Re: [PATCH v30 10/12] selftests/landlock: Add user space tests

From: Kees Cook <keescook@chromium.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: "James Morris" <jmorris@namei.org>,
	"Jann Horn" <jannh@google.com>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Anton Ivanov" <anton.ivanov@cambridgegreys.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"David Howells" <dhowells@redhat.com>,
	"Jeff Dike" <jdike@addtoit.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vincent Dagonneau" <vincent.dagonneau@ssi.gouv.fr>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	linux-security-module@vger.kernel.org, x86@kernel.org,
	"Mickaël Salaün" <mic@linux.microsoft.com>
Subject: Re: [PATCH v30 10/12] selftests/landlock: Add user space tests
Date: Fri, 19 Mar 2021 10:56:32 -0700	[thread overview]
Message-ID: <202103191026.D936362B@keescook> (raw)
In-Reply-To: <20210316204252.427806-11-mic@digikod.net>

On Tue, Mar 16, 2021 at 09:42:50PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@linux.microsoft.com>
> 
> Test all Landlock system calls, ptrace hooks semantic and filesystem
> access-control with multiple layouts.
> 
> Test coverage for security/landlock/ is 93.6% of lines.  The code not
> covered only deals with internal kernel errors (e.g. memory allocation)
> and race conditions.
> 
> Cc: James Morris <jmorris@namei.org>
> Cc: Jann Horn <jannh@google.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Serge E. Hallyn <serge@hallyn.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> Reviewed-by: Vincent Dagonneau <vincent.dagonneau@ssi.gouv.fr>
> Link: https://lore.kernel.org/r/20210316204252.427806-11-mic@digikod.net

This is terrific. I love the coverage. How did you measure this, BTW?
To increase it into memory allocation failures, have you tried
allocation fault injection:
https://www.kernel.org/doc/html/latest/fault-injection/fault-injection.html

> [...]
> +TEST(inconsistent_attr) {
> +	const long page_size = sysconf(_SC_PAGESIZE);
> +	char *const buf = malloc(page_size + 1);
> +	struct landlock_ruleset_attr *const ruleset_attr = (void *)buf;
> +
> +	ASSERT_NE(NULL, buf);
> +
> +	/* Checks copy_from_user(). */
> +	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, 0, 0));
> +	/* The size if less than sizeof(struct landlock_attr_enforce). */
> +	ASSERT_EQ(EINVAL, errno);
> +	ASSERT_EQ(-1, landlock_create_ruleset(ruleset_attr, 1, 0));
> +	ASSERT_EQ(EINVAL, errno);

Almost everywhere you're using ASSERT instead of EXPECT. Is this correct
(in the sense than as soon as an ASSERT fails the rest of the test is
skipped)? I do see you using EXPECT is some places, but I figured I'd
ask about the intention here.

> +/*
> + * TEST_F_FORK() is useful when a test drop privileges but the corresponding
> + * FIXTURE_TEARDOWN() requires them (e.g. to remove files from a directory
> + * where write actions are denied).  For convenience, FIXTURE_TEARDOWN() is
> + * also called when the test failed, but not when FIXTURE_SETUP() failed.  For
> + * this to be possible, we must not call abort() but instead exit smoothly
> + * (hence the step print).
> + */

Hm, interesting. I think this should be extracted into a separate patch
and added to the test harness proper.

Could this be solved with TEARDOWN being called on SETUP failure?

> +#define TEST_F_FORK(fixture_name, test_name) \
> +	static void fixture_name##_##test_name##_child( \
> +		struct __test_metadata *_metadata, \
> +		FIXTURE_DATA(fixture_name) *self, \
> +		const FIXTURE_VARIANT(fixture_name) *variant); \
> +	TEST_F(fixture_name, test_name) \
> +	{ \
> +		int status; \
> +		const pid_t child = fork(); \
> +		if (child < 0) \
> +			abort(); \
> +		if (child == 0) { \
> +			_metadata->no_print = 1; \
> +			fixture_name##_##test_name##_child(_metadata, self, variant); \
> +			if (_metadata->skip) \
> +				_exit(255); \
> +			if (_metadata->passed) \
> +				_exit(0); \
> +			_exit(_metadata->step); \
> +		} \
> +		if (child != waitpid(child, &status, 0)) \
> +			abort(); \
> +		if (WIFSIGNALED(status) || !WIFEXITED(status)) { \
> +			_metadata->passed = 0; \
> +			_metadata->step = 1; \
> +			return; \
> +		} \
> +		switch (WEXITSTATUS(status)) { \
> +		case 0: \
> +			_metadata->passed = 1; \
> +			break; \
> +		case 255: \
> +			_metadata->passed = 1; \
> +			_metadata->skip = 1; \
> +			break; \
> +		default: \
> +			_metadata->passed = 0; \
> +			_metadata->step = WEXITSTATUS(status); \
> +			break; \
> +		} \
> +	} \

This looks like a subset of __wait_for_test()? Could __TEST_F_IMPL() be
updated instead to do this? (Though the fork overhead might not be great
for everyone.)

-- 
Kees Cook