parser: validate invalid ASCII control characters

parser.go

@@ -558,15 +558,11 @@ func (p *parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 		return nil, nil, nil, newDecodeError(str[verr.Index:verr.Index+verr.Size], "invalid UTF-8")
 	}
 
-	i = escaped
-
 	var builder bytes.Buffer
-	// grow?
-	builder.Write(token[startIdx:i])
 
 	// The scanner ensures that the token starts and ends with quotes and that
 	// escapes are balanced.
-	for ; i < len(token)-3; i++ {
+	for i < len(token)-3 {
 		c := token[i]
 
 		//nolint:nestif
@@ -584,7 +580,7 @@ func (p *parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 						break
 					}
 				}
-
+				i++
 				continue
 			}
 
@@ -623,8 +619,14 @@ func (p *parser) parseMultilineBasicString(b []byte) ([]byte, []byte, []byte, er
 			default:
 				return nil, nil, nil, newDecodeError(token[i:i+1], "invalid escaped character %#U", c)
 			}
+			i++
 		} else {
-			builder.WriteByte(c)
+			size := utf8ValidNext(token[i:])
+			if size == 0 {
+				return nil, nil, nil, newDecodeError(token[i:i+1], "invalid character %#U", c)
+			}
+			builder.Write(token[i : i+size])
+			i += size
 		}
 	}
 
@@ -731,15 +733,13 @@ func (p *parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 		return nil, nil, nil, newDecodeError(str[verr.Index:verr.Index+verr.Size], "invalid UTF-8")
 	}
 
-	i := escaped
+	i := startIdx
 
 	var builder bytes.Buffer
-	// grow?
-	builder.Write(token[startIdx:i])
 
 	// The scanner ensures that the token starts and ends with quotes and that
 	// escapes are balanced.
-	for ; i < len(token)-1; i++ {
+	for i < len(token)-1 {
 		c := token[i]
 		if c == '\\' {
 			i++
@@ -777,8 +777,14 @@ func (p *parser) parseBasicString(b []byte) ([]byte, []byte, []byte, error) {
 			default:
 				return nil, nil, nil, newDecodeError(token[i:i+1], "invalid escaped character %#U", c)
 			}
+			i++
 		} else {
-			builder.WriteByte(c)
+			size := utf8ValidNext(token[i:])
+			if size == 0 {
+				return nil, nil, nil, newDecodeError(token[i:i+1], "invalid character %#U", c)
+			}
+			builder.Write(token[i : i+size])
+			i += size
 		}
 	}
 

unmarshaler_test.go

@@ -2113,6 +2113,66 @@ world'`,
 	}
 }
 
+func TestASCIIControlCharacters(t *testing.T) {
+	invalidCharacters := []byte{0x7F}
+	for c := byte(0x0); c <= 0x08; c++ {
+		invalidCharacters = append(invalidCharacters, c)
+	}
+	for c := byte(0x0B); c <= 0x0C; c++ {
+		invalidCharacters = append(invalidCharacters, c)
+	}
+	for c := byte(0x0E); c <= 0x1F; c++ {
+		invalidCharacters = append(invalidCharacters, c)
+	}
+
+	type stringType struct {
+		Delimiter string
+		CanEscape bool
+	}
+
+	stringTypes := map[string]stringType{
+		"basic":            {Delimiter: "\"", CanEscape: true},
+		"basicMultiline":   {Delimiter: "\"\"\"", CanEscape: true},
+		"literal":          {Delimiter: "'", CanEscape: false},
+		"literalMultiline": {Delimiter: "'''", CanEscape: false},
+	}
+
+	checkError := func(t *testing.T, input []byte) {
+		t.Helper()
+		m := map[string]interface{}{}
+		err := toml.Unmarshal(input, &m)
+		require.Error(t, err)
+
+		var de *toml.DecodeError
+		if !errors.As(err, &de) {
+			t.Fatalf("err should have been a *toml.DecodeError, but got %s (%T)", err, err)
+		}
+	}
+
+	for name, st := range stringTypes {
+		t.Run(name, func(t *testing.T) {
+			for _, c := range invalidCharacters {
+				name := fmt.Sprintf("%2X", c)
+				t.Run(name, func(t *testing.T) {
+					data := []byte("A = " + st.Delimiter + string(c) + st.Delimiter)
+					checkError(t, data)
+
+					if st.CanEscape {
+						t.Run("withEscapeBefore", func(t *testing.T) {
+							data := []byte("A = " + st.Delimiter + "\\t" + string(c) + st.Delimiter)
+							checkError(t, data)
+						})
+						t.Run("withEscapeAfter", func(t *testing.T) {
+							data := []byte("A = " + st.Delimiter + string(c) + "\\t" + st.Delimiter)
+							checkError(t, data)
+						})
+					}
+				})
+			}
+		})
+	}
+}
+
 //nolint:funlen
 func TestLocalDateTime(t *testing.T) {
 	examples := []struct {
@@ -2268,6 +2328,13 @@ xz_hash = "1a48f723fea1f17d786ce6eadd9d00914d38062d28fd9c455ed3c3801905b388"
 	require.Equal(t, expected, dist)
 }
 
+func TestIssue631(t *testing.T) {
+	v := map[string]interface{}{}
+
+	err := toml.Unmarshal([]byte("\"\\b\u007f\"= 2"), &v)
+	require.Error(t, err)
+}
+
 //nolint:funlen
 func TestDecoderStrict(t *testing.T) {
 	examples := []struct {