fix(sync-service): prevent underflows (#1015)

* fix(sync-service): prevent underflows

* chore: add changeset

* chore: remove dead confirmation depth

* chore: remove eth1conf depth from rollup config

.changeset/kind-houses-rush.md

+---
+'@eth-optimism/l2geth': patch
+---
+
+fix potential underflow when launching the chain when the last verified index is 0

l2geth/rollup/config.go

@@ -10,8 +10,6 @@ import (
 type Config struct {
 	// Maximum calldata size for a Queue Origin Sequencer Tx
 	MaxCallDataSize int
-	// Number of confs before applying a L1 to L2 tx
-	Eth1ConfirmationDepth uint64
 	// Verifier mode
 	IsVerifier bool
 	// Enable the sync service

l2geth/rollup/sync_service.go

@@ -53,7 +53,6 @@ type SyncService struct {
 	syncing                   atomic.Value
 	chainHeadSub              event.Subscription
 	OVMContext                OVMContext
-	confirmationDepth         uint64
 	pollInterval              time.Duration
 	timestampRefreshThreshold time.Duration
 	chainHeadCh               chan core.ChainHeadEvent
@@ -103,7 +102,6 @@ func NewSyncService(ctx context.Context, cfg Config, txpool *core.TxPool, bc *co
 		cancel:                    cancel,
 		verifier:                  cfg.IsVerifier,
 		enable:                    cfg.Eth1SyncServiceEnable,
-		confirmationDepth:         cfg.Eth1ConfirmationDepth,
 		syncing:                   atomic.Value{},
 		bc:                        bc,
 		txpool:                    txpool,
@@ -244,8 +242,12 @@ func (s *SyncService) initializeLatestL1(ctcDeployHeight *big.Int) error {
 		s.SetLatestL1Timestamp(context.Timestamp)
 		s.SetLatestL1BlockNumber(context.BlockNumber)
 	} else {
+		// Prevent underflows
+		if *index != 0 {
+			*index = *index - 1
+		}
 		log.Info("Found latest index", "index", *index)
-		block := s.bc.GetBlockByNumber(*index - 1)
+		block := s.bc.GetBlockByNumber(*index)
 		if block == nil {
 			block = s.bc.CurrentBlock()
 			idx := block.Number().Uint64()
@@ -254,11 +256,12 @@ func (s *SyncService) initializeLatestL1(ctcDeployHeight *big.Int) error {
 				return fmt.Errorf("Current block height greater than index")
 			}
 			s.SetLatestIndex(&idx)
-			log.Info("Block not found, resetting index", "new", idx, "old", *index-1)
+			log.Info("Block not found, resetting index", "new", idx, "old", *index)
 		}
 		txs := block.Transactions()
 		if len(txs) != 1 {
-			log.Error("Unexpected number of transactions in block: %d", len(txs))
+			log.Error("Unexpected number of transactions in block", "count", len(txs))
+			panic("Cannot recover OVM Context")
 		}
 		tx := txs[0]
 		s.SetLatestL1Timestamp(tx.L1Timestamp())