Check accessibility of Step images

antora/docs/modules/ROOT/pages/task_policy.adoc

@@ -4,8 +4,27 @@
 
 These rules are applied to Tekton task definitions.
 
+[#step_images_package]
+== link:#step_images_package[Tekton Task Step image policies]
+
+This package ensures that a Task definition contains valid values for the image references used by the Task's steps.
+
+* Package name: `step_images`
+
+[#step_images__step_images_accessible]
+=== link:#step_images__step_images_accessible[Step images are valid]
+
+Confirm that each step in the Task uses a container image that is accessible.
+
+*Solution*: Make sure the container image used in each step of the Task is pushed to the registry and that it can be fetched.
+
+* Rule type: [rule-type-indicator failure]#FAILURE#
+* FAILURE message: `Step %d uses inaccessible image ref '%s'`
+* Code: `step_images.step_images_accessible`
+* https://github.com/enterprise-contract/ec-policies/blob/{page-origin-refhash}/policy/task/step_images/step_images.rego#L14[Source, window="_blank"]
+
 [#step_image_registries_package]
-== link:#step_image_registries_package[Tekton Task Step image policies]
+== link:#step_image_registries_package[Tekton Task Step image registry policies]
 
 This package ensures that a Task definition contains expected values for the image references used by the Task's steps.
 

antora/docs/modules/ROOT/partials/task_policy_nav.adoc

@@ -1,5 +1,7 @@
 * xref:task_policy.adoc[Task Policy]
-** xref:task_policy.adoc#step_image_registries_package[Tekton Task Step image policies]
+** xref:task_policy.adoc#step_images_package[Tekton Task Step image policies]
+*** xref:task_policy.adoc#step_images__step_images_accessible[Step images are valid]
+** xref:task_policy.adoc#step_image_registries_package[Tekton Task Step image registry policies]
 *** xref:task_policy.adoc#step_image_registries__step_image_registry_prefix_list_provided[Permitted step image registry prefix list provided]
 *** xref:task_policy.adoc#step_image_registries__step_images_permitted[Step images come from permitted registry]
 ** xref:task_policy.adoc#annotations_package[Tekton Task annotations]

policy/task/step_image_registries/step_image_registries.rego

@@ -1,6 +1,6 @@
 #
 # METADATA
-# title: Tekton Task Step image policies
+# title: Tekton Task Step image registry policies
 # description: >-
 #   This package ensures that a Task definition contains expected values for the image references
 #   used by the Task's steps.

policy/task/step_images/step_images.rego

@@ -0,0 +1,37 @@
+#
+# METADATA
+# title: Tekton Task Step image policies
+# description: >-
+#   This package ensures that a Task definition contains valid values for the image references
+#   used by the Task's steps.
+#
+package step_images
+
+import rego.v1
+
+import data.lib
+
+# METADATA
+# title: Step images are valid
+# description: >-
+#   Confirm that each step in the Task uses a container image that is accessible.
+# custom:
+#   short_name: step_images_accessible
+#   failure_msg: Step %d uses inaccessible image ref '%s'
+#   solution: >-
+#     Make sure the container image used in each step of the Task is pushed to the
+#     registry and that it can be fetched.
+#
+deny contains result if {
+	input.kind == "Task"
+
+	some step_index, step in input.spec.steps
+	image_ref := step.image
+	is_null(ec.oci.image_manifest(image_ref))
+
+	result := lib.result_helper_with_term(
+		rego.metadata.chain(),
+		[step_index, image_ref],
+		image_ref,
+	)
+}

policy/task/step_images/step_images_test.rego

@@ -0,0 +1,68 @@
+package step_images_test
+
+import rego.v1
+
+import data.lib
+import data.step_images
+
+test_looks_at_tasks_only if {
+	pipeline := {
+		"kind": "Pipeline",
+		"spec": {"steps": [{"image": "registry.io/repository/not_ok"}]},
+	}
+
+	lib.assert_empty(step_images.deny) with input as pipeline
+}
+
+test_task_with_no_steps if {
+	task := {"kind": "Task"}
+
+	lib.assert_empty(step_images.deny) with input as task
+}
+
+test_task_with_valid_steps if {
+	task := {
+		"kind": "Task",
+		"spec": {"steps": [
+			{"image": "registry.io/repository/ok:1"},
+			{"image": "registry.io/repository/ok:2"},
+			{"image": "registry.io/repository/ok:3"},
+		]},
+	}
+
+	lib.assert_empty(step_images.deny) with input as task with ec.oci.image_manifest as mock_image_manifest
+}
+
+test_task_with_invalid_steps if {
+	task := {
+		"kind": "Task",
+		"spec": {"steps": [
+			{"image": "registry.io/repository/ok:1"},
+			{"image": "registry.io/repository/not_ok:2"},
+			{"image": "registry.io/repository/ok:3"},
+			{"image": "registry.io/repository/not_ok:4"},
+			{"image": "registry.io/repository/ok:5"},
+		]},
+	}
+
+	expected := {
+		{
+			"code": "step_images.step_images_accessible",
+			"msg": "Step 1 uses inaccessible image ref 'registry.io/repository/not_ok:2'",
+			"term": "registry.io/repository/not_ok:2",
+		},
+		{
+			"code": "step_images.step_images_accessible",
+			"msg": "Step 3 uses inaccessible image ref 'registry.io/repository/not_ok:4'",
+			"term": "registry.io/repository/not_ok:4",
+		},
+	}
+
+	lib.assert_equal_results(expected, step_images.deny) with input as task
+		with ec.oci.image_manifest as mock_image_manifest
+}
+
+mock_image_manifest(ref) := m if {
+	startswith(ref, "registry.io/repository/ok")
+	m := {}
+} else := null