Cast Overflow at FastHufDecoder (72375479)

[Google-Autofuzz]

Hello OpenEXR team,

As part of our fuzzing efforts at Google, we have identified an issue affecting
OpenEXR (tested with revision develop 165dcea).

To reproduce, we are attaching a Dockerfile which compiles the project with
LLVM, taking advantage of the sanitizers that it offers. More information about
how to use the attached Dockerfile can be found here:
https://docs.docker.com/engine/reference/builder/

TL;DR instructions:

• mkdir project
• cp Dockerfile /path/to/project
• docker build --no-cache /path/to/project
• docker run -it image_id_from_docker_build

From another terminal, outside the container:
docker cp /path/to/attached/reproducer running_container_hostname:/fuzzing/reproducer
(reference: https://docs.docker.com/engine/reference/commandline/cp/)

And, back inside the container:
/fuzzing/repro.sh /fuzzing/reproducer

Alternatively, and depending on the bug, you could use gcc, valgrind or other
instrumentation tools to aid in the investigation. The sanitizer error that we
encountered is here:

ImfFastHuf.cpp:220:30: runtime error: value -inf is outside the range of representable values of type 'unsigned long'
SUMMARY: AddressSanitizer: undefined-behavior ImfFastHuf.cpp:220:30 in 

We will gladly work with you so you can successfully confirm and reproduce this
issue. Do let us know if you have any feedback surrounding the documentation.

Once you have reproduced the issue, we'd appreciate to learn your expected
timeline for an update to be released. With any fix, please attribute the report
to "Google Autofuzz project".

We are also pleased to inform you that your project is eligible for inclusion to
the OSS-Fuzz project, which can provide additional continuous fuzzing, and
encourage you to investigate integration options.

Don't hesitate to let us know if you have any questions!

Google AutoFuzz Team
artifacts_72375479.zip

[peterhillman]

I can no longer reproduce the -inf. Perhaps recent changes to ImfFastHuf changed something.

In any case I believe there is nothing that needed fixing here. Undefined values could be written into arrays, but an exception is thrown before those values are used anywhere, since the data is detected as being corrupt.