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)
-}