tests: test CLONE_CLEAR_SIGHAND

Test that CLONE_CLEAR_SIGHAND resets signal handlers to SIG_DFL for the
child process and that CLONE_CLEAR_SIGHAND and CLONE_SIGHAND are
mutually exclusive.

Cc: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org
Cc: linux-api@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191014104538.3096-2-christian.brauner@ubuntu.com

MAINTAINERS

@@ -12826,6 +12826,7 @@ S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git
 F:	samples/pidfd/
 F:	tools/testing/selftests/pidfd/
+F:	tools/testing/selftests/clone3/
 K:	(?i)pidfd
 K:	(?i)clone3
 K:	\b(clone_args|kernel_clone_args)\b

tools/testing/selftests/Makefile

@@ -4,6 +4,7 @@ TARGETS += bpf
 TARGETS += breakpoints
 TARGETS += capabilities
 TARGETS += cgroup
+TARGETS += clone3
 TARGETS += cpufreq
 TARGETS += cpu-hotplug
 TARGETS += drivers/dma-buf

tools/testing/selftests/clone3/.gitignore

@@ -0,0 +1 @@
+clone3_clear_sighand

tools/testing/selftests/clone3/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0-only
+CFLAGS += -g -I../../../../usr/include/
+
+TEST_GEN_PROGS := clone3_clear_sighand
+
+include ../lib.mk

tools/testing/selftests/clone3/clone3_clear_sighand.c

@@ -0,0 +1,172 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+
+#include "../kselftest.h"
+
+#ifndef CLONE_CLEAR_SIGHAND
+#define CLONE_CLEAR_SIGHAND 0x100000000ULL
+#endif
+
+#ifndef __NR_clone3
+#define __NR_clone3 -1
+struct clone_args {
+	__aligned_u64 flags;
+	__aligned_u64 pidfd;
+	__aligned_u64 child_tid;
+	__aligned_u64 parent_tid;
+	__aligned_u64 exit_signal;
+	__aligned_u64 stack;
+	__aligned_u64 stack_size;
+	__aligned_u64 tls;
+};
+#endif
+
+static pid_t sys_clone3(struct clone_args *args, size_t size)
+{
+	return syscall(__NR_clone3, args, size);
+}
+
+static void test_clone3_supported(void)
+{
+	pid_t pid;
+	struct clone_args args = {};
+
+	if (__NR_clone3 < 0)
+		ksft_exit_skip("clone3() syscall is not supported\n");
+
+	/* Set to something that will always cause EINVAL. */
+	args.exit_signal = -1;
+	pid = sys_clone3(&args, sizeof(args));
+	if (!pid)
+		exit(EXIT_SUCCESS);
+
+	if (pid > 0) {
+		wait(NULL);
+		ksft_exit_fail_msg(
+			"Managed to create child process with invalid exit_signal\n");
+	}
+
+	if (errno == ENOSYS)
+		ksft_exit_skip("clone3() syscall is not supported\n");
+
+	ksft_print_msg("clone3() syscall supported\n");
+}
+
+static void nop_handler(int signo)
+{
+}
+
+static int wait_for_pid(pid_t pid)
+{
+	int status, ret;
+
+again:
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		if (errno == EINTR)
+			goto again;
+
+		return -1;
+	}
+
+	if (!WIFEXITED(status))
+		return -1;
+
+	return WEXITSTATUS(status);
+}
+
+static void test_clone3_clear_sighand(void)
+{
+	int ret;
+	pid_t pid;
+	struct clone_args args = {};
+	struct sigaction act;
+
+	/*
+	 * Check that CLONE_CLEAR_SIGHAND and CLONE_SIGHAND are mutually
+	 * exclusive.
+	 */
+	args.flags |= CLONE_CLEAR_SIGHAND | CLONE_SIGHAND;
+	args.exit_signal = SIGCHLD;
+	pid = sys_clone3(&args, sizeof(args));
+	if (pid > 0)
+		ksft_exit_fail_msg(
+			"clone3(CLONE_CLEAR_SIGHAND | CLONE_SIGHAND) succeeded\n");
+
+	act.sa_handler = nop_handler;
+	ret = sigemptyset(&act.sa_mask);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s - sigemptyset() failed\n",
+				   strerror(errno));
+
+	act.sa_flags = 0;
+
+	/* Register signal handler for SIGUSR1 */
+	ret = sigaction(SIGUSR1, &act, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s - sigaction(SIGUSR1, &act, NULL) failed\n",
+			strerror(errno));
+
+	/* Register signal handler for SIGUSR2 */
+	ret = sigaction(SIGUSR2, &act, NULL);
+	if (ret < 0)
+		ksft_exit_fail_msg(
+			"%s - sigaction(SIGUSR2, &act, NULL) failed\n",
+			strerror(errno));
+
+	/* Check that CLONE_CLEAR_SIGHAND works. */
+	args.flags = CLONE_CLEAR_SIGHAND;
+	pid = sys_clone3(&args, sizeof(args));
+	if (pid < 0)
+		ksft_exit_fail_msg("%s - clone3(CLONE_CLEAR_SIGHAND) failed\n",
+				   strerror(errno));
+
+	if (pid == 0) {
+		ret = sigaction(SIGUSR1, NULL, &act);
+		if (ret < 0)
+			exit(EXIT_FAILURE);
+
+		if (act.sa_handler != SIG_DFL)
+			exit(EXIT_FAILURE);
+
+		ret = sigaction(SIGUSR2, NULL, &act);
+		if (ret < 0)
+			exit(EXIT_FAILURE);
+
+		if (act.sa_handler != SIG_DFL)
+			exit(EXIT_FAILURE);
+
+		exit(EXIT_SUCCESS);
+	}
+
+	ret = wait_for_pid(pid);
+	if (ret)
+		ksft_exit_fail_msg(
+			"Failed to clear signal handler for child process\n");
+
+	ksft_test_result_pass("Cleared signal handlers for child process\n");
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	test_clone3_supported();
+	test_clone3_clear_sighand();
+
+	return ksft_exit_pass();
+}