Forbid empty AppArmor localhost profile

[tallclair]

What type of PR is this?

/kind bug

What this PR does / why we need it:

#97966 removed the requirement that AppArmor profiles be pre-loaded, but in doing so opened up localhost/ as a valid profile. When localhost/ gets passed to the CRI runtime, it strips out the localhost/ prefix before passing the empty string to runc, which then treats it as unconfined. The end result is that localhost/ is equivalent to unconfined, and could be used to evade admission policies that explicitly forbid the use of unconfined.

Also adds a pkg/security/apparmor/OWNERS file (owned by sig-node), so AppArmor changes don't require top-level approval.

Special notes for your reviewer:

Note that this validation would ideally be done as part of API validation, but because of #64841 the Kubelet just performs the check on pod admission (to the node).

Does this PR introduce a user-facing change?

#97966 was only pushed out in an alpha release, so no user-facing changes are introduced here.

NONE

/sig node
/assign @saschagrunert
/cc @liggitt

[k8s-ci-robot]

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[tallclair]

Added a pkg/security/apparmor/OWNERS file (owned by sig-node), so AppArmor changes don't require top-level approval.

[liggitt]

Added a pkg/security/apparmor/OWNERS file (owned by sig-node), so AppArmor changes don't require top-level approval.

fwiw, ValidateProfileFormat is called from ValidateAppArmorPodAnnotations and ValidatePodSecurityPolicySpecificAnnotations in API validation, so at least some parts of this package are REST API-facing

what can we do to avoid accidentally making changes to those functions in an uncontrolled way that doesn't consider the ratcheting required by API validation changes?

[tallclair]

I moved the validation method to the API validation package.

/assign @liggitt

[saschagrunert]

/test pull-kubernetes-unit

[saschagrunert]

Just one nit, otherwise LGTM

[saschagrunert]

/test pull-kubernetes-unit

[liggitt]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, saschagrunert, tallclair

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