[Zlib-devel] known bugs in distance-checking code?

[Greg Roelofs]

Are we certain the following two changes were themselves valid?

   - Perform more rigorous check for distance-too-far in inffast.c
   - Make inflate distance-too-far checks more rigorous

(from 1.2.0.5 and 1.2.0.4, respectively).  Someone reported a pile
of scanned PNGs (still unknown encoding software), most of which
fail in zlib 1.2.x with "invalid distance too far back."  Here's
an example:

	http://messy.desk.pl/mw/0000/mw__0020.png

A very similar image works fine:

	http://messy.desk.pl/mw/0000/mw__0021.png

There are no obvious errors in the image as decoded by 1.1.4, so
I'm wondering if the check itself might be too stringent?

Greg