light: fix txpool causes panic on reorgOnNewHead

panic: runtime error: invalid memory address or nil pointer dereference
Mar 04 12:22:51 sf-etclabs sh[26575]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x1c0 pc=0xc5937c]
Mar 04 12:22:51 sf-etclabs sh[26575]: goroutine 57 [running]:
Mar 04 12:22:51 sf-etclabs sh[26575]: github.com/ethereum/go-ethereum/light.(*TxPool).reorgOnNewHead(0xc00038cc60, 0x11a2960, 0xc0204bd920, 0xc0209ec480,
0xc0204bd920, 0xc02096eb00, 0x8)
Mar 04 12:22:51 sf-etclabs sh[26575]:         /root/go/src/github.com/ethereum/go-ethereum/light/txpool.go:230 +0x23c
Mar 04 12:22:51 sf-etclabs sh[26575]: github.com/ethereum/go-ethereum/light.(*TxPool).setNewHead(0xc00038cc60, 0xc0209ec480)
Mar 04 12:22:51 sf-etclabs sh[26575]:         /root/go/src/github.com/ethereum/go-ethereum/light/txpool.go:311 +0x13a
Mar 04 12:22:51 sf-etclabs sh[26575]: github.com/ethereum/go-ethereum/light.(*TxPool).eventLoop(0xc00038cc60)
Mar 04 12:22:51 sf-etclabs sh[26575]:         /root/go/src/github.com/ethereum/go-ethereum/light/txpool.go:292 +0x53
Mar 04 12:22:51 sf-etclabs sh[26575]: created by github.com/ethereum/go-ethereum/light.NewTxPool
Mar 04 12:22:51 sf-etclabs sh[26575]:         /root/go/src/github.com/ethereum/go-ethereum/light/txpool.go:109 +0x3eb

Signed-off-by: meows <b5c6@protonmail.com>

light/txpool.go

@@ -224,30 +224,38 @@ func (pool *TxPool) reorgOnNewHead(ctx context.Context, newHeader *types.Header)
 	txc := make(txStateChanges)
 	oldh := pool.chain.GetHeaderByHash(pool.head)
 	newh := newHeader
-	// find common ancestor, create list of rolled back and new block hashes
 	var oldHashes, newHashes []common.Hash
-	for oldh.Hash() != newh.Hash() {
-		if oldh.Number.Uint64() >= newh.Number.Uint64() {
-			oldHashes = append(oldHashes, oldh.Hash())
-			oldh = pool.chain.GetHeader(oldh.ParentHash, oldh.Number.Uint64()-1)
-		}
-		if oldh.Number.Uint64() < newh.Number.Uint64() {
-			newHashes = append(newHashes, newh.Hash())
-			newh = pool.chain.GetHeader(newh.ParentHash, newh.Number.Uint64()-1)
-			if newh == nil {
-				// happens when CHT syncing, nothing to do
-				newh = oldh
+
+	if oldh != nil {
+		// find common ancestor, create list of rolled back and new block hashes
+		for oldh.Hash() != newh.Hash() {
+			if oldh.Number.Uint64() >= newh.Number.Uint64() {
+				oldHashes = append(oldHashes, oldh.Hash())
+				oldh = pool.chain.GetHeader(oldh.ParentHash, oldh.Number.Uint64()-1)
+			}
+			if oldh.Number.Uint64() < newh.Number.Uint64() {
+				newHashes = append(newHashes, newh.Hash())
+				newh = pool.chain.GetHeader(newh.ParentHash, newh.Number.Uint64()-1)
+				if newh == nil {
+					// happens when CHT syncing, nothing to do
+					newh = oldh
+				}
 			}
 		}
+		if oldh.Number.Uint64() < pool.clearIdx {
+			pool.clearIdx = oldh.Number.Uint64()
+		}
+		// roll back old blocks
+		for _, hash := range oldHashes {
+			pool.rollbackTxs(hash, txc)
+		}
+		pool.head = oldh.Hash()
 	}
-	if oldh.Number.Uint64() < pool.clearIdx {
-		pool.clearIdx = oldh.Number.Uint64()
-	}
-	// roll back old blocks
-	for _, hash := range oldHashes {
-		pool.rollbackTxs(hash, txc)
+
+	if newHeader == nil {
+		return txc, nil
 	}
-	pool.head = oldh.Hash()
+
 	// check mined txs of new blocks (array is in reversed order)
 	for i := len(newHashes) - 1; i >= 0; i-- {
 		hash := newHashes[i]
@@ -365,7 +373,7 @@ func (pool *TxPool) validateTx(ctx context.Context, tx *types.Transaction) error
 	// Check the transaction doesn't exceed the current
 	// block limit gas.
 	header := pool.chain.GetHeaderByHash(pool.head)
-	if header.GasLimit < tx.Gas() {
+	if header != nil && header.GasLimit < tx.Gas() {
 		return core.ErrGasLimit
 	}