This commit fixes a potential denial of service vulnerability in logr…

…us.Writer() that could be triggered by logging text longer than 64kb without newlines. Previously, the bufio.Scanner used by Writer() would hang indefinitely when reading such text without newlines, causing the application to become unresponsive.

writer.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"io"
 	"runtime"
+	"strings"
 )
 
 // Writer at INFO level. See WriterLevel for details.
@@ -20,15 +21,18 @@ func (logger *Logger) WriterLevel(level Level) *io.PipeWriter {
 	return NewEntry(logger).WriterLevel(level)
 }
 
+// Writer returns an io.Writer that writes to the logger at the info log level
 func (entry *Entry) Writer() *io.PipeWriter {
 	return entry.WriterLevel(InfoLevel)
 }
 
+// WriterLevel returns an io.Writer that writes to the logger at the given log level
 func (entry *Entry) WriterLevel(level Level) *io.PipeWriter {
 	reader, writer := io.Pipe()
 
 	var printFunc func(args ...interface{})
 
+	// Determine which log function to use based on the specified log level
 	switch level {
 	case TraceLevel:
 		printFunc = entry.Trace
@@ -48,23 +52,50 @@ func (entry *Entry) WriterLevel(level Level) *io.PipeWriter {
 		printFunc = entry.Print
 	}
 
+	// Start a new goroutine to scan the input and write it to the logger using the specified print function.
+	// It splits the input into chunks of up to 64KB to avoid buffer overflows.
 	go entry.writerScanner(reader, printFunc)
+
+	// Set a finalizer function to close the writer when it is garbage collected
 	runtime.SetFinalizer(writer, writerFinalizer)
 
 	return writer
 }
 
+// writerScanner scans the input from the reader and writes it to the logger
 func (entry *Entry) writerScanner(reader *io.PipeReader, printFunc func(args ...interface{})) {
 	scanner := bufio.NewScanner(reader)
+
+	// Set the buffer size to the maximum token size to avoid buffer overflows
+	scanner.Buffer(make([]byte, bufio.MaxScanTokenSize), bufio.MaxScanTokenSize)
+
+	// Define a split function to split the input into chunks of up to 64KB
+	chunkSize := 64 * 1024 // 64KB
+	splitFunc := func(data []byte, atEOF bool) (int, []byte, error) {
+		if len(data) > chunkSize {
+			return chunkSize, data[:chunkSize], nil
+		}
+		return 0, nil, nil
+	}
+
+	//Use the custom split function to split the input
+	scanner.Split(splitFunc)
+
+	// Scan the input and write it to the logger using the specified print function
 	for scanner.Scan() {
-		printFunc(scanner.Text())
+		printFunc(strings.TrimRight(scanner.Text(), "\r\n"))
 	}
+
+	// If there was an error while scanning the input, log an error
 	if err := scanner.Err(); err != nil {
 		entry.Errorf("Error while reading from Writer: %s", err)
 	}
+
+	// Close the reader when we are done
 	reader.Close()
 }
 
+// WriterFinalizer is a finalizer function that closes then given writer when it is garbage collected
 func writerFinalizer(writer *io.PipeWriter) {
 	writer.Close()
 }