ZLib VS libdeflate

So the real issue here is that the lack of tree validation before the tree construction, I believe. I'm surprised that this check was not yet implemented (I actually checked libwebp to make sure that I was missing one). Given this blind spot, an automated test based on the domain knowledge is likely useless to catch this bug.

[1] https://github.com/madler/zlib/blob/master/examples/enough.c

In the source code of the Node.js opensource project, lib folder contains JavaScript code, mostly wrappers over C++ and function definitions. On the contrary, src folder contains C++ implementations of the functions, which pulls dependencies from the V8 project, the libuv project, the zlib project, the llhttp project, and many more - which are all placed at the deps folder.

A minimal viable Deflate decompressor is not exactly complex[1], although slower than mainline zlib.

[1] https://github.com/madler/zlib/tree/master/contrib/puff

ZLibrary not zlib for anyone worried about archiving algorithms. https://zlib.net/ and all the Linux repositories are safe (AFAIK).

>The following is my educated guess at what to do next and I am a week-end warrior programmer at best. If someone with more experience comments, I would listen to them over me< If you have no programming experience, this may be a lost cause. It looks like the save file has a header area followed by a list of "zlib" compressed chunks. zlib.net may have a program that can open the save file and let you see the raw information inside it. Something after the header is garbled and it is preventing Save-Editors from decompressing that chunk OR from parsing what is inside of it. If you are lucky, the garbled bit will jump out at you and you can repair it.

These appears to be the relevant changes:

2022-07-30: https://github.com/madler/zlib/commit/eff308af425b67093bab25...

2022-08-08: https://github.com/madler/zlib/commit/1eb7682f845ac9e9bf9ae3...

The second commit definitely fixed a null pointer dereference, I am not sure if the CVE is referencing something else that was fixed by the first commit.

It is actually possible to estimate the compression level without actually compressing everything again, because different levels use different strategies which can be identified in some cases. zlib in particular has three strategies [1] and preflate [2] leverages this to store the deflate stream reconstruction data without much bits.

[1] https://github.com/madler/zlib/blob/21767c6/deflate.c#L134-L...

[2] https://github.com/deus-libri/preflate/blob/master/preflate_...

It's still a heap of old school C spaghetti https://github.com/madler/zlib/commit/eff308af425b67093bab25...

zune-inflate is a port of libdeflate to safe Rust.

> The QOI benchmarks shows it only lagging a small bit behind PNG in compression ratio, while performing much faster (multiples) in both encoding and decoding.

Presumably that’s with stock libpng, which uses zlib. I wonder if anyone tried patching it to use the substantially faster (on x86) libdeflate[1] instead? It doesn’t do streaming, but you shouldn’t really need it for PNG textures.

[1] https://github.com/ebiggers/libdeflate

Eric biggers libdeflate https://github.com/ebiggers/libdeflate/blob/master/lib/deflate_decompress.c

Note that libdeflate has used essentially the same method since 2016 (https://github.com/ebiggers/libdeflate/blob/v0.4/lib/adler32...), though I recently switched it to use a slightly different method (https://github.com/ebiggers/libdeflate/blob/v1.12/lib/x86/ad...) that performs more consistently across different families of x86 CPUs.

Going away from Zlib proper but staying with its format, there’s libdeflate[1], an implementation that’s substantially faster on modern machines but can’t stream, and of course Zopfli[2], a glacially slow compressor that’s somewhat better (and occasionally much more so).

[1] https://github.com/ebiggers/libdeflate

[2] https://github.com/google/zopfli