[PATCH 2/3] selftests/landlock: Test that layering does not break refer

["Günther Noack" <gnoack3000@gmail.com>]

Regression test to exercise that layered Landlock domains do not
accidentally deny the LANDLOCK_ACCESS_FS_REFER access right.  This
used to be the case when layering a non-filesystem ruleset with a
filesystem-enforcing ruleset.  In that case, REFER operations that
would have been allowed for the individual rulesets would get denied
when layering the same rulesets.

Link: https://github.com/landlock-lsm/linux/issues/67
Link: https://github.com/landlock-lsm/go-landlock/issues/66
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
---
 tools/testing/selftests/landlock/fs_test.c | 39 ++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 6e979cef884d..c319bcea1437 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -2619,6 +2619,45 @@ TEST_F_FORK(layout1, refer_denied_by_default4)
 				layer_dir_s1d1_refer);
 }
 
+/*
+ * Regression test for layered domains: The two enforced Landlock layers both do
+ * not restrict the tested "refer" operations on their own, so they should also
+ * not restrict them when they are layered.
+ */
+static void test_layering_does_not_break_refer(
+	struct __test_metadata *const _metadata,
+	const struct landlock_ruleset_attr *const non_fs_attr)
+{
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	enforce_fs(_metadata, LANDLOCK_ACCESS_FS_REFER, layer_dir_s1d1_refer);
+
+	drop_access_rights(_metadata, non_fs_attr);
+
+	EXPECT_EQ(0, test_rename(file1_s1d1, file1_s1d2));
+	EXPECT_EQ(0, test_rename(file1_s1d2, file1_s1d1));
+	EXPECT_EQ(0, test_exchange(file2_s1d1, file2_s1d2));
+	EXPECT_EQ(0, test_exchange(file2_s1d2, file2_s1d1));
+}
+
+TEST_F_FORK(layout1, layering_with_net_does_not_break_refer)
+{
+	const struct landlock_ruleset_attr attr = {
+		.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP,
+	};
+
+	test_layering_does_not_break_refer(_metadata, &attr);
+}
+
+TEST_F_FORK(layout1, layering_with_scoped_does_not_break_refer)
+{
+	const struct landlock_ruleset_attr attr = {
+		.scoped = LANDLOCK_SCOPE_SIGNAL,
+	};
+
+	test_layering_does_not_break_refer(_metadata, &attr);
+}
+
 /*
  * Tests walking through a denied root mount.
  */
-- 
2.56.0