aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
-rw-r--r--src/validation.cpp55
1 files changed, 54 insertions, 1 deletions
diff --git a/src/validation.cpp b/src/validation.cpp
index a77362f5d6..51e40c17b5 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1856,12 +1856,65 @@ bool CChainState::ConnectBlock(const CBlock& block, CValidationState& state, CBl
// before the first had been spent. Since those coinbases are sufficiently buried its no longer possible to create further
// duplicate transactions descending from the known pairs either.
// If we're on the known chain at height greater than where BIP34 activated, we can save the db accesses needed for the BIP30 check.
+
+ // BIP34 requires that a block at height X (block X) has its coinbase
+ // scriptSig start with a CScriptNum of X (indicated height X). The above
+ // logic of no longer requiring BIP30 once BIP34 activates is flawed in the
+ // case that there is a block X before the BIP34 height of 227,931 which has
+ // an indicated height Y where Y is greater than X. The coinbase for block
+ // X would also be a valid coinbase for block Y, which could be a BIP30
+ // violation. An exhaustive search of all mainnet coinbases before the
+ // BIP34 height which have an indicated height greater than the block height
+ // reveals many occurrences. The 3 lowest indicated heights found are
+ // 209,921, 490,897, and 1,983,702 and thus coinbases for blocks at these 3
+ // heights would be the first opportunity for BIP30 to be violated.
+
+ // The search reveals a great many blocks which have an indicated height
+ // greater than 1,983,702, so we simply remove the optimization to skip
+ // BIP30 checking for blocks at height 1,983,702 or higher. Before we reach
+ // that block in another 25 years or so, we should take advantage of a
+ // future consensus change to do a new and improved version of BIP34 that
+ // will actually prevent ever creating any duplicate coinbases in the
+ // future.
+ static constexpr int BIP34_IMPLIES_BIP30_LIMIT = 1983702;
+
+ // There is no potential to create a duplicate coinbase at block 209,921
+ // because this is still before the BIP34 height and so explicit BIP30
+ // checking is still active.
+
+ // The final case is block 176,684 which has an indicated height of
+ // 490,897. Unfortunately, this issue was not discovered until about 2 weeks
+ // before block 490,897 so there was not much opportunity to address this
+ // case other than to carefully analyze it and determine it would not be a
+ // problem. Block 490,897 was, in fact, mined with a different coinbase than
+ // block 176,684, but it is important to note that even if it hadn't been or
+ // is remined on an alternate fork with a duplicate coinbase, we would still
+ // not run into a BIP30 violation. This is because the coinbase for 176,684
+ // is spent in block 185,956 in transaction
+ // d4f7fbbf92f4a3014a230b2dc70b8058d02eb36ac06b4a0736d9d60eaa9e8781. This
+ // spending transaction can't be duplicated because it also spends coinbase
+ // 0328dd85c331237f18e781d692c92de57649529bd5edf1d01036daea32ffde29. This
+ // coinbase has an indicated height of over 4.2 billion, and wouldn't be
+ // duplicatable until that height, and it's currently impossible to create a
+ // chain that long. Nevertheless we may wish to consider a future soft fork
+ // which retroactively prevents block 490,897 from creating a duplicate
+ // coinbase. The two historical BIP30 violations often provide a confusing
+ // edge case when manipulating the UTXO and it would be simpler not to have
+ // another edge case to deal with.
+
+ // testnet3 has no blocks before the BIP34 height with indicated heights
+ // post BIP34 before approximately height 486,000,000 and presumably will
+ // be reset before it reaches block 1,983,702 and starts doing unnecessary
+ // BIP30 checking again.
assert(pindex->pprev);
CBlockIndex *pindexBIP34height = pindex->pprev->GetAncestor(chainparams.GetConsensus().BIP34Height);
//Only continue to enforce if we're below BIP34 activation height or the block hash at that height doesn't correspond.
fEnforceBIP30 = fEnforceBIP30 && (!pindexBIP34height || !(pindexBIP34height->GetBlockHash() == chainparams.GetConsensus().BIP34Hash));
- if (fEnforceBIP30) {
+ // TODO: Remove BIP30 checking from block height 1,983,702 on, once we have a
+ // consensus change that ensures coinbases at those heights can not
+ // duplicate earlier coinbases.
+ if (fEnforceBIP30 || pindex->nHeight >= BIP34_IMPLIES_BIP30_LIMIT) {
for (const auto& tx : block.vtx) {
for (size_t o = 0; o < tx->vout.size(); o++) {
if (view.HaveCoin(COutPoint(tx->GetHash(), o))) {