[PATCH 4/4] tests: add pidfd_open() tests

[Christian Brauner <christian@brauner.io>]

This adds a simple test case for pidfd_open().

Signed-off-by: Christian Brauner <christian@brauner.io>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jann Horn <jannh@google.com
Cc: David Howells <dhowells@redhat.com>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Jonathan Kowalski <bl0pbl33p@gmail.com>
Cc: "Dmitry V. Levin" <ldv@altlinux.org>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
---
 tools/testing/selftests/pidfd/Makefile        |   2 +-
 .../testing/selftests/pidfd/pidfd_open_test.c | 201 ++++++++++++++++++
 2 files changed, 202 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/pidfd/pidfd_open_test.c

diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
index deaf8073bc06..b36c0be70848 100644
--- a/tools/testing/selftests/pidfd/Makefile
+++ b/tools/testing/selftests/pidfd/Makefile
@@ -1,6 +1,6 @@
 CFLAGS += -g -I../../../../usr/include/
 
-TEST_GEN_PROGS := pidfd_test
+TEST_GEN_PROGS := pidfd_test pidfd_open_test
 
 include ../lib.mk
 
diff --git a/tools/testing/selftests/pidfd/pidfd_open_test.c b/tools/testing/selftests/pidfd/pidfd_open_test.c
new file mode 100644
index 000000000000..07a262a9ef2c
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_open_test.c
@@ -0,0 +1,201 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+
+static inline int sys_pidfd_open(pid_t pid, int procfd, int pidfd,
+				 unsigned int flags)
+{
+	return syscall(__NR_pidfd_open, pid, procfd, pidfd, flags);
+}
+
+static int safe_int(const char *numstr, int *converted)
+{
+	char *err = NULL;
+	signed long int sli;
+
+	errno = 0;
+	sli = strtol(numstr, &err, 0);
+	if (errno == ERANGE && (sli == LONG_MAX || sli == LONG_MIN))
+		return -ERANGE;
+
+	if (errno != 0 && sli == 0)
+		return -EINVAL;
+
+	if (err == numstr || *err != '\0')
+		return -EINVAL;
+
+	if (sli > INT_MAX || sli < INT_MIN)
+		return -ERANGE;
+
+	*converted = (int)sli;
+	return 0;
+}
+
+static int char_left_gc(const char *buffer, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (buffer[i] == ' ' ||
+		    buffer[i] == '\t')
+			continue;
+
+		return i;
+	}
+
+	return 0;
+}
+
+static int char_right_gc(const char *buffer, size_t len)
+{
+	int i;
+
+	for (i = len - 1; i >= 0; i--) {
+		if (buffer[i] == ' '  ||
+		    buffer[i] == '\t' ||
+		    buffer[i] == '\n' ||
+		    buffer[i] == '\0')
+			continue;
+
+		return i + 1;
+	}
+
+	return 0;
+}
+
+static char *trim_whitespace_in_place(char *buffer)
+{
+	buffer += char_left_gc(buffer, strlen(buffer));
+	buffer[char_right_gc(buffer, strlen(buffer))] = '\0';
+	return buffer;
+}
+
+static pid_t get_pid_from_status_file(int *fd)
+{
+	int ret;
+	FILE *f;
+	size_t n = 0;
+	pid_t result = -1;
+	char *line = NULL;
+
+	/* fd now belongs to FILE and will be closed by fclose() */
+	f = fdopen(*fd, "r");
+	if (!f)
+		return -1;
+
+	while (getline(&line, &n, f) != -1) {
+		char *numstr;
+
+		if (strncmp(line, "Pid:", 4))
+			continue;
+
+		numstr = trim_whitespace_in_place(line + 4);
+		ret = safe_int(numstr, &result);
+		if (ret < 0)
+			goto out;
+
+		break;
+	}
+
+out:
+	free(line);
+	fclose(f);
+	*fd = -1;
+	return result;
+}
+
+int main(int argc, char **argv)
+{
+	int ret = 1;
+	int pidfd = -1, pidfd2 = -1, procfd = -1, procpidfd = -1, statusfd = -1;
+	pid_t pid;
+
+	pidfd = sys_pidfd_open(getpid(), -1, -1, 0);
+	if (pidfd < 0) {
+		ksft_print_msg("%s - failed to open pidfd\n", strerror(errno));
+		goto on_error;
+	}
+
+	procfd = open("/proc", O_DIRECTORY | O_RDONLY | O_CLOEXEC);
+	if (procfd < 0) {
+		ksft_print_msg("%s - failed to open /proc\n", strerror(errno));
+		goto on_error;
+	}
+
+	procpidfd = sys_pidfd_open(-1, procfd, pidfd, PIDFD_TO_PROCFD);
+	if (procpidfd < 0) {
+		ksft_print_msg(
+			"%s - failed to retrieve /proc/<pid> from pidfd\n",
+			strerror(errno));
+		goto on_error;
+	}
+
+	pidfd2 = sys_pidfd_open(-1, procpidfd, -1, PROCFD_TO_PIDFD);
+	if (pidfd2 < 0) {
+		ksft_print_msg(
+			"%s - failed to retrieve  pidfd from procpidfd\n",
+			strerror(errno));
+		goto on_error;
+	}
+
+	statusfd = openat(procpidfd, "status", O_CLOEXEC | O_RDONLY);
+	if (statusfd < 0) {
+		ksft_print_msg("%s - failed to open /proc/<pid>/status\n",
+			       strerror(errno));
+		goto on_error;
+	}
+
+	pid = get_pid_from_status_file(&statusfd);
+	if (pid < 0) {
+		ksft_print_msg(
+			"%s - failed to retrieve pid from /proc/<pid>/status\n",
+			strerror(errno));
+		goto on_error;
+	}
+
+	if (pid != getpid()) {
+		ksft_print_msg(
+			"%s - actual pid %d does not equal retrieved pid from /proc/<pid>/status\n",
+			strerror(errno), pid, getpid());
+		goto on_error;
+	}
+
+	ret = 0;
+
+on_error:
+	if (pidfd >= 0)
+		close(pidfd);
+
+	if (pidfd2 >= 0)
+		close(pidfd2);
+
+	if (procfd >= 0)
+		close(procfd);
+
+	if (procpidfd >= 0)
+		close(procpidfd);
+
+	if (statusfd >= 0)
+		close(statusfd);
+
+	return !ret ? ksft_exit_pass() : ksft_exit_fail();
+}
-- 
2.21.0