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# 1 : : // Copyright (c) 2014-2021 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 <node/ui_interface.h>
# 13 : : #include <sync.h>
# 14 : : #include <tinyformat.h>
# 15 : : #include <util/system.h>
# 16 : : #include <util/translation.h>
# 17 : : #include <warnings.h>
# 18 : :
# 19 : : static Mutex g_timeoffset_mutex;
# 20 : : static int64_t nTimeOffset GUARDED_BY(g_timeoffset_mutex) = 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 : 219401 : {
# 31 : 219401 : LOCK(g_timeoffset_mutex);
# 32 : 219401 : return nTimeOffset;
# 33 : 219401 : }
# 34 : :
# 35 : : int64_t GetAdjustedTime()
# 36 : 219308 : {
# 37 : 219308 : return GetTime() + GetTimeOffset();
# 38 : 219308 : }
# 39 : :
# 40 : 812 : #define BITCOIN_TIMEDATA_MAX_SAMPLES 200
# 41 : :
# 42 : : static std::set<CNetAddr> g_sources;
# 43 : : static CMedianFilter<int64_t> g_time_offsets{BITCOIN_TIMEDATA_MAX_SAMPLES, 0};
# 44 : : static bool g_warning_emitted;
# 45 : :
# 46 : : void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
# 47 : 808 : {
# 48 : 808 : LOCK(g_timeoffset_mutex);
# 49 : : // Ignore duplicates
# 50 [ - + ]: 808 : if (g_sources.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
# 51 : 0 : return;
# 52 [ + + ]: 808 : if (!g_sources.insert(ip).second)
# 53 : 156 : return;
# 54 : :
# 55 : : // Add data
# 56 : 652 : g_time_offsets.input(nOffsetSample);
# 57 [ + - ]: 652 : LogPrint(BCLog::NET, "added time data, samples %d, offset %+d (%+d minutes)\n", g_time_offsets.size(), nOffsetSample, nOffsetSample / 60);
# 58 : :
# 59 : : // There is a known issue here (see issue #4521):
# 60 : : //
# 61 : : // - The structure g_time_offsets contains up to 200 elements, after which
# 62 : : // any new element added to it will not increase its size, replacing the
# 63 : : // oldest element.
# 64 : : //
# 65 : : // - The condition to update nTimeOffset includes checking whether the
# 66 : : // number of elements in g_time_offsets is odd, which will never happen after
# 67 : : // there are 200 elements.
# 68 : : //
# 69 : : // But in this case the 'bug' is protective against some attacks, and may
# 70 : : // actually explain why we've never seen attacks which manipulate the
# 71 : : // clock offset.
# 72 : : //
# 73 : : // So we should hold off on fixing this and clean it up as part of
# 74 : : // a timing cleanup that strengthens it in a number of other ways.
# 75 : : //
# 76 [ + + ][ + + ]: 652 : if (g_time_offsets.size() >= 5 && g_time_offsets.size() % 2 == 1) {
# 77 : 196 : int64_t nMedian = g_time_offsets.median();
# 78 : 196 : std::vector<int64_t> vSorted = g_time_offsets.sorted();
# 79 : : // Only let other nodes change our time by so much
# 80 : 196 : int64_t max_adjustment = std::max<int64_t>(0, gArgs.GetIntArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT));
# 81 [ + - ][ + + ]: 196 : if (nMedian >= -max_adjustment && nMedian <= max_adjustment) {
# 82 : 192 : nTimeOffset = nMedian;
# 83 : 192 : } else {
# 84 : 4 : nTimeOffset = 0;
# 85 : :
# 86 [ + + ]: 4 : if (!g_warning_emitted) {
# 87 : : // If nobody has a time different than ours but within 5 minutes of ours, give a warning
# 88 : 2 : bool fMatch = false;
# 89 [ + + ]: 10 : for (const int64_t nOffset : vSorted) {
# 90 [ + + ][ + - ]: 10 : if (nOffset != 0 && nOffset > -5 * 60 && nOffset < 5 * 60) fMatch = true;
# [ - + ]
# 91 : 10 : }
# 92 : :
# 93 [ + - ]: 2 : if (!fMatch) {
# 94 : 2 : g_warning_emitted = true;
# 95 : 2 : bilingual_str 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);
# 96 : 2 : SetMiscWarning(strMessage);
# 97 : 2 : uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
# 98 : 2 : }
# 99 : 2 : }
# 100 : 4 : }
# 101 : :
# 102 [ + - ]: 196 : if (LogAcceptCategory(BCLog::NET)) {
# 103 : 196 : std::string log_message{"time data samples: "};
# 104 [ + + ]: 19992 : for (const int64_t n : vSorted) {
# 105 : 19992 : log_message += strprintf("%+d ", n);
# 106 : 19992 : }
# 107 : 196 : log_message += strprintf("| median offset = %+d (%+d minutes)", nTimeOffset, nTimeOffset / 60);
# 108 [ + - ]: 196 : LogPrint(BCLog::NET, "%s\n", log_message);
# 109 : 196 : }
# 110 : 196 : }
# 111 : 652 : }
# 112 : :
# 113 : : void TestOnlyResetTimeData()
# 114 : 4 : {
# 115 : 4 : LOCK(g_timeoffset_mutex);
# 116 : 4 : nTimeOffset = 0;
# 117 : 4 : g_sources.clear();
# 118 : 4 : g_time_offsets = CMedianFilter<int64_t>{BITCOIN_TIMEDATA_MAX_SAMPLES, 0};
# 119 : 4 : g_warning_emitted = false;
# 120 : 4 : }
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