nbns_responder.c

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/**
 * @file nbns_responder.c
 * @brief NBNS responder (NetBIOS Name Service)
 *
 * @section License
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * Copyright (C) 2010-2024 Oryx Embedded SARL. All rights reserved.
 *
 * This file is part of CycloneTCP Open.
 *
 * 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.
 *
 * @author Oryx Embedded SARL (www.oryx-embedded.com)
 * @version 2.4.0
 **/
 
//Switch to the appropriate trace level
#define TRACE_LEVEL NBNS_TRACE_LEVEL
 
//Dependencies
#include "core/net.h"
#include "netbios/nbns_responder.h"
#include "netbios/nbns_common.h"
#include "dns/dns_debug.h"
#include "debug.h"
 
//Check TCP/IP stack configuration
#if (NBNS_RESPONDER_SUPPORT == ENABLED && IPV4_SUPPORT == ENABLED)
 
 
/**
 * @brief Process NBNS query message
 * @param[in] interface Underlying network interface
 * @param[in] pseudoHeader UDP pseudo header
 * @param[in] udpHeader UDP header
 * @param[in] message Pointer to the NBNS query message
 * @param[in] length Length of the message
 **/
 
void nbnsProcessQuery(NetInterface *interface, const Ipv4PseudoHeader *pseudoHeader,
   const UdpHeader *udpHeader, const NbnsHeader *message, size_t length)
{
   size_t pos;
   DnsQuestion *question;
 
   //The NBNS query shall contain one question
   if(ntohs(message->qdcount) != 1)
      return;
 
   //Parse NetBIOS name
   pos = nbnsParseName(message, length, sizeof(DnsHeader), NULL);
 
   //Invalid name?
   if(!pos)
      return;
   //Malformed NBNS query message?
   if((pos + sizeof(DnsQuestion)) > length)
      return;
 
   //Point to the corresponding entry
   question = DNS_GET_QUESTION(message, pos);
 
   //Check the class and the type of the request
   if(ntohs(question->qclass) != DNS_RR_CLASS_IN)
      return;
   if(ntohs(question->qtype) != DNS_RR_TYPE_NB)
      return;
 
   //Compare NetBIOS names
   if(nbnsCompareName(message, length, sizeof(DnsHeader), interface->hostname))
   {
      uint16_t destPort;
      IpAddr destIpAddr;
 
      //A response packet is always sent to the source UDP port and source IP
      //address of the request packet
      destIpAddr.length = sizeof(Ipv4Addr);
      destIpAddr.ipv4Addr = pseudoHeader->srcAddr;
 
      //Convert the port number to host byte order
      destPort = ntohs(udpHeader->srcPort);
 
      //Send NBNS response
      nbnsSendResponse(interface, &destIpAddr, destPort, message->id);
   }
}
 
 
/**
 * @brief Send NBNS response message
 * @param[in] interface Underlying network interface
 * @param[in] destIpAddr Destination IP address
 * @param[in] destPort destination port
 * @param[in] id 16-bit identifier to be used when sending NBNS query
 **/
 
error_t nbnsSendResponse(NetInterface *interface,
   const IpAddr *destIpAddr, uint16_t destPort, uint16_t id)
{
   error_t error;
   uint_t i;
   size_t length;
   size_t offset;
   NetBuffer *buffer;
   NbnsHeader *message;
   NbnsAddrEntry *addrEntry;
   DnsResourceRecord *record;
   Ipv4AddrEntry *entry;
   NetTxAncillary ancillary;
 
   //Initialize status code
   error = NO_ERROR;
 
   //Allocate a memory buffer to hold the NBNS response message
   buffer = udpAllocBuffer(DNS_MESSAGE_MAX_SIZE, &offset);
   //Failed to allocate buffer?
   if(buffer == NULL)
      return ERROR_OUT_OF_MEMORY;
 
   //Point to the NBNS header
   message = netBufferAt(buffer, offset);
 
   //Take the identifier from the query message
   message->id = id;
 
   //Format NBNS response header
   message->qr = 1;
   message->opcode = DNS_OPCODE_QUERY;
   message->aa = 1;
   message->tc = 0;
   message->rd = 1;
   message->ra = 1;
   message->z = 0;
   message->b = 0;
   message->rcode = DNS_RCODE_NOERROR;
   message->qdcount = 0;
   message->ancount = 0;
   message->nscount = 0;
   message->arcount = 0;
 
   //NBNS response message length
   length = sizeof(DnsHeader);
 
   //The NBNS response contains 1 answer resource record
   for(i = 0; i < IPV4_ADDR_LIST_SIZE && message->ancount == 0; i++)
   {
      //Point to the current entry
      entry = &interface->ipv4Context.addrList[i];
 
      //Check the state of the address
      if(entry->state == IPV4_ADDR_STATE_VALID)
      {
         //Check whether the address belongs to the same subnet as the source
         //address of the query
         if(ipv4IsOnSubnet(entry, destIpAddr->ipv4Addr))
         {
            //Encode the host name using the NBNS name notation
            length += nbnsEncodeName(interface->hostname,
               (uint8_t *) message + length);
 
            //Point to the corresponding resource record
            record = DNS_GET_RESOURCE_RECORD(message, length);
 
            //Fill in resource record
            record->rtype = HTONS(DNS_RR_TYPE_NB);
            record->rclass = HTONS(DNS_RR_CLASS_IN);
            record->ttl = HTONL(NBNS_DEFAULT_RESOURCE_RECORD_TTL);
            record->rdlength = HTONS(sizeof(NbnsAddrEntry));
 
            //Point to the address entry array
            addrEntry = (NbnsAddrEntry *) record->rdata;
 
            //Fill in address entry
            addrEntry->flags = HTONS(NBNS_G_UNIQUE | NBNS_ONT_BNODE);
            addrEntry->addr = entry->addr;
 
            //Update the length of the NBNS response message
            length += sizeof(DnsResourceRecord) + sizeof(NbnsAddrEntry);
 
            //Number of resource records in the answer section
            message->ancount++;
         }
      }
   }
 
   //Valid NBNS response?
   if(message->ancount > 0)
   {
      //The ANCOUNT field specifies the number of resource records in the
      //answer section
      message->ancount = htons(message->ancount);
 
      //Adjust the length of the multi-part buffer
      netBufferSetLength(buffer, offset + length);
 
      //Debug message
      TRACE_INFO("Sending NBNS message (%" PRIuSIZE " bytes)...\r\n", length);
      //Dump message
      dnsDumpMessage((DnsHeader *) message, length);
 
      //Additional options can be passed to the stack along with the packet
      ancillary = NET_DEFAULT_TX_ANCILLARY;
 
      //This flag tells the stack that the destination is on a locally attached
      //network and not to perform a lookup of the routing table
      ancillary.dontRoute = TRUE;
 
      //A response packet is always sent to the source UDP port and source IP
      //address of the request packet
      error = udpSendBuffer(interface, NULL, NBNS_PORT, destIpAddr, destPort,
         buffer, offset, &ancillary);
   }
 
   //Free previously allocated memory
   netBufferFree(buffer);
 
   //Return status code
   return error;
}
 
#endif