trie: remove inconsistent trie nodes during sync in path mode (ethereum#28595)

This fixes a database corruption issue that could occur during state healing.
When sync is aborted while certain modifications were already committed, and a
reorg occurs, the database would contain incorrect trie nodes stored by path.
These nodes need to detected/deleted in order to obtain a complete and fully correct state
after state healing.

---------

Co-authored-by: Felix Lange <fjl@twurst.com>

Author: 2 people

ethdb/dbtest/testsuite.go

@@ -273,9 +273,13 @@ func TestDatabaseSuite(t *testing.T, New func() ethdb.KeyValueStore) {
 		b.Put([]byte("5"), nil)
 		b.Delete([]byte("1"))
 		b.Put([]byte("6"), nil)
-		b.Delete([]byte("3"))
+
+		b.Delete([]byte("3")) // delete then put
 		b.Put([]byte("3"), nil)
 
+		b.Put([]byte("7"), nil) // put then delete
+		b.Delete([]byte("7"))
+
 		if err := b.Write(); err != nil {
 			t.Fatal(err)
 		}

trie/sync.go

@@ -116,10 +116,9 @@ type LeafCallback func(keys [][]byte, path []byte, leaf []byte, parent common.Ha
 
 // nodeRequest represents a scheduled or already in-flight trie node retrieval request.
 type nodeRequest struct {
-	hash    common.Hash // Hash of the trie node to retrieve
-	path    []byte      // Merkle path leading to this node for prioritization
-	data    []byte      // Data content of the node, cached until all subtrees complete
-	deletes [][]byte    // List of internal path segments for trie nodes to delete
+	hash common.Hash // Hash of the trie node to retrieve
+	path []byte      // Merkle path leading to this node for prioritization
+	data []byte      // Data content of the node, cached until all subtrees complete
 
 	parent   *nodeRequest // Parent state node referencing this entry
 	deps     int          // Number of dependencies before allowed to commit this node
@@ -146,38 +145,85 @@ type CodeSyncResult struct {
 	Data []byte      // Data content of the retrieved bytecode
 }
 
+// nodeOp represents an operation upon the trie node. It can either represent a
+// deletion to the specific node or a node write for persisting retrieved node.
+type nodeOp struct {
+	owner common.Hash // identifier of the trie (empty for account trie)
+	path  []byte      // path from the root to the specified node.
+	blob  []byte      // the content of the node (nil for deletion)
+	hash  common.Hash // hash of the node content (empty for node deletion)
+}
+
+// isDelete indicates if the operation is a database deletion.
+func (op *nodeOp) isDelete() bool {
+	return len(op.blob) == 0
+}
+
 // syncMemBatch is an in-memory buffer of successfully downloaded but not yet
 // persisted data items.
 type syncMemBatch struct {
-	nodes   map[string][]byte      // In-memory membatch of recently completed nodes
-	hashes  map[string]common.Hash // Hashes of recently completed nodes
-	deletes map[string]struct{}    // List of paths for trie node to delete
-	codes   map[common.Hash][]byte // In-memory membatch of recently completed codes
-	size    uint64                 // Estimated batch-size of in-memory data.
+	scheme string                 // State scheme identifier
+	codes  map[common.Hash][]byte // In-memory batch of recently completed codes
+	nodes  []nodeOp               // In-memory batch of recently completed/deleted nodes
+	size   uint64                 // Estimated batch-size of in-memory data.
 }
 
 // newSyncMemBatch allocates a new memory-buffer for not-yet persisted trie nodes.
-func newSyncMemBatch() *syncMemBatch {
+func newSyncMemBatch(scheme string) *syncMemBatch {
 	return &syncMemBatch{
-		nodes:   make(map[string][]byte),
-		hashes:  make(map[string]common.Hash),
-		deletes: make(map[string]struct{}),
-		codes:   make(map[common.Hash][]byte),
+		scheme: scheme,
+		codes:  make(map[common.Hash][]byte),
 	}
 }
 
-// hasNode reports the trie node with specific path is already cached.
-func (batch *syncMemBatch) hasNode(path []byte) bool {
-	_, ok := batch.nodes[string(path)]
-	return ok
-}
-
 // hasCode reports the contract code with specific hash is already cached.
 func (batch *syncMemBatch) hasCode(hash common.Hash) bool {
 	_, ok := batch.codes[hash]
 	return ok
 }
 
+// addCode caches a contract code database write operation.
+func (batch *syncMemBatch) addCode(hash common.Hash, code []byte) {
+	batch.codes[hash] = code
+	batch.size += common.HashLength + uint64(len(code))
+}
+
+// addNode caches a node database write operation.
+func (batch *syncMemBatch) addNode(owner common.Hash, path []byte, blob []byte, hash common.Hash) {
+	if batch.scheme == rawdb.PathScheme {
+		if owner == (common.Hash{}) {
+			batch.size += uint64(len(path) + len(blob))
+		} else {
+			batch.size += common.HashLength + uint64(len(path)+len(blob))
+		}
+	} else {
+		batch.size += common.HashLength + uint64(len(blob))
+	}
+	batch.nodes = append(batch.nodes, nodeOp{
+		owner: owner,
+		path:  path,
+		blob:  blob,
+		hash:  hash,
+	})
+}
+
+// delNode caches a node database delete operation.
+func (batch *syncMemBatch) delNode(owner common.Hash, path []byte) {
+	if batch.scheme != rawdb.PathScheme {
+		log.Error("Unexpected node deletion", "owner", owner, "path", path, "scheme", batch.scheme)
+		return // deletion is not supported in hash mode.
+	}
+	if owner == (common.Hash{}) {
+		batch.size += uint64(len(path))
+	} else {
+		batch.size += common.HashLength + uint64(len(path))
+	}
+	batch.nodes = append(batch.nodes, nodeOp{
+		owner: owner,
+		path:  path,
+	})
+}
+
 // Sync is the main state trie synchronisation scheduler, which provides yet
 // unknown trie hashes to retrieve, accepts node data associated with said hashes
 // and reconstructs the trie step by step until all is done.
@@ -196,7 +242,7 @@ func NewSync(root common.Hash, database ethdb.KeyValueReader, callback LeafCallb
 	ts := &Sync{
 		scheme:   scheme,
 		database: database,
-		membatch: newSyncMemBatch(),
+		membatch: newSyncMemBatch(scheme),
 		nodeReqs: make(map[string]*nodeRequest),
 		codeReqs: make(map[common.Hash]*codeRequest),
 		queue:    prque.New[int64, any](nil), // Ugh, can contain both string and hash, whyyy
@@ -210,16 +256,17 @@ func NewSync(root common.Hash, database ethdb.KeyValueReader, callback LeafCallb
 // parent for completion tracking. The given path is a unique node path in
 // hex format and contain all the parent path if it's layered trie node.
 func (s *Sync) AddSubTrie(root common.Hash, path []byte, parent common.Hash, parentPath []byte, callback LeafCallback) {
-	// Short circuit if the trie is empty or already known
 	if root == types.EmptyRootHash {
 		return
 	}
-	if s.membatch.hasNode(path) {
-		return
-	}
 	owner, inner := ResolvePath(path)
-	if rawdb.HasTrieNode(s.database, owner, inner, root, s.scheme) {
+	exist, inconsistent := s.hasNode(owner, inner, root)
+	if exist {
+		// The entire subtrie is already present in the database.
 		return
+	} else if inconsistent {
+		// There is a pre-existing node with the wrong hash in DB, remove it.
+		s.membatch.delNode(owner, inner)
 	}
 	// Assemble the new sub-trie sync request
 	req := &nodeRequest{
@@ -371,39 +418,42 @@ func (s *Sync) ProcessNode(result NodeSyncResult) error {
 }
 
 // Commit flushes the data stored in the internal membatch out to persistent
-// storage, returning any occurred error.
+// storage, returning any occurred error. The whole data set will be flushed
+// in an atomic database batch.
 func (s *Sync) Commit(dbw ethdb.Batch) error {
 	// Flush the pending node writes into database batch.
 	var (
 		account int
 		storage int
 	)
-	for path, value := range s.membatch.nodes {
-		owner, inner := ResolvePath([]byte(path))
-		if owner == (common.Hash{}) {
-			account += 1
+	for _, op := range s.membatch.nodes {
+		if op.isDelete() {
+			// node deletion is only supported in path mode.
+			if op.owner == (common.Hash{}) {
+				rawdb.DeleteAccountTrieNode(dbw, op.path)
+			} else {
+				rawdb.DeleteStorageTrieNode(dbw, op.owner, op.path)
+			}
+			deletionGauge.Inc(1)
 		} else {
-			storage += 1
+			if op.owner == (common.Hash{}) {
+				account += 1
+			} else {
+				storage += 1
+			}
+			rawdb.WriteTrieNode(dbw, op.owner, op.path, op.hash, op.blob, s.scheme)
 		}
-		rawdb.WriteTrieNode(dbw, owner, inner, s.membatch.hashes[path], value, s.scheme)
 	}
 	accountNodeSyncedGauge.Inc(int64(account))
 	storageNodeSyncedGauge.Inc(int64(storage))
 
-	// Flush the pending node deletes into the database batch.
-	// Please note that each written and deleted node has a
-	// unique path, ensuring no duplication occurs.
-	for path := range s.membatch.deletes {
-		owner, inner := ResolvePath([]byte(path))
-		rawdb.DeleteTrieNode(dbw, owner, inner, common.Hash{} /* unused */, s.scheme)
-	}
 	// Flush the pending code writes into database batch.
 	for hash, value := range s.membatch.codes {
 		rawdb.WriteCode(dbw, hash, value)
 	}
 	codeSyncedGauge.Inc(int64(len(s.membatch.codes)))
 
-	s.membatch = newSyncMemBatch() // reset the batch
+	s.membatch = newSyncMemBatch(s.scheme) // reset the batch
 	return nil
 }
 
@@ -476,12 +526,15 @@ func (s *Sync) children(req *nodeRequest, object node) ([]*nodeRequest, error) {
 		// child as invalid. This is essential in the case of path mode
 		// scheme; otherwise, state healing might overwrite existing child
 		// nodes silently while leaving a dangling parent node within the
-		// range of this internal path on disk. This would break the
-		// guarantee for state healing.
+		// range of this internal path on disk and the persistent state
+		// ends up with a very weird situation that nodes on the same path
+		// are not inconsistent while they all present in disk. This property
+		// would break the guarantee for state healing.
 		//
 		// While it's possible for this shortNode to overwrite a previously
 		// existing full node, the other branches of the fullNode can be
-		// retained as they remain untouched and complete.
+		// retained as they are not accessible with the new shortNode, and
+		// also the whole sub-trie is still untouched and complete.
 		//
 		// This step is only necessary for path mode, as there is no deletion
 		// in hash mode at all.
@@ -498,8 +551,7 @@ func (s *Sync) children(req *nodeRequest, object node) ([]*nodeRequest, error) {
 					exists = rawdb.ExistsStorageTrieNode(s.database, owner, append(inner, key[:i]...))
 				}
 				if exists {
-					req.deletes = append(req.deletes, key[:i])
-					deletionGauge.Inc(1)
+					s.membatch.delNode(owner, append(inner, key[:i]...))
 					log.Debug("Detected dangling node", "owner", owner, "path", append(inner, key[:i]...))
 				}
 			}
@@ -521,6 +573,7 @@ func (s *Sync) children(req *nodeRequest, object node) ([]*nodeRequest, error) {
 	var (
 		missing = make(chan *nodeRequest, len(children))
 		pending sync.WaitGroup
+		batchMu sync.Mutex
 	)
 	for _, child := range children {
 		// Notify any external watcher of a new key/value node
@@ -538,34 +591,32 @@ func (s *Sync) children(req *nodeRequest, object node) ([]*nodeRequest, error) {
 				}
 			}
 		}
-		// If the child references another node, resolve or schedule
+		// If the child references another node, resolve or schedule.
+		// We check all children concurrently.
 		if node, ok := (child.node).(hashNode); ok {
-			// Try to resolve the node from the local database
-			if s.membatch.hasNode(child.path) {
-				continue
-			}
-			// Check the presence of children concurrently
+			path := child.path
+			hash := common.BytesToHash(node)
 			pending.Add(1)
-			go func(child childNode) {
+			go func() {
 				defer pending.Done()
-
-				// If database says duplicate, then at least the trie node is present
-				// and we hold the assumption that it's NOT legacy contract code.
-				var (
-					chash        = common.BytesToHash(node)
-					owner, inner = ResolvePath(child.path)
-				)
-				if rawdb.HasTrieNode(s.database, owner, inner, chash, s.scheme) {
+				owner, inner := ResolvePath(path)
+				exist, inconsistent := s.hasNode(owner, inner, hash)
+				if exist {
 					return
+				} else if inconsistent {
+					// There is a pre-existing node with the wrong hash in DB, remove it.
+					batchMu.Lock()
+					s.membatch.delNode(owner, inner)
+					batchMu.Unlock()
 				}
 				// Locally unknown node, schedule for retrieval
 				missing <- &nodeRequest{
-					path:     child.path,
-					hash:     chash,
+					path:     path,
+					hash:     hash,
 					parent:   req,
 					callback: req.callback,
 				}
-			}(child)
+			}()
 		}
 	}
 	pending.Wait()
@@ -587,21 +638,10 @@ func (s *Sync) children(req *nodeRequest, object node) ([]*nodeRequest, error) {
 // committed themselves.
 func (s *Sync) commitNodeRequest(req *nodeRequest) error {
 	// Write the node content to the membatch
-	s.membatch.nodes[string(req.path)] = req.data
-	s.membatch.hashes[string(req.path)] = req.hash
+	owner, path := ResolvePath(req.path)
+	s.membatch.addNode(owner, path, req.data, req.hash)
 
-	// The size tracking refers to the db-batch, not the in-memory data.
-	if s.scheme == rawdb.PathScheme {
-		s.membatch.size += uint64(len(req.path) + len(req.data))
-	} else {
-		s.membatch.size += common.HashLength + uint64(len(req.data))
-	}
-	// Delete the internal nodes which are marked as invalid
-	for _, segment := range req.deletes {
-		path := append(req.path, segment...)
-		s.membatch.deletes[string(path)] = struct{}{}
-		s.membatch.size += uint64(len(path))
-	}
+	// Removed the completed node request
 	delete(s.nodeReqs, string(req.path))
 	s.fetches[len(req.path)]--
 
@@ -622,8 +662,9 @@ func (s *Sync) commitNodeRequest(req *nodeRequest) error {
 // committed themselves.
 func (s *Sync) commitCodeRequest(req *codeRequest) error {
 	// Write the node content to the membatch
-	s.membatch.codes[req.hash] = req.data
-	s.membatch.size += common.HashLength + uint64(len(req.data))
+	s.membatch.addCode(req.hash, req.data)
+
+	// Removed the completed code request
 	delete(s.codeReqs, req.hash)
 	s.fetches[len(req.path)]--
 
@@ -639,6 +680,28 @@ func (s *Sync) commitCodeRequest(req *codeRequest) error {
 	return nil
 }
 
+// hasNode reports whether the specified trie node is present in the database.
+// 'exists' is true when the node exists in the database and matches the given root
+// hash. The 'inconsistent' return value is true when the node exists but does not
+// match the expected hash.
+func (s *Sync) hasNode(owner common.Hash, path []byte, hash common.Hash) (exists bool, inconsistent bool) {
+	// If node is running with hash scheme, check the presence with node hash.
+	if s.scheme == rawdb.HashScheme {
+		return rawdb.HasLegacyTrieNode(s.database, hash), false
+	}
+	// If node is running with path scheme, check the presence with node path.
+	var blob []byte
+	var dbHash common.Hash
+	if owner == (common.Hash{}) {
+		blob, dbHash = rawdb.ReadAccountTrieNode(s.database, path)
+	} else {
+		blob, dbHash = rawdb.ReadStorageTrieNode(s.database, owner, path)
+	}
+	exists = hash == dbHash
+	inconsistent = !exists && len(blob) != 0
+	return exists, inconsistent
+}
+
 // ResolvePath resolves the provided composite node path by separating the
 // path in account trie if it's existent.
 func ResolvePath(path []byte) (common.Hash, []byte) {