validation: Don't use m_chain.Tip() in FlushStateToDisk
What the developer wrote
Authored by Martin Zumsande
validation: Don't use m_chain.Tip() in FlushStateToDisk
In DisconnectBlock(), we can call FlushStateToDisk after updating
the coins but before changing the tip, which is still at the
disconnected block. This means that the ChainStateFlushed
signal would have the wrong block in the locator.
Also remove an outdated comment - the wallet doesn't use
ChainStateFlushed anymore, currently only indexes do.
Co-authored-by: Lőrinc <pap.lorinc@gmail.com>
What changed, and why it matters
This commit fixes a minor bookkeeping bug in Bitcoin Core. When flushing state to disk during a block disconnection, the code was incorrectly reporting the current chain tip (the block being disconnected) as the flushed block, instead of the last block actually written to disk. This could mislead indexers or other listeners tracking the chain's flushed state, but it does not directly allow theft, double-spending, or consensus failure.
Treat as a routine correctness fix. Index operators and downstream services consuming ChainStateFlushed should ensure they handle reorg/disconnect edge cases gracefully. No emergency deployment is warranted solely for this change.
Security signals we found
Incorrect state reporting in a chain-state flush signal
Potential inconsistency between on-disk state and signaled locator during reorg/disconnect paths
Indexers relying on ChainStateFlushed could observe a stale or mismatched block locator
Evidence from the diff
In Chainstate::FlushStateToDisk, the ChainStateFlushed signal previously used GetLocator(m_chain.Tip()). During DisconnectBlock, FlushStateToDisk can run after coins are updated but before m_chain.Tip() is moved back from the disconnected block, so the locator pointed to the wrong block. The patch changes the locator to use m_last_flushed_block, which reflects the actual persisted state. An outdated comment about wallets using the signal is also removed.
Changed components
src/validation.cppChainstate::FlushStateToDiskChainStateFlushed signalblock indexers (e.g., coinstats, address, txindex)Inspect captured patch +1 / −2
diff --git a/src/validation.cpp b/src/validation.cpp
index 9df377fb..3f4b60e6 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2841,8 +2841,7 @@ bool Chainstate::FlushStateToDisk(
}
if (full_flush_completed) {
if (m_chainman.m_options.signals) {
- // Update best block in wallet (so we can detect restored wallets).
- m_chainman.m_options.signals->ChainStateFlushed(this->GetRole(), GetLocator(m_chain.Tip()));
+ m_chainman.m_options.signals->ChainStateFlushed(this->GetRole(), GetLocator(m_last_flushed_block));
}
if (!m_chainman.m_interrupt && ShouldCompactChainstate(m_chainman.IsInitialBlockDownload())) {
Why this scored 28/100
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