Hello Jay
Sergey has suggested a valid point- If the CRC was generated with incorrect
chunk data, the approach I suggested will succeed and we would still end up in
the exception within the parse_<chunk> methods. Hence going by if (...) checks
is appropriate.
Few minor corrections to the webrev.01 are as follows:
. Correction to the subtraction value from -2 to -1 in the following lines
The original code had -2 because, one extra Unsigned byte was getting read
prior to the size calculation.
The current changes advance the calculation by a few lines ahead of reading
extra UnsignedByte.
431 int compressedProfileLength = chunkLength - keyword.length()
- 2;
671 int textLength = chunkLength - keyword.length() - 2;
. The result of these two operations are not the same due to the order of
execution.
If you had checked the logic and corrected the usage, it should be fine.
// Original code
518 chunkLength -= metadata.sPLT_paletteName.length() + 1;
// Code in the webrev
526 int remainingChunkLength = chunkLength -
527 metadata.sPLT_paletteName.length() + 1;
. All the if conditions in the proposed fix check whether remSize < 0. I
believe, we will need size "<=" 0 check.
Reason is that new <Type>[0] will succeed but subsequent read with
stream.read* method will throw "ArrayIndexOutOfBounds: 0" exception.
Thank you
Have a good day
Prahalad N.
-----Original Message-----
From: Sergey Bylokhov
Sent: Thursday, January 25, 2018 5:44 AM
To: Prahalad Kumar Narayanan; Jayathirth D V; 2d-dev
Subject: Re: [OpenJDK 2D-Dev] [11] RFR JDK-8191023: PngReader throws
NegativeArraySizeException when keyword length exceeds chunk size
On 22/01/2018 23:17, Prahalad Kumar Narayanan wrote:
> My suggestion was to -
> . 'Generate' CRC from Chunk data and compare it with the retrieved value at
> Line 731 'before' proceeding to process any of the chunks.
> . In mal-formed chunks (corrupted chunk length /or chunk data), the CRC check
> will fail thus giving an effective way to identify a valid chunk.
> . Many of the if (...) conditions that 've been added to parse_<Chunk>
> methods can be avoided with CRC check done upfront.
Is it possible that CRC will be broken/malformed as well as a chunk data?(For
example if it is generated on top of incorrect data?), if yes then we should
check the data itself for correct/incorrect values.
--
Best regards, Sergey.
