path: root/src/dns/gnunet-service-dns.c

/*
     This file is part of GNUnet.
     Copyright (C) 2012 GNUnet e.V.

     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 of the License,
     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
     Affero General Public License for more details.
*/

/**
 * @file dns/gnunet-service-dns.c
 * @brief service to intercept and modify DNS queries (and replies) of this system
 * @author Christian Grothoff
 *
 * For "secure" interaction with the legacy DNS system, we permit
 * replies only to arrive within a 5s window (and they must match
 * ports, IPs and request IDs).  Furthermore, we let the OS pick a
 * source port, opening up to 128 sockets per address family (IPv4 or
 * IPv6).  Those sockets are closed if they are not in use for 5s
 * (which means they will be freshly randomized afterwards).  For new
 * requests, we pick a random slot in the array with 128 socket slots
 * (and re-use an existing socket if the slot is still in use).  Thus
 * each request will be given one of 128 random source ports, and the
 * 128 random source ports will also change "often" (less often if the
 * system is very busy, each time if we are mostly idle).  At the same
 * time, the system will never use more than 256 UDP sockets.
 */
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_applications.h"
#include "gnunet_constants.h"
#include "gnunet_protocols.h"
#include "gnunet_signatures.h"
#include "dns.h"
#include "gnunet_dns_service.h"
#include "gnunet_dnsparser_lib.h"
#include "gnunet_dnsstub_lib.h"
#include "gnunet_statistics_service.h"
#include "gnunet_tun_lib.h"

/**
 * Port number for DNS
 */
#define DNS_PORT 53


/**
 * Generic logging shorthand
 */
#define LOG(kind, ...)                          \
  GNUNET_log_from (kind, "dns", __VA_ARGS__);


/**
 * Phases each request goes through.
 */
enum RequestPhase
{
  /**
   * Request has just been received.
   */
  RP_INIT,

  /**
   * Showing the request to all monitor clients.  If
   * client list is empty, will enter QUERY phase.
   */
  RP_REQUEST_MONITOR,

  /**
   * Showing the request to PRE-RESOLUTION clients to find an answer.
   * If client list is empty, will trigger global DNS request.
   */
  RP_QUERY,

  /**
   * Global Internet query is now pending.
   */
  RP_INTERNET_DNS,

  /**
   * Client (or global DNS request) has resulted in a response.
   * Forward to all POST-RESOLUTION clients.  If client list is empty,
   * will enter RESPONSE_MONITOR phase.
   */
  RP_MODIFY,

  /**
   * Showing the request to all monitor clients.  If
   * client list is empty, give the result to the hijacker (and be done).
   */
  RP_RESPONSE_MONITOR,

  /**
   * Some client has told us to drop the request.
   */
  RP_DROP
};


/**
 * Entry we keep for each client.
 */
struct ClientRecord
{
  /**
   * Kept in doubly-linked list.
   */
  struct ClientRecord *next;

   /**
   * Kept in doubly-linked list.
    */
  struct ClientRecord *prev;

  /**
   * Handle to the client.
   */
  struct GNUNET_SERVICE_Client *client;

  /**
   * Message queue to talk to @a client.
   */
  struct GNUNET_MQ_Handle *mq;

  /**
   * Flags for the client.
   */
  enum GNUNET_DNS_Flags flags;

};


/**
 * Entry we keep for each active request.
 */
struct RequestRecord
{

  /**
   * List of clients that still need to see this request (each entry
   * is set to NULL when the client is done).
   */
  struct ClientRecord **client_wait_list;

  /**
   * Payload of the UDP packet (the UDP payload), can be either query
   * or already the response.
   */
  char *payload;

  /**
   * Socket we are using to transmit this request (must match if we receive
   * a response).
   */
  struct GNUNET_DNSSTUB_RequestSocket *rs;

  /**
   * Source address of the original request (for sending response).
   */
  struct sockaddr_storage src_addr;

  /**
   * Destination address of the original request (for potential use as exit).
   */
  struct sockaddr_storage dst_addr;

  /**
   * ID of this request, also basis for hashing.  Lowest 16 bit will
   * be our message ID when doing a global DNS request and our index
   * into the 'requests' array.
   */
  uint64_t request_id;

  /**
   * Number of bytes in payload.
   */
  size_t payload_length;

  /**
   * Length of the @e client_wait_list.
   */
  unsigned int client_wait_list_length;

  /**
   * In which phase this this request?
   */
  enum RequestPhase phase;

};


/**
 * Global return value from 'main'.
 */
static int global_ret;

/**
 * The configuration to use
 */
static const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Statistics.
 */
static struct GNUNET_STATISTICS_Handle *stats;

/**
 * Handle to DNS hijacker helper process ("gnunet-helper-dns").
 */
static struct GNUNET_HELPER_Handle *hijacker;

/**
 * Command-line arguments we are giving to the hijacker process.
 */
static char *helper_argv[8];

/**
 * Head of DLL of clients we consult.
 */
static struct ClientRecord *clients_head;

/**
 * Tail of DLL of clients we consult.
 */
static struct ClientRecord *clients_tail;

/**
 * Array of all open requests.
 */
static struct RequestRecord requests[UINT16_MAX