fix fnplugin storagemounts validation

[totegamma]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR fixes the path-scope validation for bind mounts.

The current implementation validates that mount paths are under the current kustomization directory with strings.HasPrefix(filepath.Clean(mount.Src), "../") but filepath.Clean("../") returns ".." so the check doesn’t work when mounts.src is exactly "../"

like

apiVersion: com.example.kustomize/v1
kind: Test
metadata:
  name: test-transformer
  annotations:
    config.kubernetes.io/function: |
      container:
        image: test
        mounts:
          - type: bind
            src: ../
            dst: /mount

https://go.dev/play/p/7YfrHGwOKnf

Other considerations

The current implementation lets '../' pass, so running kustomize build subdir instead of kustomize build . can read files in the current working directory—that is, the parent of the kustomization file—yet even this unintended reach justifies a fix.

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[k8s-ci-robot]

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[koba1t]

Hi @totegamma

Thanks for open PR.
Please add tests that reproduce the issue this PR fixes, following the guide below.

https://github.com/kubernetes-sigs/kustomize/blob/master/CONTRIBUTING.md#reviewer-guide

• The PR should have two distinct commits:
  • The first commit should add a test demonstrating incorrect behavior
  • The second commit should include the bug fix
  • Some sample PRs:
    • https://github.com/kubernetes-sigs/kustomize/pull/5263/commits
    • https://github.com/kubernetes-sigs/kustomize/pull/3931/commits
  • The regression test is absolutely required, and we cannot accept bug fixes without tests.

[k8s-ci-robot]

This PR has multiple commits, and the default merge method is: merge.
You can request commits to be squashed using the label: tide/merge-method-squash

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[koba1t]

/ok-to-test

[koba1t]

Hi @totegamma
Thanks for your help!
I think this change is valuable and almost looks good for me.

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: koba1t, totegamma

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