[OpenJDK 2D-Dev] [12] RFR JDK-8211422: Reading PNG with corrupt CRC for IEND chunk throws IIOException

Jayathirth Rao jayathirth.d.v at oracle.com
Tue Oct 23 13:38:41 UTC 2018

Hello All,
Please review the following fix in JDK12:
Bug : https://bugs.openjdk.java.net/browse/JDK-8211422 <https://bugs.openjdk.java.net/browse/JDK-8211422> 
Webrev: http://cr.openjdk.java.net/~jdv/8211422/webrev.00/ <http://cr.openjdk.java.net/~jdv/8211422/webrev.00/> 
Issue : When we try to read PNG image with corrupt/no 4 byte CRC data for IEND chunk we throw IIOException. We see this issue only after JDK-8164971 <https://bugs.openjdk.java.net/browse/JDK-8164971>.
Root cause : In JDK-8164971 <https://bugs.openjdk.java.net/browse/JDK-8164971> fix we made changes to continue reading metadata until we reach IEND chunk. Before JDK-8164971 <https://bugs.openjdk.java.net/browse/JDK-8164971> change we used to stop reading metadata as soon as we hit first IDAT chunk. According to PNG spec there can be more than one IDAT chunk/ more headers after IDAT chunk. So we need to read metadata until we hit IEND chunk. But in case of this bug we have IEND chunk but it has corrupt/no CRC chunk, so we throw IIOException(According to PNG spec every PNG chunk should contain 4 byte CRC). But lot of other decoders accept these kind of images which has no CRC chunk for IEND chunk. 
Solution : There is no need to verify CRC for IEND chunk(Chunk data length for IEND is 0). Stop reading metadata once we hit Chunk type info for IEND chunk.
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