src/timedata.cpp

   1 // Copyright (c) 2014-2017 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #if defined(HAVE_CONFIG_H)
   6 #include <config/bitcoin-config.h>
   7 #endif
   8
   9 #include <timedata.h>
  10
  11 #include <netaddress.h>
  12 #include <sync.h>
  13 #include <ui_interface.h>
  14 #include <util.h>
  15 #include <utilstrencodings.h>
  16 #include <warnings.h>
  17
  18
  19 static CCriticalSection cs_nTimeOffset;
  20 static int64_t nTimeOffset = 0;
  21
  22 /**
  23  * "Never go to sea with two chronometers; take one or three."
  24  * Our three time sources are:
  25  *  - System clock
  26  *  - Median of other nodes clocks
  27  *  - The user (asking the user to fix the system clock if the first two disagree)
  28  */
  29 int64_t GetTimeOffset()
  30 {
  31     LOCK(cs_nTimeOffset);
  32     return nTimeOffset;
  33 }
  34
  35 int64_t GetAdjustedTime()
  36 {
  37     return GetTime() + GetTimeOffset();
  38 }
  39
  40 static int64_t abs64(int64_t n)
  41 {
  42     return (n >= 0 ? n : -n);
  43 }
  44
  45 #define BITCOIN_TIMEDATA_MAX_SAMPLES 200
  46
  47 void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
  48 {
  49     LOCK(cs_nTimeOffset);
  50     // Ignore duplicates
  51     static std::set<CNetAddr> setKnown;
  52     if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
  53         return;
  54     if (!setKnown.insert(ip).second)
  55         return;
  56
  57     // Add data
  58     static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
  59     vTimeOffsets.input(nOffsetSample);
  60     LogPrint(BCLog::NET,"added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample/60);
  61
  62     // There is a known issue here (see issue #4521):
  63     //
  64     // - The structure vTimeOffsets contains up to 200 elements, after which
  65     // any new element added to it will not increase its size, replacing the
  66     // oldest element.
  67     //
  68     // - The condition to update nTimeOffset includes checking whether the
  69     // number of elements in vTimeOffsets is odd, which will never happen after
  70     // there are 200 elements.
  71     //
  72     // But in this case the 'bug' is protective against some attacks, and may
  73     // actually explain why we've never seen attacks which manipulate the
  74     // clock offset.
  75     //
  76     // So we should hold off on fixing this and clean it up as part of
  77     // a timing cleanup that strengthens it in a number of other ways.
  78     //
  79     if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1)
  80     {
  81         int64_t nMedian = vTimeOffsets.median();
  82         std::vector<int64_t> vSorted = vTimeOffsets.sorted();
  83         // Only let other nodes change our time by so much
  84         if (abs64(nMedian) <= std::max<int64_t>(0, gArgs.GetArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT)))
  85         {
  86             nTimeOffset = nMedian;
  87         }
  88         else
  89         {
  90             nTimeOffset = 0;
  91
  92             static bool fDone;
  93             if (!fDone)
  94             {
  95                 // If nobody has a time different than ours but within 5 minutes of ours, give a warning
  96                 bool fMatch = false;
  97                 for (int64_t nOffset : vSorted)
  98                     if (nOffset != 0 && abs64(nOffset) < 5 * 60)
  99                         fMatch = true;
 100
 101                 if (!fMatch)
 102                 {
 103                     fDone = true;
 104                     std::string strMessage = strprintf(_("Please check that your computer's date and time are correct! If your clock is wrong, %s will not work properly."), _(PACKAGE_NAME));
 105                     SetMiscWarning(strMessage);
 106                     uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
 107                 }
 108             }
 109         }
 110
 111         if (LogAcceptCategory(BCLog::NET)) {
 112             for (int64_t n : vSorted) {
 113                 LogPrint(BCLog::NET, "%+d  ", n);
 114             }
 115             LogPrint(BCLog::NET, "|  ");
 116
 117             LogPrint(BCLog::NET, "nTimeOffset = %+d  (%+d minutes)\n", nTimeOffset, nTimeOffset/60);
 118         }
 119     }
 120 }