PngReader: NegativeArraySizeException in parse_zTXt_chunk when keyword length exceeds chunk size

FULL PRODUCT VERSION :
- OpenJDK Runtime Environment (build 9.0.1+11)
- Java(TM) SE Runtime Environment (build 10-ea+30)

ADDITIONAL OS VERSION INFORMATION :
Ubuntu Linux 64-bit

A DESCRIPTION OF THE PROBLEM :
The ImageReader com.sun.imageio.plugins.png.PNGImageReader throws a NegativeArraySizeException when attempting to read malformed PNG image files with zTXt sections containing keywords where a terminating null byte is not found within the length of the zTXt chunk.


This bug was found using AFL + JQF.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run the test program attached below. Note: This issue only arises when the ImageReader's "readMetaData" is set to "true".

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
An IOException should be thrown (e.g. javax.imagio.IIOException).
ACTUAL -
A java.lang.NegativeArraySizeException is thrown.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.NegativeArraySizeException
at java.desktop/com.sun.imageio.plugins.png.PNGImageReader.parse_zTXt_chunk(PNGImageReader.java:660)
at java.desktop/com.sun.imageio.plugins.png.PNGImageReader.readMetadata(PNGImageReader.java:817)
at java.desktop/com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1310)
at java.desktop/com.sun.imageio.plugins.png.PNGImageReader.read(PNGImageReader.java:1674)
at java.desktop/javax.imageio.ImageReader.read(ImageReader.java:938)
at PngReaderZtxtChunkSizeIssue.main(PngReaderZtxtChunkSizeIssue.java:26

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.util.Base64;
import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;

public class PngReaderZtxtChunkSizeIssue {

    // PNG image test case (encoded as base64)
    private static String inputImageBase64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCA" +
        "AAAAA6fptVAAAABHpUWHRhYWFhYWFhYQAAAApJREFUGFdj+A8AAQEBAFpNb/EAAAAASUVORK5CYIIK";

    public static void main(String[] args) throws java.io.IOException {
        // Convert test case into input stream
        byte[] inputBytes = Base64.getDecoder().decode(inputImageBase64);
        InputStream in = new ByteArrayInputStream(inputBytes);

        // Make sure we are testing PNGImageReader
        ImageReader reader = ImageIO.getImageReadersByFormatName("png").next();
        assert reader.getClass().getName().equals("com.sun.imageio.plugins.png.PNGImageReader");

        // Set input and mark ignoreMetadata = false
        reader.setInput(ImageIO.createImageInputStream(in), true, false);

        reader.read(0); // Throws java.lang.NegativeArraySizeException!
        reader.dispose();
    }
}
---------- END SOURCE ----------