[PATCH v5 3/7] selftests/landlock: Test IOCTL support

[Günther Noack]

Hi!

On Mon, Nov 20, 2023 at 09:41:20PM +0100, Mickaël Salaün wrote:
> On Fri, Nov 17, 2023 at 04:49:16PM +0100, Günther Noack wrote:
> > +FIXTURE_VARIANT(ioctl)
> > +{
> > +	const __u64 handled;
> > +	const __u64 permitted;
> 
> Why not "allowed" like the rule's field? Same for the variant names.

Just for consistency with the ftruncate tests which also named it like that... %-)

Sounds good though, I'll just rename it in both places.


> > +	const mode_t open_mode;
> > +	/*
> > +	 * These are the expected IOCTL results for a representative IOCTL from
> > +	 * each of the IOCTL groups.  We only distinguish the 0 and EACCES
> > +	 * results here, and treat other errors as 0.
> 
> In this case, why not use a boolean instead of a semi-correct error
> code?

I found it slightly less convoluted.  When we use booleans here, we need to map
between error codes and booleans at a different layer.  At the same time, we
already have various test_foo_ioctl() and test_foo() functions, and they are
sometimes also used in other contexts like test_fs_ioc_getflags_ioctl().  These
test_foo() helpers generally return error codes so far, and it felt more
important to stay consistent with that.  If we want to keep that both, the only
other place to map between booleans and error codes would be with ternary
operators or such in the EXPECT_EQ clauses, but that also felt like it would
turn unreadable... %-)

I can change it if you feel strongly about it though. Let me know.

> > +	 */
> > +	const int expected_fioqsize_result; /* G1 */
> > +	const int expected_fibmap_result; /* G2 */
> > +	const int expected_fionread_result; /* G3 */
> > +	const int expected_fs_ioc_zero_range_result; /* G4 */
> > +	const int expected_fs_ioc_getflags_result; /* other */
> > +};
> > +
> > +/* clang-format off */
> > +FIXTURE_VARIANT_ADD(ioctl, ioctl_handled_i_permitted_none) {
> 
> You can remove all the variant's "ioctl_" prefixes.

Done.


> > +	/* clang-format on */
> > +	.handled = LANDLOCK_ACCESS_FS_EXECUTE | LANDLOCK_ACCESS_FS_IOCTL,
> > +	.permitted = LANDLOCK_ACCESS_FS_EXECUTE,
> 
> You could use 0 instead and don't add the related rule in this case.

Done.


> Great tests!

Thanks :)


> > +static int test_fioqsize_ioctl(int fd)
> > +{
> > +	size_t sz;
> > +
> > +	if (ioctl(fd, FIOQSIZE, &sz) < 0)
> > +		return errno;
> > +	return 0;
> > +}
> > +
> > +static int test_fibmap_ioctl(int fd)
> > +{
> > +	int blk = 0;
> > +
> > +	/*
> > +	 * We only want to distinguish here whether Landlock already caught it,
> > +	 * so we treat anything but EACCESS as success.  (It commonly returns
> > +	 * EPERM when missing CAP_SYS_RAWIO.)
> > +	 */
> > +	if (ioctl(fd, FIBMAP, &blk) < 0 && errno == EACCES)
> > +		return errno;
> > +	return 0;
> > +}
> > +
> > +static int test_fionread_ioctl(int fd)
> > +{
> > +	size_t sz = 0;
> > +
> > +	if (ioctl(fd, FIONREAD, &sz) < 0 && errno == EACCES)
> > +		return errno;
> > +	return 0;
> > +}
> > +
> > +#define FS_IOC_ZERO_RANGE _IOW('X', 57, struct space_resv)
> > +
> > +static int test_fs_ioc_zero_range_ioctl(int fd)
> > +{
> > +	struct space_resv {
> > +		__s16 l_type;
> > +		__s16 l_whence;
> > +		__s64 l_start;
> > +		__s64 l_len; /* len == 0 means until end of file */
> > +		__s32 l_sysid;
> > +		__u32 l_pid;
> > +		__s32 l_pad[4]; /* reserved area */
> > +	} reservation = {};
> > +	/*
> > +	 * This can fail for various reasons, but we only want to distinguish
> > +	 * here whether Landlock already caught it, so we treat anything but
> > +	 * EACCES as success.
> > +	 */
> > +	if (ioctl(fd, FS_IOC_ZERO_RANGE, &reservation) < 0 && errno == EACCES)
> 
> What are the guarantees that an error different than EACCES would not
> mask EACCES and then make tests pass whereas they should not?

It is indeed possible that one of these ioctls legitimately returns EACCES after
Landlock was letting that ioctl through, and then we could not tell apart
whether Landlock blocked it or whether the underlying IOCTL command returned
that.  I double checked that this is not the case for these specific
invocations.  But with some other IOCTL commands in these groups, I believe I
was getting EACCES sometimes from the IOCTL.  So we only use one representative
IOCTL from each IOCTL group, for which it happened to work.

To convince yourself, you can see in the tests that we have both "success" and
"blocked" examples in the tests for each of these IOCTL commands, and the
Landlock rules are the only difference between these examples. Therefore, we
know that it is actually Landlock returning the EACCES and not the underlying
IOCTL.

> > +		return errno;
> > +	return 0;
> > +}
> > +
> > +TEST_F_FORK(ioctl, handle_dir_access_file)
> > +{
> > +	const int flag = 0;
> > +	const struct rule rules[] = {
> > +		{
> > +			.path = dir_s1d1,
> > +			.access = variant->permitted,
> > +		},
> > +		{},
> > +	};
> > +	int fd, ruleset_fd;
> 
> Please rename fd into something like file_fd.

Done.


> > +TEST_F_FORK(ioctl, handle_file_access_file)
> > +{
> > +	const char *const path = file1_s1d1;
> > +	const int flag = 0;
> > +	const struct rule rules[] = {
> > +		{
> > +			.path = path,
> > +			.access = variant->permitted,
> > +		},
> > +		{},
> > +	};
> > +	int fd, ruleset_fd;
> > +
> > +	if (variant->permitted & LANDLOCK_ACCESS_FS_READ_DIR) {
> > +		/* This access right can not be granted on files. */
> > +		return;
> > +	}
> 
> You should use SKIP().

Done.


> > +	/* Enables Landlock. */
> > +	ruleset_fd = create_ruleset(_metadata, variant->handled, rules);
> > +	ASSERT_LE(0, ruleset_fd);
> > +	enforce_ruleset(_metadata, ruleset_fd);
> > +	ASSERT_EQ(0, close(ruleset_fd));
> > +
> > +	fd = open(path, variant->open_mode);
> > +	ASSERT_LE(0, fd);
> > +
> > +	/*
> > +	 * Checks that IOCTL commands in each IOCTL group return the expected
> > +	 * errors.
> > +	 */
> > +	EXPECT_EQ(variant->expected_fioqsize_result, test_fioqsize_ioctl(fd));
> > +	EXPECT_EQ(variant->expected_fibmap_result, test_fibmap_ioctl(fd));
> > +	EXPECT_EQ(variant->expected_fionread_result, test_fionread_ioctl(fd));
> > +	EXPECT_EQ(variant->expected_fs_ioc_zero_range_result,
> > +		  test_fs_ioc_zero_range_ioctl(fd));
> > +	EXPECT_EQ(variant->expected_fs_ioc_getflags_result,
> > +		  test_fs_ioc_getflags_ioctl(fd));
> > +
> > +	/* Checks that unrestrictable commands are unrestricted. */
> > +	EXPECT_EQ(0, ioctl(fd, FIOCLEX));
> > +	EXPECT_EQ(0, ioctl(fd, FIONCLEX));
> > +	EXPECT_EQ(0, ioctl(fd, FIONBIO, &flag));
> > +	EXPECT_EQ(0, ioctl(fd, FIOASYNC, &flag));
> > +
> > +	ASSERT_EQ(0, close(fd));
> > +}
> 
> Don't you want to create and use a common helper with most of these
> TEST_F_FORK blocks? It would highlight what is the same or different,
> and it would also enables to extend the coverage to other file types
> (e.g. character device).

I did not find a good way to factor this out, to be honest, and so preferred to
keep it unrolled.

I try to follow the rule of not putting too many "if" conditions and logic into
my tests (it helps to keep the tests straightforward and understandable), and I
find it more straightforward to spell out these few EXPECT_EQs three times than
introducing a "test_all_ioctl_expectations()" helper function :)

—Günther