Heap-buffer-overflow in derive_collocated_motion_vectors

[bobfriesenhahn]

In the course of GraphicsMagick oss-fuzz testing, oss-fuzz issue 382930465 was reported regarding an intermittent "heap buffer overflow" reachable via libheif. The issue may in fact be in libde265, but it is not clear give how ambiguous the oss-fuzz reports are. I tested by hand with the latest libde265 code and valgrind shows many uses of uninitialized data. The uninitialized values are from both heap and stack.

This is the oss-fuzz test-case:

This is valgrind memcheck output produced on my own system:

valgrind.log

[bobfriesenhahn]

While I am not sure if the underlying cause has been rectified, oss-fuzz says that this issue is no longer reproduced. Closing now.