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[Winlogbeat] Prevent Winlogbeat from dropping events with invalid XML #11006

Merged
merged 6 commits into from Mar 1, 2019
@@ -174,12 +174,6 @@ func (l *winEventLog) Read() ([]Record, error) {
}

r, err := l.buildRecordFromXML(l.outputBuf.Bytes(), err)
if err != nil {
logp.Err("%s Dropping event. %v", l.logPrefix, err)
incrementMetric(dropReasons, err)
continue
}

r.Offset = checkpoint.EventLogState{
Name: l.channelName,
RecordNumber: r.RecordID,
@@ -231,8 +225,8 @@ func (l *winEventLog) eventHandles(maxRead int) ([]win.EvtHandle, int, error) {

func (l *winEventLog) buildRecordFromXML(x []byte, recoveredErr error) (Record, error) {
e, err := sys.UnmarshalEventXML(x)
if err != nil {
return Record{}, fmt.Errorf("Failed to unmarshal XML='%s'. %v", x, err)
if err != nil && recoveredErr == nil {
recoveredErr = err
}

err = sys.PopulateAccount(&e.User)
@@ -26,7 +26,8 @@ import (
// UnmarshalEventXML unmarshals the given XML into a new Event.
func UnmarshalEventXML(rawXML []byte) (Event, error) {
var event Event
err := xml.Unmarshal(rawXML, &event)
decoder := xml.NewDecoder(newXmlSafeReader(rawXML))
err := decoder.Decode(&event)
return event, err
}

@@ -0,0 +1,78 @@
// 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.

package sys

import (
"bytes"
"fmt"
"io"
"unicode"
"unicode/utf8"
)

// The type xmlSafeReader escapes UTF control characters in the io.Reader
// it wraps, so that it can be fed to Go's xml parser.
// Characters for which `unicode.IsControl` returns true will be output as
// an hexadecimal unicode escape sequence "\\uNNNN".
type xmlSafeReader struct {
inner io.Reader
backing [256]byte
buf []byte
code []byte
}

var _ io.Reader = (*xmlSafeReader)(nil)

func output(n int) (int, error) {
if n == 0 {
return 0, io.EOF
}
return n, nil
}

// Read implements the io.Reader interface.
func (r *xmlSafeReader) Read(d []byte) (n int, err error) {
if len(r.code) > 0 {
n = copy(d, r.code)
r.code = r.code[n:]
return output(n)
}
if len(r.buf) == 0 {
n, _ = r.inner.Read(r.backing[:])
r.buf = r.backing[:n]
}
for i := 0; i < len(r.buf); {
code, size := utf8.DecodeRune(r.buf[i:])
if unicode.IsControl(code) {
n = copy(d, r.buf[:i])
r.buf = r.buf[n+1:]
r.code = []byte(fmt.Sprintf("\\u%04x", code))
m := copy(d[n:], r.code)
r.code = r.code[m:]
return output(n + m)
}
i += size
}
n = copy(d, r.buf)
r.buf = r.buf[n:]
return output(n)
}

func newXmlSafeReader(rawXML []byte) io.Reader {

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@houndci-bot

houndci-bot Mar 1, 2019

func newXmlSafeReader should be newXMLSafeReader

return &xmlSafeReader{inner: bytes.NewReader(rawXML)}
}
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