The Linux kernel before 4.8 allows local users to bypass ASLR on setuid programs (such as /bin/su) because install_exec_creds() is called too late in load_elf_binary() in fs/binfmt_elf.c, and thus the ptrace_may_access() check has a race condition when reading /proc/pid/stat.
https://usn.ubuntu.com/4008-3/
https://usn.ubuntu.com/4008-2/
https://usn.ubuntu.com/4008-1/
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00039.html