pdns/dnsproxy.cc

   1 /*
   2  * This file is part of PowerDNS or dnsdist.
   3  * Copyright -- PowerDNS.COM B.V. and its contributors
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of version 2 of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * In addition, for the avoidance of any doubt, permission is granted to
  10  * link this program with OpenSSL and to (re)distribute the binaries
  11  * produced as the result of such linking.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  */
  22 #ifdef HAVE_CONFIG_H
  23 #include "config.h"
  24 #endif
  25 #include "packetcache.hh"
  26 #include "utility.hh"
  27 #include "dnsproxy.hh"
  28 #include "pdnsexception.hh"
  29 #include <sys/types.h>
  30 #include <errno.h>
  31 #include "dns.hh"
  32 #include "logger.hh"
  33 #include "statbag.hh"
  34 #include "dns_random.hh"
  35 #include "stubresolver.hh"
  36 #include "arguments.hh"
  37
  38 extern StatBag S;
  39
  40 DNSProxy::DNSProxy(const string &remote)
  41 {
  42   pthread_mutex_init(&d_lock,0);
  43   d_resanswers=S.getPointer("recursing-answers");
  44   d_resquestions=S.getPointer("recursing-questions");
  45   d_udpanswers=S.getPointer("udp-answers");
  46
  47   vector<string> addresses;
  48   stringtok(addresses, remote, " ,\t");
  49   d_remote = ComboAddress(addresses[0], 53);
  50
  51   if((d_sock=socket(d_remote.sin4.sin_family, SOCK_DGRAM,0))<0) {
  52     throw PDNSException(string("socket: ")+strerror(errno));
  53   }
  54
  55   ComboAddress local;
  56   if(d_remote.sin4.sin_family==AF_INET) {
  57     local = ComboAddress("0.0.0.0");
  58   }
  59   else {
  60     local = ComboAddress("::");
  61   }
  62
  63   unsigned int n=0;
  64   for(;n<10;n++) {
  65     local.sin4.sin_port = htons(10000+dns_random(50000));
  66
  67     if(::bind(d_sock, (struct sockaddr *)&local, local.getSocklen()) >= 0)
  68       break;
  69   }
  70   if(n==10) {
  71     closesocket(d_sock);
  72     d_sock=-1;
  73     throw PDNSException(string("binding dnsproxy socket: ")+strerror(errno));
  74   }
  75
  76   if(connect(d_sock, (sockaddr *)&d_remote, d_remote.getSocklen())<0) {
  77     throw PDNSException("Unable to UDP connect to remote nameserver "+d_remote.toStringWithPort()+": "+stringerror());
  78   }
  79
  80   d_xor=dns_random(0xffff);
  81   g_log<<Logger::Error<<"DNS Proxy launched, local port "<<ntohs(local.sin4.sin_port)<<", remote "<<d_remote.toStringWithPort()<<endl;
  82 }
  83
  84 void DNSProxy::go()
  85 {
  86   pthread_t tid;
  87   pthread_create(&tid,0,&launchhelper,this);
  88 }
  89
  90 //! look up qname target with r->qtype, plonk it in the answer section of 'r' with name aname
  91 bool DNSProxy::completePacket(DNSPacket *r, const DNSName& target,const DNSName& aname)
  92 {
  93   if(r->d_tcp) {
  94     vector<DNSZoneRecord> ips;
  95     int ret1 = 0, ret2 = 0;
  96
  97     if(r->qtype == QType::A || r->qtype == QType::ANY)
  98       ret1 = stubDoResolve(target, QType::A, ips);
  99     if(r->qtype == QType::AAAA || r->qtype == QType::ANY)
 100       ret2 = stubDoResolve(target, QType::AAAA, ips);
 101
 102     if(ret1 != RCode::NoError || ret2 != RCode::NoError) {
 103       g_log<<Logger::Error<<"Error resolving for ALIAS "<<target<<", returning SERVFAIL"<<endl;
 104     }
 105
 106     for (auto &ip : ips)
 107     {
 108       ip.dr.d_name = aname;
 109       r->addRecord(ip);
 110     }
 111
 112     uint16_t len=htons(r->getString().length());
 113     string buffer((const char*)&len, 2);
 114     buffer.append(r->getString());
 115     writen2WithTimeout(r->getSocket(), buffer.c_str(), buffer.length(), ::arg().asNum("tcp-idle-timeout"));
 116
 117     return true;
 118   }
 119
 120   uint16_t id;
 121   {
 122     Lock l(&d_lock);
 123     id=getID_locked();
 124
 125     ConntrackEntry ce;
 126     ce.id       = r->d.id;
 127     ce.remote =   r->d_remote;
 128     ce.outsock  = r->getSocket();
 129     ce.created  = time( NULL );
 130     ce.qtype = r->qtype.getCode();
 131     ce.qname = target;
 132     ce.anyLocal = r->d_anyLocal;
 133     ce.complete = r;
 134     ce.aname=aname;
 135     d_conntrack[id]=ce;
 136   }
 137
 138   vector<uint8_t> packet;
 139   DNSPacketWriter pw(packet, target, r->qtype.getCode());
 140   pw.getHeader()->rd=true;
 141   pw.getHeader()->id=id ^ d_xor;
 142
 143   if(send(d_sock,&packet[0], packet.size() , 0)<0) { // zoom
 144     g_log<<Logger::Error<<"Unable to send a packet to our recursing backend: "<<stringerror()<<endl;
 145   }
 146
 147   return true;
 148
 149 }
 150
 151
 152 /** This finds us an unused or stale ID. Does not actually clean the contents */
 153 int DNSProxy::getID_locked()
 154 {
 155   map_t::iterator i;
 156   for(int n=0;;++n) {
 157     i=d_conntrack.find(n);
 158     if(i==d_conntrack.end()) {
 159       return n;
 160     }
 161     else if(i->second.created<time(0)-60) {
 162       if(i->second.created) {
 163         g_log<<Logger::Warning<<"Recursive query for remote "<<
 164           i->second.remote.toStringWithPort()<<" with internal id "<<n<<
 165           " was not answered by backend within timeout, reusing id"<<endl;
 166         delete i->second.complete;
 167         S.inc("recursion-unanswered");
 168       }
 169       return n;
 170     }
 171   }
 172 }
 173
 174 void DNSProxy::mainloop(void)
 175 {
 176   try {
 177     char buffer[1500];
 178     ssize_t len;
 179
 180     struct msghdr msgh;
 181     struct iovec iov;
 182     char cbuf[256];
 183     ComboAddress fromaddr;
 184
 185     for(;;) {
 186       socklen_t fromaddrSize = sizeof(fromaddr);
 187       len=recvfrom(d_sock, buffer, sizeof(buffer),0, (struct sockaddr*) &fromaddr, &fromaddrSize); // answer from our backend
 188       if(len<(ssize_t)sizeof(dnsheader)) {
 189         if(len<0)
 190           g_log<<Logger::Error<<"Error receiving packet from recursor backend: "<<stringerror()<<endl;
 191         else if(len==0)
 192           g_log<<Logger::Error<<"Error receiving packet from recursor backend, EOF"<<endl;
 193         else
 194           g_log<<Logger::Error<<"Short packet from recursor backend, "<<len<<" bytes"<<endl;
 195
 196         continue;
 197       }
 198       if (fromaddr != d_remote) {
 199         g_log<<Logger::Error<<"Got answer from unexpected host "<<fromaddr.toStringWithPort()<<" instead of our recursor backend "<<d_remote.toStringWithPort()<<endl;
 200         continue;
 201       }
 202       (*d_resanswers)++;
 203       (*d_udpanswers)++;
 204       dnsheader d;
 205       memcpy(&d,buffer,sizeof(d));
 206       {
 207         Lock l(&d_lock);
 208 #if BYTE_ORDER == BIG_ENDIAN
 209         // this is needed because spoof ID down below does not respect the native byteorder
 210         d.id = ( 256 * (uint16_t)buffer[1] ) + (uint16_t)buffer[0];
 211 #endif
 212         map_t::iterator i=d_conntrack.find(d.id^d_xor);
 213         if(i==d_conntrack.end()) {
 214           g_log<<Logger::Error<<"Discarding untracked packet from recursor backend with id "<<(d.id^d_xor)<<
 215             ". Conntrack table size="<<d_conntrack.size()<<endl;
 216           continue;
 217         }
 218         else if(i->second.created==0) {
 219           g_log<<Logger::Error<<"Received packet from recursor backend with id "<<(d.id^d_xor)<<" which is a duplicate"<<endl;
 220           continue;
 221         }
 222
 223         d.id=i->second.id;
 224         memcpy(buffer,&d,sizeof(d));  // commit spoofed id
 225
 226         DNSPacket p(false),q(false);
 227         p.parse(buffer,(size_t)len);
 228         q.parse(buffer,(size_t)len);
 229
 230         if(p.qtype.getCode() != i->second.qtype || p.qdomain != i->second.qname) {
 231           g_log<<Logger::Error<<"Discarding packet from recursor backend with id "<<(d.id^d_xor)<<
 232             ", qname or qtype mismatch ("<<p.qtype.getCode()<<" v " <<i->second.qtype<<", "<<p.qdomain<<" v "<<i->second.qname<<")"<<endl;
 233           continue;
 234         }
 235
 236         /* Set up iov and msgh structures. */
 237         memset(&msgh, 0, sizeof(struct msghdr));
 238         string reply; // needs to be alive at time of sendmsg!
 239         if(i->second.complete) {
 240
 241           MOADNSParser mdp(false, p.getString());
 242           //      cerr<<"Got completion, "<<mdp.d_answers.size()<<" answers, rcode: "<<mdp.d_header.rcode<<endl;
 243           for(MOADNSParser::answers_t::const_iterator j=mdp.d_answers.begin(); j!=mdp.d_answers.end(); ++j) {
 244             //      cerr<<"comp: "<<(int)j->first.d_place-1<<" "<<j->first.d_label<<" " << DNSRecordContent::NumberToType(j->first.d_type)<<" "<<j->first.d_content->getZoneRepresentation()<<endl;
 245             if(j->first.d_place == DNSResourceRecord::ANSWER || (j->first.d_place == DNSResourceRecord::AUTHORITY && j->first.d_type == QType::SOA)) {
 246
 247               if(j->first.d_type == i->second.qtype || (i->second.qtype == QType::ANY && (j->first.d_type == QType::A || j->first.d_type == QType::AAAA))) {
 248                 DNSZoneRecord dzr;
 249                 dzr.dr.d_name=i->second.aname;
 250                 dzr.dr.d_type = j->first.d_type;
 251                 dzr.dr.d_ttl=j->first.d_ttl;
 252                 dzr.dr.d_place= j->first.d_place;
 253                 dzr.dr.d_content=j->first.d_content;
 254                 i->second.complete->addRecord(dzr);
 255               }
 256             }
 257           }
 258           i->second.complete->setRcode(mdp.d_header.rcode);
 259           reply=i->second.complete->getString();
 260           iov.iov_base = (void*)reply.c_str();
 261           iov.iov_len = reply.length();
 262           delete i->second.complete;
 263           i->second.complete=0;
 264         }
 265         else {
 266           iov.iov_base = buffer;
 267           iov.iov_len = len;
 268         }
 269         msgh.msg_iov = &iov;
 270         msgh.msg_iovlen = 1;
 271         msgh.msg_name = (struct sockaddr*)&i->second.remote;
 272         msgh.msg_namelen = i->second.remote.getSocklen();
 273         msgh.msg_control=NULL;
 274
 275         if(i->second.anyLocal) {
 276           addCMsgSrcAddr(&msgh, cbuf, i->second.anyLocal.get_ptr(), 0);
 277         }
 278         if(sendmsg(i->second.outsock, &msgh, 0) < 0)
 279           g_log<<Logger::Warning<<"dnsproxy.cc: Error sending reply with sendmsg (socket="<<i->second.outsock<<"): "<<strerror(errno)<<endl;
 280
 281         i->second.created=0;
 282       }
 283     }
 284   }
 285   catch(PDNSException &ae) {
 286     g_log<<Logger::Error<<"Fatal error in DNS proxy: "<<ae.reason<<endl;
 287   }
 288   catch(std::exception &e) {
 289     g_log<<Logger::Error<<"Communicator thread died because of STL error: "<<e.what()<<endl;
 290   }
 291   catch( ... )
 292   {
 293     g_log << Logger::Error << "Caught unknown exception." << endl;
 294   }
 295   g_log<<Logger::Error<<"Exiting because DNS proxy failed"<<endl;
 296   _exit(1);
 297 }
 298
 299 DNSProxy::~DNSProxy() {
 300   if (d_sock>-1) {
 301     try {
 302       closesocket(d_sock);
 303     }
 304     catch(const PDNSException& e) {
 305     }
 306   }
 307
 308   d_sock=-1;
 309 }