Linux Local Privilege Escalation via SUID /proc/pid/mem Write (zx2c4)

any patch is a bugfix unless you can prove that you do not ever run that code (which realistically means that this only eliminates things that you can compile out of the kernel)

note that is is very possible for bugfixes to contain bugs themselves.

you may try to argue that some patches implement new things, but since (unless you can configure your system to not use the new code) this changes how the existing code works, it has the potential to fix bugs (if by no other means than by accidentally eliminating a potential race condition)