selftests/landlock: Test IOCTL with memfds

Because the LANDLOCK_ACCESS_FS_IOCTL_DEV right is associated with the
opened file during open(2), IOCTLs are supposed to work with files
which are opened by means other than open(2).
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://lore.kernel.org/r/20240419161122.2023765-4-gnoack@google.comSigned-off-by: Mickaël Salaün <mic@digikod.net>

tools/testing/selftests/landlock/fs_test.c

@@ -3849,20 +3849,48 @@ TEST_F_FORK(ftruncate, open_and_ftruncate_in_different_processes)
 	ASSERT_EQ(0, close(socket_fds[1]));
 }
 
-TEST(memfd_ftruncate)
+/* Invokes the FS_IOC_GETFLAGS IOCTL and returns its errno or 0. */
+static int test_fs_ioc_getflags_ioctl(int fd)
 {
-	int fd;
+	uint32_t flags;
+
+	if (ioctl(fd, FS_IOC_GETFLAGS, &flags) < 0)
+		return errno;
+	return 0;
+}
 
-	fd = memfd_create("name", MFD_CLOEXEC);
-	ASSERT_LE(0, fd);
+TEST(memfd_ftruncate_and_ioctl)
+{
+	const struct landlock_ruleset_attr attr = {
+		.handled_access_fs = ACCESS_ALL,
+	};
+	int ruleset_fd, fd, i;
 
 	/*
-	 * Checks that ftruncate is permitted on file descriptors that are
-	 * created in ways other than open(2).
+	 * We exercise the same test both with and without Landlock enabled, to
+	 * ensure that it behaves the same in both cases.
 	 */
-	EXPECT_EQ(0, test_ftruncate(fd));
+	for (i = 0; i < 2; i++) {
+		/* Creates a new memfd. */
+		fd = memfd_create("name", MFD_CLOEXEC);
+		ASSERT_LE(0, fd);
 
-	ASSERT_EQ(0, close(fd));
+		/*
+		 * Checks that operations associated with the opened file
+		 * (ftruncate, ioctl) are permitted on file descriptors that are
+		 * created in ways other than open(2).
+		 */
+		EXPECT_EQ(0, test_ftruncate(fd));
+		EXPECT_EQ(0, test_fs_ioc_getflags_ioctl(fd));
+
+		ASSERT_EQ(0, close(fd));
+
+		/* Enables Landlock. */
+		ruleset_fd = landlock_create_ruleset(&attr, sizeof(attr), 0);
+		ASSERT_LE(0, ruleset_fd);
+		enforce_ruleset(_metadata, ruleset_fd);
+		ASSERT_EQ(0, close(ruleset_fd));
+	}
 }
 
 static int test_fionread_ioctl(int fd)