RepoSpec path can exit repo directory

[annasong20]

Describe the bug
RepoSpec doesn't currently audit its Path, or the path to the root within the repo. This, in combination with fileLoader not checking the root, can lead to remote roots that traverse the user's local file system.

Specifically, urls of the form https://github.com/org/repo//../../../.., where the Path is "../../../..", can be used to escape the repo to access the user's local directories.

Files that can reproduce the issue
Test here: 6e60afe#diff-5bce8892c5c28e9ea5ca5ee37a1f2a74e63b9499656c9616df78d8b7ea23e5f1R505

Expected output
As in test, an error should be thrown stating that the loader cannot traverse outside of the repo directory.

Actual output
The Run() method currently executes without error. The loader exits the repo directory and loads the local root.

Kustomize version
Commit on master branch: 997e6fc

Additional context
#4797, #4848

After discussion, @KnVerey, @natasha41575 agreed that this issue has contained severity because local roots accessed need to contain a kustomization.yaml file.

[annasong20]

/kind triage/accepted

[k8s-ci-robot]

@annasong20: The label(s) kind/triage/accepted cannot be applied, because the repository doesn't have them.

In response to this:

/kind triage/accepted

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[annasong20]

/triage accepted

[annasong20]

/assign

[annasong20]

Should be fixed by #4885