[RFC 3/4] selftests/landlock: Test ioctl support

[Günther Noack]

Exercise the use of Landlock's ioctl restriction: If ioctl is
restricted, the use of ioctl fails with a freshly opened /dev/tty
file.

Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
---
 tools/testing/selftests/landlock/fs_test.c | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index fdd7d439ce4..1f827604374 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -3655,6 +3655,68 @@ TEST(memfd_ftruncate)
 	ASSERT_EQ(0, close(fd));
 }
 
+/*
+ * Invokes ioctl(2) and returns its errno or 0.
+ * The provided fd needs to be a tty for this to work.
+ */
+static int test_tty_ioctl(int fd)
+{
+	struct winsize ws;
+
+	if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
+		return errno;
+	return 0;
+}
+
+/*
+ * Attempt ioctl on /dev/tty0 and /dev/tty1,
+ * with file descriptors opened before and after landlocking.
+ */
+TEST_F_FORK(layout1, ioctl)
+{
+	const struct rule rules[] = {
+		{
+			.path = "/dev/tty1",
+			.access = LANDLOCK_ACCESS_FS_IOCTL,
+		},
+		/* Implicitly: No ioctl access on /dev/tty0. */
+		{},
+	};
+	const __u64 handled = LANDLOCK_ACCESS_FS_IOCTL;
+	int ruleset_fd;
+	int old_tty0_fd, tty0_fd, tty1_fd;
+
+	old_tty0_fd = open("/dev/tty0", O_RDWR);
+	ASSERT_LE(0, old_tty0_fd);
+
+	/* Checks that ioctl works before landlocking. */
+	EXPECT_EQ(0, test_tty_ioctl(old_tty0_fd));
+
+	/* Enable Landlock. */
+	ruleset_fd = create_ruleset(_metadata, handled, rules);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Checks that ioctl with existing FD works after landlocking. */
+	EXPECT_EQ(0, test_tty_ioctl(old_tty0_fd));
+
+	/* Checks that same ioctl fails when file is opened after landlocking. */
+	tty0_fd = open("/dev/tty0", O_RDWR);
+	ASSERT_LE(0, tty0_fd);
+	EXPECT_EQ(EACCES, test_tty_ioctl(tty0_fd));
+
+	/* Checks that same ioctl fails when file is opened after landlocking. */
+	tty1_fd = open("/dev/tty1", O_RDWR);
+	ASSERT_LE(0, tty1_fd);
+	EXPECT_EQ(0, test_tty_ioctl(tty1_fd));
+
+	/* Close all TTY file descriptors. */
+	ASSERT_EQ(0, close(old_tty0_fd));
+	ASSERT_EQ(0, close(tty0_fd));
+	ASSERT_EQ(0, close(tty1_fd));
+}
+
 /* clang-format off */
 FIXTURE(layout1_bind) {};
 /* clang-format on */
-- 
2.40.1