pdns/stubresolver.cc

   1 #ifdef HAVE_CONFIG_H
   2 #include "config.h"
   3 #endif
   4
   5 #include "logger.hh"
   6 #include "arguments.hh"
   7 #include "version.hh"
   8 #include "misc.hh"
   9
  10 #include "sstuff.hh"
  11 #include "dnswriter.hh"
  12 #include "dns_random.hh"
  13 #include "namespaces.hh"
  14 #include "statbag.hh"
  15 #include "stubresolver.hh"
  16
  17 // s_resolversForStub contains the ComboAddresses that are used by
  18 // stubDoResolve
  19 static vector<ComboAddress> s_resolversForStub;
  20
  21 /*
  22  * Returns false if no resolvers are configured, while emitting a warning about this
  23  */
  24 bool resolversDefined()
  25 {
  26   if (s_resolversForStub.empty()) {
  27     L<<Logger::Warning<<"No upstream resolvers configured, stub resolving (including secpoll and ALIAS) impossible."<<endl;
  28     return false;
  29   }
  30   return true;
  31 }
  32
  33 /*
  34  * Fill the s_resolversForStub vector with addresses for the upstream resolvers.
  35  * First, parse the `resolver` configuration option for IP addresses to use.
  36  * If that doesn't work, parse /etc/resolv.conf and add those nameservers to
  37  * s_resolversForStub.
  38  */
  39 void stubParseResolveConf()
  40 {
  41   if(::arg().mustDo("resolver")) {
  42     vector<string> parts;
  43     stringtok(parts, ::arg()["resolver"], " ,\t");
  44     for (const auto& addr : parts)
  45       s_resolversForStub.push_back(ComboAddress(addr, 53));
  46   }
  47
  48   if (s_resolversForStub.empty()) {
  49     ifstream ifs("/etc/resolv.conf");
  50     if(!ifs)
  51       return;
  52
  53     string line;
  54     while(std::getline(ifs, line)) {
  55       boost::trim_right_if(line, is_any_of(" \r\n\x1a"));
  56       boost::trim_left(line); // leading spaces, let's be nice
  57
  58       string::size_type tpos = line.find_first_of(";#");
  59       if(tpos != string::npos)
  60         line.resize(tpos);
  61
  62       if(boost::starts_with(line, "nameserver ") || boost::starts_with(line, "nameserver\t")) {
  63         vector<string> parts;
  64         stringtok(parts, line, " \t,"); // be REALLY nice
  65         for(vector<string>::const_iterator iter = parts.begin()+1; iter != parts.end(); ++iter) {
  66           try {
  67             s_resolversForStub.push_back(ComboAddress(*iter, 53));
  68           }
  69           catch(...)
  70           {
  71           }
  72         }
  73       }
  74     }
  75   }
  76   // Emit a warning if there are no stubs.
  77   resolversDefined();
  78 }
  79
  80 // s_resolversForStub contains the ComboAddresses that are used to resolve the
  81 int stubDoResolve(const DNSName& qname, uint16_t qtype, vector<DNSZoneRecord>& ret)
  82 {
  83   if (!resolversDefined())
  84     return RCode::ServFail;
  85
  86   vector<uint8_t> packet;
  87
  88   DNSPacketWriter pw(packet, qname, qtype);
  89   pw.getHeader()->id=dns_random(0xffff);
  90   pw.getHeader()->rd=1;
  91
  92   string msg ="Doing stub resolving, using resolvers: ";
  93   for (const auto& server : s_resolversForStub) {
  94     msg += server.toString() + ", ";
  95   }
  96   L<<Logger::Debug<<msg.substr(0, msg.length() - 2)<<endl;
  97
  98   for(const ComboAddress& dest :  s_resolversForStub) {
  99     Socket sock(dest.sin4.sin_family, SOCK_DGRAM);
 100     sock.setNonBlocking();
 101     sock.connect(dest);
 102     sock.send(string(packet.begin(), packet.end()));
 103
 104     string reply;
 105
 106     waitForData(sock.getHandle(), 2, 0);
 107     try {
 108     retry:
 109       sock.read(reply); // this calls recv
 110       if(reply.size() > sizeof(struct dnsheader)) {
 111         struct dnsheader d;
 112         memcpy(&d, reply.c_str(), sizeof(d));
 113         if(d.id != pw.getHeader()->id)
 114           goto retry;
 115       }
 116     }
 117     catch(...) {
 118       continue;
 119     }
 120     MOADNSParser mdp(false, reply);
 121     if(mdp.d_header.rcode == RCode::ServFail)
 122       continue;
 123
 124     for(MOADNSParser::answers_t::const_iterator i=mdp.d_answers.begin(); i!=mdp.d_answers.end(); ++i) {
 125       if(i->first.d_place == 1 && i->first.d_type==qtype) {
 126         DNSZoneRecord zrr;
 127         zrr.dr = i->first;
 128         zrr.auth=true;
 129         ret.push_back(zrr);
 130       }
 131     }
 132     L<<Logger::Debug<<"Question got answered by "<<dest.toString()<<endl;
 133     return mdp.d_header.rcode;
 134   }
 135   return RCode::ServFail;
 136 }