Redis 6.0.9 fixes a potential heap overflow when using a heap allocator other
than jemalloc or glibc's malloc.

When using a system with no malloc_usable_size(), zmalloc_size() assumed
that the heap allocator always returns blocks that are long-padded.

This may not always be the case, and will result with zmalloc_size()
returning a size that is bigger than allocated. At least in one case
this leads to out of bound write, process crash and a potential security
vulnerability.

Effectively this does not affect the vast majority of users, who use
jemalloc or glibc.

https://raw.githubusercontent.com/redis/redis/6.0/00-RELEASENOTES
https://github.com/redis/redis/pull/7963