120 lines
3.7 KiB
C++
120 lines
3.7 KiB
C++
// Copyright (c) 2014 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#if defined(HAVE_CONFIG_H)
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#include "config/bitcoin-config.h"
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#endif
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#include "timedata.h"
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#include "netbase.h"
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#include "sync.h"
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#include "ui_interface.h"
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#include "util.h"
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#include "utilstrencodings.h"
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#include <boost/foreach.hpp>
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using namespace std;
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static CCriticalSection cs_nTimeOffset;
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static int64_t nTimeOffset = 0;
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/**
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* "Never go to sea with two chronometers; take one or three."
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* Our three time sources are:
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* - System clock
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* - Median of other nodes clocks
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* - The user (asking the user to fix the system clock if the first two disagree)
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*/
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int64_t GetTimeOffset()
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{
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LOCK(cs_nTimeOffset);
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return nTimeOffset;
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}
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int64_t GetAdjustedTime()
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{
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return GetTime() + GetTimeOffset();
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}
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static int64_t abs64(int64_t n)
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{
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return (n >= 0 ? n : -n);
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}
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#define BITCOIN_TIMEDATA_MAX_SAMPLES 200
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void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
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{
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LOCK(cs_nTimeOffset);
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// Ignore duplicates
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static set<CNetAddr> setKnown;
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if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
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return;
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if (!setKnown.insert(ip).second)
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return;
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// Add data
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static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
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vTimeOffsets.input(nOffsetSample);
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LogPrint("net","added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample/60);
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// There is a known issue here (see issue #4521):
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//
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// - The structure vTimeOffsets contains up to 200 elements, after which
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// any new element added to it will not increase its size, replacing the
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// oldest element.
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//
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// - The condition to update nTimeOffset includes checking whether the
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// number of elements in vTimeOffsets is odd, which will never happen after
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// there are 200 elements.
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//
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// But in this case the 'bug' is protective against some attacks, and may
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// actually explain why we've never seen attacks which manipulate the
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// clock offset.
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//
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// So we should hold off on fixing this and clean it up as part of
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// a timing cleanup that strengthens it in a number of other ways.
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//
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if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1)
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{
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int64_t nMedian = vTimeOffsets.median();
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std::vector<int64_t> vSorted = vTimeOffsets.sorted();
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// Only let other nodes change our time by so much
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if (abs64(nMedian) < 70 * 60)
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{
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nTimeOffset = nMedian;
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}
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else
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{
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nTimeOffset = 0;
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static bool fDone;
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if (!fDone)
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{
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// If nobody has a time different than ours but within 5 minutes of ours, give a warning
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bool fMatch = false;
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BOOST_FOREACH(int64_t nOffset, vSorted)
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if (nOffset != 0 && abs64(nOffset) < 5 * 60)
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fMatch = true;
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if (!fMatch)
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{
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fDone = true;
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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));
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strMiscWarning = strMessage;
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uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
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}
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}
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}
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BOOST_FOREACH(int64_t n, vSorted)
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LogPrint("net", "%+d ", n);
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LogPrint("net", "| ");
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LogPrint("net", "nTimeOffset = %+d (%+d minutes)\n", nTimeOffset, nTimeOffset/60);
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}
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}
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