core/state/snapshot: check difflayer staleness early (ethereum#27255)

This PR adds a staleness-check to AccountRLP, before checking the bloom-filter and potentially going directly into the disklayer.

---------

Co-authored-by: rjl493456442 <garyrong0905@gmail.com>

core/state/snapshot/difflayer.go

@@ -292,9 +292,14 @@ func (dl *diffLayer) Account(hash common.Hash) (*Account, error) {
 //
 // Note the returned account is not a copy, please don't modify it.
 func (dl *diffLayer) AccountRLP(hash common.Hash) ([]byte, error) {
+	dl.lock.RLock()
+	// Check staleness before reaching further.
+	if dl.Stale() {
+		dl.lock.RUnlock()
+		return nil, ErrSnapshotStale
+	}
 	// Check the bloom filter first whether there's even a point in reaching into
 	// all the maps in all the layers below
-	dl.lock.RLock()
 	hit := dl.diffed.Contains(accountBloomHasher(hash))
 	if !hit {
 		hit = dl.diffed.Contains(destructBloomHasher(hash))
@@ -361,6 +366,11 @@ func (dl *diffLayer) Storage(accountHash, storageHash common.Hash) ([]byte, erro
 	// Check the bloom filter first whether there's even a point in reaching into
 	// all the maps in all the layers below
 	dl.lock.RLock()
+	// Check staleness before reaching further.
+	if dl.Stale() {
+		dl.lock.RUnlock()
+		return nil, ErrSnapshotStale
+	}
 	hit := dl.diffed.Contains(storageBloomHasher{accountHash, storageHash})
 	if !hit {
 		hit = dl.diffed.Contains(destructBloomHasher(accountHash))

core/state/snapshot/snapshot_test.go

@@ -185,6 +185,10 @@ func TestDiskLayerExternalInvalidationPartialFlatten(t *testing.T) {
 // be returned with junk data. This version of the test retains the bottom diff
 // layer to check the usual mode of operation where the accumulator is retained.
 func TestDiffLayerExternalInvalidationPartialFlatten(t *testing.T) {
+	// Un-commenting this triggers the bloom set to be deterministic. The values below
+	// were used to trigger the flaw described in https://github.com/ethereum/go-ethereum/issues/27254.
+	// bloomDestructHasherOffset, bloomAccountHasherOffset, bloomStorageHasherOffset = 14, 24, 5
+
 	// Create an empty base layer and a snapshot tree out of it
 	base := &diskLayer{
 		diskdb: rawdb.NewMemoryDatabase(),