jp: bounds-check the index in the at() function

[arpitjain099]

Explanation

The at jmespath function can panic with an index-out-of-range when an assertion expression requests an index outside the array's bounds (or a negative index). Because the array argument can be derived from the payload being evaluated, a crafted assertion expression can crash the assertion evaluation. This PR is a bug fix that turns that panic into a normal error the engine already handles.

Related issue

n/a (no existing issue; found by code review). Happy to open a tracking issue if you prefer.

Milestone of this PR

n/a

What type of PR is this

/kind bug

Proposed Changes

jpfAt in pkg/jp/functions/at.go guards both of its argument type assertions with comma-ok, but then indexes the slice with slice[int(index)] without a bounds check, so an out-of-range or negative index panics. A crafted assertion expression such as at(@, `999`) (or at(@, `-1`)) evaluated against a shorter array crashes the assertion evaluation, and there is no recover on that path. This returns an error for an out-of-range or negative index, which the engine already surfaces, instead of indexing blindly.

Proof Manifests

This is an internal robustness fix to the JMESPath at function rather than a policy-behavior change, so there are no Kubernetes/Kyverno manifests to attach. The fix is covered by unit tests in pkg/jp/functions/at_test.go that assert an out-of-range index and a negative index each return an error instead of panicking. Before the fix, evaluating at(@, `999`) against a two-element array panics; after, it returns index out of range: 999 (array length 2).

Checklist

• I have read the contributing guidelines.
• I have read the PR documentation guide and followed the process including adding proof manifests to this PR. (internal function fix, not a user-facing policy change, so no proof manifests apply; see the note above)
• This is a bug fix and I have added unit tests that prove my fix is effective.
• This is a feature and I have added CLI tests that are applicable.
• My PR needs to be cherry picked to a specific release branch which is .

Further Comments

The sibling functions (concat, wildcard, json_parse) all guard their argument access; only at indexed unchecked, so this brings it in line with them.