A turning point for CVE numbers

udev acts on uevents, which are a userspace interface exposed by the kernel. Some time ago the sequence of events for existing devices was changed in a way that broke pretty much every userspace configuration in existence, so userspace was very much broken. The answer was "shrug, deal with it".

And that's a legitimate answer to give of course, it's their kernel after all. The problem is taking that approach _and_ then going around proudly proclaiming "we do not break userspace".