[PATCH v9 9/9] landlock: Add KUnit tests for LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess <utilityemal77@gmail.com>]

Add the landlock_ruleset KUnit suite with three tests for the
no_inherit handling in landlock_unmask_layers():

- test_unmask_no_inherit_propagates: a rule with no_inherit unmasks
  access and sets the no_inherit bit on the layer mask.
- test_unmask_multilayer_no_inherit: no_inherit on one layer of a
  multi-layer rule only affects that layer.
- test_unmask_no_inherit_sequential: applying a descendant rule
  (no_inherit) followed by an ancestor rule causes the ancestor to be
  skipped, modeling a path walk.  This exercises the same skip branch
  that a pre-set no_inherit mask would, via realistic rule application.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---

Notes:
    Changes since v8:
    - Reduced from five tests to three, dropping test_unmask_no_inherit_skip
      and test_unmask_no_inherit_both_set (which set the per-layer no_inherit
      bit synthetically). Kept test_unmask_no_inherit_propagates,
      test_unmask_multilayer_no_inherit, and test_unmask_no_inherit_sequential,
      which exercise the same skip branch through realistic rule application.
    - Rebased onto mic/next.

 security/landlock/ruleset.c | 137 ++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)

diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index ca7cfa45c90a..144b6fc19f79 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -6,6 +6,7 @@
  * Copyright © 2018-2020 ANSSI
  */
 
+#include <kunit/test.h>
 #include <linux/bits.h>
 #include <linux/bug.h>
 #include <linux/cleanup.h>
@@ -766,3 +767,139 @@ landlock_init_layer_masks(const struct landlock_ruleset *const domain,
 
 	return handled_accesses;
 }
+
+#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
+
+/*
+ * Helper to allocate a rule with @num_layers layers and initialize
+ * its num_layers field.  Caller must fill in individual layers.
+ */
+static struct landlock_rule *alloc_rule(struct kunit *test, u32 num_layers)
+{
+	struct landlock_rule *rule;
+
+	rule = kzalloc(struct_size(rule, layers, num_layers), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, rule);
+	rule->num_layers = num_layers;
+	return rule;
+}
+
+/*
+ * Build a layer_masks with the first @num_layers layers' access set to
+ * @val, and all no_inherit flags cleared.  Layers beyond @num_layers stay
+ * zeroed, matching what landlock_init_layer_masks() produces for a domain
+ * with that many layers.
+ */
+static void fill_masks(struct layer_masks *masks, access_mask_t val,
+		       size_t num_layers)
+{
+	memset(masks, 0, sizeof(*masks));
+	for (size_t i = 0; i < num_layers; i++)
+		masks->layers[i].access = val;
+}
+
+/* Verify that a rule with no_inherit unmasks access and propagates the flag. */
+static void test_unmask_no_inherit_propagates(struct kunit *const test)
+{
+	struct landlock_rule *rule = alloc_rule(test, 1);
+	struct layer_masks masks;
+	const access_mask_t req = BIT_ULL(0) | BIT_ULL(1);
+
+	rule->layers[0].level = 1;
+	rule->layers[0].access = BIT_ULL(0);
+	rule->layers[0].flags.no_inherit = true;
+
+	fill_masks(&masks, req, 1);
+	landlock_unmask_layers(rule, &masks);
+
+	/* access bit 0 should be cleared, bit 1 remains */
+	KUNIT_EXPECT_EQ(test, (access_mask_t)masks.layers[0].access,
+			BIT_ULL(1));
+	KUNIT_EXPECT_TRUE(test, masks.layers[0].no_inherit);
+	KUNIT_EXPECT_EQ(test, (access_mask_t)masks.layers[1].access, 0);
+	kfree(rule);
+}
+
+/*
+ * Verify that no_inherit on layer 1 of a multi-layer rule only affects
+ * layer 1; layer 2 still contributes normally.
+ */
+static void test_unmask_multilayer_no_inherit(struct kunit *const test)
+{
+	struct landlock_rule *rule = alloc_rule(test, 2);
+	struct layer_masks masks;
+	const access_mask_t req = BIT_ULL(0) | BIT_ULL(1);
+
+	rule->layers[0].level = 1;
+	rule->layers[0].access = BIT_ULL(0);
+	rule->layers[0].flags.no_inherit = true;
+
+	rule->layers[1].level = 2;
+	rule->layers[1].access = BIT_ULL(1);
+
+	fill_masks(&masks, req, 2);
+	landlock_unmask_layers(rule, &masks);
+
+	/* Layer 1: bit 0 cleared, no_inherit set */
+	KUNIT_EXPECT_EQ(test, (access_mask_t)masks.layers[0].access, BIT_ULL(1));
+	KUNIT_EXPECT_TRUE(test, masks.layers[0].no_inherit);
+
+	/* Layer 2: bit 1 cleared, no_inherit not set */
+	KUNIT_EXPECT_EQ(test, (access_mask_t)masks.layers[1].access, BIT_ULL(0));
+	KUNIT_EXPECT_FALSE(test, masks.layers[1].no_inherit);
+	kfree(rule);
+}
+
+/*
+ * Verify that when applying two rules sequentially (as happens during
+ * a path walk), no_inherit from the first rule prevents the second
+ * rule from contributing to that layer.
+ */
+static void test_unmask_no_inherit_sequential(struct kunit *const test)
+{
+	struct landlock_rule *rule1 = alloc_rule(test, 1);
+	struct landlock_rule *rule2 = alloc_rule(test, 1);
+	struct layer_masks masks;
+	const access_mask_t req = BIT_ULL(0) | BIT_ULL(1);
+
+	/* Rule 1: no_inherit on layer 1, grants access bit 0 */
+	rule1->layers[0].level = 1;
+	rule1->layers[0].access = BIT_ULL(0);
+	rule1->layers[0].flags.no_inherit = true;
+
+	/* Rule 2: also on layer 1, grants access bit 1 (ancestor rule) */
+	rule2->layers[0].level = 1;
+	rule2->layers[0].access = BIT_ULL(1);
+
+	/* Apply rule1 first (descendant), then rule2 (ancestor) */
+	fill_masks(&masks, req, 1);
+	landlock_unmask_layers(rule1, &masks);
+	landlock_unmask_layers(rule2, &masks);
+
+	/*
+	 * Rule2 should be skipped because rule1 set no_inherit.
+	 * bit 0 cleared by rule1, bit 1 remains because rule2 skipped.
+	 */
+	KUNIT_EXPECT_EQ(test, (access_mask_t)masks.layers[0].access, BIT_ULL(1));
+	KUNIT_EXPECT_TRUE(test, masks.layers[0].no_inherit);
+	kfree(rule1);
+	kfree(rule2);
+}
+
+static struct kunit_case test_cases[] = {
+	/* clang-format off */
+	KUNIT_CASE(test_unmask_no_inherit_propagates),
+	KUNIT_CASE(test_unmask_multilayer_no_inherit),
+	KUNIT_CASE(test_unmask_no_inherit_sequential),
+	{}
+	/* clang-format on */
+};
+
+static struct kunit_suite test_suite = {
+	.name = "landlock_ruleset",
+	.test_cases = test_cases,
+};
+
+kunit_test_suite(test_suite);
+
+#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
-- 
2.54.0