An issue was discovered in the Linux kernel through 4.17.10. There is a
NULL pointer dereference and panic in hfsplus_lookup() in fs/hfsplus/dir.c
when opening a file (that is purportedly a hard link) in an hfs+ filesystem
that has malformed catalog data, and is mounted read-only without a
metadata directory.

Wen Xu discovered that the HFS+ filesystem implementation in the Linux
kernel did not properly handle malformed catalog data in some situations.
An attacker could use this to construct a malicious HFS+ image that, when
mounted, could cause a denial of service (system crash).