ASA-2019-00404 – FreeBSD: Kernel stack disclosure in UFS/FFS

The Berkeley Fast File System (FFS) is an implementation of the UNIX File System (UFS) filesystem used by FreeBSD. A bug causes up to three bytes of kernel stack memory to be written to disk as uninitialized directory entry padding. This data can be viewed by any user with read access to the directory. Additionally, a malicious user with write access to a directory can cause up to 254 bytes of kernel stack memory to be exposed. Some amount of the kernel stack is disclosed and written out to the filesystem.