selftests/landlock: Test signal scoping

Provide tests for the signal scoping.  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: SIGTRAP, SIGURG, SIGHUP, and SIGTSTP.
Signed-off-by: Tahera Fahimi <fahimitahera@gmail.com>
Link: https://lore.kernel.org/r/15dc202bb7f0a462ddeaa0c1cd630d2a7c6fa5c5.1725657728.git.fahimitahera@gmail.com
[mic: Fix commit message, use dedicated variables per process, properly
close FDs, extend send_sig_to_parent to make sure scoping works as
expected]
Signed-off-by: Mickaël Salaün <mic@digikod.net>

tools/testing/selftests/landlock/scoped_signal_test.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Signal Scoping
+ *
+ * Copyright © 2024 Tahera Fahimi <fahimitahera@gmail.com>
+ */
+
+#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"
+#include "scoped_common.h"
+
+/* This variable is used for handling several signals. */
+static volatile sig_atomic_t is_signaled;
+
+/* clang-format off */
+FIXTURE(scoping_signals) {};
+/* clang-format on */
+
+FIXTURE_VARIANT(scoping_signals)
+{
+	int sig;
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(scoping_signals, sigtrap) {
+	/* clang-format on */
+	.sig = SIGTRAP,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(scoping_signals, sigurg) {
+	/* clang-format on */
+	.sig = SIGURG,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(scoping_signals, sighup) {
+	/* clang-format on */
+	.sig = SIGHUP,
+};
+
+/* clang-format off */
+FIXTURE_VARIANT_ADD(scoping_signals, sigtstp) {
+	/* clang-format on */
+	.sig = SIGTSTP,
+};
+
+FIXTURE_SETUP(scoping_signals)
+{
+	drop_caps(_metadata);
+
+	is_signaled = 0;
+}
+
+FIXTURE_TEARDOWN(scoping_signals)
+{
+}
+
+static void scope_signal_handler(int sig, siginfo_t *info, void *ucontext)
+{
+	if (sig == SIGTRAP || sig == SIGURG || sig == SIGHUP || sig == SIGTSTP)
+		is_signaled = 1;
+}
+
+/*
+ * In this test, a child process sends a signal to parent before and
+ * after getting scoped.
+ */
+TEST_F(scoping_signals, send_sig_to_parent)
+{
+	int pipe_parent[2];
+	int status;
+	pid_t child;
+	pid_t parent = getpid();
+	struct sigaction action = {
+		.sa_sigaction = scope_signal_handler,
+		.sa_flags = SA_SIGINFO,
+
+	};
+
+	ASSERT_EQ(0, pipe2(pipe_parent, O_CLOEXEC));
+	ASSERT_LE(0, sigaction(variant->sig, &action, NULL));
+
+	/* The process should not have already been signaled. */
+	EXPECT_EQ(0, is_signaled);
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		char buf_child;
+		int err;
+
+		EXPECT_EQ(0, close(pipe_parent[1]));
+
+		/*
+		 * The child process can send signal to parent when
+		 * domain is not scoped.
+		 */
+		err = kill(parent, variant->sig);
+		ASSERT_EQ(0, err);
+		ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1));
+		EXPECT_EQ(0, close(pipe_parent[0]));
+
+		create_scoped_domain(_metadata, LANDLOCK_SCOPE_SIGNAL);
+
+		/*
+		 * The child process cannot send signal to the parent
+		 * anymore.
+		 */
+		err = kill(parent, variant->sig);
+		ASSERT_EQ(-1, err);
+		ASSERT_EQ(EPERM, errno);
+
+		/*
+		 * No matter of the domain, a process should be able to
+		 * send a signal to itself.
+		 */
+		ASSERT_EQ(0, is_signaled);
+		ASSERT_EQ(0, raise(variant->sig));
+		ASSERT_EQ(1, is_signaled);
+
+		_exit(_metadata->exit_code);
+		return;
+	}
+	EXPECT_EQ(0, close(pipe_parent[0]));
+
+	/* Waits for a first signal to be received, without race condition. */
+	while (!is_signaled && !usleep(1))
+		;
+	ASSERT_EQ(1, is_signaled);
+	ASSERT_EQ(1, write(pipe_parent[1], ".", 1));
+	EXPECT_EQ(0, close(pipe_parent[1]));
+	is_signaled = 0;
+
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
+	    WEXITSTATUS(status) != EXIT_SUCCESS)
+		_metadata->exit_code = KSFT_FAIL;
+
+	EXPECT_EQ(0, is_signaled);
+}
+
+/* clang-format off */
+FIXTURE(scoped_domains) {};
+/* clang-format on */
+
+#include "scoped_base_variants.h"
+
+FIXTURE_SETUP(scoped_domains)
+{
+	drop_caps(_metadata);
+}
+
+FIXTURE_TEARDOWN(scoped_domains)
+{
+}
+
+/*
+ * This test ensures that a scoped process cannot send signal out of
+ * scoped domain.
+ */
+TEST_F(scoped_domains, check_access_signal)
+{
+	pid_t child;
+	pid_t parent = getpid();
+	int status;
+	bool can_signal_child, can_signal_parent;
+	int pipe_parent[2], pipe_child[2];
+	char buf_parent;
+	int err;
+
+	can_signal_parent = !variant->domain_child;
+	can_signal_child = !variant->domain_parent;
+
+	if (variant->domain_both)
+		create_scoped_domain(_metadata, LANDLOCK_SCOPE_SIGNAL);
+
+	ASSERT_EQ(0, pipe2(pipe_parent, O_CLOEXEC));
+	ASSERT_EQ(0, pipe2(pipe_child, O_CLOEXEC));
+
+	child = fork();
+	ASSERT_LE(0, child);
+	if (child == 0) {
+		char buf_child;
+
+		EXPECT_EQ(0, close(pipe_child[0]));
+		EXPECT_EQ(0, close(pipe_parent[1]));
+
+		if (variant->domain_child)
+			create_scoped_domain(_metadata, LANDLOCK_SCOPE_SIGNAL);
+
+		ASSERT_EQ(1, write(pipe_child[1], ".", 1));
+		EXPECT_EQ(0, close(pipe_child[1]));
+
+		/* Waits for the parent to send signals. */
+		ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1));
+		EXPECT_EQ(0, close(pipe_parent[0]));
+
+		err = kill(parent, 0);
+		if (can_signal_parent) {
+			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 a signal to itself.
+		 */
+		ASSERT_EQ(0, raise(0));
+
+		_exit(_metadata->exit_code);
+		return;
+	}
+	EXPECT_EQ(0, close(pipe_parent[0]));
+	EXPECT_EQ(0, close(pipe_child[1]));
+
+	if (variant->domain_parent)
+		create_scoped_domain(_metadata, LANDLOCK_SCOPE_SIGNAL);
+
+	ASSERT_EQ(1, read(pipe_child[0], &buf_parent, 1));
+	EXPECT_EQ(0, close(pipe_child[0]));
+
+	err = kill(child, 0);
+	if (can_signal_child) {
+		ASSERT_EQ(0, err);
+	} else {
+		ASSERT_EQ(-1, err);
+		ASSERT_EQ(EPERM, errno);
+	}
+	ASSERT_EQ(0, raise(0));
+
+	ASSERT_EQ(1, write(pipe_parent[1], ".", 1));
+	EXPECT_EQ(0, close(pipe_parent[1]));
+	ASSERT_EQ(child, waitpid(child, &status, 0));
+
+	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
+	    WEXITSTATUS(status) != EXIT_SUCCESS)
+		_metadata->exit_code = KSFT_FAIL;
+}
+
+TEST_HARNESS_MAIN