Subject: Re: [PATCH v3 3/6] selftest/Landlock: Signal restriction tests

From: Mickaël Salaün <[email-masked]>
Date: Tue, 20 Aug 2024 17:57:37 +0200

On Thu, Aug 15, 2024 at 12:29:22PM -0600, Tahera Fahimi wrote:
> This patch expands Landlock ABI version 6 by providing tests for
> signal scoping mechanism. Base on kill(2), if the signal is 0,
> no signal will be sent, but the permission of a process to send
> a signal will be checked. Likewise, this test consider one signal
> for each signal category.
> 
> Signed-off-by: Tahera Fahimi <[email-masked]>
> ---
> Chnages in versions:
> V2:
> * Moving tests from ptrace_test.c to scoped_signal_test.c
> * Remove debugging statements.
> * Covering all basic restriction scenarios by sending 0 as signal
> V1:
> * Expanding Landlock ABI version 6 by providing basic tests for
>   four signals to test signal scoping mechanism.
> ---
>  .../selftests/landlock/scoped_signal_test.c   | 302 ++++++++++++++++++
>  1 file changed, 302 insertions(+)
>  create mode 100644 tools/testing/selftests/landlock/scoped_signal_test.c
> 
> diff --git a/tools/testing/selftests/landlock/scoped_signal_test.c b/tools/testing/selftests/landlock/scoped_signal_test.c
> new file mode 100644
> index 000000000000..92958c6266ca
> --- /dev/null
> +++ b/tools/testing/selftests/landlock/scoped_signal_test.c
> @@ -0,0 +1,302 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Landlock tests - Signal Scoping
> + *
> + * Copyright © 2017-2020 Mickaël Salaün <[email-masked]>
> + * Copyright © 2019-2020 ANSSI
> + */
> +
> +#define _GNU_SOURCE
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <linux/landlock.h>
> +#include <signal.h>
> +#include <sys/prctl.h>
> +#include <sys/types.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +
> +#include "common.h"
> +
> +static sig_atomic_t signaled;
> +
> +static void create_signal_domain(struct __test_metadata *const _metadata)

You can add a create_scoped_domain() helper in scoped_common.h with a
"scope" argument, and use it as well for the abstract unix socket tests.

> +{
> +	int ruleset_fd;
> +	const struct landlock_ruleset_attr ruleset_attr = {
> +		.scoped = LANDLOCK_SCOPED_SIGNAL,
> +	};
> +
> +	ruleset_fd =
> +		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
> +	EXPECT_LE(0, ruleset_fd)

Again, please use ASSERT_* when it doesn't make sense to continue the
tests if something goes wrong.  In this case, if the domain creation
failed, something is very wrong and we should stop right away.
Everything that follow would not make any sense to test.

> +	{
> +		TH_LOG("Failed to create a ruleset: %s", strerror(errno));
> +	}
> +	enforce_ruleset(_metadata, ruleset_fd);
> +	EXPECT_EQ(0, close(ruleset_fd));

Here, EXPECT is OK because not being able to close the FD would not
impact the rest of the tests.

> +}
> +
> +static void scope_signal_handler(int sig, siginfo_t *info, void *ucontext)
> +{
> +	if (sig == SIGHUP || sig == SIGURG || sig == SIGTSTP ||
> +	    sig == SIGTRAP || sig == SIGUSR1) {
> +		signaled = 1;
> +	}
> +}
> +
> +/* clang-format off */
> +FIXTURE(signal_scoping) {};
> +/* clang-format on */
> +
> +FIXTURE_VARIANT(signal_scoping)

You should include scoped_common.h which would declare these variants
(see my reviews for the abstract unix socket tests).

> +{
> +	const int sig;

"sig" should not be part of this variant, but a TEST_F() should be
created for each useful signal.  Instead of using
signal_scoping/scoped_domains, different signal only need to be tested
against one domain topology e.g., only a sandboxed/scoped child.

These variants should be used to test the same semantic as for the
abstract unix socket: TEST_F(scoped_domains, to_child) and
TEST_F(scoped_domains, to_parent)

> +	const bool domain_both;
> +	const bool domain_parent;
> +	const bool domain_child;
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_without_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = false,
> +	.domain_parent = false,
> +	.domain_child = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_child_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = false,
> +	.domain_parent = false,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_parent_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_sibling_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_sibling_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = true,
> +	.domain_parent = false,
> +	.domain_child = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_nested_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = true,
> +	.domain_parent = false,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_nested_and_parent_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain) {
> +	/* clang-format on */
> +	.sig = 0,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* Default Action: Terminate*/
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain_SIGHUP) {
> +	/* clang-format on */
> +	.sig = SIGHUP,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_forked_domain_SIGHUP) {
> +	/* clang-format on */
> +	.sig = SIGHUP,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* Default Action: Ignore*/
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain_SIGURG) {
> +	/* clang-format on */
> +	.sig = SIGURG,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_forked_domain_SIGURG) {
> +	/* clang-format on */
> +	.sig = SIGURG,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* Default Action: Stop*/
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain_SIGTSTP) {
> +	/* clang-format on */
> +	.sig = SIGTSTP,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_forked_domain_SIGTSTP) {
> +	/* clang-format on */
> +	.sig = SIGTSTP,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* Default Action: Coredump*/
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain_SIGTRAP) {
> +	/* clang-format on */
> +	.sig = SIGTRAP,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, allow_with_forked_domain_SIGTRAP) {
> +	/* clang-format on */
> +	.sig = SIGTRAP,
> +	.domain_both = false,
> +	.domain_parent = true,
> +	.domain_child = false,
> +};
> +
> +/* clang-format off */
> +FIXTURE_VARIANT_ADD(signal_scoping, deny_with_forked_domain_SIGUSR1) {
> +	/* clang-format on */
> +	.sig = SIGUSR1,
> +	.domain_both = true,
> +	.domain_parent = true,
> +	.domain_child = true,
> +};
> +
> +FIXTURE_SETUP(signal_scoping)
> +{
> +}
> +
> +FIXTURE_TEARDOWN(signal_scoping)
> +{
> +}
> +
> +TEST_F(signal_scoping, test_signal)

This test should only test one kind of signal (hence no signal
variants), but it should be splitted in two tests (i.e. to_child and
to_parent).  All the different signals should be tested with a dedicated
test with the same domain topology.

The code of this test should then be organized the same way and look
pretty similar to the other TEST_F(scoped_signal, to_child) from the
abstract unix socket test file.

> +{
> +	pid_t child;
> +	pid_t parent = getpid();
> +	int status;
> +	bool can_signal;
> +	int pipe_parent[2];
> +	struct sigaction action = {
> +		.sa_sigaction = scope_signal_handler,
> +		.sa_flags = SA_SIGINFO,
> +
> +	};
> +
> +	can_signal = !variant->domain_child;
> +
> +	if (variant->sig > 0)
> +		ASSERT_LE(0, sigaction(variant->sig, &action, NULL));
> +
> +	if (variant->domain_both) {
> +		create_signal_domain(_metadata);
> +		if (!__test_passed(_metadata))

We should not explicitly call __test_passed().  Just use ASSERT_* in
create_scoped_domain().

> +			/* Aborts before forking. */
> +			return;
> +	}
> +	ASSERT_EQ(0, pipe2(pipe_parent, O_CLOEXEC));
> +
> +	child = fork();
> +	ASSERT_LE(0, child);
> +	if (child == 0) {
> +		char buf_child;
> +		int err;
> +
> +		ASSERT_EQ(0, close(pipe_parent[1]));
> +		if (variant->domain_child)
> +			create_signal_domain(_metadata);
> +
> +		/* Waits for the parent to be in a domain, if any. */
> +		ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1));
> +
> +		err = kill(parent, variant->sig);
> +		if (can_signal) {
> +			ASSERT_EQ(0, err);
> +		} else {
> +			ASSERT_EQ(-1, err);
> +			ASSERT_EQ(EPERM, errno);
> +		}
> +		/* no matter of the domain, a process should be able to send

Please follow the comment formatting rules everywhere as I explained
before:

/*
 * No matter of the domain, a process should be able to send
 * a signal to itself.
 */

> +		 * a signal to itself.
> +		 */
> +		ASSERT_EQ(0, raise(variant->sig));
> +		if (variant->sig > 0)
> +			ASSERT_EQ(1, signaled);
> +		_exit(_metadata->exit_code);
> +		return;
> +	}
> +	ASSERT_EQ(0, close(pipe_parent[0]));
> +	if (variant->domain_parent)
> +		create_signal_domain(_metadata);
> +
> +	/* Signals that the parent is in a domain, if any. */
> +	ASSERT_EQ(1, write(pipe_parent[1], ".", 1));
> +
> +	if (can_signal && variant->sig > 0) {
> +		ASSERT_EQ(-1, pause());
> +		ASSERT_EQ(EINTR, errno);
> +		ASSERT_EQ(1, signaled);
> +	} else {
> +		ASSERT_EQ(0, signaled);
> +	}
> +
> +	ASSERT_EQ(child, waitpid(child, &status, 0));
> +
> +	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
> +	    WEXITSTATUS(status) != EXIT_SUCCESS)
> +		_metadata->exit_code = KSFT_FAIL;
> +}
> +
> +TEST_HARNESS_MAIN
> -- 
> 2.34.1
> 
>