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validation: don't modify genesis during snapshot load

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Avoid modifying the genesis block index entry during snapshot load. This
is because, in a future change that fixes LoadBlockIndex for UTXO
snapshots, we detect block index entries that are reliant on
assumed-valid ancestors and treat them specially.

Since the genesis block doesn't have BLOCK_VALID_SCRIPTS, it would be
erroneously marked BLOCK_ASSUMED_VALID during snapshot load if we didn't
skip it here. This would cause a "setBlockIndexCandidates() empty"
assertion to be tripped since all block index entries would be marked
assume-valid due to genesis, which is never re-validated.

There's probably no good reason to modify the genesis block index entry
during snapshot load anyway...
This commit is contained in:
James O'Beirne 2021-10-28 15:15:10 -04:00
parent af4275e8db
commit d0c6e61f5d
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2 changed files with 13 additions and 3 deletions
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3
src/test/validation_chainstatemanager_tests.cpp
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@ -232,6 +232,9 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
*chainman.ActiveChainstate().m_from_snapshot_blockhash,
*chainman.SnapshotBlockhash());
// Ensure that the genesis block was not marked assumed-valid.
BOOST_CHECK(!chainman.ActiveChain().Genesis()->IsAssumedValid());
const AssumeutxoData& au_data = *ExpectedAssumeutxo(snapshot_height, ::Params());
const CBlockIndex* tip = chainman.ActiveTip();

13
src/validation.cpp
View file

@ -4909,7 +4909,14 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
// Fake various pieces of CBlockIndex state:
CBlockIndex* index = nullptr;
for (int i = 0; i <= snapshot_chainstate.m_chain.Height(); ++i) {
// Don't make any modifications to the genesis block.
// This is especially important because we don't want to erroneously
// apply BLOCK_ASSUMED_VALID to genesis, which would happen if we didn't skip
// it here (since it apparently isn't BLOCK_VALID_SCRIPTS).
constexpr int AFTER_GENESIS_START{1};
for (int i = AFTER_GENESIS_START; i <= snapshot_chainstate.m_chain.Height(); ++i) {
index = snapshot_chainstate.m_chain[i];
// Fake nTx so that LoadBlockIndex() loads assumed-valid CBlockIndex
@ -4918,7 +4925,7 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
index->nTx = 1;
}
// Fake nChainTx so that GuessVerificationProgress reports accurately
index->nChainTx = index->pprev ? index->pprev->nChainTx + index->nTx : 1;
index->nChainTx = index->pprev->nChainTx + index->nTx;
// Mark unvalidated block index entries beneath the snapshot base block as assumed-valid.
if (!index->IsValid(BLOCK_VALID_SCRIPTS)) {
@ -4929,7 +4936,7 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
// Fake BLOCK_OPT_WITNESS so that CChainState::NeedsRedownload()
// won't ask to rewind the entire assumed-valid chain on startup.
if (index->pprev && DeploymentActiveAt(*index, ::Params().GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
if (DeploymentActiveAt(*index, ::Params().GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
index->nStatus |= BLOCK_OPT_WITNESS;
}