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vm: handle very big int creation properly

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Determine size as in reference implementation instead of
`big.Int.BitLen()`

Close #1437.
This commit is contained in:
Evgenii Stratonikov 2020-10-06 14:47:55 +03:00
parent 0dcf42ac24
commit 96bca91e4b
3 changed files with 48 additions and 6 deletions
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15
pkg/vm/stackitem/item.go
View file

@ -350,8 +350,19 @@ type BigInteger struct {
// NewBigInteger returns an new BigInteger object.
func NewBigInteger(value *big.Int) *BigInteger {
if value.BitLen() > MaxBigIntegerSizeBits {
panic("integer is too big")
const tooBigErrMsg = "integer is too big"
// There are 2 cases, when `BitLen` differs from actual size:
// 1. Positive integer with highest bit on byte boundary = 1.
// 2. Negative integer with highest bit on byte boundary = 1
// minus some value. (-0x80 -> 0x80, -0x7F -> 0x81, -0x81 -> 0x7FFF).
sz := value.BitLen()
if sz > MaxBigIntegerSizeBits {
panic(tooBigErrMsg)
} else if sz == MaxBigIntegerSizeBits {
if value.Sign() == 1 || value.TrailingZeroBits() != MaxBigIntegerSizeBits-1 {
panic(tooBigErrMsg)
}
}
return &BigInteger{
value: value,

29
pkg/vm/stackitem/item_test.go
View file

@ -4,6 +4,7 @@ import (
"math/big"
"testing"
"github.com/nspcc-dev/neo-go/pkg/encoding/bigint"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)
@ -436,6 +437,34 @@ func TestMarshalJSON(t *testing.T) {
}
}
func TestNewVeryBigInteger(t *testing.T) {
check := func(ok bool, v *big.Int) {
bs := bigint.ToBytes(v)
if ok {
assert.True(t, len(bs)*8 <= MaxBigIntegerSizeBits)
} else {
assert.True(t, len(bs)*8 > MaxBigIntegerSizeBits)
assert.Panics(t, func() { NewBigInteger(v) })
}
}
maxBitSet := big.NewInt(1)
maxBitSet.Lsh(maxBitSet, MaxBigIntegerSizeBits-1)
check(false, maxBitSet)
check(true, new(big.Int).Neg(maxBitSet))
minus1 := new(big.Int).Sub(maxBitSet, big.NewInt(1))
check(true, minus1)
check(true, new(big.Int).Neg(minus1))
plus1 := new(big.Int).Add(maxBitSet, big.NewInt(1))
check(false, plus1)
check(false, new(big.Int).Neg(plus1))
check(false, new(big.Int).Mul(maxBitSet, big.NewInt(2)))
}
func TestDeepCopy(t *testing.T) {
testCases := []struct {
name string

10
pkg/vm/vm_test.go
View file

@ -994,7 +994,7 @@ func TestArith(t *testing.T) {
func TestADDBigResult(t *testing.T) {
prog := makeProgram(opcode.ADD)
runWithArgs(t, prog, nil, getBigInt(stackitem.MaxBigIntegerSizeBits, -1), 1)
runWithArgs(t, prog, nil, getBigInt(stackitem.MaxBigIntegerSizeBits-1, -1), 1) // 0x7FFF...
}
func TestMULBigResult(t *testing.T) {
@ -1035,7 +1035,9 @@ func TestArithNegativeArguments(t *testing.T) {
func TestSUBBigResult(t *testing.T) {
prog := makeProgram(opcode.SUB)
runWithArgs(t, prog, nil, getBigInt(stackitem.MaxBigIntegerSizeBits, -1), -1)
bi := getBigInt(stackitem.MaxBigIntegerSizeBits-1, -1)
runWithArgs(t, prog, new(big.Int).Sub(big.NewInt(-1), bi), -1, bi)
runWithArgs(t, prog, nil, -2, bi)
}
func TestSHR(t *testing.T) {
@ -1198,7 +1200,7 @@ func TestINC(t *testing.T) {
func TestINCBigResult(t *testing.T) {
prog := makeProgram(opcode.INC, opcode.INC)
vm := load(prog)
x := getBigInt(stackitem.MaxBigIntegerSizeBits, -2)
x := getBigInt(stackitem.MaxBigIntegerSizeBits-1, -2)
vm.estack.PushVal(x)
require.NoError(t, vm.Step())
@ -1212,7 +1214,7 @@ func TestINCBigResult(t *testing.T) {
func TestDECBigResult(t *testing.T) {
prog := makeProgram(opcode.DEC, opcode.DEC)
vm := load(prog)
x := getBigInt(stackitem.MaxBigIntegerSizeBits, -2)
x := getBigInt(stackitem.MaxBigIntegerSizeBits-1, -1)
x.Neg(x)
vm.estack.PushVal(x)