[core] fix: block multiple cx xfers per tx

core/vm/contracts_write.go

@@ -283,16 +283,22 @@ func (c *crossShardXferPrecompile) RunWriteCapable(
 	// now do the actual transfer
 	// step 1 -> remove funds from the precompile address
 	evm.Transfer(evm.StateDB, contract.Address(), toAddress, value, types.SubtractionOnly)
-	// step 2 -> make a cross link
-	// note that the transaction hash is added by state_processor.go to this receipt
-	// and that the receiving shard does not care about the `From` but we use the original
-	// instead of the precompile address for consistency
-	evm.CXReceipt = &types.CXReceipt{
-		From:      fromAddress,
-		To:        &toAddress,
-		ShardID:   fromShardID,
-		ToShardID: toShardID,
-		Amount:    value,
+	// make sure that cxreceipt is already nil to prevent multiple calls to the precompile
+	// in the same transaction
+	if evm.CXReceipt == nil {
+		// step 2 -> make a cross link
+		// note that the transaction hash is added by state_processor.go to this receipt
+		// and that the receiving shard does not care about the `From` but we use the original
+		// instead of the precompile address for consistency
+		evm.CXReceipt = &types.CXReceipt{
+			From:      fromAddress,
+			To:        &toAddress,
+			ShardID:   fromShardID,
+			ToShardID: toShardID,
+			Amount:    value,
+		}
+	} else {
+		return nil, errors.New("cannot call cross shard precompile again in same tx")
 	}
 	return nil, nil
 }

core/vm/contracts_write_test.go

@@ -3,7 +3,6 @@ package vm
 import (
 	"bytes"
 	"errors"
-	"fmt"
 	"math/big"
 	"testing"
 
@@ -66,7 +65,7 @@ func CalculateMigrationGasFn() CalculateMigrationGasFunc {
 }
 
 func testWriteCapablePrecompile(test writeCapablePrecompileTest, t *testing.T, env *EVM, p WriteCapablePrecompiledContract) {
-	t.Run(fmt.Sprintf("%s", test.name), func(t *testing.T) {
+	t.Run(test.name, func(t *testing.T) {
 		contract := NewContract(AccountRef(common.HexToAddress("1337")), AccountRef(common.HexToAddress("1338")), test.value, 0)
 		gas, err := p.RequiredGas(env, contract, test.input)
 		if err != nil {