Affected: Go: github.com/opencontainers/runc

### Impact When setting up the container rootfs, `setupPtmx` and `setupDevSymlinks` call `os.Remove` and `os.Symlink` with a `filepath.Join` string which allow an image with `/dev` as a symlink to trick runc into deleting files called `ptmx` on the host or creating a hardcoded set of symlinks with specific names and targets in an arbitrary pre-existing host directory.

Please note that this issue is not exploitable under Docker because [it creates a top-level `ro` layer that masks any malicious `/dev` symlink present in the container image](https://github.com/moby/moby/blob/docker-v29.4.1/daemon/initlayer/setup_unix.go) (this is also done without mounting the lower layers so there is no opportunity for the malicious `/dev` symlink to trick it into resolving to some other path). Unfortunately, Podman and containerd^† do not do this and so users using those higher-level runtimes with runc can be exploited via a malicious image.

This issue mirrors a [somewhat similar issue in crun](https://github.com/containers/crun/security/advisories/GHSA-7vwr-4279-7gq5), which was also published recently.

###### † Actually, at the time the issue was analysed, [containerd had dead code that implemented this feature](https://github.com/containerd/containerd/blob/v2.2.3/pkg/rootfs/init_linux.go) but the implementation contained several security issues that would arguably have made it more exploitable than in runc. Luckily, the code appears to have never been used (at l…