[PATCH v4 6/8] selftests/landlock: Add capability restriction tests

["Mickaël Salaün" <mic@digikod.net>]

Add tests to exercise LANDLOCK_PERMISSION_CAPABILITY_USE enforcement.  A
sandboxed process is denied a handled capability when no rule grants it,
and an explicit rule restores it.  Unknown capability values above
CAP_LAST_CAP are accepted at rule-add time yet have no runtime effect,
because deny-by-default still applies once the domain is enforced.
Stacking tests cover the per-layer allow/deny combinations, including a
layer that does not handle the permission, and invalid rule attributes
return the expected errors.

Three tests exercise non-standard capability contexts: enforcing a
domain via CAP_SYS_ADMIN authorization without no_new_privs, restricting
capabilities gained through the kernel's user namespace ownership bypass
(cap_capable_helper), and checking CAP_SYS_ADMIN against a descendant
user namespace, with an unsandboxed positive control, to confirm the
decision is independent of the target.

Audit tests verify denied and allowed capabilities, per-member quiet
interactions, and CAP_OPT_NOAUDIT suppression.  Trace tests cover
accepted, rejected, and no-op rule adds, and normal, quiet, and
CAP_OPT_NOAUDIT denials.

Test coverage for security/landlock is 91.8% of 2864 lines according to
LLVM 22.

Cc: Christian Brauner <brauner@kernel.org>
Cc: Günther Noack <gnoack@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---

Changes since v3:
https://patch.msgid.link/20260726161400.3010511-11-mic@digikod.net
- Cover the EFAULT result for an invalid capability rule pointer.
- Drop CAP_AUDIT_CONTROL after cleaning up the audit fixture.
- Isolate cap_stacking and cap_audit in private UTS namespaces before
  their successful sethostname() calls.
- Add trace tests for successful and rejected rules, effective no-ops,
  and normal, quiet, and CAP_OPT_NOAUDIT denials.
- Extend audit coverage for normal-denial controls, same-member
  allow/quiet overlap, and youngest-denier behavior.
- Test target-user-namespace independence with an unsandboxed positive
  control.

Changes since v2:
https://patch.msgid.link/20260527181127.879771-8-mic@digikod.net
- Rebased for ABI 11 and the renamed capability rule attribute (perm
  plus allowed_capabilities/quiet_capabilities).
- Add per-member quiet audit tests for the capability permission:
  cap_audit.quieted, plus quiet-only and allow+quiet legs in
  add_rule_bad_attr and the add_cap_rule_full helper.
- add_rule_bad_attr: drop the dead quiet_capabilities reset after the
  allow+quiet rule and reset it explicitly where the following rule
  needs an allow-only attr, clarifying intent.
- Strengthen the audit tests with positive controls: cap_audit.quieted
  and cap_audit.noaudit_probe_not_logged now also assert that a normal
  (non-quiet, non-noaudit) capability denial in the same domain IS
  logged, proving suppression is not global.  cap_audit.quieted also
  asserts the quieted capability is still denied (EPERM), not merely
  unlogged.
- Add cap_audit.quiet_unknown_bit_no_effect (an unknown quiet bit does
  not suppress a known capability denial).

Changes since v1:
https://patch.msgid.link/20260312100444.2609563-8-mic@digikod.net
- Reflow comments after check-linux.sh comment fixes.
- Rename LANDLOCK_PERM_NAMESPACE_ENTER references to
  LANDLOCK_PERM_NAMESPACE_USE and bump the abi_version expectation
  to 11 (companion changes to the introducing commit).
- Add add_rule_unknown_no_runtime_effect: assert that a rule listing
  only unknown capability bits is accepted at rule-add time but has
  no runtime effect, so an actual CAP_* exercise (sethostname with
  CAP_SYS_ADMIN) is still denied by deny-by-default once the domain
  is enforced.
- Add cap_stacking parent_denies variant covering the inverse
  direction of stacking: layer 1 denies CAP_SYS_ADMIN, layer 2
  allows, capability still denied.  Completes the per-layer walker
  direction coverage.
- Assert records.domain == 0 in cap_audit.allowed so the test also
  checks that no domain-allocation record is emitted when nothing
  is denied.
---
 tools/testing/selftests/landlock/base_test.c |   19 +
 tools/testing/selftests/landlock/cap_test.c  | 1364 ++++++++++++++++++
 tools/testing/selftests/landlock/trace.h     |   24 +
 3 files changed, 1407 insertions(+)
 create mode 100644 tools/testing/selftests/landlock/cap_test.c

diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 58fe322d8637..89c0d96607de 100644
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -142,6 +142,25 @@ TEST(errata)
 	ASSERT_EQ(EINVAL, errno);
 }
 
+#define PERMISSION_LAST LANDLOCK_PERMISSION_CAPABILITY_USE
+
+TEST(ruleset_with_unknown_permission)
+{
+	__u64 permission_mask;
+
+	for (permission_mask = 1ULL << 63; permission_mask != PERMISSION_LAST;
+	     permission_mask >>= 1) {
+		struct landlock_ruleset_attr ruleset_attr = {
+			.handled_permissions = permission_mask,
+		};
+
+		/* Unknown handled_permissions values must be rejected. */
+		ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr,
+						      sizeof(ruleset_attr), 0));
+		ASSERT_EQ(EINVAL, errno);
+	}
+}
+
 /* Tests ordering of syscall argument checks. */
 TEST(create_ruleset_checks_ordering)
 {
diff --git a/tools/testing/selftests/landlock/cap_test.c b/tools/testing/selftests/landlock/cap_test.c
new file mode 100644
index 000000000000..8673934aac11
--- /dev/null
+++ b/tools/testing/selftests/landlock/cap_test.c
@@ -0,0 +1,1364 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Capability restriction
+ *
+ * Copyright © 2026 Cloudflare, Inc.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/capability.h>
+#include <linux/landlock.h>
+#include <sched.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/wait.h>
+#include <sys/xattr.h>
+#include <unistd.h>
+
+#include "audit.h"
+#include "common.h"
+#include "trace.h"
+
+#define TRACE_TASK "cap_test"
+
+static bool list_has_xattr(const char *list, ssize_t len, const char *name)
+{
+	const char *p;
+
+	for (p = list; p < list + len; p += strlen(p) + 1)
+		if (strcmp(p, name) == 0)
+			return true;
+	return false;
+}
+
+static int create_cap_ruleset(void)
+{
+	const struct landlock_ruleset_attr attr = {
+		.handled_permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+	};
+
+	return landlock_create_ruleset(&attr, sizeof(attr), 0);
+}
+
+static int add_cap_rule(int ruleset_fd, __u64 cap)
+{
+	const struct landlock_capability_attr attr = {
+		.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+		.allowed_capabilities = (1ULL << cap),
+	};
+
+	return landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY, &attr,
+				 0);
+}
+
+static int add_cap_rule_full(int ruleset_fd, __u64 allowed, __u64 quiet)
+{
+	const struct landlock_capability_attr attr = {
+		.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+		.allowed_capabilities = allowed,
+		.quiet_capabilities = quiet,
+	};
+
+	return landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY, &attr,
+				 0);
+}
+
+TEST(add_rule_bad_attr)
+{
+	const struct landlock_ruleset_attr ns_only_attr = {
+		.handled_permissions = LANDLOCK_PERMISSION_NAMESPACE_USE,
+	};
+	int ruleset_fd;
+	struct landlock_capability_attr attr = {};
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Invalid rule pointer returns EFAULT. */
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					NULL, 0));
+	ASSERT_EQ(EFAULT, errno);
+
+	/* Empty permissions selector returns ENOMSG. */
+	attr.permissions = 0;
+	attr.allowed_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, 0));
+	ASSERT_EQ(ENOMSG, errno);
+
+	/* Useless rule: neither allowed nor quiet capabilities set. */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = 0;
+	attr.quiet_capabilities = 0;
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, 0));
+	ASSERT_EQ(ENOMSG, errno);
+
+	/* Quiet-only rule (empty allowed set) is legal. */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = 0;
+	attr.quiet_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	/* Allow and quiet different members in the same rule. */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = (1ULL << CAP_SYS_ADMIN);
+	attr.quiet_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	/* Valid capability selector plus an extra unhandled selector bit. */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE |
+			   LANDLOCK_PERMISSION_NAMESPACE_USE;
+	attr.allowed_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, 0));
+	ASSERT_EQ(EINVAL, errno);
+
+	/* permissions with wrong type. */
+	attr.permissions = LANDLOCK_PERMISSION_NAMESPACE_USE;
+	attr.allowed_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, 0));
+	ASSERT_EQ(EINVAL, errno);
+
+	/*
+	 * Unknown capability bits (e.g. bit 63) are silently accepted for
+	 * forward compatibility.  Only known bits are stored.
+	 */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = 1ULL << 63;
+	attr.quiet_capabilities = 0;
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	/*
+	 * LANDLOCK_ADD_RULE_QUIET (and any other flag) is filesystem/network
+	 * only and must be rejected for capability rules, even when every attr
+	 * field is otherwise valid.
+	 */
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, LANDLOCK_ADD_RULE_QUIET));
+	ASSERT_EQ(EINVAL, errno);
+
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Ruleset handles LANDLOCK_PERMISSION_NAMESPACE_USE but not
+	 * LANDLOCK_PERMISSION_CAPABILITY_USE: adding a capability rule must be
+	 * rejected.
+	 */
+	ruleset_fd =
+		landlock_create_ruleset(&ns_only_attr, sizeof(ns_only_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+	attr.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE;
+	attr.allowed_capabilities = (1ULL << CAP_NET_RAW);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&attr, 0));
+	ASSERT_EQ(EINVAL, errno);
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
+/*
+ * Unknown capability values above CAP_LAST_CAP are silently accepted
+ * (allow-list: they have no effect since the kernel never checks them).
+ */
+TEST(add_rule_unknown)
+{
+	int ruleset_fd;
+	struct landlock_capability_attr attr = {
+		.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+	};
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Just above CAP_LAST_CAP should succeed. */
+	attr.allowed_capabilities = (1ULL << (CAP_LAST_CAP + 1));
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	/* High values (below bit 63) should succeed. */
+	attr.allowed_capabilities = (1ULL << 62);
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
+/*
+ * A rule that lists only capability bits unknown to the running kernel is
+ * accepted by landlock_add_rule() but has no runtime effect: once the domain is
+ * enforced, any actual CAP_* capability is still denied by the per-category
+ * deny-by-default behaviour.  This documents the forward-compatibility
+ * contract: unknown bits are silently accepted so the same policy can be loaded
+ * across kernels, but they never grant a capability that the running kernel
+ * knows nothing about.
+ */
+TEST(add_rule_unknown_no_runtime_effect)
+{
+	const struct landlock_ruleset_attr ruleset_attr = {
+		.handled_permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+	};
+	struct landlock_capability_attr attr = {
+		.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+		/* Only unknown bits above CAP_LAST_CAP. */
+		.allowed_capabilities = (1ULL << (CAP_LAST_CAP + 1)) |
+					(1ULL << 62),
+	};
+	int ruleset_fd;
+
+	disable_caps(_metadata);
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+				       &attr, 0));
+
+	/*
+	 * Isolate hostname changes and establish a baseline: with CAP_SYS_ADMIN
+	 * and absent the domain, sethostname(2) succeeds.  This ensures the
+	 * EPERM below is attributable to Landlock rather than to a missing
+	 * capability, and fails if the hook always allows.
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWUTS));
+	ASSERT_EQ(0, sethostname("baseline", 8));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * CAP_SYS_ADMIN is a real, known capability but was not authorised by
+	 * the rule above; deny-by-default applies.  sethostname(2) requires
+	 * CAP_SYS_ADMIN.
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(-1, sethostname("test", 4));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+/* clang-format off */
+FIXTURE(cap_enforce) {};
+/* clang-format on */
+
+FIXTURE_VARIANT(cap_enforce)
+{
+	const bool is_sandboxed;
+	const bool handle_caps;
+	const __u64 allowed_cap;
+	const int expected_sysadmin;
+	const int expected_chroot;
+};
+
+/*
+ * Unsandboxed baseline: no Landlock domain is enforced.  Both capabilities
+ * should work normally.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_enforce, unsandboxed) {
+	.is_sandboxed = false,
+	.handle_caps = false,
+	.allowed_cap = 0,
+	.expected_sysadmin = 0,
+	.expected_chroot = 0,
+};
+/* clang-format on */
+
+/*
+ * Denied: capabilities are handled but no rule allows them.  All capability
+ * checks must be denied by Landlock even if the capability is effective.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_enforce, denied) {
+	.is_sandboxed = true,
+	.handle_caps = true,
+	.allowed_cap = 0,
+	.expected_sysadmin = EPERM,
+	.expected_chroot = EPERM,
+};
+/* clang-format on */
+
+/*
+ * Allowed: CAP_SYS_ADMIN is allowed by rule, CAP_SYS_CHROOT is not.  Only the
+ * explicitly allowed capability should succeed.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_enforce, allowed) {
+	.is_sandboxed = true,
+	.handle_caps = true,
+	.allowed_cap = CAP_SYS_ADMIN,
+	.expected_sysadmin = 0,
+	.expected_chroot = EPERM,
+};
+/* clang-format on */
+
+/*
+ * Unhandled: the ruleset does not handle LANDLOCK_PERMISSION_CAPABILITY_USE at
+ * all (only handles FS access).  Both capabilities should work since the domain
+ * does not restrict them.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_enforce, unhandled) {
+	.is_sandboxed = true,
+	.handle_caps = false,
+	.allowed_cap = 0,
+	.expected_sysadmin = 0,
+	.expected_chroot = 0,
+};
+/* clang-format on */
+
+FIXTURE_SETUP(cap_enforce)
+{
+	disable_caps(_metadata);
+}
+
+FIXTURE_TEARDOWN(cap_enforce)
+{
+}
+
+/*
+ * Capability enforcement: tests the four fundamental enforcement scenarios
+ * (unsandboxed baseline, denied, allowed, unhandled) using two independent
+ * capability checks (sethostname for CAP_SYS_ADMIN, chroot for CAP_SYS_CHROOT).
+ */
+TEST_F(cap_enforce, use)
+{
+	int ruleset_fd;
+
+	/* Isolate hostname changes from other tests. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWUTS));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	if (variant->is_sandboxed) {
+		if (variant->handle_caps) {
+			ruleset_fd = create_cap_ruleset();
+		} else {
+			const struct landlock_ruleset_attr attr = {
+				.handled_access_fs =
+					LANDLOCK_ACCESS_FS_READ_FILE,
+			};
+
+			ruleset_fd =
+				landlock_create_ruleset(&attr, sizeof(attr), 0);
+		}
+		ASSERT_LE(0, ruleset_fd);
+
+		if (variant->allowed_cap)
+			ASSERT_EQ(0, add_cap_rule(ruleset_fd,
+						  variant->allowed_cap));
+
+		enforce_ruleset(_metadata, ruleset_fd);
+		EXPECT_EQ(0, close(ruleset_fd));
+	}
+
+	/* Test CAP_SYS_ADMIN via sethostname. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	if (variant->expected_sysadmin) {
+		EXPECT_EQ(-1, sethostname("test", 4));
+		EXPECT_EQ(variant->expected_sysadmin, errno);
+	} else {
+		EXPECT_EQ(0, sethostname("test", 4));
+	}
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/* Test CAP_SYS_CHROOT via chroot. */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	if (variant->expected_chroot) {
+		EXPECT_EQ(-1, chroot("/"));
+		EXPECT_EQ(variant->expected_chroot, errno);
+	} else {
+		EXPECT_EQ(0, chroot("/"));
+	}
+}
+
+/*
+ * Layer stacking: both layers must allow CAP_SYS_ADMIN for the capability to be
+ * exercisable.  Variants cover the three per-layer combinations that exercise
+ * distinct walker paths (allow/deny, allow/allow, deny/allow), an unsandboxed
+ * baseline, and a mixed-layer case where one layer does not handle
+ * LANDLOCK_PERMISSION_CAPABILITY_USE at all.
+ */
+/* clang-format off */
+FIXTURE(cap_stacking) {};
+/* clang-format on */
+
+FIXTURE_VARIANT(cap_stacking)
+{
+	const bool is_sandboxed;
+	const bool first_layer_allows;
+	const bool second_layer_allows;
+	const bool second_layer_is_fs_only;
+	const int expected_sysadmin;
+	const int expected_chroot;
+};
+
+/*
+ * Unsandboxed baseline: no Landlock layers are stacked.  Both capabilities
+ * should work normally.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_stacking, unsandboxed) {
+	.is_sandboxed = false,
+	.first_layer_allows = false,
+	.second_layer_allows = false,
+	.expected_sysadmin = 0,
+	.expected_chroot = 0,
+};
+/* clang-format on */
+
+/* Layer 1 allows CAP_SYS_ADMIN, layer 2 denies -> denied. */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_stacking, deny) {
+	.is_sandboxed = true,
+	.first_layer_allows = true,
+	.second_layer_allows = false,
+	.expected_sysadmin = EPERM,
+	.expected_chroot = EPERM,
+};
+/* clang-format on */
+
+/* Both layers allow CAP_SYS_ADMIN -> sysadmin succeeds, chroot still denied. */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_stacking, allow) {
+	.is_sandboxed = true,
+	.first_layer_allows = true,
+	.second_layer_allows = true,
+	.expected_sysadmin = 0,
+	.expected_chroot = EPERM,
+};
+/* clang-format on */
+
+/*
+ * Layer 1 denies CAP_SYS_ADMIN, layer 2 allows -> still denied: a child layer
+ * cannot grant what an ancestor layer withheld.  Complements the
+ * parent-allows/child-denies variant; together they verify the walker checks
+ * both layers and accepts only the (allow, allow) cell.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_stacking, parent_denies) {
+	.is_sandboxed = true,
+	.first_layer_allows = false,
+	.second_layer_allows = true,
+	.expected_sysadmin = EPERM,
+	.expected_chroot = EPERM,
+};
+/* clang-format on */
+
+/*
+ * Mixed layers: first layer handles LANDLOCK_PERMISSION_CAPABILITY_USE (denies
+ * all caps), second layer is FS-only (does not handle it).  The permission
+ * walker iterates from youngest (layer 1) to oldest (layer 0) and must skip the
+ * FS-only layer to find the denying layer beneath.
+ */
+/* clang-format off */
+FIXTURE_VARIANT_ADD(cap_stacking, mixed_layers) {
+	/* clang-format on */
+	.is_sandboxed = true,
+	.first_layer_allows = false,
+	.second_layer_is_fs_only = true,
+	.expected_sysadmin = EPERM,
+	.expected_chroot = EPERM,
+};
+
+FIXTURE_SETUP(cap_stacking)
+{
+	disable_caps(_metadata);
+
+	/* Isolate every successful sethostname() from the other tests. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWUTS));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+FIXTURE_TEARDOWN(cap_stacking)
+{
+}
+
+TEST_F(cap_stacking, two_layers)
+{
+	int ruleset_fd;
+
+	if (variant->is_sandboxed) {
+		/*
+		 * First layer: handles LANDLOCK_PERMISSION_CAPABILITY_USE; rule
+		 * added per variant.
+		 */
+		ruleset_fd = create_cap_ruleset();
+		ASSERT_LE(0, ruleset_fd);
+		if (variant->first_layer_allows)
+			ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_SYS_ADMIN));
+
+		enforce_ruleset(_metadata, ruleset_fd);
+		EXPECT_EQ(0, close(ruleset_fd));
+
+		if (variant->second_layer_is_fs_only) {
+			/*
+			 * Second layer: FS-only (does not handle
+			 * LANDLOCK_PERMISSION_CAPABILITY_USE).  The permission
+			 * walker must skip this layer.
+			 */
+			const struct landlock_ruleset_attr fs_attr = {
+				.handled_access_fs =
+					LANDLOCK_ACCESS_FS_READ_FILE,
+			};
+
+			ruleset_fd = landlock_create_ruleset(
+				&fs_attr, sizeof(fs_attr), 0);
+		} else {
+			/* Second layer: cap allow or deny. */
+			ruleset_fd = create_cap_ruleset();
+			if (variant->second_layer_allows)
+				ASSERT_EQ(0, add_cap_rule(ruleset_fd,
+							  CAP_SYS_ADMIN));
+		}
+		ASSERT_LE(0, ruleset_fd);
+		enforce_ruleset(_metadata, ruleset_fd);
+		EXPECT_EQ(0, close(ruleset_fd));
+	}
+
+	/* Test CAP_SYS_ADMIN via sethostname. */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	if (variant->expected_sysadmin) {
+		EXPECT_EQ(-1, sethostname("test", 4));
+		EXPECT_EQ(variant->expected_sysadmin, errno);
+	} else {
+		EXPECT_EQ(0, sethostname("test", 4));
+	}
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/* Test CAP_SYS_CHROOT via chroot. */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	if (variant->expected_chroot) {
+		EXPECT_EQ(-1, chroot("/"));
+		EXPECT_EQ(variant->expected_chroot, errno);
+	} else {
+		EXPECT_EQ(0, chroot("/"));
+	}
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+}
+
+/*
+ * Verify that LANDLOCK_PERMISSION_CAPABILITY_USE enforces when the domain is
+ * applied without no_new_privs, using CAP_SYS_ADMIN for
+ * landlock_restrict_self() authorization instead.  Privileged processes (e.g.
+ * container managers) can sandbox themselves this way.
+ */
+TEST(cap_without_nnp)
+{
+	int ruleset_fd;
+
+	disable_caps(_metadata);
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Allow CAP_SYS_CHROOT but not CAP_SYS_ADMIN. */
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_SYS_CHROOT));
+
+	/*
+	 * Enforce WITHOUT NNP: landlock_restrict_self() succeeds when the
+	 * caller has CAP_SYS_ADMIN (checked before the new domain takes
+	 * effect).
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * CAP_SYS_ADMIN is still in effective set but Landlock denies it:
+	 * cap_capable() returns 0, then hook_capable() returns -EPERM.
+	 */
+	EXPECT_EQ(-1, sethostname("test", 4));
+	EXPECT_EQ(EPERM, errno);
+
+	/* CAP_SYS_CHROOT is allowed by the rule. */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	EXPECT_EQ(0, chroot("/"));
+}
+
+/*
+ * Verify that capabilities gained through user namespace ownership are still
+ * restricted by LANDLOCK_PERMISSION_CAPABILITY_USE.  When a process creates a
+ * user namespace, the kernel grants CAP_FULL_SET in the new namespace via
+ * cap_capable_helper()'s ownership bypass.  Landlock's hook_capable() must
+ * still deny capabilities not in the allowed set, ensuring that user namespace
+ * creation cannot be used to escape capability restrictions.
+ */
+TEST(cap_userns_ownership_bypass)
+{
+	pid_t child;
+	int status;
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		int ruleset_fd;
+
+		disable_caps(_metadata);
+
+		ruleset_fd = create_cap_ruleset();
+		ASSERT_LE(0, ruleset_fd);
+
+		/* Allow CAP_SYS_ADMIN only. */
+		ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_SYS_ADMIN));
+		enforce_ruleset(_metadata, ruleset_fd);
+		EXPECT_EQ(0, close(ruleset_fd));
+
+		/*
+		 * Create a user namespace.  This is unprivileged and does not
+		 * require capabilities.  LANDLOCK_PERMISSION_NAMESPACE_USE is
+		 * not handled so namespace creation is unrestricted.
+		 */
+		ASSERT_EQ(0, unshare(CLONE_NEWUSER));
+
+		/*
+		 * After unshare(CLONE_NEWUSER), the kernel set cap_effective =
+		 * CAP_FULL_SET in the new namespace.  Create a UTS namespace
+		 * (requires CAP_SYS_ADMIN in the new user NS).  Landlock allows
+		 * CAP_SYS_ADMIN.
+		 */
+		ASSERT_EQ(0, unshare(CLONE_NEWUTS))
+		{
+			TH_LOG("unshare(CLONE_NEWUTS): %s", strerror(errno));
+		}
+
+		/*
+		 * sethostname checks against uts_ns->user_ns, which is now the
+		 * new user NS.  CAP_SYS_ADMIN is allowed.
+		 */
+		EXPECT_EQ(0, sethostname("test", 4));
+
+		/*
+		 * chroot checks against current_user_ns(), which is the new
+		 * user NS.  The process has CAP_SYS_CHROOT in cap_effective
+		 * (from user NS creation), so cap_capable() returns 0.  But
+		 * Landlock denies because no rule allows CAP_SYS_CHROOT.
+		 */
+		EXPECT_EQ(-1, chroot("/"));
+		EXPECT_EQ(EPERM, errno);
+
+		_exit(_metadata->exit_code);
+		return;
+	}
+
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
+	    WEXITSTATUS(status) != EXIT_SUCCESS)
+		_metadata->exit_code = KSFT_FAIL;
+}
+
+/*
+ * Verify that capability restrictions do not depend on which user namespace the
+ * kernel checks.  An actor in the initial user namespace can enter a descendant
+ * user namespace with CAP_SYS_ADMIN.  With the same Linux capability state,
+ * handling capability use without an allow rule must deny that target-namespace
+ * check even though the target differs from current_user_ns().
+ */
+TEST(cap_target_userns_independent)
+{
+	int sockets[2], status, target_userns_fd;
+	pid_t actor, target;
+
+	disable_caps(_metadata);
+	ASSERT_EQ(0,
+		  socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sockets));
+
+	target = fork();
+	ASSERT_LE(0, target);
+	if (target == 0) {
+		int fd;
+
+		close(sockets[0]);
+		if (unshare(CLONE_NEWUSER))
+			_exit(255);
+		fd = open("/proc/self/ns/user", O_RDONLY | O_CLOEXEC);
+		if (fd < 0 || send_fd(sockets[1], fd))
+			_exit(255);
+		close(fd);
+		close(sockets[1]);
+		_exit(EXIT_SUCCESS);
+	}
+
+	close(sockets[1]);
+	target_userns_fd = recv_fd(sockets[0]);
+	ASSERT_LE(0, target_userns_fd);
+	EXPECT_EQ(0, close(sockets[0]));
+	ASSERT_EQ(target, waitpid(target, &status, 0));
+	ASSERT_TRUE(WIFEXITED(status));
+	ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	for (int sandboxed = 0; sandboxed <= 1; sandboxed++) {
+		actor = fork();
+		ASSERT_LE(0, actor);
+		if (actor == 0) {
+			int ret, saved_errno;
+
+			if (sandboxed) {
+				int ruleset_fd = create_cap_ruleset();
+
+				if (ruleset_fd < 0 ||
+				    prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
+				    landlock_restrict_self(ruleset_fd, 0) ||
+				    close(ruleset_fd))
+					_exit(255);
+			}
+
+			ret = setns(target_userns_fd, CLONE_NEWUSER);
+			saved_errno = errno;
+			_exit(ret ? saved_errno : EXIT_SUCCESS);
+		}
+
+		ASSERT_EQ(actor, waitpid(actor, &status, 0));
+		ASSERT_TRUE(WIFEXITED(status));
+		EXPECT_EQ(sandboxed ? EPERM : EXIT_SUCCESS,
+			  WEXITSTATUS(status));
+	}
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, close(target_userns_fd));
+}
+
+/* Audit tests */
+
+static int matches_log_cap(int audit_fd, int cap_number)
+{
+	static const char log_template[] = REGEX_LANDLOCK_PREFIX
+		" blockers=capability\\.use capability=%d $";
+	char log_match[sizeof(log_template) + 10];
+	int log_match_len;
+
+	log_match_len = snprintf(log_match, sizeof(log_match), log_template,
+				 cap_number);
+	if (log_match_len >= sizeof(log_match))
+		return -E2BIG;
+
+	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match,
+				  NULL);
+}
+
+FIXTURE(cap_audit)
+{
+	struct audit_filter audit_filter;
+	int audit_fd;
+};
+
+FIXTURE_SETUP(cap_audit)
+{
+	ASSERT_TRUE(is_in_init_user_ns());
+
+	disable_caps(_metadata);
+
+	/* Isolate the allowed test's successful sethostname(). */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWUTS));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	set_cap(_metadata, CAP_AUDIT_CONTROL);
+	self->audit_fd = audit_init_with_exe_filter(&self->audit_filter);
+	EXPECT_LE(0, self->audit_fd);
+	clear_cap(_metadata, CAP_AUDIT_CONTROL);
+}
+
+FIXTURE_TEARDOWN(cap_audit)
+{
+	set_cap(_metadata, CAP_AUDIT_CONTROL);
+	EXPECT_EQ(0, audit_cleanup(self->audit_fd, &self->audit_filter));
+	clear_cap(_metadata, CAP_AUDIT_CONTROL);
+}
+
+/*
+ * Verifies that a denied capability produces the expected audit record with the
+ * correct capability number and blocker string.
+ */
+TEST_F(cap_audit, denied)
+{
+	struct audit_records records;
+	int ruleset_fd;
+	__u64 domain_id;
+
+	/* Baseline: chroot works before Landlock. */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	ASSERT_EQ(0, chroot("/"));
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	/* Allow CAP_AUDIT_CONTROL for child-side audit cleanup. */
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/* Deny CAP_SYS_CHROOT (no allow rule). */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	EXPECT_EQ(-1, chroot("/"));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	EXPECT_EQ(0, matches_log_cap(self->audit_fd, CAP_SYS_CHROOT));
+
+	/*
+	 * The domain allocation record is emitted in the same event as the
+	 * first denial; anchor its status=allocated and enforcing pid.  Both
+	 * access and domain records are now consumed, so none remain.
+	 */
+	EXPECT_EQ(0, matches_log_domain_allocated(self->audit_fd, getpid(),
+						  &domain_id));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+TEST_F(cap_audit, allowed)
+{
+	struct audit_records records;
+	int ruleset_fd;
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_SYS_ADMIN));
+	/* Allow CAP_AUDIT_CONTROL for child-side audit cleanup. */
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, sethostname("test", 4));
+
+	/* No records: allowed operations never trigger audit logging. */
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/* An allowed capability remains allowed when the same rule also quiets it. */
+TEST_F(cap_audit, allow_and_quiet_same_member)
+{
+	struct audit_records records;
+	int ruleset_fd;
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule_full(ruleset_fd,
+				       (1ULL << CAP_SYS_ADMIN) |
+					       (1ULL << CAP_AUDIT_CONTROL),
+				       1ULL << CAP_SYS_ADMIN));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(0, sethostname("test", 4));
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/*
+	 * Quiet is inert for the allowed member: nothing is denied or logged.
+	 */
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/*
+ * A quieted capability denial is still denied (EPERM); only its audit record is
+ * suppressed.  Quiet-only rule (empty allowed set).
+ */
+TEST_F(cap_audit, quieted)
+{
+	struct audit_records records;
+	int ruleset_fd;
+	__u64 domain_id;
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	/* Allow CAP_AUDIT_CONTROL for child-side audit cleanup. */
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	ASSERT_EQ(0,
+		  add_cap_rule_full(ruleset_fd, 0, (1ULL << CAP_SYS_CHROOT)));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	EXPECT_EQ(-1, chroot("/"));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	/*
+	 * Positive control: CAP_SYS_ADMIN is denied but not quieted, so its
+	 * denial IS logged.  This proves quieting is per-member, not global.
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	EXPECT_EQ(-1, sethostname("test", 4));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	/*
+	 * The quieted CAP_SYS_CHROOT denial is suppressed; the CAP_SYS_ADMIN
+	 * denial is logged.
+	 */
+	EXPECT_EQ(0, matches_log_cap(self->audit_fd, CAP_SYS_ADMIN));
+	EXPECT_EQ(0, matches_log_domain_allocated(self->audit_fd, getpid(),
+						  &domain_id));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/*
+ * Only the youngest denying layer decides quieting: a parent cannot silence a
+ * denial by a deeper layer that handles but does not quiet the capability.
+ */
+TEST_F(cap_audit, quiet_youngest_layer_wins)
+{
+	struct audit_records records;
+	int ruleset_fd;
+	__u64 domain_id;
+
+	/* Baseline: commoncap allows chroot before Landlock. */
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	ASSERT_EQ(0, chroot("/"));
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	/* Parent layer: denies and quiets CAP_SYS_CHROOT. */
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule_full(ruleset_fd, 1ULL << CAP_AUDIT_CONTROL,
+				       1ULL << CAP_SYS_CHROOT));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/* Child layer: denies CAP_SYS_CHROOT without quieting it. */
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	EXPECT_EQ(-1, chroot("/"));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	/*
+	 * The child is the youngest denier and does not quiet: log the denial.
+	 */
+	EXPECT_EQ(0, matches_log_cap(self->audit_fd, CAP_SYS_CHROOT));
+	EXPECT_EQ(0, matches_log_domain_allocated(self->audit_fd, getpid(),
+						  &domain_id));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/*
+ * Quieting an unknown capability bit has no effect: a rule that quiets only a
+ * bit above CAP_LAST_CAP still logs the denial of a known capability.
+ */
+TEST_F(cap_audit, quiet_unknown_bit_no_effect)
+{
+	struct audit_records records;
+	int ruleset_fd;
+	__u64 domain_id;
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	/* Quiet only an unknown bit (bit 63 is above CAP_LAST_CAP). */
+	ASSERT_EQ(0, add_cap_rule_full(ruleset_fd, 0, (1ULL << 63)));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	set_cap(_metadata, CAP_SYS_CHROOT);
+	EXPECT_EQ(-1, chroot("/"));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_CHROOT);
+
+	/* The unknown quiet bit does not suppress the known denial. */
+	EXPECT_EQ(0, matches_log_cap(self->audit_fd, CAP_SYS_CHROOT));
+	EXPECT_EQ(0, matches_log_domain_allocated(self->audit_fd, getpid(),
+						  &domain_id));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/*
+ * A capability check made with CAP_OPT_NOAUDIT is denied by Landlock but not
+ * logged: hook_capable() emits no Landlock audit record when the caller passes
+ * CAP_OPT_NOAUDIT, so the denial is silent here even though CAP_SYS_ADMIN is
+ * neither allowed nor quieted.  The probe is the
+ * ns_capable_noaudit(CAP_SYS_ADMIN) call in simple_xattr_list(), reached
+ * through tmpfs, which decides whether trusted.* xattrs are visible to
+ * listxattr(2).
+ */
+TEST_F(cap_audit, noaudit_probe_not_logged)
+{
+	struct audit_records records;
+	int ruleset_fd, fd;
+	__u64 domain_id;
+	char list[256];
+	ssize_t len;
+
+	/*
+	 * Private tmpfs holding a trusted.* xattr so its listxattr(2)
+	 * visibility depends only on the CAP_SYS_ADMIN noaudit probe.
+	 */
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWNS));
+	ASSERT_EQ(0, mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL));
+	ASSERT_EQ(0, mount("test", "/tmp", "tmpfs", 0, NULL));
+	fd = open("/tmp/f", O_CREAT | O_RDWR | O_CLOEXEC, 0600);
+	ASSERT_LE(0, fd);
+	ASSERT_EQ(0, fsetxattr(fd, "trusted.landlock_test", "x", 1, 0));
+
+	/* Baseline: with CAP_SYS_ADMIN, the trusted xattr is listed. */
+	len = flistxattr(fd, list, sizeof(list));
+	ASSERT_LE(0, len);
+	ASSERT_TRUE(list_has_xattr(list, len, "trusted.landlock_test"));
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	/* Allow CAP_AUDIT_CONTROL for child-side audit cleanup. */
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, CAP_AUDIT_CONTROL));
+	/* CAP_SYS_ADMIN is neither allowed nor quieted. */
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * CAP_SYS_ADMIN is still effective, but Landlock denies the noaudit
+	 * probe, so the trusted.* xattr is filtered out of the listing.
+	 */
+	len = flistxattr(fd, list, sizeof(list));
+	ASSERT_LE(0, len);
+	EXPECT_FALSE(list_has_xattr(list, len, "trusted.landlock_test"));
+	EXPECT_EQ(0, close(fd));
+
+	/* The denied noaudit probe leaves no audit record nor denial. */
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+
+	/*
+	 * Positive control: a normal (audited) CAP_SYS_ADMIN denial in the same
+	 * domain IS logged.  This proves the empty record set above is caused
+	 * by CAP_OPT_NOAUDIT, not by an always-allow or always-silent bug.
+	 */
+	EXPECT_EQ(-1, sethostname("test", 4));
+	EXPECT_EQ(EPERM, errno);
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+
+	EXPECT_EQ(0, matches_log_cap(self->audit_fd, CAP_SYS_ADMIN));
+	EXPECT_EQ(0, matches_log_domain_allocated(self->audit_fd, getpid(),
+						  &domain_id));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+}
+
+/* Trace tests */
+
+/* clang-format off */
+FIXTURE(cap_trace) {
+	/* clang-format on */
+	int tracefs_ok;
+};
+
+FIXTURE_SETUP(cap_trace)
+{
+	int ret;
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	ASSERT_EQ(0, unshare(CLONE_NEWNS));
+	ASSERT_EQ(0, mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL));
+
+	ret = tracefs_fixture_setup();
+	if (ret) {
+		clear_cap(_metadata, CAP_SYS_ADMIN);
+		self->tracefs_ok = 0;
+		SKIP(return, "tracefs not available");
+	}
+	self->tracefs_ok = 1;
+
+	ASSERT_EQ(0, tracefs_enable_event(TRACEFS_CREATE_RULESET_ENABLE, true));
+	ASSERT_EQ(0, tracefs_enable_event(TRACEFS_ADD_RULE_CAPABILITY_ENABLE,
+					  true));
+	ASSERT_EQ(0, tracefs_enable_event(
+			     TRACEFS_DENY_PERMISSION_CAPABILITY_ENABLE, true));
+	ASSERT_EQ(0, tracefs_clear());
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+FIXTURE_TEARDOWN(cap_trace)
+{
+	if (!self->tracefs_ok)
+		return;
+
+	set_cap(_metadata, CAP_SYS_ADMIN);
+	tracefs_enable_event(TRACEFS_CREATE_RULESET_ENABLE, false);
+	tracefs_enable_event(TRACEFS_ADD_RULE_CAPABILITY_ENABLE, false);
+	tracefs_enable_event(TRACEFS_DENY_PERMISSION_CAPABILITY_ENABLE, false);
+	tracefs_fixture_teardown();
+	clear_cap(_metadata, CAP_SYS_ADMIN);
+}
+
+/*
+ * Check the permission fields and version history, including two rejected calls
+ * and two successful calls that do not extend the effective policy: a repeated
+ * rule and an unknown-only rule.
+ */
+TEST_F(cap_trace, rule_events)
+{
+	const char *const version_1 =
+		REGEX_ADD_RULE_CAPABILITY_VERSION(TRACE_TASK, "1");
+	const char *const version_2 =
+		REGEX_ADD_RULE_CAPABILITY_VERSION(TRACE_TASK, "2");
+	const char *const version_3 =
+		REGEX_ADD_RULE_CAPABILITY_VERSION(TRACE_TASK, "3");
+	const struct landlock_capability_attr valid_attr = {
+		.permissions = LANDLOCK_PERMISSION_CAPABILITY_USE,
+		.allowed_capabilities = 1ULL << CAP_SYS_ADMIN,
+		.quiet_capabilities = 1ULL << CAP_SYS_CHROOT,
+	};
+	const struct landlock_capability_attr invalid_attr = {
+		.permissions = LANDLOCK_PERMISSION_NAMESPACE_USE,
+		.allowed_capabilities = 1ULL << CAP_SYS_ADMIN,
+	};
+	char expected[32], field[64];
+	char *buf;
+	int ruleset_fd;
+
+	if (!self->tracefs_ok)
+		SKIP(return, "tracefs not available");
+
+	ASSERT_EQ(0, tracefs_clear_buf());
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	ASSERT_EQ(0, add_cap_rule_full(ruleset_fd, 1ULL << CAP_SYS_ADMIN,
+				       1ULL << CAP_SYS_CHROOT));
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&invalid_attr, 0));
+	ASSERT_EQ(EINVAL, errno);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_CAPABILITY,
+					&valid_attr, LANDLOCK_ADD_RULE_QUIET));
+	ASSERT_EQ(EINVAL, errno);
+	ASSERT_EQ(0, add_cap_rule_full(ruleset_fd, 1ULL << CAP_SYS_ADMIN,
+				       1ULL << CAP_SYS_CHROOT));
+	ASSERT_EQ(0, add_cap_rule(ruleset_fd, 63));
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	buf = tracefs_read_buf();
+	ASSERT_NE(NULL, buf);
+
+	ASSERT_EQ(1,
+		  tracefs_count_matches(buf, REGEX_CREATE_RULESET(TRACE_TASK)));
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_CREATE_RULESET(TRACE_TASK),
+			     "handled_permissions", field, sizeof(field)));
+	EXPECT_STREQ("capability.use", field);
+
+	ASSERT_EQ(3,
+		  tracefs_count_matches(buf, "landlock_add_rule_capability: "));
+	ASSERT_EQ(3, tracefs_count_matches(
+			     buf, REGEX_ADD_RULE_CAPABILITY(TRACE_TASK)));
+	EXPECT_EQ(1, tracefs_count_matches(buf, version_1));
+	EXPECT_EQ(1, tracefs_count_matches(buf, version_2));
+	EXPECT_EQ(1, tracefs_count_matches(buf, version_3));
+
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_1, "permissions", field,
+					   sizeof(field)));
+	EXPECT_STREQ("capability.use", field);
+	ASSERT_EQ(0,
+		  tracefs_extract_field(buf, version_1, "allowed_capabilities",
+					field, sizeof(field)));
+	snprintf(expected, sizeof(expected), "0x%llx", 1ULL << CAP_SYS_ADMIN);
+	EXPECT_STREQ(expected, field);
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_1, "quiet_capabilities",
+					   field, sizeof(field)));
+	snprintf(expected, sizeof(expected), "0x%llx", 1ULL << CAP_SYS_CHROOT);
+	EXPECT_STREQ(expected, field);
+
+	/* The rejected calls emit no event and do not consume version 2. */
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_2, "permissions", field,
+					   sizeof(field)));
+	EXPECT_STREQ("capability.use", field);
+	ASSERT_EQ(0,
+		  tracefs_extract_field(buf, version_2, "allowed_capabilities",
+					field, sizeof(field)));
+	snprintf(expected, sizeof(expected), "0x%llx", 1ULL << CAP_SYS_ADMIN);
+	EXPECT_STREQ(expected, field);
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_2, "quiet_capabilities",
+					   field, sizeof(field)));
+	snprintf(expected, sizeof(expected), "0x%llx", 1ULL << CAP_SYS_CHROOT);
+	EXPECT_STREQ(expected, field);
+
+	/* The unknown-only call succeeds but contributes no effective bits. */
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_3, "permissions", field,
+					   sizeof(field)));
+	EXPECT_STREQ("capability.use", field);
+	ASSERT_EQ(0,
+		  tracefs_extract_field(buf, version_3, "allowed_capabilities",
+					field, sizeof(field)));
+	EXPECT_STREQ("0x0", field);
+	ASSERT_EQ(0, tracefs_extract_field(buf, version_3, "quiet_capabilities",
+					   field, sizeof(field)));
+	EXPECT_STREQ("0x0", field);
+
+	free(buf);
+}
+
+enum cap_trace_denial_kind {
+	CAP_TRACE_DENY,
+	CAP_TRACE_DENY_QUIET,
+	CAP_TRACE_DENY_NOAUDIT,
+};
+
+static void exercise_cap_trace_denial(struct __test_metadata *const _metadata,
+				      const enum cap_trace_denial_kind kind)
+{
+	int ruleset_fd, fd = -1;
+	char list[256];
+	ssize_t len;
+
+	disable_caps(_metadata);
+
+	if (kind == CAP_TRACE_DENY_NOAUDIT) {
+		set_cap(_metadata, CAP_SYS_ADMIN);
+		set_cap(_metadata, CAP_SYS_CHROOT);
+		ASSERT_EQ(0, mount("test", "/tmp", "tmpfs", 0, NULL));
+		fd = open("/tmp/f", O_CREAT | O_RDWR | O_CLOEXEC, 0600);
+		ASSERT_LE(0, fd);
+		ASSERT_EQ(0, fsetxattr(fd, "trusted.landlock_test", "x", 1, 0));
+
+		/* Baseline: CAP_SYS_ADMIN exposes the trusted xattr. */
+		len = flistxattr(fd, list, sizeof(list));
+		ASSERT_LE(0, len);
+		ASSERT_TRUE(list_has_xattr(list, len, "trusted.landlock_test"));
+	} else {
+		set_cap(_metadata, CAP_SYS_CHROOT);
+	}
+
+	ruleset_fd = create_cap_ruleset();
+	ASSERT_LE(0, ruleset_fd);
+	if (kind == CAP_TRACE_DENY_QUIET)
+		ASSERT_EQ(0, add_cap_rule_full(ruleset_fd, 0,
+					       1ULL << CAP_SYS_CHROOT));
+	enforce_ruleset(_metadata, ruleset_fd);
+	EXPECT_EQ(0, close(ruleset_fd));
+
+	if (kind == CAP_TRACE_DENY_NOAUDIT) {
+		/* Probe CAP_SYS_ADMIN with CAP_OPT_NOAUDIT. */
+		len = flistxattr(fd, list, sizeof(list));
+		ASSERT_LE(0, len);
+		EXPECT_FALSE(
+			list_has_xattr(list, len, "trusted.landlock_test"));
+		EXPECT_EQ(0, close(fd));
+
+		/* Control: an ordinary denial in the same domain is traced. */
+		EXPECT_EQ(-1, chroot("/"));
+		EXPECT_EQ(EPERM, errno);
+		clear_cap(_metadata, CAP_SYS_ADMIN);
+		clear_cap(_metadata, CAP_SYS_CHROOT);
+	} else {
+		EXPECT_EQ(-1, chroot("/"));
+		EXPECT_EQ(EPERM, errno);
+		clear_cap(_metadata, CAP_SYS_CHROOT);
+	}
+}
+
+static void test_cap_trace_denial(struct __test_metadata *const _metadata,
+				  const enum cap_trace_denial_kind kind,
+				  const int expected_capability,
+				  const char *const expected_logged)
+{
+	char expected[16], field[64];
+	int status;
+	char *buf;
+	pid_t child;
+
+	ASSERT_EQ(0, tracefs_clear_buf());
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		exercise_cap_trace_denial(_metadata, kind);
+		_exit(_metadata->exit_code);
+	}
+
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	ASSERT_TRUE(WIFEXITED(status));
+	ASSERT_EQ(EXIT_SUCCESS, WEXITSTATUS(status));
+
+	buf = tracefs_read_buf();
+	ASSERT_NE(NULL, buf);
+	ASSERT_EQ(1, tracefs_count_matches(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK)))
+	{
+		TH_LOG("Expected one capability denial event\n%s", buf);
+	}
+
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK),
+			     "domain", field, sizeof(field)));
+	EXPECT_STRNE("0", field);
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK),
+			     "same_exec", field, sizeof(field)));
+	EXPECT_STREQ("1", field);
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK),
+			     "logged", field, sizeof(field)));
+	EXPECT_STREQ(expected_logged, field);
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK),
+			     "blockers", field, sizeof(field)));
+	EXPECT_STREQ("use", field);
+	ASSERT_EQ(0, tracefs_extract_field(
+			     buf, REGEX_DENY_PERMISSION_CAPABILITY(TRACE_TASK),
+			     "capability", field, sizeof(field)));
+	snprintf(expected, sizeof(expected), "%d", expected_capability);
+	EXPECT_STREQ(expected, field);
+
+	free(buf);
+}
+
+TEST_F(cap_trace, deny)
+{
+	if (!self->tracefs_ok)
+		SKIP(return, "tracefs not available");
+	test_cap_trace_denial(_metadata, CAP_TRACE_DENY, CAP_SYS_CHROOT, "1");
+}
+
+TEST_F(cap_trace, deny_quiet)
+{
+	if (!self->tracefs_ok)
+		SKIP(return, "tracefs not available");
+	test_cap_trace_denial(_metadata, CAP_TRACE_DENY_QUIET, CAP_SYS_CHROOT,
+			      "0");
+}
+
+/*
+ * A CAP_OPT_NOAUDIT probe is denied without any record.  The audit counterpart
+ * checks the missing audit record; this one checks that the CAP_SYS_ADMIN probe
+ * emits no trace event, while the CAP_SYS_CHROOT denial that follows it in the
+ * same domain still does.
+ */
+TEST_F(cap_trace, noaudit_probe_not_traced)
+{
+	if (!self->tracefs_ok)
+		SKIP(return, "tracefs not available");
+	test_cap_trace_denial(_metadata, CAP_TRACE_DENY_NOAUDIT, CAP_SYS_CHROOT,
+			      "1");
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/landlock/trace.h b/tools/testing/selftests/landlock/trace.h
index 568c13d8eee4..36e8f16171b0 100644
--- a/tools/testing/selftests/landlock/trace.h
+++ b/tools/testing/selftests/landlock/trace.h
@@ -33,6 +33,8 @@
 	TRACEFS_LANDLOCK_DIR "/landlock_add_rule_net_port/enable"
 #define TRACEFS_ADD_RULE_NAMESPACE_ENABLE \
 	TRACEFS_LANDLOCK_DIR "/landlock_add_rule_namespace/enable"
+#define TRACEFS_ADD_RULE_CAPABILITY_ENABLE \
+	TRACEFS_LANDLOCK_DIR "/landlock_add_rule_capability/enable"
 #define TRACEFS_CHECK_RULE_FS_ENABLE \
 	TRACEFS_LANDLOCK_DIR "/landlock_check_rule_inode/enable"
 #define TRACEFS_CHECK_RULE_NET_ENABLE \
@@ -43,6 +45,8 @@
 	TRACEFS_LANDLOCK_DIR "/landlock_deny_access_net/enable"
 #define TRACEFS_DENY_PERMISSION_NAMESPACE_ENABLE \
 	TRACEFS_LANDLOCK_DIR "/landlock_deny_permission_namespace/enable"
+#define TRACEFS_DENY_PERMISSION_CAPABILITY_ENABLE \
+	TRACEFS_LANDLOCK_DIR "/landlock_deny_permission_capability/enable"
 #define TRACEFS_DENY_PTRACE_ENABLE \
 	TRACEFS_LANDLOCK_DIR "/landlock_deny_ptrace/enable"
 #define TRACEFS_DENY_SCOPE_SIGNAL_ENABLE \
@@ -110,6 +114,17 @@
 #define REGEX_ADD_RULE_NAMESPACE(task) \
 	REGEX_ADD_RULE_NAMESPACE_VERSION(task, "[0-9]\\+")
 
+#define REGEX_ADD_RULE_CAPABILITY_VERSION(task, version) \
+	TRACE_PREFIX(task)                               \
+	"landlock_add_rule_capability: "                 \
+	"ruleset=[0-9a-f]\\+\\." version " "             \
+	"permissions=[a-z._|]* "                         \
+	"allowed_capabilities=0x[0-9a-f]\\+ "            \
+	"quiet_capabilities=0x[0-9a-f]\\+$"
+
+#define REGEX_ADD_RULE_CAPABILITY(task) \
+	REGEX_ADD_RULE_CAPABILITY_VERSION(task, "[0-9]\\+")
+
 #define REGEX_CREATE_RULESET(task)        \
 	TRACE_PREFIX(task)                \
 	"landlock_create_ruleset: "       \
@@ -173,6 +188,15 @@
 	"namespace_type=0x[0-9a-f]\\+ "        \
 	"namespace_id=[0-9]\\+$"
 
+#define REGEX_DENY_PERMISSION_CAPABILITY(task)  \
+	TRACE_PREFIX(task)                      \
+	"landlock_deny_permission_capability: " \
+	"domain=[0-9a-f]\\+ "                   \
+	"same_exec=[01] "                       \
+	"logged=[01] "                          \
+	"blockers=[a-z_|]* "                    \
+	"capability=[0-9]\\+$"
+
 #define REGEX_DENY_PTRACE(task)      \
 	TRACE_PREFIX(task)           \
 	"landlock_deny_ptrace: "     \
-- 
2.55.0