kustomize fails on empty kustomization.yaml file without meaningful message

[marekiwaniak]

After applying checkov -d . --framework kustomize onto existing project I got generic error.

2023-05-23 14:08:01,563 [MainThread  ] [ERROR]  Exception traceback:
Traceback (most recent call last):
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/main.py", line 463, in run
    self.scan_reports = runner_registry.run(
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/common/runners/runner_registry.py", line 102, in run
    self.runners[0].run(root_folder, external_checks_dir=external_checks_dir, files=files,
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 557, in run
    self.run_kustomize_to_k8s(root_folder, files, runner_filter)
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 498, in run_kustomize_to_k8s
    self.kustomizeProcessedFolderAndMeta[kustomize_dir] = self._parseKustomization(kustomize_dir)
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 271, in _parseKustomization
    if 'resources' in fileContent:
TypeError: argument of type 'NoneType' is not iterable
Traceback (most recent call last):
  File "/home/marek/.local/bin/checkov", line 9, in <module>
    sys.exit(Checkov().run())
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/main.py", line 463, in run
    self.scan_reports = runner_registry.run(
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/common/runners/runner_registry.py", line 102, in run
    self.runners[0].run(root_folder, external_checks_dir=external_checks_dir, files=files,
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 557, in run
    self.run_kustomize_to_k8s(root_folder, files, runner_filter)
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 498, in run_kustomize_to_k8s
    self.kustomizeProcessedFolderAndMeta[kustomize_dir] = self._parseKustomization(kustomize_dir)
  File "/home/marek/.local/lib/python3.10/site-packages/checkov/kustomize/runner.py", line 271, in _parseKustomization
    if 'resources' in fileContent:
TypeError: argument of type 'NoneType' is not iterable

After some digging inside _parseKustomization at kustomize/runner.py:247 and applying try block loop body I found out file that was causing me the issue. I had following folders in kubernetess directory: base, prod,stage,dev. But dev contained totally empty kustomization.yaml file. Filling this file with yaml content solves the issue.

However maybe its worth to add some checks on fileContent object before we attempt to examine it for its contents.

checkov -v
2.3.234

[robinsmidsrod]

Alternatively, this could be turned into a failing policy saying that an empty kustomization file is confusing/undefined behavior/something else and should be avoided. Either case, it shouldn't crash the scanner.