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| -rw-r--r-- | src/timedata.cpp | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/src/timedata.cpp b/src/timedata.cpp index 8a095d26dc..6c3bd9a48d 100644 --- a/src/timedata.cpp +++ b/src/timedata.cpp @@ -49,6 +49,24 @@ void AddTimeData(const CNetAddr& ip, int64_t nTime) static CMedianFilter<int64_t> vTimeOffsets(200,0); vTimeOffsets.input(nOffsetSample); LogPrintf("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(); |