src/coremods/core_dns.cpp

   1 /*
   2  * InspIRCd -- Internet Relay Chat Daemon
   3  *
   4  *   Copyright (C) 2019 Robby <robby@chatbelgie.be>
   5  *   Copyright (C) 2015, 2017-2020 Sadie Powell <sadie@witchery.services>
   6  *   Copyright (C) 2013-2016 Attila Molnar <attilamolnar@hush.com>
   7  *   Copyright (C) 2013, 2015-2016 Adam <Adam@anope.org>
   8  *
   9  * This file is part of InspIRCd.  InspIRCd is free software: you can
  10  * redistribute it and/or modify it under the terms of the GNU General Public
  11  * License as published by the Free Software Foundation, version 2.
  12  *
  13  * This program is distributed in the hope that it will be useful, but WITHOUT
  14  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  15  * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
  16  * details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20  */
  21
  22 #include "inspircd.h"
  23 #include "modules/dns.h"
  24 #include <iostream>
  25 #include <fstream>
  26
  27 #ifdef _WIN32
  28 #include <Iphlpapi.h>
  29 #pragma comment(lib, "Iphlpapi.lib")
  30 #endif
  31
  32 namespace DNS
  33 {
  34         /** Maximum value of a dns request id, 16 bits wide, 0xFFFF.
  35          */
  36         const unsigned int MAX_REQUEST_ID = 0xFFFF;
  37 }
  38
  39 using namespace DNS;
  40
  41 /** A full packet sent or received to/from the nameserver
  42  */
  43 class Packet : public Query
  44 {
  45         void PackName(unsigned char* output, unsigned short output_size, unsigned short& pos, const std::string& name)
  46         {
  47                 if (pos + name.length() + 2 > output_size)
  48                         throw Exception("Unable to pack name");
  49
  50                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Packing name " + name);
  51
  52                 irc::sepstream sep(name, '.');
  53                 std::string token;
  54
  55                 while (sep.GetToken(token))
  56                 {
  57                         output[pos++] = token.length();
  58                         memcpy(&output[pos], token.data(), token.length());
  59                         pos += token.length();
  60                 }
  61
  62                 output[pos++] = 0;
  63         }
  64
  65         std::string UnpackName(const unsigned char* input, unsigned short input_size, unsigned short& pos)
  66         {
  67                 std::string name;
  68                 unsigned short pos_ptr = pos, lowest_ptr = input_size;
  69                 bool compressed = false;
  70
  71                 if (pos_ptr >= input_size)
  72                         throw Exception("Unable to unpack name - no input");
  73
  74                 while (input[pos_ptr] > 0)
  75                 {
  76                         unsigned short offset = input[pos_ptr];
  77
  78                         if (offset & POINTER)
  79                         {
  80                                 if ((offset & POINTER) != POINTER)
  81                                         throw Exception("Unable to unpack name - bogus compression header");
  82                                 if (pos_ptr + 1 >= input_size)
  83                                         throw Exception("Unable to unpack name - bogus compression header");
  84
  85                                 /* Place pos at the second byte of the first (farthest) compression pointer */
  86                                 if (compressed == false)
  87                                 {
  88                                         ++pos;
  89                                         compressed = true;
  90                                 }
  91
  92                                 pos_ptr = (offset & LABEL) << 8 | input[pos_ptr + 1];
  93
  94                                 /* Pointers can only go back */
  95                                 if (pos_ptr >= lowest_ptr)
  96                                         throw Exception("Unable to unpack name - bogus compression pointer");
  97                                 lowest_ptr = pos_ptr;
  98                         }
  99                         else
 100                         {
 101                                 if (pos_ptr + offset + 1 >= input_size)
 102                                         throw Exception("Unable to unpack name - offset too large");
 103                                 if (!name.empty())
 104                                         name += ".";
 105                                 for (unsigned i = 1; i <= offset; ++i)
 106                                         name += input[pos_ptr + i];
 107
 108                                 pos_ptr += offset + 1;
 109                                 if (compressed == false)
 110                                         /* Move up pos */
 111                                         pos = pos_ptr;
 112                         }
 113                 }
 114
 115                 /* +1 pos either to one byte after the compression pointer or one byte after the ending \0 */
 116                 ++pos;
 117
 118                 if (name.empty())
 119                         throw Exception("Unable to unpack name - no name");
 120
 121                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Unpack name " + name);
 122
 123                 return name;
 124         }
 125
 126         Question UnpackQuestion(const unsigned char* input, unsigned short input_size, unsigned short& pos)
 127         {
 128                 Question q;
 129
 130                 q.name = this->UnpackName(input, input_size, pos);
 131
 132                 if (pos + 4 > input_size)
 133                         throw Exception("Unable to unpack question");
 134
 135                 q.type = static_cast<QueryType>(input[pos] << 8 | input[pos + 1]);
 136                 pos += 2;
 137
 138                 // Skip over query class code
 139                 pos += 2;
 140
 141                 return q;
 142         }
 143
 144         ResourceRecord UnpackResourceRecord(const unsigned char* input, unsigned short input_size, unsigned short& pos)
 145         {
 146                 ResourceRecord record = static_cast<ResourceRecord>(this->UnpackQuestion(input, input_size, pos));
 147
 148                 if (pos + 6 > input_size)
 149                         throw Exception("Unable to unpack resource record");
 150
 151                 record.ttl = (input[pos] << 24) | (input[pos + 1] << 16) | (input[pos + 2] << 8) | input[pos + 3];
 152                 pos += 4;
 153
 154                 uint16_t rdlength = input[pos] << 8 | input[pos + 1];
 155                 pos += 2;
 156
 157                 switch (record.type)
 158                 {
 159                         case QUERY_A:
 160                         {
 161                                 if (pos + 4 > input_size)
 162                                         throw Exception("Unable to unpack resource record");
 163
 164                                 irc::sockets::sockaddrs addrs;
 165                                 memset(&addrs, 0, sizeof(addrs));
 166
 167                                 addrs.in4.sin_family = AF_INET;
 168                                 addrs.in4.sin_addr.s_addr = input[pos] | (input[pos + 1] << 8) | (input[pos + 2] << 16)  | (input[pos + 3] << 24);
 169                                 pos += 4;
 170
 171                                 record.rdata = addrs.addr();
 172                                 break;
 173                         }
 174                         case QUERY_AAAA:
 175                         {
 176                                 if (pos + 16 > input_size)
 177                                         throw Exception("Unable to unpack resource record");
 178
 179                                 irc::sockets::sockaddrs addrs;
 180                                 memset(&addrs, 0, sizeof(addrs));
 181
 182                                 addrs.in6.sin6_family = AF_INET6;
 183                                 for (int j = 0; j < 16; ++j)
 184                                         addrs.in6.sin6_addr.s6_addr[j] = input[pos + j];
 185                                 pos += 16;
 186
 187                                 record.rdata = addrs.addr();
 188
 189                                 break;
 190                         }
 191                         case QUERY_CNAME:
 192                         case QUERY_PTR:
 193                         {
 194                                 record.rdata = this->UnpackName(input, input_size, pos);
 195                                 if (!InspIRCd::IsHost(record.rdata))
 196                                         throw Exception("Invalid name"); // XXX: Causes the request to time out
 197
 198                                 break;
 199                         }
 200                         case QUERY_TXT:
 201                         {
 202                                 if (pos + rdlength > input_size)
 203                                         throw Exception("Unable to unpack txt resource record");
 204
 205                                 record.rdata = std::string(reinterpret_cast<const char *>(input + pos), rdlength);
 206                                 pos += rdlength;
 207
 208                                 if (record.rdata.find_first_of("\r\n\0", 0, 3) != std::string::npos)
 209                                         throw Exception("Invalid character in txt record");
 210
 211                                 break;
 212                         }
 213                         default:
 214                                 break;
 215                 }
 216
 217                 if (!record.name.empty() && !record.rdata.empty())
 218                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, record.name + " -> " + record.rdata);
 219
 220                 return record;
 221         }
 222
 223  public:
 224         static const int POINTER = 0xC0;
 225         static const int LABEL = 0x3F;
 226         static const int HEADER_LENGTH = 12;
 227
 228         /* ID for this packet */
 229         RequestId id;
 230         /* Flags on the packet */
 231         unsigned short flags;
 232
 233         Packet() : id(0), flags(0)
 234         {
 235         }
 236
 237         void Fill(const unsigned char* input, const unsigned short len)
 238         {
 239                 if (len < HEADER_LENGTH)
 240                         throw Exception("Unable to fill packet");
 241
 242                 unsigned short packet_pos = 0;
 243
 244                 this->id = (input[packet_pos] << 8) | input[packet_pos + 1];
 245                 packet_pos += 2;
 246
 247                 this->flags = (input[packet_pos] << 8) | input[packet_pos + 1];
 248                 packet_pos += 2;
 249
 250                 unsigned short qdcount = (input[packet_pos] << 8) | input[packet_pos + 1];
 251                 packet_pos += 2;
 252
 253                 unsigned short ancount = (input[packet_pos] << 8) | input[packet_pos + 1];
 254                 packet_pos += 2;
 255
 256                 unsigned short nscount = (input[packet_pos] << 8) | input[packet_pos + 1];
 257                 packet_pos += 2;
 258
 259                 unsigned short arcount = (input[packet_pos] << 8) | input[packet_pos + 1];
 260                 packet_pos += 2;
 261
 262                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "qdcount: " + ConvToStr(qdcount) + " ancount: " + ConvToStr(ancount) + " nscount: " + ConvToStr(nscount) + " arcount: " + ConvToStr(arcount));
 263
 264                 if (qdcount != 1)
 265                         throw Exception("Question count != 1 in incoming packet");
 266
 267                 this->question = this->UnpackQuestion(input, len, packet_pos);
 268
 269                 for (unsigned i = 0; i < ancount; ++i)
 270                         this->answers.push_back(this->UnpackResourceRecord(input, len, packet_pos));
 271         }
 272
 273         unsigned short Pack(unsigned char* output, unsigned short output_size)
 274         {
 275                 if (output_size < HEADER_LENGTH)
 276                         throw Exception("Unable to pack packet");
 277
 278                 unsigned short pos = 0;
 279
 280                 output[pos++] = this->id >> 8;
 281                 output[pos++] = this->id & 0xFF;
 282                 output[pos++] = this->flags >> 8;
 283                 output[pos++] = this->flags & 0xFF;
 284                 output[pos++] = 0; // Question count, high byte
 285                 output[pos++] = 1; // Question count, low byte
 286                 output[pos++] = 0; // Answer count, high byte
 287                 output[pos++] = 0; // Answer count, low byte
 288                 output[pos++] = 0;
 289                 output[pos++] = 0;
 290                 output[pos++] = 0;
 291                 output[pos++] = 0;
 292
 293                 {
 294                         Question& q = this->question;
 295
 296                         if (q.type == QUERY_PTR)
 297                         {
 298                                 irc::sockets::sockaddrs ip;
 299                                 irc::sockets::aptosa(q.name, 0, ip);
 300
 301                                 if (q.name.find(':') != std::string::npos)
 302                                 {
 303                                         static const char* const hex = "0123456789abcdef";
 304                                         char reverse_ip[128];
 305                                         unsigned reverse_ip_count = 0;
 306                                         for (int j = 15; j >= 0; --j)
 307                                         {
 308                                                 reverse_ip[reverse_ip_count++] = hex[ip.in6.sin6_addr.s6_addr[j] & 0xF];
 309                                                 reverse_ip[reverse_ip_count++] = '.';
 310                                                 reverse_ip[reverse_ip_count++] = hex[ip.in6.sin6_addr.s6_addr[j] >> 4];
 311                                                 reverse_ip[reverse_ip_count++] = '.';
 312                                         }
 313                                         reverse_ip[reverse_ip_count++] = 0;
 314
 315                                         q.name = reverse_ip;
 316                                         q.name += "ip6.arpa";
 317                                 }
 318                                 else
 319                                 {
 320                                         unsigned long forward = ip.in4.sin_addr.s_addr;
 321                                         ip.in4.sin_addr.s_addr = forward << 24 | (forward & 0xFF00) << 8 | (forward & 0xFF0000) >> 8 | forward >> 24;
 322
 323                                         q.name = ip.addr() + ".in-addr.arpa";
 324                                 }
 325                         }
 326
 327                         this->PackName(output, output_size, pos, q.name);
 328
 329                         if (pos + 4 >= output_size)
 330                                 throw Exception("Unable to pack packet");
 331
 332                         short s = htons(q.type);
 333                         memcpy(&output[pos], &s, 2);
 334                         pos += 2;
 335
 336                         // Query class, always IN
 337                         output[pos++] = 0;
 338                         output[pos++] = 1;
 339                 }
 340
 341                 return pos;
 342         }
 343 };
 344
 345 class MyManager : public Manager, public Timer, public EventHandler
 346 {
 347         typedef TR1NS::unordered_map<Question, Query, Question::hash> cache_map;
 348         cache_map cache;
 349
 350         irc::sockets::sockaddrs myserver;
 351         bool unloading;
 352
 353         /** Maximum number of entries in cache
 354          */
 355         static const unsigned int MAX_CACHE_SIZE = 1000;
 356
 357         static bool IsExpired(const Query& record, time_t now = ServerInstance->Time())
 358         {
 359                 const ResourceRecord& req = record.answers[0];
 360                 return (req.created + static_cast<time_t>(req.ttl) < now);
 361         }
 362
 363         /** Check the DNS cache to see if request can be handled by a cached result
 364          * @return true if a cached result was found.
 365          */
 366         bool CheckCache(DNS::Request* req, const DNS::Question& question)
 367         {
 368                 ServerInstance->Logs->Log(MODNAME, LOG_SPARSE, "cache: Checking cache for " + question.name);
 369
 370                 cache_map::iterator it = this->cache.find(question);
 371                 if (it == this->cache.end())
 372                         return false;
 373
 374                 Query& record = it->second;
 375                 if (IsExpired(record))
 376                 {
 377                         this->cache.erase(it);
 378                         return false;
 379                 }
 380
 381                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "cache: Using cached result for " + question.name);
 382                 record.cached = true;
 383                 req->OnLookupComplete(&record);
 384                 return true;
 385         }
 386
 387         /** Add a record to the dns cache
 388          * @param r The record
 389          */
 390         void AddCache(Query& r)
 391         {
 392                 if (cache.size() >= MAX_CACHE_SIZE)
 393                         cache.clear();
 394
 395                 // Determine the lowest TTL value and use that as the TTL of the cache entry
 396                 unsigned int cachettl = UINT_MAX;
 397                 for (std::vector<ResourceRecord>::const_iterator i = r.answers.begin(); i != r.answers.end(); ++i)
 398                 {
 399                         const ResourceRecord& rr = *i;
 400                         if (rr.ttl < cachettl)
 401                                 cachettl = rr.ttl;
 402                 }
 403
 404                 cachettl = std::min(cachettl, (unsigned int)5*60);
 405                 ResourceRecord& rr = r.answers.front();
 406                 // Set TTL to what we've determined to be the lowest
 407                 rr.ttl = cachettl;
 408                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "cache: added cache for " + rr.name + " -> " + rr.rdata + " ttl: " + ConvToStr(rr.ttl));
 409                 this->cache[r.question] = r;
 410         }
 411
 412         void Close()
 413         {
 414                 // Shutdown the socket if it exists.
 415                 if (HasFd())
 416                 {
 417                         SocketEngine::Shutdown(this, 2);
 418                         SocketEngine::Close(this);
 419                 }
 420
 421                 // Remove all entries from the cache.
 422                 cache.clear();
 423         }
 424
 425  public:
 426         DNS::Request* requests[MAX_REQUEST_ID+1];
 427
 428         MyManager(Module* c) : Manager(c), Timer(5*60, true)
 429                 , unloading(false)
 430         {
 431                 for (unsigned int i = 0; i <= MAX_REQUEST_ID; ++i)
 432                         requests[i] = NULL;
 433                 ServerInstance->Timers.AddTimer(this);
 434         }
 435
 436         ~MyManager()
 437         {
 438                 // Ensure Process() will fail for new requests
 439                 Close();
 440                 unloading = true;
 441
 442                 for (unsigned int i = 0; i <= MAX_REQUEST_ID; ++i)
 443                 {
 444                         DNS::Request* request = requests[i];
 445                         if (!request)
 446                                 continue;
 447
 448                         Query rr(request->question);
 449                         rr.error = ERROR_UNKNOWN;
 450                         request->OnError(&rr);
 451
 452                         delete request;
 453                 }
 454         }
 455
 456         void Process(DNS::Request* req) CXX11_OVERRIDE
 457         {
 458                 if ((unloading) || (req->creator->dying))
 459                         throw Exception("Module is being unloaded");
 460
 461                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Processing request to lookup " + req->question.name + " of type " + ConvToStr(req->question.type) + " to " + this->myserver.addr());
 462
 463                 /* Create an id */
 464                 unsigned int tries = 0;
 465                 int id;
 466                 do
 467                 {
 468                         id = ServerInstance->GenRandomInt(DNS::MAX_REQUEST_ID+1);
 469
 470                         if (++tries == DNS::MAX_REQUEST_ID*5)
 471                         {
 472                                 // If we couldn't find an empty slot this many times, do a sequential scan as a last
 473                                 // resort. If an empty slot is found that way, go on, otherwise throw an exception
 474                                 id = -1;
 475                                 for (unsigned int i = 0; i <= DNS::MAX_REQUEST_ID; i++)
 476                                 {
 477                                         if (!this->requests[i])
 478                                         {
 479                                                 id = i;
 480                                                 break;
 481                                         }
 482                                 }
 483
 484                                 if (id == -1)
 485                                         throw Exception("DNS: All ids are in use");
 486
 487                                 break;
 488                         }
 489                 }
 490                 while (this->requests[id]);
 491
 492                 req->id = id;
 493                 this->requests[req->id] = req;
 494
 495                 Packet p;
 496                 p.flags = QUERYFLAGS_RD;
 497                 p.id = req->id;
 498                 p.question = req->question;
 499
 500                 unsigned char buffer[524];
 501                 unsigned short len = p.Pack(buffer, sizeof(buffer));
 502
 503                 /* Note that calling Pack() above can actually change the contents of p.question.name, if the query is a PTR,
 504                  * to contain the value that would be in the DNS cache, which is why this is here.
 505                  */
 506                 if (req->use_cache && this->CheckCache(req, p.question))
 507                 {
 508                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Using cached result");
 509                         delete req;
 510                         return;
 511                 }
 512
 513                 // Update name in the original request so question checking works for PTR queries
 514                 req->question.name = p.question.name;
 515
 516                 if (SocketEngine::SendTo(this, buffer, len, 0, this->myserver) != len)
 517                         throw Exception("DNS: Unable to send query");
 518
 519                 // Add timer for timeout
 520                 ServerInstance->Timers.AddTimer(req);
 521         }
 522
 523         void RemoveRequest(DNS::Request* req) CXX11_OVERRIDE
 524         {
 525                 if (requests[req->id] == req)
 526                         requests[req->id] = NULL;
 527         }
 528
 529         std::string GetErrorStr(Error e) CXX11_OVERRIDE
 530         {
 531                 switch (e)
 532                 {
 533                         case ERROR_UNLOADED:
 534                                 return "Module is unloading";
 535                         case ERROR_TIMEDOUT:
 536                                 return "Request timed out";
 537                         case ERROR_NOT_AN_ANSWER:
 538                         case ERROR_NONSTANDARD_QUERY:
 539                         case ERROR_FORMAT_ERROR:
 540                         case ERROR_MALFORMED:
 541                                 return "Malformed answer";
 542                         case ERROR_SERVER_FAILURE:
 543                         case ERROR_NOT_IMPLEMENTED:
 544                         case ERROR_REFUSED:
 545                         case ERROR_INVALIDTYPE:
 546                                 return "Nameserver failure";
 547                         case ERROR_DOMAIN_NOT_FOUND:
 548                         case ERROR_NO_RECORDS:
 549                                 return "Domain not found";
 550                         case ERROR_NONE:
 551                         case ERROR_UNKNOWN:
 552                         default:
 553                                 return "Unknown error";
 554                 }
 555         }
 556
 557         std::string GetTypeStr(QueryType qt) CXX11_OVERRIDE
 558         {
 559                 switch (qt)
 560                 {
 561                         case QUERY_A:
 562                                 return "A";
 563                         case QUERY_AAAA:
 564                                 return "AAAA";
 565                         case QUERY_CNAME:
 566                                 return "CNAME";
 567                         case QUERY_PTR:
 568                                 return "PTR";
 569                         case QUERY_TXT:
 570                                 return "TXT";
 571                         default:
 572                                 return "UNKNOWN";
 573                 }
 574         }
 575
 576         void OnEventHandlerError(int errcode) CXX11_OVERRIDE
 577         {
 578                 ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "UDP socket got an error event");
 579         }
 580
 581         void OnEventHandlerRead() CXX11_OVERRIDE
 582         {
 583                 unsigned char buffer[524];
 584                 irc::sockets::sockaddrs from;
 585                 socklen_t x = sizeof(from);
 586
 587                 int length = SocketEngine::RecvFrom(this, buffer, sizeof(buffer), 0, &from.sa, &x);
 588
 589                 if (length < Packet::HEADER_LENGTH)
 590                         return;
 591
 592                 if (myserver != from)
 593                 {
 594                         std::string server1 = from.str();
 595                         std::string server2 = myserver.str();
 596                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Got a result from the wrong server! Bad NAT or DNS forging attempt? '%s' != '%s'",
 597                                 server1.c_str(), server2.c_str());
 598                         return;
 599                 }
 600
 601                 Packet recv_packet;
 602                 bool valid = false;
 603
 604                 try
 605                 {
 606                         recv_packet.Fill(buffer, length);
 607                         valid = true;
 608                 }
 609                 catch (Exception& ex)
 610                 {
 611                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, ex.GetReason());
 612                 }
 613
 614                 // recv_packet.id must be filled in here
 615                 DNS::Request* request = this->requests[recv_packet.id];
 616                 if (request == NULL)
 617                 {
 618                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Received an answer for something we didn't request");
 619                         return;
 620                 }
 621
 622                 if (request->question != recv_packet.question)
 623                 {
 624                         // This can happen under high latency, drop it silently, do not fail the request
 625                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Received an answer that isn't for a question we asked");
 626                         return;
 627                 }
 628
 629                 if (!valid)
 630                 {
 631                         ServerInstance->stats.DnsBad++;
 632                         recv_packet.error = ERROR_MALFORMED;
 633                         request->OnError(&recv_packet);
 634                 }
 635                 else if (recv_packet.flags & QUERYFLAGS_OPCODE)
 636                 {
 637                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Received a nonstandard query");
 638                         ServerInstance->stats.DnsBad++;
 639                         recv_packet.error = ERROR_NONSTANDARD_QUERY;
 640                         request->OnError(&recv_packet);
 641                 }
 642                 else if (!(recv_packet.flags & QUERYFLAGS_QR) || (recv_packet.flags & QUERYFLAGS_RCODE))
 643                 {
 644                         Error error = ERROR_UNKNOWN;
 645
 646                         switch (recv_packet.flags & QUERYFLAGS_RCODE)
 647                         {
 648                                 case 1:
 649                                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "format error");
 650                                         error = ERROR_FORMAT_ERROR;
 651                                         break;
 652                                 case 2:
 653                                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "server error");
 654                                         error = ERROR_SERVER_FAILURE;
 655                                         break;
 656                                 case 3:
 657                                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "domain not found");
 658                                         error = ERROR_DOMAIN_NOT_FOUND;
 659                                         break;
 660                                 case 4:
 661                                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "not implemented");
 662                                         error = ERROR_NOT_IMPLEMENTED;
 663                                         break;
 664                                 case 5:
 665                                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "refused");
 666                                         error = ERROR_REFUSED;
 667                                         break;
 668                                 default:
 669                                         break;
 670                         }
 671
 672                         ServerInstance->stats.DnsBad++;
 673                         recv_packet.error = error;
 674                         request->OnError(&recv_packet);
 675                 }
 676                 else if (recv_packet.answers.empty())
 677                 {
 678                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "No resource records returned");
 679                         ServerInstance->stats.DnsBad++;
 680                         recv_packet.error = ERROR_NO_RECORDS;
 681                         request->OnError(&recv_packet);
 682                 }
 683                 else
 684                 {
 685                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "Lookup complete for " + request->question.name);
 686                         ServerInstance->stats.DnsGood++;
 687                         request->OnLookupComplete(&recv_packet);
 688                         this->AddCache(recv_packet);
 689                 }
 690
 691                 ServerInstance->stats.Dns++;
 692
 693                 /* Request's destructor removes it from the request map */
 694                 delete request;
 695         }
 696
 697         bool Tick(time_t now) CXX11_OVERRIDE
 698         {
 699                 unsigned long expired = 0;
 700                 for (cache_map::iterator it = this->cache.begin(); it != this->cache.end(); )
 701                 {
 702                         const Query& query = it->second;
 703                         if (IsExpired(query, now))
 704                         {
 705                                 expired++;
 706                                 this->cache.erase(it++);
 707                         }
 708                         else
 709                                 ++it;
 710                 }
 711
 712                 if (expired)
 713                         ServerInstance->Logs->Log(MODNAME, LOG_DEBUG, "cache: purged %lu expired DNS entries", expired);
 714
 715                 return true;
 716         }
 717
 718         void Rehash(const std::string& dnsserver, std::string sourceaddr, unsigned int sourceport)
 719         {
 720                 irc::sockets::aptosa(dnsserver, DNS::PORT, myserver);
 721
 722                 /* Initialize mastersocket */
 723                 Close();
 724                 int s = socket(myserver.family(), SOCK_DGRAM, 0);
 725                 this->SetFd(s);
 726
 727                 /* Have we got a socket? */
 728                 if (this->HasFd())
 729                 {
 730                         SocketEngine::SetReuse(s);
 731                         SocketEngine::NonBlocking(s);
 732
 733                         irc::sockets::sockaddrs bindto;
 734                         if (sourceaddr.empty())
 735                         {
 736                                 // set a sourceaddr for irc::sockets::aptosa() based on the servers af type
 737                                 if (myserver.family() == AF_INET)
 738                                         sourceaddr = "0.0.0.0";
 739                                 else if (myserver.family() == AF_INET6)
 740                                         sourceaddr = "::";
 741                         }
 742                         irc::sockets::aptosa(sourceaddr, sourceport, bindto);
 743
 744                         if (SocketEngine::Bind(this->GetFd(), bindto) < 0)
 745                         {
 746                                 /* Failed to bind */
 747                                 ServerInstance->Logs->Log(MODNAME, LOG_SPARSE, "Error binding dns socket - hostnames will NOT resolve");
 748                                 SocketEngine::Close(this->GetFd());
 749                                 this->SetFd(-1);
 750                         }
 751                         else if (!SocketEngine::AddFd(this, FD_WANT_POLL_READ | FD_WANT_NO_WRITE))
 752                         {
 753                                 ServerInstance->Logs->Log(MODNAME, LOG_SPARSE, "Internal error starting DNS - hostnames will NOT resolve.");
 754                                 SocketEngine::Close(this->GetFd());
 755                                 this->SetFd(-1);
 756                         }
 757
 758                         if (bindto.family() != myserver.family())
 759                                 ServerInstance->Logs->Log(MODNAME, LOG_SPARSE, "Nameserver address family differs from source address family - hostnames might not resolve");
 760                 }
 761                 else
 762                 {
 763                         ServerInstance->Logs->Log(MODNAME, LOG_SPARSE, "Error creating DNS socket - hostnames will NOT resolve");
 764                 }
 765         }
 766 };
 767
 768 class ModuleDNS : public Module
 769 {
 770         MyManager manager;
 771         std::string DNSServer;
 772         std::string SourceIP;
 773         unsigned int SourcePort;
 774
 775         void FindDNSServer()
 776         {
 777 #ifdef _WIN32
 778                 // attempt to look up their nameserver from the system
 779                 ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "WARNING: <dns:server> not defined, attempting to find a working server in the system settings...");
 780
 781                 PFIXED_INFO pFixedInfo;
 782                 DWORD dwBufferSize = sizeof(FIXED_INFO);
 783                 pFixedInfo = (PFIXED_INFO) HeapAlloc(GetProcessHeap(), 0, sizeof(FIXED_INFO));
 784
 785                 if (pFixedInfo)
 786                 {
 787                         if (GetNetworkParams(pFixedInfo, &dwBufferSize) == ERROR_BUFFER_OVERFLOW)
 788                         {
 789                                 HeapFree(GetProcessHeap(), 0, pFixedInfo);
 790                                 pFixedInfo = (PFIXED_INFO) HeapAlloc(GetProcessHeap(), 0, dwBufferSize);
 791                         }
 792
 793                         if (pFixedInfo)
 794                         {
 795                                 if (GetNetworkParams(pFixedInfo, &dwBufferSize) == NO_ERROR)
 796                                         DNSServer = pFixedInfo->DnsServerList.IpAddress.String;
 797
 798                                 HeapFree(GetProcessHeap(), 0, pFixedInfo);
 799                         }
 800
 801                         if (!DNSServer.empty())
 802                         {
 803                                 ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "<dns:server> set to '%s' as first active resolver in the system settings.", DNSServer.c_str());
 804                                 return;
 805                         }
 806                 }
 807
 808                 ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "No viable nameserver found! Defaulting to nameserver '127.0.0.1'!");
 809 #else
 810                 // attempt to look up their nameserver from /etc/resolv.conf
 811                 ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "WARNING: <dns:server> not defined, attempting to find working server in /etc/resolv.conf...");
 812
 813                 std::ifstream resolv("/etc/resolv.conf");
 814
 815                 while (resolv >> DNSServer)
 816                 {
 817                         if (DNSServer == "nameserver")
 818                         {
 819                                 resolv >> DNSServer;
 820                                 if (DNSServer.find_first_not_of("0123456789.") == std::string::npos || DNSServer.find_first_not_of("0123456789ABCDEFabcdef:") == std::string::npos)
 821                                 {
 822                                         ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "<dns:server> set to '%s' as first resolver in /etc/resolv.conf.",DNSServer.c_str());
 823                                         return;
 824                                 }
 825                         }
 826                 }
 827
 828                 ServerInstance->Logs->Log(MODNAME, LOG_DEFAULT, "/etc/resolv.conf contains no viable nameserver entries! Defaulting to nameserver '127.0.0.1'!");
 829 #endif
 830                 DNSServer = "127.0.0.1";
 831         }
 832
 833  public:
 834         ModuleDNS() : manager(this)
 835                 , SourcePort(0)
 836         {
 837         }
 838
 839         void ReadConfig(ConfigStatus& status) CXX11_OVERRIDE
 840         {
 841                 std::string oldserver = DNSServer;
 842                 const std::string oldip = SourceIP;
 843                 const unsigned int oldport = SourcePort;
 844
 845                 ConfigTag* tag = ServerInstance->Config->ConfValue("dns");
 846                 DNSServer = tag->getString("server");
 847                 SourceIP = tag->getString("sourceip");
 848                 SourcePort = tag->getUInt("sourceport", 0, 0, UINT16_MAX);
 849
 850                 if (DNSServer.empty())
 851                         FindDNSServer();
 852
 853                 if (oldserver != DNSServer || oldip != SourceIP || oldport != SourcePort)
 854                         this->manager.Rehash(DNSServer, SourceIP, SourcePort);
 855         }
 856
 857         void OnUnloadModule(Module* mod) CXX11_OVERRIDE
 858         {
 859                 for (unsigned int i = 0; i <= MAX_REQUEST_ID; ++i)
 860                 {
 861                         DNS::Request* req = this->manager.requests[i];
 862                         if (!req)
 863                                 continue;
 864
 865                         if (req->creator == mod)
 866                         {
 867                                 Query rr(req->question);
 868                                 rr.error = ERROR_UNLOADED;
 869                                 req->OnError(&rr);
 870
 871                                 delete req;
 872                         }
 873                 }
 874         }
 875
 876         Version GetVersion() CXX11_OVERRIDE
 877         {
 878                 return Version("Provides support for DNS lookups", VF_CORE|VF_VENDOR);
 879         }
 880 };
 881
 882 MODULE_INIT(ModuleDNS)
 883