From 15be763bb36b6b6b4fc2477c00b1a47eec8cdebd Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Wed, 14 Jul 2021 10:00:25 +0300
Subject: [PATCH] vm: limit POW, fix #2060

Calculating pow(pow(2, 255), 0xffffffff) takes unknown amount of time. See
also neo-project/neo-vm#422.
---
 pkg/vm/vm.go      | 2 +-
 pkg/vm/vm_test.go | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 7ae6d5cdf..09c00699d 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -918,7 +918,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 	case opcode.POW:
 		exp := v.estack.Pop().BigInt()
 		a := v.estack.Pop().BigInt()
-		if ei := exp.Int64(); !exp.IsInt64() || ei > math.MaxInt32 || ei < 0 {
+		if ei := exp.Int64(); !exp.IsInt64() || ei > maxSHLArg || ei < 0 {
 			panic("invalid exponent")
 		}
 		v.estack.PushVal(new(big.Int).Exp(a, exp, nil))
diff --git a/pkg/vm/vm_test.go b/pkg/vm/vm_test.go
index 484b3cda1..b497ffc9b 100644
--- a/pkg/vm/vm_test.go
+++ b/pkg/vm/vm_test.go
@@ -6,7 +6,6 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
-	"math"
 	"math/big"
 	"math/rand"
 	"testing"
@@ -719,7 +718,7 @@ func TestPOW(t *testing.T) {
 	t.Run("good, negative, odd", getTestFuncForVM(prog, -8, -2, 3))
 	t.Run("zero", getTestFuncForVM(prog, 1, 3, 0))
 	t.Run("negative exponent", getTestFuncForVM(prog, nil, 3, -1))
-	t.Run("too big exponent", getTestFuncForVM(prog, nil, 1, math.MaxInt32+1))
+	t.Run("too big exponent", getTestFuncForVM(prog, nil, 1, maxSHLArg+1))
 }
 
 func TestSQRT(t *testing.T) {