

#ifdef TELNET_DEBUG

  printf("==> %s()\n", __FUNCTION__);

#endif

  if(packet->payload_packet_len < 3)

    return(0);

  if(!((packet->payload[0] == 0xff)

       && (packet->payload[1] > 0xf9)

       && (packet->payload[1] != 0xff)

       && (packet->payload[2] < 0x28)))

    return(0);

  a = 3;

  while (a < packet->payload_packet_len - 2) {

    // commands start with a 0xff byte followed by a command byte >= 0xf0 and < 0xff

    // command bytes 0xfb to 0xfe are followed by an option byte <= 0x28

    if(!(packet->payload[a] != 0xff ||

    (packet->payload[a] == 0xff && (packet->payload[a + 1] >= 0xf0) && (packet->payload[a + 1] <= 0xfa)) ||

    (packet->payload[a] == 0xff && (packet->payload[a + 1] >= 0xfb) && (packet->payload[a + 1] != 0xff)

     && (packet->payload[a + 2] <= 0x28))))

      return(0);

    a += 3;

  }

  return 1;

}

/* ************************************************************************ */

/* this detection also works asymmetrically */

static void ndpi_search_telnet_tcp(struct ndpi_detection_module_struct *ndpi_struct,

           struct ndpi_flow_struct *flow) {

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

  if(search_iac(ndpi_struct) == 1) {

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

    ndpi_int_telnet_add_connection(ndpi_struct, flow);

    return;

  }

  NDPI_EXCLUDE_DISSECTOR(ndpi_struct, flow);

  return;

}

void init_telnet_dissector(struct ndpi_detection_module_struct *ndpi_struct)

{

  register_dissector("Telnet", ndpi_struct,

                     ndpi_search_telnet_tcp,

                     NDPI_SELECTION_BITMASK_PROTOCOL_V4_V6_TCP_WITH_PAYLOAD_WITHOUT_RETRANSMISSION,

                     1, NDPI_PROTOCOL_TELNET);

}