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

[Mickaël Salaün]

On 02/05/2023 19:17, Günther Noack wrote:
> 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. */

We should create a new PTS mount point, create a new session, and use 
that for tests to limit the dependency on the test environment and not 
mess with it.


> +		{},
> +	};
> +	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. */

Enable*s*

> +	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));

/dev, or rather the test PTS mount point, and its parent, should also be 
tested. We can use three layers in the same test for that.


> +
> +	/* 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 */