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// Copyright (c) 2014-2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif
#include <timedata.h>
#include <netaddress.h>
#include <sync.h>
#include <ui_interface.h>
#include <util/system.h>
#include <util/strencodings.h>
#include <warnings.h>
static CCriticalSection cs_nTimeOffset;
static int64_t nTimeOffset GUARDED_BY(cs_nTimeOffset) = 0;
/**
* "Never go to sea with two chronometers; take one or three."
* Our three time sources are:
* - System clock
* - Median of other nodes clocks
* - The user (asking the user to fix the system clock if the first two disagree)
*/
int64_t GetTimeOffset()
{
LOCK(cs_nTimeOffset);
return nTimeOffset;
}
int64_t GetAdjustedTime()
{
return GetTime() + GetTimeOffset();
}
static int64_t abs64(int64_t n)
{
return (n >= 0 ? n : -n);
}
#define BITCOIN_TIMEDATA_MAX_SAMPLES 200
void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
{
LOCK(cs_nTimeOffset);
// Ignore duplicates
static std::set<CNetAddr> setKnown;
if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
return;
if (!setKnown.insert(ip).second)
return;
// Add data
static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
vTimeOffsets.input(nOffsetSample);
LogPrint(BCLog::NET,"added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample/60);
// There is a known issue here (see issue #4521):
//
// - The structure vTimeOffsets contains up to 200 elements, after which
// any new element added to it will not increase its size, replacing the
// oldest element.
//
// - The condition to update nTimeOffset includes checking whether the
// number of elements in vTimeOffsets is odd, which will never happen after
// there are 200 elements.
//
// But in this case the 'bug' is protective against some attacks, and may
// actually explain why we've never seen attacks which manipulate the
// clock offset.
//
// So we should hold off on fixing this and clean it up as part of
// a timing cleanup that strengthens it in a number of other ways.
//
if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1)
{
int64_t nMedian = vTimeOffsets.median();
std::vector<int64_t> vSorted = vTimeOffsets.sorted();
// Only let other nodes change our time by so much
if (abs64(nMedian) <= std::max<int64_t>(0, gArgs.GetArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT)))
{
nTimeOffset = nMedian;
}
else
{
nTimeOffset = 0;
static bool fDone;
if (!fDone)
{
// If nobody has a time different than ours but within 5 minutes of ours, give a warning
bool fMatch = false;
for (const int64_t nOffset : vSorted)
if (nOffset != 0 && abs64(nOffset) < 5 * 60)
fMatch = true;
if (!fMatch)
{
fDone = true;
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);
SetMiscWarning(strMessage);
uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
}
}
}
if (LogAcceptCategory(BCLog::NET)) {
for (const int64_t n : vSorted) {
LogPrint(BCLog::NET, "%+d ", n); /* Continued */
}
LogPrint(BCLog::NET, "| "); /* Continued */
LogPrint(BCLog::NET, "nTimeOffset = %+d (%+d minutes)\n", nTimeOffset, nTimeOffset/60);
}
}
}
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