Allow rejection of NaN and Inf float values on encode and decode.

Signed-off-by: Ben Luddy <bluddy@redhat.com>

decode.go

@@ -208,6 +208,18 @@ func (e *UnknownFieldError) Error() string {
 	return fmt.Sprintf("cbor: found unknown field at map element index %d", e.Index)
 }
 
+// UnacceptableDataItemError is returned when unmarshaling a CBOR input that contains a data item
+// that is not acceptable to a specific CBOR-based application protocol ("invalid or unexpected" as
+// described in RFC 8949 Section 5 Paragraph 3).
+type UnacceptableDataItemError struct {
+	CBORType string
+	Message  string
+}
+
+func (e UnacceptableDataItemError) Error() string {
+	return fmt.Sprintf("cbor: data item of cbor type %s is not accepted by protocol: %s", e.CBORType, e.Message)
+}
+
 // DupMapKeyMode specifies how to enforce duplicate map key. Two map keys are considered duplicates if:
 //  1. When decoding into a struct, both keys match the same struct field. The keys are also
 //     considered duplicates if neither matches any field and decoding to interface{} would produce
@@ -496,6 +508,43 @@ func (tttam TimeTagToAnyMode) valid() bool {
 	return tttam >= 0 && tttam < maxTimeTagToAnyMode
 }
 
+// NaNDecodeMode specifies how to decode floating-point values (major type 7, additional information
+// 25 through 27) representing NaN (not-a-number).
+type NaNDecodeMode int
+
+const (
+	// NaNDecodeAccept will decode NaN values to Go float32 or float64.
+	NaNDecodeAccept NaNDecodeMode = iota
+
+	// NaNDecodeReject will return an UnacceptableDataItemError on an attempt to decode a NaN value.
+	NaNDecodeReject
+
+	maxNaNDecode
+)
+
+func (ndm NaNDecodeMode) valid() bool {
+	return ndm >= 0 && ndm < maxNaNDecode
+}
+
+// InfDecodeMode specifies how to decode floating-point values (major type 7, additional information
+// 25 through 27) representing positive or negative infinity.
+type InfDecodeMode int
+
+const (
+	// InfDecodeAccept will decode infinite values to Go float32 or float64.
+	InfDecodeAccept InfDecodeMode = iota
+
+	// InfDecodeReject will return an UnacceptableDataItemError on an attempt to decode an
+	// infinite value.
+	InfDecodeReject
+
+	maxInfDecode
+)
+
+func (idm InfDecodeMode) valid() bool {
+	return idm >= 0 && idm < maxInfDecode
+}
+
 // DecOptions specifies decoding options.
 type DecOptions struct {
 	// DupMapKey specifies whether to enforce duplicate map key.
@@ -592,6 +641,14 @@ type DecOptions struct {
 	// TimeTagToAnyMode specifies how to decode CBOR tag 0 and 1 into an empty interface (any).
 	// Based on the specified mode, Unmarshal can return a time.Time value or a time string in a specific format.
 	TimeTagToAny TimeTagToAnyMode
+
+	// NaNDec specifies how to decode floating-point values (major type 7, additional
+	// information 25 through 27) representing NaN (not-a-number).
+	NaNDec NaNDecodeMode
+
+	// InfDec specifies how to decode floating-point values (major type 7, additional
+	// information 25 through 27) representing positive or negative infinity.
+	InfDec InfDecodeMode
 }
 
 // DecMode returns DecMode with immutable options and no tags (safe for concurrency).
@@ -749,6 +806,14 @@ func (opts DecOptions) decMode() (*decMode, error) {
 		return nil, errors.New("cbor: invalid TimeTagToAny " + strconv.Itoa(int(opts.TimeTagToAny)))
 	}
 
+	if !opts.NaNDec.valid() {
+		return nil, errors.New("cbor: invalid NaNDec " + strconv.Itoa(int(opts.NaNDec)))
+	}
+
+	if !opts.InfDec.valid() {
+		return nil, errors.New("cbor: invalid InfDec " + strconv.Itoa(int(opts.InfDec)))
+	}
+
 	dm := decMode{
 		dupMapKey:             opts.DupMapKey,
 		timeTag:               opts.TimeTag,
@@ -769,6 +834,8 @@ func (opts DecOptions) decMode() (*decMode, error) {
 		fieldNameByteString:   opts.FieldNameByteString,
 		unrecognizedTagToAny:  opts.UnrecognizedTagToAny,
 		timeTagToAny:          opts.TimeTagToAny,
+		nanDec:                opts.NaNDec,
+		infDec:                opts.InfDec,
 	}
 
 	return &dm, nil
@@ -841,6 +908,8 @@ type decMode struct {
 	fieldNameByteString   FieldNameByteStringMode
 	unrecognizedTagToAny  UnrecognizedTagToAnyMode
 	timeTagToAny          TimeTagToAnyMode
+	nanDec                NaNDecodeMode
+	infDec                InfDecodeMode
 }
 
 var defaultDecMode, _ = DecOptions{}.decMode()
@@ -867,6 +936,8 @@ func (dm *decMode) DecOptions() DecOptions {
 		FieldNameByteString:   dm.fieldNameByteString,
 		UnrecognizedTagToAny:  dm.unrecognizedTagToAny,
 		TimeTagToAny:          dm.timeTagToAny,
+		NaNDec:                dm.nanDec,
+		InfDec:                dm.infDec,
 	}
 }
 
@@ -1181,12 +1252,21 @@ func (d *decoder) parseToValue(v reflect.Value, tInfo *typeInfo) error { //nolin
 		switch ai {
 		case 25:
 			f := float64(float16.Frombits(uint16(val)).Float32())
+			if err := d.acceptableFloat(f); err != nil {
+				return err
+			}
 			return fillFloat(t, f, v)
 		case 26:
 			f := float64(math.Float32frombits(uint32(val)))
+			if err := d.acceptableFloat(f); err != nil {
+				return err
+			}
 			return fillFloat(t, f, v)
 		case 27:
 			f := math.Float64frombits(val)
+			if err := d.acceptableFloat(f); err != nil {
+				return err
+			}
 			return fillFloat(t, f, v)
 		default: // ai <= 24
 			switch ai {
@@ -1373,10 +1453,19 @@ func (d *decoder) parseToTime() (time.Time, bool, error) {
 		switch ai {
 		case 25:
 			f = float64(float16.Frombits(uint16(val)).Float32())
+			if err := d.acceptableFloat(f); err != nil {
+				return time.Time{}, false, err
+			}
 		case 26:
 			f = float64(math.Float32frombits(uint32(val)))
+			if err := d.acceptableFloat(f); err != nil {
+				return time.Time{}, false,err
+			}
 		case 27:
 			f = math.Float64frombits(val)
+			if err := d.acceptableFloat(f); err != nil {
+				return time.Time{}, false, err
+			}
 		default:
 			return time.Time{}, false, &UnmarshalTypeError{CBORType: t.String(), GoType: typeTime.String()}
 		}
@@ -1617,12 +1706,21 @@ func (d *decoder) parse(skipSelfDescribedTag bool) (interface{}, error) { //noli
 			return nil, nil
 		case 25:
 			f := float64(float16.Frombits(uint16(val)).Float32())
+			if err := d.acceptableFloat(f); err != nil {
+				return nil, err
+			}
 			return f, nil
 		case 26:
 			f := float64(math.Float32frombits(uint32(val)))
+			if err := d.acceptableFloat(f); err != nil {
+				return nil, err
+			}
 			return f, nil
 		case 27:
 			f := math.Float64frombits(val)
+			if err := d.acceptableFloat(f); err != nil {
+				return nil, err
+			}
 			return f, nil
 		}
 	case cborTypeArray:
@@ -1641,6 +1739,22 @@ func (d *decoder) parse(skipSelfDescribedTag bool) (interface{}, error) { //noli
 	return nil, nil
 }
 
+func (d *decoder) acceptableFloat(f float64) error {
+	switch {
+	case d.dm.nanDec == NaNDecodeReject && math.IsNaN(f):
+		return &UnacceptableDataItemError{
+			CBORType: cborTypePrimitives.String(),
+			Message:  "floating-point NaN",
+		}
+	case d.dm.infDec == InfDecodeReject && math.IsInf(f, 0):
+		return &UnacceptableDataItemError{
+			CBORType: cborTypePrimitives.String(),
+			Message:  "floating-point infinity",
+		}
+	}
+	return nil
+}
+
 // parseByteString parses a CBOR encoded byte string. The returned byte slice
 // may be backed directly by the input. The second return value will be true if
 // and only if the slice is backed by a copy of the input. Callers are