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fix: account for recursion when stringing to avoid overflow (gnolang#…
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…1315)

Addresses gnolang#1291. This is to fix the issue causing the entire interpreter
process to crash, not the underlying issue that is causing it to panic
in the first place.

---------

Co-authored-by: Morgan <[email protected]>
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@deelawn @thehowl @gfanton
2 people authored and gfanton committed Jan 18, 2024
1 parent 3017762 commit 8cd3a3b
Showing 1 changed file with 153 additions and 21 deletions.
174 changes: 153 additions & 21 deletions gnovm/pkg/gnolang/values_string.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,47 @@ import (
"strings"
)

type protectedStringer interface {
ProtectedString(*seenValues) string
}

// This indicates the maximum ancticipated depth of the stack when printing a Value type.
const defaultSeenValuesSize = 32

type seenValues struct {
values []Value
}

func (sv *seenValues) Put(v Value) {
sv.values = append(sv.values, v)
}

func (sv *seenValues) Contains(v Value) bool {
for _, vv := range sv.values {
if vv == v {
return true
}
}

return false
}

// Pop should be called by using a defer after each Put.
// Consider why this is necessary:
// - we are printing an array of structs
// - each invocation of struct.ProtectedString adds the value to the seenValues
// - without calling Pop before exiting struct.ProtectedString, the next call to
// struct.ProtectedString in the array.ProtectedString loop will not result in the value
// being printed if the value has already been print
// - this is NOT recursion and SHOULD be printed
func (sv *seenValues) Pop() {
sv.values = sv.values[:len(sv.values)-1]
}

func newSeenValues() *seenValues {
return &seenValues{values: make([]Value, 0, defaultSeenValuesSize)}
}

func (v StringValue) String() string {
return strconv.Quote(string(v))
}
Expand All @@ -24,10 +65,21 @@ func (dbv DataByteValue) String() string {
}

func (av *ArrayValue) String() string {
return av.ProtectedString(newSeenValues())
}

func (av *ArrayValue) ProtectedString(seen *seenValues) string {
if seen.Contains(av) {
return fmt.Sprintf("%p", av)
}

seen.Put(av)
defer seen.Pop()

ss := make([]string, len(av.List))
if av.Data == nil {
for i, e := range av.List {
ss[i] = e.String()
ss[i] = e.ProtectedString(seen)
}
// NOTE: we may want to unify the representation,
// but for now tests expect this to be different.
Expand All @@ -41,17 +93,30 @@ func (av *ArrayValue) String() string {
}

func (sv *SliceValue) String() string {
return sv.ProtectedString(newSeenValues())
}

func (sv *SliceValue) ProtectedString(seen *seenValues) string {
if sv.Base == nil {
return "nil-slice"
}

if seen.Contains(sv) {
return fmt.Sprintf("%p", sv)
}

if ref, ok := sv.Base.(RefValue); ok {
return fmt.Sprintf("slice[%v]", ref)
}

seen.Put(sv)
defer seen.Pop()

vbase := sv.Base.(*ArrayValue)
if vbase.Data == nil {
ss := make([]string, sv.Length)
for i, e := range vbase.List[sv.Offset : sv.Offset+sv.Length] {
ss[i] = e.String()
ss[i] = e.ProtectedString(seen)
}
return "slice[" + strings.Join(ss, ",") + "]"
}
Expand All @@ -62,16 +127,40 @@ func (sv *SliceValue) String() string {
}

func (pv PointerValue) String() string {
// NOTE: cannot do below, due to recursion problems.
// TODO: create a different String2(...) function.
// return fmt.Sprintf("&%s", v.TypedValue.String())
return fmt.Sprintf("&%p.(*%s)", pv.TV, pv.TV.T.String())
return pv.ProtectedString(newSeenValues())
}

func (pv PointerValue) ProtectedString(seen *seenValues) string {
if seen.Contains(pv) {
return fmt.Sprintf("%p", &pv)
}

seen.Put(pv)
defer seen.Pop()

// Handle nil TV's, avoiding a nil pointer deref below.
if pv.TV == nil {
return "&<nil>"
}

return fmt.Sprintf("&%s", pv.TV.ProtectedString(seen))
}

func (sv *StructValue) String() string {
return sv.ProtectedString(newSeenValues())
}

func (sv *StructValue) ProtectedString(seen *seenValues) string {
if seen.Contains(sv) {
return fmt.Sprintf("%p", sv)
}

seen.Put(sv)
defer seen.Pop()

ss := make([]string, len(sv.Fields))
for i, f := range sv.Fields {
ss[i] = f.String()
ss[i] = f.ProtectedString(seen)
}
return "struct{" + strings.Join(ss, ",") + "}"
}
Expand Down Expand Up @@ -104,9 +193,21 @@ func (v *BoundMethodValue) String() string {
}

func (mv *MapValue) String() string {
return mv.ProtectedString(newSeenValues())
}

func (mv *MapValue) ProtectedString(seen *seenValues) string {
if mv.List == nil {
return "zero-map"
}

if seen.Contains(mv) {
return fmt.Sprintf("%p", mv)
}

seen.Put(mv)
defer seen.Pop()

ss := make([]string, 0, mv.GetLength())
next := mv.List.Head
for next != nil {
Expand Down Expand Up @@ -177,9 +278,26 @@ func (tv *TypedValue) Sprint(m *Machine) string {
res := m.Eval(Call(Sel(&ConstExpr{TypedValue: *tv}, "Error")))
return res[0].GetString()
}

return tv.ProtectedSprint(newSeenValues(), true)
}

func (tv *TypedValue) ProtectedSprint(seen *seenValues, considerDeclaredType bool) string {
if seen.Contains(tv.V) {
return fmt.Sprintf("%p", tv)
}

// print declared type
if _, ok := tv.T.(*DeclaredType); ok {
return tv.String()
if _, ok := tv.T.(*DeclaredType); ok && considerDeclaredType {
return tv.ProtectedString(seen)
}

// This is a special case that became necessary after adding `ProtectedString()` methods to
// reliably prevent recursive print loops.
if tv.V != nil {
if v, ok := tv.V.(RefValue); ok {
return v.String()
}
}

// otherwise, default behavior.
Expand Down Expand Up @@ -225,9 +343,7 @@ func (tv *TypedValue) Sprint(m *Machine) string {
if tv.V == nil {
return "invalid-pointer"
}
return tv.V.(PointerValue).String()
case *ArrayType, *SliceType, *StructType, *MapType, *TypeType, *NativeType:
return printNilOrValue(tv, tv.V)
return tv.V.(PointerValue).ProtectedString(seen)
case *FuncType:
switch fv := tv.V.(type) {
case nil:
Expand All @@ -253,8 +369,22 @@ func (tv *TypedValue) Sprint(m *Machine) string {
return tv.V.(*PackageValue).String()
case *ChanType:
panic("not yet implemented")
// return tv.V.(*ChanValue).String()
case *TypeType:
return tv.V.(TypeValue).String()
default:
// The remaining types may have a nil value.
if tv.V == nil {
return nilStr + " " + tv.T.String()
}

// *ArrayType, *SliceType, *StructType, *MapType
if ps, ok := tv.V.(protectedStringer); ok {
return ps.ProtectedString(seen)
} else if s, ok := tv.V.(fmt.Stringer); ok {
// *NativeType
return s.String()
}

if debug {
panic(fmt.Sprintf(
"unexpected type %s",
Expand All @@ -265,18 +395,15 @@ func (tv *TypedValue) Sprint(m *Machine) string {
}
}

func printNilOrValue(tv *TypedValue, valueType interface{}) string {
if tv.V == nil {
return nilStr + " " + tv.T.String()
}
return fmt.Sprintf("%v", valueType)
}

// ----------------------------------------
// TypedValue.String()

// For gno debugging/testing.
func (tv TypedValue) String() string {
return tv.ProtectedString(newSeenValues())
}

func (tv TypedValue) ProtectedString(seen *seenValues) string {
if tv.IsUndefined() {
return "(undefined)"
}
Expand Down Expand Up @@ -313,12 +440,17 @@ func (tv TypedValue) String() string {
vs = fmt.Sprintf("%v", tv.GetFloat32())
case Float64Type:
vs = fmt.Sprintf("%v", tv.GetFloat64())
// Complex types that require recusion protection.
default:
vs = nilStr
}
} else {
vs = fmt.Sprintf("%v", tv.V)
vs = tv.ProtectedSprint(seen, false)
if base := baseOf(tv.T); base == StringType || base == UntypedStringType {
vs = strconv.Quote(vs)
}
}

ts := tv.T.String()
return fmt.Sprintf("(%s %s)", vs, ts) // TODO improve
}

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