native: drop Refuel method from GAS

It can be used to attack the network (amplifying DOS), so it's broken
beyond repair. See also neo-project/neo#2560 and neo-project/neo#2561.

pkg/compiler/native_test.go

@@ -121,9 +121,7 @@ func TestNativeHelpersCompile(t *testing.T) {
 		{"unregisterCandidate", []string{pub}},
 		{"getAccountState", []string{u160}},
 	}, nep17TestCases...))
-	runNativeTestCases(t, cs.GAS.ContractMD, "gas", append([]nativeTestCase{
-		{"refuel", []string{u160, "123"}},
-	}, nep17TestCases...))
+	runNativeTestCases(t, cs.GAS.ContractMD, "gas", nep17TestCases)
 	runNativeTestCases(t, cs.Oracle.ContractMD, "oracle", []nativeTestCase{
 		{"getPrice", nil},
 		{"request", []string{`"url"`, "nil", `"callback"`, "nil", "123"}},

pkg/core/interop_system_test.go

@@ -683,10 +683,6 @@ func getTestContractState(bc *Blockchain) (*state.Contract, *state.Contract) {
 	emit.Opcodes(w.BinWriter, opcode.CALLT, 1, 0, opcode.RET)
 	callT2Off := w.Len()
 	emit.Opcodes(w.BinWriter, opcode.CALLT, 0, 0, opcode.RET)
-	refuelOff := w.Len()
-	emit.Opcodes(w.BinWriter, opcode.PUSH2, opcode.PACK)
-	emit.AppCallNoArgs(w.BinWriter, bc.contracts.GAS.Hash, "refuel", callflag.States|callflag.AllowNotify)
-	emit.Opcodes(w.BinWriter, opcode.DROP)
 	burnGasOff := w.Len()
 	emit.Syscall(w.BinWriter, interopnames.SystemRuntimeBurnGas)
 	emit.Opcodes(w.BinWriter, opcode.RET)
@@ -859,18 +855,8 @@ func getTestContractState(bc *Blockchain) (*state.Contract, *state.Contract) {
 			},
 			ReturnType: smartcontract.VoidType,
 		},
-		{
-			Name:   "refuelGas",
-			Offset: refuelOff,
-			Parameters: []manifest.Parameter{
-				manifest.NewParameter("account", smartcontract.Hash160Type),
-				manifest.NewParameter("gasRefuel", smartcontract.IntegerType),
-				manifest.NewParameter("gasBurn", smartcontract.IntegerType),
-			},
-			ReturnType: smartcontract.VoidType,
-		},
 	}
-	m.Permissions = make([]manifest.Permission, 3)
+	m.Permissions = make([]manifest.Permission, 2)
 	m.Permissions[0].Contract.Type = manifest.PermissionHash
 	m.Permissions[0].Contract.Value = bc.contracts.NEO.Hash
 	m.Permissions[0].Methods.Add("balanceOf")
@@ -879,10 +865,6 @@ func getTestContractState(bc *Blockchain) (*state.Contract, *state.Contract) {
 	m.Permissions[1].Contract.Value = util.Uint160{}
 	m.Permissions[1].Methods.Add("method")
 
-	m.Permissions[2].Contract.Type = manifest.PermissionHash
-	m.Permissions[2].Contract.Value = bc.contracts.GAS.Hash
-	m.Permissions[2].Methods.Add("refuel")
-
 	cs := &state.Contract{
 		ContractBase: state.ContractBase{
 			Hash:     h,

pkg/core/native/native_gas.go

@@ -2,20 +2,15 @@ package native
 
 import (
 	"errors"
-	"fmt"
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/dao"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
-	"github.com/nspcc-dev/neo-go/pkg/core/interop/runtime"
 	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract"
-	"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
-	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
 	"github.com/nspcc-dev/neo-go/pkg/util"
-	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
 // GAS represents GAS native contract.
@@ -45,12 +40,6 @@ func newGAS(init int64) *GAS {
 
 	g.nep17TokenNative = *nep17
 
-	desc := newDescriptor("refuel", smartcontract.VoidType,
-		manifest.NewParameter("account", smartcontract.Hash160Type),
-		manifest.NewParameter("amount", smartcontract.IntegerType))
-	md := newMethodAndPrice(g.refuel, 1<<15, callflag.States|callflag.AllowNotify)
-	g.AddMethod(md, desc)
-
 	return g
 }
 
@@ -85,24 +74,6 @@ func (g *GAS) balanceFromBytes(si *state.StorageItem) (*big.Int, error) {
 	return &acc.Balance, err
 }
 
-func (g *GAS) refuel(ic *interop.Context, args []stackitem.Item) stackitem.Item {
-	acc := toUint160(args[0])
-	gas := toBigInt(args[1])
-
-	if !gas.IsInt64() || gas.Sign() == -1 {
-		panic("invalid GAS value")
-	}
-
-	ok, err := runtime.CheckHashedWitness(ic, acc)
-	if !ok || err != nil {
-		panic(fmt.Errorf("%w: %v", ErrInvalidWitness, err))
-	}
-
-	g.burn(ic, acc, gas)
-	ic.VM.GasLimit += gas.Int64()
-	return stackitem.Null{}
-}
-
 // Initialize initializes GAS contract.
 func (g *GAS) Initialize(ic *interop.Context) error {
 	if err := g.nep17TokenNative.Initialize(ic); err != nil {

pkg/core/native_gas_test.go

@@ -4,74 +4,13 @@ import (
 	"math/big"
 	"testing"
 
-	"github.com/nspcc-dev/neo-go/internal/random"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/trigger"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/nspcc-dev/neo-go/pkg/vm"
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
-	"github.com/nspcc-dev/neo-go/pkg/wallet"
 	"github.com/stretchr/testify/require"
 )
 
-func TestGAS_Refuel(t *testing.T) {
-	bc := newTestChain(t)
-
-	cs, _ := getTestContractState(bc)
-	require.NoError(t, bc.contracts.Management.PutContractState(bc.dao, cs))
-
-	const (
-		sysFee  = 10_000000
-		burnFee = sysFee + 12345678
-	)
-
-	accs := []*wallet.Account{
-		newAccountWithGAS(t, bc),
-		newAccountWithGAS(t, bc),
-	}
-
-	t.Run("good, refuel from self", func(t *testing.T) {
-		before0 := bc.GetUtilityTokenBalance(accs[0].Contract.ScriptHash())
-		aer, err := invokeContractMethodGeneric(bc, sysFee, bc.contracts.GAS.Hash, "refuel",
-			accs[0], accs[0].Contract.ScriptHash(), int64(burnFee))
-		require.NoError(t, err)
-		require.Equal(t, vm.HaltState, aer.VMState)
-
-		after0 := bc.GetUtilityTokenBalance(accs[0].Contract.ScriptHash())
-		tx, _, _ := bc.GetTransaction(aer.Container)
-		require.Equal(t, before0, new(big.Int).Add(after0, big.NewInt(tx.SystemFee+tx.NetworkFee+burnFee)))
-	})
-
-	t.Run("good, refuel from other", func(t *testing.T) {
-		before0 := bc.GetUtilityTokenBalance(accs[0].Contract.ScriptHash())
-		before1 := bc.GetUtilityTokenBalance(accs[1].Contract.ScriptHash())
-		aer, err := invokeContractMethodGeneric(bc, sysFee, cs.Hash, "refuelGas",
-			accs, accs[1].Contract.ScriptHash(), int64(burnFee), int64(burnFee))
-		require.NoError(t, err)
-		require.Equal(t, vm.HaltState, aer.VMState)
-
-		after0 := bc.GetUtilityTokenBalance(accs[0].Contract.ScriptHash())
-		after1 := bc.GetUtilityTokenBalance(accs[1].Contract.ScriptHash())
-
-		tx, _, _ := bc.GetTransaction(aer.Container)
-		require.Equal(t, before0, new(big.Int).Add(after0, big.NewInt(tx.SystemFee+tx.NetworkFee)))
-		require.Equal(t, before1, new(big.Int).Add(after1, big.NewInt(burnFee)))
-	})
-
-	t.Run("bad, invalid witness", func(t *testing.T) {
-		aer, err := invokeContractMethodGeneric(bc, sysFee, cs.Hash, "refuelGas",
-			accs, random.Uint160(), int64(1), int64(1))
-		require.NoError(t, err)
-		require.Equal(t, vm.FaultState, aer.VMState)
-	})
-
-	t.Run("bad, invalid GAS amount", func(t *testing.T) {
-		aer, err := invokeContractMethodGeneric(bc, sysFee, cs.Hash, "refuelGas",
-			accs, accs[0].Contract.ScriptHash(), int64(0), int64(1))
-		require.NoError(t, err)
-		require.Equal(t, vm.FaultState, aer.VMState)
-	})
-}
-
 func TestGAS_Roundtrip(t *testing.T) {
 	bc := newTestChain(t)
 

pkg/interop/native/gas/gas.go

@@ -37,10 +37,3 @@ func Transfer(from, to interop.Hash160, amount int, data interface{}) bool {
 	return contract.Call(interop.Hash160(Hash), "transfer",
 		contract.All, from, to, amount, data).(bool)
 }
-
-// Refuel makes some GAS from the provided account available
-// for the current execution. It represents `refuel` method of GAS native contract.
-func Refuel(from interop.Hash160, amount int) {
-	contract.Call(interop.Hash160(Hash), "refuel",
-		contract.States|contract.AllowNotify, from, amount)
-}