youki container escape and denial of service due to arbitrary write gadgets and procfs write redirects

Youki is a container runtime written in Rust. In versions 0.5.6 and below, youki’s apparmor handling performs insufficiently strict write-target validation, and when combined with path substitution during pathname resolution, can allow writes to unintended procfs locations. While resolving a path component-by-component, a shared-mount race can substitute intermediate components and redirect the final target. This issue is fixed in version 0.5.7.