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Prevent zero length values in slices and maps in codec #2819

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merged 5 commits into from
Mar 8, 2024
Merged

Prevent zero length values in slices and maps in codec #2819

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8e72e65
Prevent zero length values in codec
StephenButtolph Mar 6, 2024
36fd2cc
Allow zero length values but prevent them in dynamic environments
StephenButtolph Mar 6, 2024
57f9c5c
reduce diff
StephenButtolph Mar 6, 2024
c9f5d96
fix-reuse
StephenButtolph Mar 6, 2024
d59fa06
add map tests
StephenButtolph Mar 8, 2024
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2 changes: 2 additions & 0 deletions codec/codec.go
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,8 @@ var (
ErrDoesNotImplementInterface = errors.New("does not implement interface")
ErrUnexportedField = errors.New("unexported field")
ErrExtraSpace = errors.New("trailing buffer space")
ErrMarshalZeroLength = errors.New("can't marshal zero length value")
ErrUnmarshalZeroLength = errors.New("can't unmarshal zero length value")
)

// Codec marshals and unmarshals
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25 changes: 25 additions & 0 deletions codec/reflectcodec/type_codec.go
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Expand Up @@ -159,6 +159,10 @@ func (c *genericCodec) size(
return 0, false, err
}

if size == 0 {
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Do we also want to enforce this on reflect.Array?

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or on reflect.Struct for serialized fields?

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on another note, would it make more sense to check this after iterating over each innerItem?

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Originally, this implementation banned zero length structs and zero length arrays (as everything else has a non-zero size). However, we currently use zero length structs in production: https://github.com/ava-labs/avalanchego/blob/master/vms/platformvm/txs/codec.go#L115.

So, rather than preventing 0 length values. We prevent 0 length entries in dynamically allocated structures. (i.e. anything with a length encoded in the format). This ensures that processing is O(n) in the number of bytes (whereas before it could have been O(2^n).

As for if the size should be checked in each innerItem, we don't need to do this. If the size is 0 of an instance, it is guaranteed to always be 0 based on the type (because we don't have optional fields).

return 0, false, fmt.Errorf("can't marshal slice of zero length values: %w", codec.ErrMarshalZeroLength)
}

// For fixed-size types we manually calculate lengths rather than
// processing each element separately to improve performance.
if constSize {
Expand Down Expand Up @@ -235,6 +239,10 @@ func (c *genericCodec) size(
return 0, false, err
}

if keySize == 0 && valueSize == 0 {
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return 0, false, fmt.Errorf("can't marshal map with zero length entries: %w", codec.ErrMarshalZeroLength)
}

switch {
case keyConstSize && valueConstSize:
numElts := value.Len()
Expand Down Expand Up @@ -394,9 +402,13 @@ func (c *genericCodec) marshal(
return p.Err
}
for i := 0; i < numElts; i++ { // Process each element in the slice
startOffset := p.Offset
if err := c.marshal(value.Index(i), p, typeStack); err != nil {
return err
}
if startOffset == p.Offset {
return fmt.Errorf("couldn't marshal slice of zero length values: %w", codec.ErrMarshalZeroLength)
}
}
return nil
case reflect.Array:
Expand Down Expand Up @@ -479,6 +491,8 @@ func (c *genericCodec) marshal(
allKeyBytes := slices.Clone(p.Bytes[startOffset:p.Offset])
p.Offset = startOffset
for _, key := range sortedKeys {
keyStartOffset := p.Offset

// pack key
startIndex := key.startIndex - startOffset
endIndex := key.endIndex - startOffset
Expand All @@ -492,6 +506,9 @@ func (c *genericCodec) marshal(
if err := c.marshal(value.MapIndex(key.key), p, typeStack); err != nil {
return err
}
if keyStartOffset == p.Offset {
return fmt.Errorf("couldn't marshal map with zero length entries: %w", codec.ErrMarshalZeroLength)
}
}

return nil
Expand Down Expand Up @@ -625,9 +642,14 @@ func (c *genericCodec) unmarshal(
zeroValue := reflect.Zero(innerType)
for i := 0; i < numElts; i++ {
value.Set(reflect.Append(value, zeroValue))

startOffset := p.Offset
if err := c.unmarshal(p, value.Index(i), typeStack); err != nil {
return err
}
if startOffset == p.Offset {
return fmt.Errorf("couldn't unmarshal slice of zero length values: %w", codec.ErrUnmarshalZeroLength)
}
}
return nil
case reflect.Array:
Expand Down Expand Up @@ -755,6 +777,9 @@ func (c *genericCodec) unmarshal(
if err := c.unmarshal(p, mapValue, typeStack); err != nil {
return err
}
if keyStartOffset == p.Offset {
return fmt.Errorf("couldn't unmarshal map with zero length entries: %w", codec.ErrUnmarshalZeroLength)
}

// Assign the key-value pair in the map
value.SetMapIndex(mapKey, mapValue)
Expand Down
75 changes: 66 additions & 9 deletions codec/test_codec.go
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Expand Up @@ -36,7 +36,9 @@ var (
TestNilSliceSerialization,
TestEmptySliceSerialization,
TestSliceWithEmptySerialization,
TestSliceWithEmptySerializationOutOfMemory,
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TestSliceWithEmptySerializationError,
TestMapWithEmptySerialization,
TestMapWithEmptySerializationError,
TestSliceTooLarge,
TestNegativeNumbers,
TestTooLargeUnmarshal,
Expand Down Expand Up @@ -731,7 +733,7 @@ func TestEmptySliceSerialization(codec GeneralCodec, t testing.TB) {
require.Equal(val, valUnmarshaled)
}

// Test marshaling slice that is not nil and not empty
// Test marshaling empty slice of zero length structs
func TestSliceWithEmptySerialization(codec GeneralCodec, t testing.TB) {
require := require.New(t)

Expand All @@ -745,9 +747,9 @@ func TestSliceWithEmptySerialization(codec GeneralCodec, t testing.TB) {
require.NoError(manager.RegisterCodec(0, codec))

val := &nestedSliceStruct{
Arr: make([]emptyStruct, 1000),
Arr: make([]emptyStruct, 0),
}
expected := []byte{0x00, 0x00, 0x00, 0x00, 0x03, 0xE8} // codec version (0x00, 0x00) then 1000 for numElts
expected := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00} // codec version (0x00, 0x00) then (0x00, 0x00, 0x00, 0x00) for numElts
result, err := manager.Marshal(0, val)
require.NoError(err)
require.Equal(expected, result)
Expand All @@ -760,10 +762,10 @@ func TestSliceWithEmptySerialization(codec GeneralCodec, t testing.TB) {
version, err := manager.Unmarshal(expected, &unmarshaled)
require.NoError(err)
require.Zero(version)
require.Len(unmarshaled.Arr, 1000)
require.Empty(unmarshaled.Arr)
}

func TestSliceWithEmptySerializationOutOfMemory(codec GeneralCodec, t testing.TB) {
func TestSliceWithEmptySerializationError(codec GeneralCodec, t testing.TB) {
require := require.New(t)

type emptyStruct struct{}
Expand All @@ -776,14 +778,69 @@ func TestSliceWithEmptySerializationOutOfMemory(codec GeneralCodec, t testing.TB
require.NoError(manager.RegisterCodec(0, codec))

val := &nestedSliceStruct{
Arr: make([]emptyStruct, math.MaxInt32),
Arr: make([]emptyStruct, 1),
}
_, err := manager.Marshal(0, val)
require.ErrorIs(err, ErrMaxSliceLenExceeded)
require.ErrorIs(err, ErrMarshalZeroLength)

_, err = manager.Size(0, val)
require.ErrorIs(err, ErrMarshalZeroLength)

b := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x01} // codec version (0x00, 0x00) then (0x00, 0x00, 0x00, 0x01) for numElts

unmarshaled := nestedSliceStruct{}
_, err = manager.Unmarshal(b, &unmarshaled)
require.ErrorIs(err, ErrUnmarshalZeroLength)
}

// Test marshaling empty map of zero length structs
func TestMapWithEmptySerialization(codec GeneralCodec, t testing.TB) {
require := require.New(t)

type emptyStruct struct{}

manager := NewDefaultManager()
require.NoError(manager.RegisterCodec(0, codec))

val := make(map[emptyStruct]emptyStruct)
expected := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00} // codec version (0x00, 0x00) then (0x00, 0x00, 0x00, 0x00) for numElts
result, err := manager.Marshal(0, val)
require.NoError(err)
require.Equal(expected, result)

bytesLen, err := manager.Size(0, val)
require.NoError(err)
require.Equal(6, bytesLen) // 2 byte codec version + 4 byte length prefix
require.Len(result, bytesLen)

var unmarshaled map[emptyStruct]emptyStruct
version, err := manager.Unmarshal(expected, &unmarshaled)
require.NoError(err)
require.Zero(version)
require.Empty(unmarshaled)
}

func TestMapWithEmptySerializationError(codec GeneralCodec, t testing.TB) {
require := require.New(t)

type emptyStruct struct{}

manager := NewDefaultManager()
require.NoError(manager.RegisterCodec(0, codec))

val := map[emptyStruct]emptyStruct{
{}: {},
}
_, err := manager.Marshal(0, val)
require.ErrorIs(err, ErrMarshalZeroLength)

_, err = manager.Size(0, val)
require.ErrorIs(err, ErrMarshalZeroLength)

b := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x01} // codec version (0x00, 0x00) then (0x00, 0x00, 0x00, 0x01) for numElts

var unmarshaled map[emptyStruct]emptyStruct
_, err = manager.Unmarshal(b, &unmarshaled)
require.ErrorIs(err, ErrUnmarshalZeroLength)
}

func TestSliceTooLarge(codec GeneralCodec, t testing.TB) {
Expand Down
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