Limit the number of bytes read by LineReader in Filebeat (#19552)

(cherry picked from commit 0e049f0)

CHANGELOG.next.asciidoc

@@ -247,6 +247,7 @@ field. You can revert this change by configuring tags for the module and omittin
 - Fix memory leak in tcp and unix input sources. {pull}19459[19459]
 - Fix Cisco ASA dissect pattern for 313008 & 313009 messages. {pull}19149[19149]
 - Fix bug with empty filter values in system/service {pull}19812[19812]
+- Fix Filebeat OOMs on very long lines {issue}19500[19500], {pull}19552[19552]
 
 *Heartbeat*
 

filebeat/input/log/harvester.go

@@ -631,6 +631,8 @@ func (h *Harvester) newLogFileReader() (reader.Reader, error) {
 	var r reader.Reader
 	var err error
 
+	logp.Debug("harvester", "newLogFileReader with config.MaxBytes: %d", h.config.MaxBytes)
+
 	// TODO: NewLineReader uses additional buffering to deal with encoding and testing
 	//       for new lines in input stream. Simple 8-bit based encodings, or plain
 	//       don't require 'complicated' logic.
@@ -644,10 +646,17 @@ func (h *Harvester) newLogFileReader() (reader.Reader, error) {
 		return nil, err
 	}
 
+	// Configure MaxBytes limit for EncodeReader as multiplied by 4
+	// for the worst case scenario where incoming UTF32 charchers are decoded to the single byte UTF-8 characters.
+	// This limit serves primarily to avoid memory bload or potential OOM with expectedly long lines in the file.
+	// The further size limiting is performed by LimitReader at the end of the readers pipeline as needed.
+	encReaderMaxBytes := h.config.MaxBytes * 4
+
 	r, err = readfile.NewEncodeReader(reader, readfile.Config{
 		Codec:      h.encoding,
 		BufferSize: h.config.BufferSize,
 		Terminator: h.config.LineTerminator,
+		MaxBytes:   encReaderMaxBytes,
 	})
 	if err != nil {
 		return nil, err

libbeat/reader/readfile/encode.go

@@ -38,6 +38,7 @@ type Config struct {
 	Codec      encoding.Encoding
 	BufferSize int
 	Terminator LineTerminator
+	MaxBytes   int
 }
 
 // New creates a new Encode reader from input reader by applying

libbeat/reader/readfile/line.go

@@ -28,12 +28,15 @@ import (
 	"github.com/elastic/beats/v7/libbeat/logp"
 )
 
+const unlimited = 0
+
 // lineReader reads lines from underlying reader, decoding the input stream
 // using the configured codec. The reader keeps track of bytes consumed
 // from raw input stream for every decoded line.
 type LineReader struct {
 	reader     io.Reader
 	bufferSize int
+	maxBytes   int // max bytes per line limit to avoid OOM with malformatted files
 	nl         []byte
 	decodedNl  []byte
 	inBuffer   *streambuf.Buffer
@@ -62,6 +65,7 @@ func NewLineReader(input io.Reader, config Config) (*LineReader, error) {
 	return &LineReader{
 		reader:     input,
 		bufferSize: config.BufferSize,
+		maxBytes:   config.MaxBytes,
 		decoder:    config.Codec.NewDecoder(),
 		nl:         nl,
 		decodedNl:  terminator,
@@ -121,17 +125,17 @@ func (r *LineReader) advance() error {
 	// Initial check if buffer has already a newLine character
 	idx := r.inBuffer.IndexFrom(r.inOffset, r.nl)
 
-	// fill inBuffer until newline sequence has been found in input buffer
+	// Fill inBuffer until newline sequence has been found in input buffer
 	for idx == -1 {
-		// increase search offset to reduce iterations on buffer when looping
+		// Increase search offset to reduce iterations on buffer when looping
 		newOffset := r.inBuffer.Len() - len(r.nl)
 		if newOffset > r.inOffset {
 			r.inOffset = newOffset
 		}
 
 		buf := make([]byte, r.bufferSize)
 
-		// try to read more bytes into buffer
+		// Try to read more bytes into buffer
 		n, err := r.reader.Read(buf)
 
 		// Appends buffer also in case of err
@@ -140,16 +144,39 @@ func (r *LineReader) advance() error {
 			return err
 		}
 
-		// empty read => return buffer error (more bytes required error)
+		// Empty read => return buffer error (more bytes required error)
 		if n == 0 {
 			return streambuf.ErrNoMoreBytes
 		}
 
 		// Check if buffer has newLine character
 		idx = r.inBuffer.IndexFrom(r.inOffset, r.nl)
+
+		// If max bytes limit per line is set, then drop the lines that are longer
+		if r.maxBytes != 0 {
+			// If newLine is found, drop the lines longer than maxBytes
+			for idx != -1 && idx > r.maxBytes {
+				r.logger.Warnf("Exceeded %d max bytes in line limit, skipped %d bytes line", r.maxBytes, idx)
+				err = r.inBuffer.Advance(idx + len(r.nl))
+				r.inBuffer.Reset()
+				r.inOffset = 0
+				idx = r.inBuffer.IndexFrom(r.inOffset, r.nl)
+			}
+
+			// If newLine is not found and the incoming data buffer exceeded max bytes limit, then skip until the next newLine
+			if idx == -1 && r.inBuffer.Len() > r.maxBytes {
+				skipped, err := r.skipUntilNewLine(buf)
+				if err != nil {
+					r.logger.Error("Error skipping until new line, err:", err)
+					return err
+				}
+				r.logger.Warnf("Exceeded %d max bytes in line limit, skipped %d bytes line", r.maxBytes, skipped)
+				idx = r.inBuffer.IndexFrom(r.inOffset, r.nl)
+			}
+		}
 	}
 
-	// found encoded byte sequence for newline in buffer
+	// Found encoded byte sequence for newline in buffer
 	// -> decode input sequence into outBuffer
 	sz, err := r.decode(idx + len(r.nl))
 	if err != nil {
@@ -158,20 +185,63 @@ func (r *LineReader) advance() error {
 		sz = idx + len(r.nl)
 	}
 
-	// consume transformed bytes from input buffer
+	// Consume transformed bytes from input buffer
 	err = r.inBuffer.Advance(sz)
 	r.inBuffer.Reset()
 
-	// continue scanning input buffer from last position + 1
+	// Continue scanning input buffer from last position + 1
 	r.inOffset = idx + 1 - sz
 	if r.inOffset < 0 {
-		// fix inOffset if newline has encoding > 8bits + firl line has been decoded
+		// Fix inOffset if newline has encoding > 8bits + firl line has been decoded
 		r.inOffset = 0
 	}
 
 	return err
 }
 
+func (r *LineReader) skipUntilNewLine(buf []byte) (int, error) {
+	// The length of the line skipped
+	skipped := r.inBuffer.Len()
+
+	// Clean up the buffer
+	err := r.inBuffer.Advance(skipped)
+	r.inBuffer.Reset()
+
+	// Reset inOffset
+	r.inOffset = 0
+
+	if err != nil {
+		return 0, err
+	}
+
+	// Read until the new line is found
+	for idx := -1; idx == -1; {
+		n, err := r.reader.Read(buf)
+
+		// Check bytes read for newLine
+		if n > 0 {
+			idx = bytes.Index(buf[:n], r.nl)
+
+			if idx != -1 {
+				r.inBuffer.Append(buf[idx+len(r.nl) : n])
+				skipped += idx
+			} else {
+				skipped += n
+			}
+		}
+
+		if err != nil {
+			return skipped, err
+		}
+
+		if n == 0 {
+			return skipped, streambuf.ErrNoMoreBytes
+		}
+	}
+
+	return skipped, nil
+}
+
 func (r *LineReader) decode(end int) (int, error) {
 	var err error
 	buffer := make([]byte, 1024)