| 44 | static bool g_warning_emitted; |
| 45 | |
| 46 | void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample) |
| 47 | { |
| 48 | LOCK(g_timeoffset_mutex); |
| 49 | // Ignore duplicates |
| 50 | if (g_sources.size() == BITCOIN_TIMEDATA_MAX_SAMPLES) |
| 51 | return; |
| 52 | if (!g_sources.insert(ip).second) |
| 53 | return; |
| 54 | |
| 55 | // Add data |
| 56 | g_time_offsets.input(nOffsetSample); |
| 57 | 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 | if (g_time_offsets.size() >= 5 && g_time_offsets.size() % 2 == 1) { |
| 77 | int64_t nMedian = g_time_offsets.median(); |
| 78 | std::vector<int64_t> vSorted = g_time_offsets.sorted(); |
| 79 | // Only let other nodes change our time by so much |
| 80 | int64_t max_adjustment = std::max<int64_t>(0, gArgs.GetIntArg("-maxtimeadjustment", DEFAULT_MAX_TIME_ADJUSTMENT)); |
| 81 | if (nMedian >= -max_adjustment && nMedian <= max_adjustment) { |
| 82 | nTimeOffset = nMedian; |
| 83 | } else { |
| 84 | nTimeOffset = 0; |
| 85 | |
| 86 | if (!g_warning_emitted) { |
| 87 | // If nobody has a time different than ours but within 5 minutes of ours, give a warning |
| 88 | bool fMatch = false; |
| 89 | for (const int64_t nOffset : vSorted) { |
| 90 | if (nOffset != 0 && nOffset > -5 * 60 && nOffset < 5 * 60) fMatch = true; |
| 91 | } |
| 92 | |
| 93 | if (!fMatch) { |
| 94 | g_warning_emitted = true; |
| 95 | 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 | SetMiscWarning(strMessage); |
| 97 | uiInterface.ThreadSafeMessageBox(strMessage, "", CClientUIInterface::MSG_WARNING); |
| 98 | } |
| 99 | } |
| 100 | } |
| 101 | |
| 102 | if (LogAcceptCategory(BCLog::NET)) { |
| 103 | std::string log_message{"time data samples: "}; |