The waitid implementation in kernel/exit.c in the Linux kernel through 4.13.4 accesses rusage data structures in unintended cases, which allows local users to obtain sensitive information, and bypass the KASLR protection mechanism, via a crafted system call.
https://twitter.com/grsecurity/status/914079864478666753
https://twitter.com/_argp/status/914021130712870912
https://grsecurity.net/~spender/exploits/wait_for_kaslr_to_be_effective.c
https://github.com/torvalds/linux/commit/6c85501f2fabcfc4fc6ed976543d252c4eaf4be9