Re: [PATCH v6 2/2] selftests: add tests for pidfd_send_signal()

On Mon, Dec 31, 2018 at 12:27:13AM +0100, Christian Brauner wrote:

On Sun, Dec 30, 2018 at 03:02:45PM -0600, Serge Hallyn wrote:

quoted

On Sat, Dec 29, 2018 at 11:27:56PM +0100, Christian Brauner wrote:

quoted

As suggested by Andrew Morton in [1] add selftests for the new
sys_pidfd_send_signal() syscall.
This tests whether we can send a signal to an existing process and whether
sending a signal to a process that has already exited fails with ESRCH.

[1]: https://lore.kernel.org/lkml/20181228152012.dbf0508c2508138efc5f2bbe@linux-foundation.org/ (local)

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <redacted>
Cc: Kees Cook <redacted>
Cc: Serge Hallyn <serge@hallyn.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

Not saying you need to do this, but it would be neat if you could test
sending to a pid which has been recycled :)

Yeah, I thought about it but it's a little weird code. First of all, we
can't set /proc/sys/kernel/pid_max to a very low value since this is a
system wide setting. So we need to recycle a lot via fork(). Something
along the lines of:
- unshare pid namespace
- fork to create pid 1 in new pid namespace
- cycle with fork() until pid > 300 since pids lower than 300 are
  reserved by the kernel.
  (That means if we simply use the first fork() after we created pid 1 we
  would never be able to recycle the pid since we skip over it. :))
- get pidfd to the pid > 300 we just created
- wait on the pid > 300
- cycle via fork() until we have reached the same pid > 300 again
- send SIGSTOP to that recycled process
- test that we cannot send SIGCONT to this SIGSTOPed task via the pidfd we
  received before
- send SIGCONT to the SIGSTOPed recycled pid and exit

Ok, I have something like this in my tree now that tests for pid
recycling. I'm going to send it out tomorrow since I reckon Andrew and
others will be off today.
But fwiw it sits in https://github.com/brauner/linux/commits/2018-12-02/procfds

Christian

quoted

quoted

Cc: Jann Horn <jannh@google.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <redacted>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Florian Weimer <redacted>
Signed-off-by: Christian Brauner <christian@brauner.io>
---
/* Changelog */
v6:
- patch introduced
v5..v0:
- patch not present
---
 tools/testing/selftests/Makefile           |   1 +
 tools/testing/selftests/pidfd/Makefile     |   6 +
 tools/testing/selftests/pidfd/pidfd_test.c | 130 +++++++++++++++++++++
 3 files changed, 137 insertions(+)
 create mode 100644 tools/testing/selftests/pidfd/Makefile
 create mode 100644 tools/testing/selftests/pidfd/pidfd_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 24b9934fb269..63b0d8a0ebf7 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile

@@ -27,6 +27,7 @@ TARGETS += net
 TARGETS += netfilter
 TARGETS += networking/timestamping
 TARGETS += nsfs
+TARGETS += pidfd
 TARGETS += powerpc
 TARGETS += proc
 TARGETS += pstore

diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
new file mode 100644
index 000000000000..deaf8073bc06
--- /dev/null
+++ b/tools/testing/selftests/pidfd/Makefile

@@ -0,0 +1,6 @@
+CFLAGS += -g -I../../../../usr/include/
+
+TEST_GEN_PROGS := pidfd_test
+
+include ../lib.mk
+

diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
new file mode 100644
index 000000000000..edcd59979b10
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_test.c

@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/types.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
+					unsigned int flags)
+{
+	return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
+
+static int signal_received;
+
+static void do_exit_success(int sig)
+{
+	signal_received = 1;
+}
+
+/*
+ * Straightforward test to see whether pidfd_send_signal() works is to send
+ * a signal to ourselves.
+ */
+static int test_pidfd_send_signal_simple_success(void)
+{
+	int pidfd, ret;
+	const char *test_name = "pidfd_send_signal send SIGUSR1";
+
+	pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
+	if (pidfd < 0)
+		ksft_exit_fail_msg(
+			"%s test: Failed to open process file descriptor\n",
+			test_name);
+
+	signal(SIGUSR1, do_exit_success);
+
+	ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
+	close(pidfd);
+	if (ret < 0)
+		ksft_exit_fail_msg("%s test: Failed to send signal\n",
+				   test_name);
+
+	if (signal_received != 1)
+		ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+				   test_name);
+
+	signal_received = 0;
+	ksft_test_result_pass("%s test: Sent signal\n", test_name);
+	return 0;
+}
+
+static void wait_for_pid(pid_t pid)
+{
+	int status, ret;
+
+again:
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		if (errno == EINTR)
+			goto again;
+
+		return;
+	}
+
+	if (ret != pid)
+		goto again;
+}
+
+static int test_pidfd_send_signal_exited_fail(void)
+{
+	int pidfd, ret, saved_errno;
+	char buf[256];
+	pid_t pid;
+	const char *test_name = "pidfd_send_signal signal exited process";
+
+	pid = fork();
+	if (pid < 0)
+		ksft_exit_fail_msg("%s test: Failed to create new process\n",
+				   test_name);
+
+	if (pid == 0)
+		_exit(EXIT_SUCCESS);
+
+	snprintf(buf, sizeof(buf), "/proc/%d", pid);
+
+	pidfd = open(buf, O_DIRECTORY | O_CLOEXEC);
+
+	wait_for_pid(pid);
+
+	if (pidfd < 0)
+		ksft_exit_fail_msg(
+			"%s test: Failed to open process file descriptor\n",
+			test_name);
+
+	ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
+	saved_errno = errno;
+	close(pidfd);
+	if (ret == 0)
+		ksft_exit_fail_msg(
+			"%s test: Managed to send signal to process even though it should have failed\n",
+			test_name);
+
+	if (saved_errno != ESRCH)
+		ksft_exit_fail_msg(
+			"%s test: Expected to receive ESRCH as errno value but received %d instead\n",
+			test_name, saved_errno);
+
+	ksft_test_result_pass("%s test: Failed to send signal as expected\n",
+			      test_name);
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+
+	test_pidfd_send_signal_simple_success();
+	test_pidfd_send_signal_exited_fail();
+
+	return ksft_exit_pass();
+}

-- 
2.19.1