[$] Hardening magic links

There are some "magic links" in kernel pseudo-filesystems, like procfs,that can be-have been-(ab)used to cause security problems, such as acontainer-confinement breach in 2019.Aleksa Sarai has long been working on ways to blunt the impact of thesemagic links. He led a filesystem session at the2023 Linux Storage, Filesystem,Memory-Management and BPF Summit to discuss the status of those efforts.