pdns/shuffle.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
  26 #include <string>
  27
  28 #include "shuffle.hh"
  29 #include "dns_random.hh"
  30 #include "dnsparser.hh"
  31
  32 // shuffle, maintaining some semblance of order
  33 void pdns::shuffle(std::vector<DNSZoneRecord>& rrs)
  34 {
  35   std::vector<DNSZoneRecord>::iterator first, second;
  36
  37   // We assume the CNAMES are listed first in the ANSWER section and the the other records
  38   // and we want to shuffle the other records only
  39
  40   // First we scan for the first non-CNAME ANSWER record
  41   for (first = rrs.begin(); first != rrs.end(); ++first) {
  42     if (first->dr.d_place == DNSResourceRecord::ANSWER && first->dr.d_type != QType::CNAME) {
  43       break;
  44     }
  45   }
  46   // And then for one past the last ANSWER record
  47   for (second = first; second != rrs.end(); ++second)
  48     if (second->dr.d_place != DNSResourceRecord::ANSWER)
  49       break;
  50
  51   // Now shuffle the non-CNAME ANSWER records
  52   dns_random_engine r;
  53   if (second - first > 1) {
  54     shuffle(first, second, r);
  55   }
  56
  57   // now shuffle the ADDITIONAL records in the same manner as the ANSWER records
  58   for (first = second; first != rrs.end(); ++first) {
  59     if (first->dr.d_place == DNSResourceRecord::ADDITIONAL && first->dr.d_type != QType::CNAME) {
  60       break;
  61     }
  62   }
  63   for (second = first; second != rrs.end(); ++second) {
  64     if (second->dr.d_place != DNSResourceRecord::ADDITIONAL) {
  65       break;
  66     }
  67   }
  68
  69   if (second - first > 1) {
  70     shuffle(first, second, r);
  71   }
  72   // we don't shuffle the rest
  73 }
  74
  75 // shuffle, maintaining some semblance of order
  76 static void shuffle(std::vector<DNSRecord>& rrs, bool includingAdditionals)
  77 {
  78   // This shuffles in the same style as the above method, keeping CNAME in the front and RRSIGs at the end
  79   std::vector<DNSRecord>::iterator first, second;
  80   for (first = rrs.begin(); first != rrs.end(); ++first) {
  81     if (first->d_place == DNSResourceRecord::ANSWER && first->d_type != QType::CNAME) {
  82       break;
  83     }
  84   }
  85   for (second = first; second != rrs.end(); ++second) {
  86     if (second->d_place != DNSResourceRecord::ANSWER || second->d_type == QType::RRSIG) {
  87       break;
  88     }
  89   }
  90
  91   pdns::dns_random_engine r;
  92   if (second - first > 1) {
  93     shuffle(first, second, r);
  94   }
  95
  96   if (!includingAdditionals) {
  97     return;
  98   }
  99
 100   // now shuffle the additional records
 101   for (first = second; first != rrs.end(); ++first) {
 102     if (first->d_place == DNSResourceRecord::ADDITIONAL && first->d_type != QType::CNAME) {
 103       break;
 104     }
 105   }
 106   for (second = first; second != rrs.end(); ++second) {
 107     if (second->d_place != DNSResourceRecord::ADDITIONAL) {
 108       break;
 109     }
 110   }
 111
 112   if (second - first > 1) {
 113     shuffle(first, second, r);
 114   }
 115   // we don't shuffle the rest
 116 }
 117
 118 static uint16_t mapTypesToOrder(uint16_t type)
 119 {
 120   if (type == QType::CNAME)
 121     return 0;
 122   if (type == QType::RRSIG)
 123     return 65535;
 124   else
 125     return 1;
 126 }
 127
 128 // make sure rrs is sorted in d_place order to avoid surprises later
 129 // then shuffle the parts that desire shuffling
 130 void pdns::orderAndShuffle(vector<DNSRecord>& rrs, bool includingAdditionals)
 131 {
 132   std::stable_sort(rrs.begin(), rrs.end(), [](const DNSRecord& a, const DNSRecord& b) {
 133     return std::tuple(a.d_place, mapTypesToOrder(a.d_type)) < std::tuple(b.d_place, mapTypesToOrder(b.d_type));
 134   });
 135   shuffle(rrs, includingAdditionals);
 136 }