Path traversal in confidential-containers guest-components

Summary

Confidential Containers Guest Components provides guest tools and components for confidential container workloads. From 0.16.0 until 0.20.0, a crafted OCI image layer can make image_rs::stream::unpack::unpack() create a hardlink outside its destination directory. In image-rs/src/stream/unpack.rs, try_hardlink_fallback() validates the hardlink source but computes the destination with destination.join(&entry_rel). Rust Path::join replaces the base when entry_rel is an absolute tar entry path, so fs::hard_link(&src_canon, &dst_entry_abs) can write attacker-controlled content to an arbitrary absolute path. In Confidential Containers the workload owner already controls trusted image content, so the issue is a workload-owner escape into the pod virtual machine rather than a crossing of the image trust boundary, but it may enable access to pod virtual machine capabilities and attestation abuse. This issue is fixed in version 0.20.0.