Bitcoin Core  0.20.99
P2P Digital Currency
timedata.cpp
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1 // Copyright (c) 2014-2020 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)
7 #endif
8 
9 #include <timedata.h>
10 
11 #include <netaddress.h>
12 #include <node/ui_interface.h>
13 #include <sync.h>
14 #include <util/system.h>
15 #include <util/translation.h>
16 #include <warnings.h>
17 
19 static int64_t nTimeOffset GUARDED_BY(g_timeoffset_mutex) = 0;
20 
28 int64_t GetTimeOffset()
29 {
30  LOCK(g_timeoffset_mutex);
31  return nTimeOffset;
32 }
33 
34 int64_t GetAdjustedTime()
35 {
36  return GetTime() + GetTimeOffset();
37 }
38 
39 #define BITCOIN_TIMEDATA_MAX_SAMPLES 200
40 
41 void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
42 {
43  LOCK(g_timeoffset_mutex);
44  // Ignore duplicates
45  static std::set<CNetAddr> setKnown;
46  if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
47  return;
48  if (!setKnown.insert(ip).second)
49  return;
50 
51  // Add data
53  vTimeOffsets.input(nOffsetSample);
54  LogPrint(BCLog::NET, "added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample / 60);
55 
56  // There is a known issue here (see issue #4521):
57  //
58  // - The structure vTimeOffsets contains up to 200 elements, after which
59  // any new element added to it will not increase its size, replacing the
60  // oldest element.
61  //
62  // - The condition to update nTimeOffset includes checking whether the
63  // number of elements in vTimeOffsets is odd, which will never happen after
64  // there are 200 elements.
65  //
66  // But in this case the 'bug' is protective against some attacks, and may
67  // actually explain why we've never seen attacks which manipulate the
68  // clock offset.
69  //
70  // So we should hold off on fixing this and clean it up as part of
71  // a timing cleanup that strengthens it in a number of other ways.
72  //
73  if (vTimeOffsets.size() >= 5 && vTimeOffsets.size() % 2 == 1) {
74  int64_t nMedian = vTimeOffsets.median();
75  std::vector<int64_t> vSorted = vTimeOffsets.sorted();
76  // Only let other nodes change our time by so much
77  int64_t max_adjustment = std::max<int64_t>(0, gArgs.GetArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT));
78  if (nMedian >= -max_adjustment && nMedian <= max_adjustment) {
79  nTimeOffset = nMedian;
80  } else {
81  nTimeOffset = 0;
82 
83  static bool fDone;
84  if (!fDone) {
85  // If nobody has a time different than ours but within 5 minutes of ours, give a warning
86  bool fMatch = false;
87  for (const int64_t nOffset : vSorted) {
88  if (nOffset != 0 && nOffset > -5 * 60 && nOffset < 5 * 60) fMatch = true;
89  }
90 
91  if (!fMatch) {
92  fDone = true;
93  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);
94  SetMiscWarning(strMessage);
95  uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING);
96  }
97  }
98  }
99 
101  for (const int64_t n : vSorted) {
102  LogPrint(BCLog::NET, "%+d ", n); /* Continued */
103  }
104  LogPrint(BCLog::NET, "| "); /* Continued */
105  LogPrint(BCLog::NET, "nTimeOffset = %+d (%+d minutes)\n", nTimeOffset, nTimeOffset / 60);
106  }
107  }
108 }
#define LogPrint(category,...)
Definition: logging.h:182
Bilingual messages:
Definition: translation.h:16
#define BITCOIN_TIMEDATA_MAX_SAMPLES
Definition: timedata.cpp:39
#define strprintf
Format arguments and return the string or write to given std::ostream (see tinyformat::format doc for...
Definition: tinyformat.h:1164
void SetMiscWarning(const bilingual_str &warning)
Definition: warnings.cpp:20
Median filter over a stream of values.
Definition: timedata.h:22
#define PACKAGE_NAME
int64_t GetTimeOffset()
"Never go to sea with two chronometers; take one or three." Our three time sources are: ...
Definition: timedata.cpp:28
std::vector< T > sorted() const
Definition: timedata.h:67
void input(T value)
Definition: timedata.h:37
static int64_t nTimeOffset GUARDED_BY(g_timeoffset_mutex)=0
#define LOCK(cs)
Definition: sync.h:230
bilingual_str _(const char *psz)
Translation function.
Definition: translation.h:57
static bool LogAcceptCategory(BCLog::LogFlags category)
Return true if log accepts specified category.
Definition: logging.h:153
Network address.
Definition: netaddress.h:119
static Mutex g_timeoffset_mutex
Definition: timedata.cpp:18
std::string GetArg(const std::string &strArg, const std::string &strDefault) const
Return string argument or default value.
Definition: system.cpp:466
int64_t GetAdjustedTime()
Definition: timedata.cpp:34
ArgsManager gArgs
Definition: system.cpp:76
CClientUIInterface uiInterface
void AddTimeData(const CNetAddr &ip, int64_t nOffsetSample)
Definition: timedata.cpp:41
int64_t GetTime()
Return system time (or mocked time, if set)
Definition: time.cpp:23
int size() const
Definition: timedata.h:62
static const int64_t DEFAULT_MAX_TIME_ADJUSTMENT
Definition: timedata.h:13
T median() const
Definition: timedata.h:49