graph/db: fix race in DisconnectBlockAtHeight cache access
What the developer wrote
Authored by Elle Mouton
graph/db: fix race in DisconnectBlockAtHeight cache access
The DisconnectBlockAtHeight method was modifying the rejectCache and
chanCache without holding the cacheMu lock. This caused races with
other operations that properly held the lock, such as AddChannelEdge
which modifies the caches in its OnCommit callback while the batch
scheduler holds cacheMu.
Fix by acquiring cacheMu before removing channels from the caches.
What changed, and why it matters
This commit fixes a concurrency bug in LND's channel graph database. When disconnecting a block, the code was removing entries from internal caches without holding the proper lock, while other code paths correctly lock the same caches. This can cause data races, potentially leading to corrupted cache state, inconsistent channel graph views, or crashes under concurrent load.
Apply the patch. Consider running the race detector (go test -race) on graph/db package tests covering block disconnect and channel edge addition paths. Review other cache-modifying methods for consistent cacheMu usage.
Security signals we found
Concurrency race condition on shared cache
Missing mutex lock around cache mutation
Potential cache corruption or inconsistent graph state
Crash or undefined behavior under concurrent block reorganization and channel updates
Evidence from the diff
The patch adds s.cacheMu.Lock()/Unlock() around cache removal in SQLStore.DisconnectBlockAtHeight. Previously, removedChans were iterated to call rejectCache.remove and chanCache.remove without holding cacheMu, while AddChannelEdge’s OnCommit callback modifies the same caches under cacheMu held by the batch scheduler. This is a classic read-modify-write race on shared in-memory cache state.
Changed components
graph/db/sql_store.goSQLStore.DisconnectBlockAtHeightrejectCachechanCacheInspect captured patch +2 / −0
diff --git a/graph/db/sql_store.go b/graph/db/sql_store.go
index 6507707..2bfcce5 100644
--- a/graph/db/sql_store.go
+++ b/graph/db/sql_store.go
@@ -2911,10 +2911,12 @@ func (s *SQLStore) DisconnectBlockAtHeight(height uint32) (
"height: %w", err)
}
+ s.cacheMu.Lock()
for _, channel := range removedChans {
s.rejectCache.remove(channel.ChannelID)
s.chanCache.remove(channel.ChannelID)
}
+ s.cacheMu.Unlock()
return removedChans, nil
}
Why this scored 49/100
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