[winlogbeat] Clean up rune handling (#32198) (#32356)

* Take into account RuneErrors when decoding XML codes

* Add more unit tests

* Parse multibyte utf8 encodings at the end of backing array

(cherry picked from commit 157c327)

Co-authored-by: Marc Guasch <marc-gr@users.noreply.github.com>

libbeat/common/encoding/xml/safe_reader.go

@@ -53,12 +53,22 @@ func (r *SafeReader) Read(d []byte) (n int, err error) {
 		return output(n)
 	}
 	if len(r.buf) == 0 {
-		n, _ = r.inner.Read(r.backing[:])
+		n, _ := r.inner.Read(r.backing[:])
 		r.buf = r.backing[:n]
 	}
 	for i := 0; i < len(r.buf); {
+		if !utf8.FullRune(r.buf[i:]) {
+			n = copy(d, r.buf[:i])
+			rn := copy(r.backing[:], r.buf[i:])
+			nn, err := r.inner.Read(r.backing[rn:])
+			if err != nil && err != io.EOF {
+				return 0, err
+			}
+			r.buf = r.backing[:rn+nn]
+			return output(n)
+		}
 		code, size := utf8.DecodeRune(r.buf[i:])
-		if !unicode.IsSpace(code) && unicode.IsControl(code) {
+		if code == utf8.RuneError || (!unicode.IsSpace(code) && unicode.IsControl(code)) {
 			n = copy(d, r.buf[:i])
 			r.buf = r.buf[n+1:]
 			r.code = []byte(fmt.Sprintf("\\u%04x", code))

libbeat/common/encoding/xml/safe_reader_test.go

@@ -0,0 +1,139 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//go:build !integration
+// +build !integration
+
+package xml
+
+import (
+	"encoding/xml"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInvalidXMLIsSanitized(t *testing.T) {
+	tests := []struct {
+		name  string
+		input []byte
+		want  map[string]interface{}
+		err   error
+	}{
+		{
+			name: "control space",
+			input: []byte(`<person><Name ID="123">John` + "\t" + `
+</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "John",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+		{
+			name:  "crlf",
+			input: []byte(`<person><Name ID="123">John` + "\r\n" + `</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "John",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+		{
+			name:  "single invalid",
+			input: []byte(`<person><Name ID="123">John` + "\x80" + `</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "John\\ufffd",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+		{
+			name:  "double invalid",
+			input: []byte(`<person><Name ID="123">` + "\x80" + `John` + "\x80" + `</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "\\ufffdJohn\\ufffd",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+		{
+			name:  "happy single invalid",
+			input: []byte(`<person><Name ID="123">😊John` + "\x80" + `</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "😊John\\ufffd",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+		{
+			name:  "invalid tag",
+			input: []byte(`<person><Name ID` + "\x80" + `="123">John</Name></person>`),
+			want:  nil,
+			err:   &xml.SyntaxError{Msg: "attribute name without = in element", Line: 1},
+		},
+		{
+			name:  "invalid tag value",
+			input: []byte(`<person><Name ID="` + "\x80" + `123">John</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "John",
+						"ID":    "\\ufffd123",
+					},
+				},
+			},
+		},
+		{
+			name:  "unhappy",
+			input: []byte(`<person><Name ID="123">John is` + strings.Repeat(" ", 223) + ` 😞</Name></person>`),
+			want: map[string]interface{}{
+				"person": map[string]interface{}{
+					"Name": map[string]interface{}{
+						"#text": "John is" + strings.Repeat(" ", 223) + " 😞",
+						"ID":    "123",
+					},
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			d := NewDecoder(NewSafeReader(test.input))
+			out, err := d.Decode()
+			assert.Equal(t, test.err, err)
+			assert.Equal(t, test.want, out)
+		})
+	}
+}