common/hexutil: reject big integer inputs > 256 bits

This follows the change to common/math big integer parsing in PR #3699.

common/hexutil/hexutil.go

@@ -49,6 +49,7 @@ var (
 	ErrOddLength     = errors.New("hex string has odd length")
 	ErrUint64Range   = errors.New("hex number does not fit into 64 bits")
 	ErrUintRange     = fmt.Errorf("hex number does not fit into %d bits", uintBits)
+	ErrBig256Range   = errors.New("hex number does not fit into 256 bits")
 )
 
 // Decode decodes a hex string with 0x prefix.
@@ -126,11 +127,15 @@ func init() {
 }
 
 // DecodeBig decodes a hex string with 0x prefix as a quantity.
+// Numbers larger than 256 bits are not accepted.
 func DecodeBig(input string) (*big.Int, error) {
 	raw, err := checkNumber(input)
 	if err != nil {
 		return nil, err
 	}
+	if len(raw) > 64 {
+		return nil, ErrBig256Range
+	}
 	words := make([]big.Word, len(raw)/bigWordNibbles+1)
 	end := len(raw)
 	for i := range words {

common/hexutil/hexutil_test.go

@@ -83,6 +83,10 @@ var (
 		{input: `0x01`, wantErr: ErrLeadingZero},
 		{input: `0xx`, wantErr: ErrSyntax},
 		{input: `0x1zz01`, wantErr: ErrSyntax},
+		{
+			input:   `0x10000000000000000000000000000000000000000000000000000000000000000`,
+			wantErr: ErrBig256Range,
+		},
 		// valid
 		{input: `0x0`, want: big.NewInt(0)},
 		{input: `0x2`, want: big.NewInt(0x2)},
@@ -99,6 +103,10 @@ var (
 			input: `0xffffffffffffffffffffffffffffffffffff`,
 			want:  referenceBig("ffffffffffffffffffffffffffffffffffff"),
 		},
+		{
+			input: `0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff`,
+			want:  referenceBig("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"),
+		},
 	}
 
 	decodeUint64Tests = []unmarshalTest{

common/hexutil/json.go

@@ -91,9 +91,12 @@ func UnmarshalJSON(typname string, input, out []byte) error {
 	return nil
 }
 
-// Big marshals/unmarshals as a JSON string with 0x prefix. The zero value marshals as
-// "0x0". Negative integers are not supported at this time. Attempting to marshal them
-// will return an error.
+// Big marshals/unmarshals as a JSON string with 0x prefix.
+// The zero value marshals as "0x0".
+//
+// Negative integers are not supported at this time. Attempting to marshal them will
+// return an error. Values larger than 256bits are rejected by Unmarshal but will be
+// marshaled without error.
 type Big big.Int
 
 // MarshalJSON implements json.Marshaler.
@@ -119,6 +122,9 @@ func (b *Big) UnmarshalJSON(input []byte) error {
 	if err != nil {
 		return err
 	}
+	if len(raw) > 64 {
+		return ErrBig256Range
+	}
 	words := make([]big.Word, len(raw)/bigWordNibbles+1)
 	end := len(raw)
 	for i := range words {

common/hexutil/json_test.go

@@ -130,6 +130,10 @@ var unmarshalBigTests = []unmarshalTest{
 	{input: `"0x01"`, wantErr: ErrLeadingZero},
 	{input: `"0xx"`, wantErr: ErrSyntax},
 	{input: `"0x1zz01"`, wantErr: ErrSyntax},
+	{
+		input:   `"0x10000000000000000000000000000000000000000000000000000000000000000"`,
+		wantErr: ErrBig256Range,
+	},
 
 	// valid encoding
 	{input: `""`, want: big.NewInt(0)},
@@ -148,6 +152,10 @@ var unmarshalBigTests = []unmarshalTest{
 		input: `"0xffffffffffffffffffffffffffffffffffff"`,
 		want:  referenceBig("ffffffffffffffffffffffffffffffffffff"),
 	},
+	{
+		input: `"0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"`,
+		want:  referenceBig("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"),
+	},
 }
 
 func TestUnmarshalBig(t *testing.T) {