core/state/snapshot: fix race condition (ethereum#24685)

Fixes three race conditions found through fuzzing by David Theodore

core/state/snapshot/difflayer.go

@@ -258,6 +258,9 @@ func (dl *diffLayer) Root() common.Hash {
 
 // Parent returns the subsequent layer of a diff layer.
 func (dl *diffLayer) Parent() snapshot {
+	dl.lock.RLock()
+	defer dl.lock.RUnlock()
+
 	return dl.parent
 }
 

eth/protocols/snap/sync.go

@@ -422,6 +422,8 @@ type Syncer struct {
 	storageSynced  uint64             // Number of storage slots downloaded
 	storageBytes   common.StorageSize // Number of storage trie bytes persisted to disk
 
+	extProgress *SyncProgress // progress that can be exposed to external caller.
+
 	// Request tracking during healing phase
 	trienodeHealIdlers map[string]struct{} // Peers that aren't serving trie node requests
 	bytecodeHealIdlers map[string]struct{} // Peers that aren't serving bytecode requests
@@ -477,6 +479,8 @@ func NewSyncer(db ethdb.KeyValueStore) *Syncer {
 		trienodeHealReqs: make(map[uint64]*trienodeHealRequest),
 		bytecodeHealReqs: make(map[uint64]*bytecodeHealRequest),
 		stateWriter:      db.NewBatch(),
+
+		extProgress: new(SyncProgress),
 	}
 }
 
@@ -633,6 +637,21 @@ func (s *Syncer) Sync(root common.Hash, cancel chan struct{}) error {
 			s.assignTrienodeHealTasks(trienodeHealResps, trienodeHealReqFails, cancel)
 			s.assignBytecodeHealTasks(bytecodeHealResps, bytecodeHealReqFails, cancel)
 		}
+		// Update sync progress
+		s.lock.Lock()
+		s.extProgress = &SyncProgress{
+			AccountSynced:      s.accountSynced,
+			AccountBytes:       s.accountBytes,
+			BytecodeSynced:     s.bytecodeSynced,
+			BytecodeBytes:      s.bytecodeBytes,
+			StorageSynced:      s.storageSynced,
+			StorageBytes:       s.storageBytes,
+			TrienodeHealSynced: s.trienodeHealSynced,
+			TrienodeHealBytes:  s.trienodeHealBytes,
+			BytecodeHealSynced: s.bytecodeHealSynced,
+			BytecodeHealBytes:  s.bytecodeHealBytes,
+		}
+		s.lock.Unlock()
 		// Wait for something to happen
 		select {
 		case <-s.update:
@@ -705,6 +724,9 @@ func (s *Syncer) loadSyncStatus() {
 					}
 				}
 			}
+			s.lock.Lock()
+			defer s.lock.Unlock()
+
 			s.snapped = len(s.tasks) == 0
 
 			s.accountSynced = progress.AccountSynced
@@ -802,25 +824,12 @@ func (s *Syncer) saveSyncStatus() {
 func (s *Syncer) Progress() (*SyncProgress, *SyncPending) {
 	s.lock.Lock()
 	defer s.lock.Unlock()
-
-	progress := &SyncProgress{
-		AccountSynced:      s.accountSynced,
-		AccountBytes:       s.accountBytes,
-		BytecodeSynced:     s.bytecodeSynced,
-		BytecodeBytes:      s.bytecodeBytes,
-		StorageSynced:      s.storageSynced,
-		StorageBytes:       s.storageBytes,
-		TrienodeHealSynced: s.trienodeHealSynced,
-		TrienodeHealBytes:  s.trienodeHealBytes,
-		BytecodeHealSynced: s.bytecodeHealSynced,
-		BytecodeHealBytes:  s.bytecodeHealBytes,
-	}
 	pending := new(SyncPending)
 	if s.healer != nil {
 		pending.TrienodeHeal = uint64(len(s.healer.trieTasks))
 		pending.BytecodeHeal = uint64(len(s.healer.codeTasks))
 	}
-	return progress, pending
+	return s.extProgress, pending
 }
 
 // cleanAccountTasks removes account range retrieval tasks that have already been