An issue was discovered in the Linux kernel through 4.18.8. The vmacache_flush_all function in mm/vmacache.c mishandles sequence number overflows. An attacker can trigger a use-after-free (and possibly gain privileges) via certain thread creation, map, unmap, invalidation, and dereference operations.
sbeattie | as of 2018-09-26, fixes for this issue are applied to all kernels uploaded to RELEASE-proposed today. and should be released around Monday, Oct 1, 2018.