Merge tag 'threads-v5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull thread management updates from Christian Brauner:

 - A pidfd's fdinfo file currently contains the field "Pid:\t<pid>"
   where <pid> is the pid of the process in the pid namespace of the
   procfs instance the fdinfo file for the pidfd was opened in.

   The fdinfo file has now gained a new "NSpid:\t<ns-pid1>[\t<ns-pid2>[...]]"
   field which lists the pids of the process in all child pid namespaces
   provided the pid namespace of the procfs instance it is looked up
   under has an ancestoral relationship with the pid namespace of the
   process. If it does not 0 will be shown and no further pid namespaces
   will be listed. Tests included. (Christian Kellner)

 - If the process the pidfd references has already exited, print -1 for
   the Pid and NSpid fields in the pidfd's fdinfo file. Tests included.
   (me)

 - Add CLONE_CLEAR_SIGHAND. This lets callers clear all signal handler
   that are not SIG_DFL or SIG_IGN at process creation time. This
   originated as a feature request from glibc to improve performance and
   elimate races in their posix_spawn() implementation. Tests included.
   (me)

 - Add support for choosing a specific pid for a process with clone3().
   This is the feature which was part of the thread update for v5.4 but
   after a discussion at LPC in Lisbon we decided to delay it for one
   more cycle in order to make the interface more generic. This has now
   done. It is now possible to choose a specific pid in a whole pid
   namespaces (sub)hierarchy instead of just one pid namespace. In order
   to choose a specific pid the caller must have CAP_SYS_ADMIN in all
   owning user namespaces of the target pid namespaces. Tests included.
   (Adrian Reber)

 - Test improvements and extensions. (Andrei Vagin, me)

* tag 'threads-v5.5' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  selftests/clone3: skip if clone3() is ENOSYS
  selftests/clone3: check that all pids are released on error paths
  selftests/clone3: report a correct number of fails
  selftests/clone3: flush stdout and stderr before clone3() and _exit()
  selftests: add tests for clone3() with *set_tid
  fork: extend clone3() to support setting a PID
  selftests: add tests for clone3()
  tests: test CLONE_CLEAR_SIGHAND
  clone3: add CLONE_CLEAR_SIGHAND
  pid: use pid_has_task() in pidfd_open()
  exit: use pid_has_task() in do_wait()
  pid: use pid_has_task() in __change_pid()
  test: verify fdinfo for pidfd of reaped process
  pidfd: check pid has attached task in fdinfo
  pidfd: add tests for NSpid info in fdinfo
  pidfd: add NSpid entries to fdinfo

9 files changed, 1098 insertions, 1 deletions

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 0b6b81ba4421..0fb95f25944d 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -5,6 +5,7 @@ TARGETS += bpf
 TARGETS += breakpoints
 TARGETS += capabilities
 TARGETS += cgroup
+TARGETS += clone3
 TARGETS += cpufreq
 TARGETS += cpu-hotplug
 TARGETS += drivers/dma-buf
diff --git a/tools/testing/selftests/clone3/.gitignore b/tools/testing/selftests/clone3/.gitignore
new file mode 100644
index 000000000000..0dc4f32c6cb8
--- /dev/null
+++ b/tools/testing/selftests/clone3/.gitignore
@@ -0,0 +1,3 @@
+clone3
+clone3_clear_sighand
+clone3_set_tid
diff --git a/tools/testing/selftests/clone3/Makefile b/tools/testing/selftests/clone3/Makefile
new file mode 100644
index 000000000000..cf976c732906
--- /dev/null
+++ b/tools/testing/selftests/clone3/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -g -I../../../../usr/include/
+
+TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid
+
+include ../lib.mk
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
new file mode 100644
index 000000000000..f14c269a5a18
--- /dev/null
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -0,0 +1,202 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/* Based on Christian Brauner's clone3() example */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <inttypes.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <sched.h>
+
+#include "../kselftest.h"
+#include "clone3_selftests.h"
+
+/*
+ * Different sizes of struct clone_args
+ */
+#ifndef CLONE3_ARGS_SIZE_V0
+#define CLONE3_ARGS_SIZE_V0 64
+#endif
+
+enum test_mode {
+	CLONE3_ARGS_NO_TEST,
+	CLONE3_ARGS_ALL_0,
+	CLONE3_ARGS_INVAL_EXIT_SIGNAL_BIG,
+	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
+	CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
+	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+};
+
+static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
+{
+	struct clone_args args = {
+		.flags = flags,
+		.exit_signal = SIGCHLD,
+	};
+
+	struct clone_args_extended {
+		struct clone_args args;
+		__aligned_u64 excess_space[2];
+	} args_ext;
+
+	pid_t pid = -1;
+	int status;
+
+	memset(&args_ext, 0, sizeof(args_ext));
+	if (size > sizeof(struct clone_args))
+		args_ext.excess_space[1] = 1;
+
+	if (size == 0)
+		size = sizeof(struct clone_args);
+
+	switch (test_mode) {
+	case CLONE3_ARGS_ALL_0:
+		args.flags = 0;
+		args.exit_signal = 0;
+		break;
+	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_BIG:
+		args.exit_signal = 0xbadc0ded00000000ULL;
+		break;
+	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG:
+		args.exit_signal = 0x0000000080000000ULL;
+		break;
+	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG:
+		args.exit_signal = 0x0000000000000100ULL;
+		break;
+	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
+		args.exit_signal = 0x00000000000000f0ULL;
+		break;
+	}
+
+	memcpy(&args_ext.args, &args, sizeof(struct clone_args));
+
+	pid = sys_clone3((struct clone_args *)&args_ext, size);
+	if (pid < 0) {
+		ksft_print_msg("%s - Failed to create new process\n",
+				strerror(errno));
+		return -errno;
+	}
+
+	if (pid == 0) {
+		ksft_print_msg("I am the child, my PID is %d\n", getpid());
+		_exit(EXIT_SUCCESS);
+	}
+
+	ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
+			getpid(), pid);
+
+	if (waitpid(-1, &status, __WALL) < 0) {
+		ksft_print_msg("Child returned %s\n", strerror(errno));
+		return -errno;
+	}
+	if (WEXITSTATUS(status))
+		return WEXITSTATUS(status);
+
+	return 0;
+}
+
+static void test_clone3(uint64_t flags, size_t size, int expected,
+		       enum test_mode test_mode)
+{
+	int ret;
+
+	ksft_print_msg(
+		"[%d] Trying clone3() with flags %#" PRIx64 " (size %zu)\n",
+		getpid(), flags, size);
+	ret = call_clone3(flags, size, test_mode);
+	ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
+			getpid(), ret, expected);
+	if (ret != expected)
+		ksft_test_result_fail(
+			"[%d] Result (%d) is different than expected (%d)\n",
+			getpid(), ret, expected);
+	else
+		ksft_test_result_pass(
+			"[%d] Result (%d) matches expectation (%d)\n",
+			getpid(), ret, expected);
+}
+
+int main(int argc, char *argv[])
+{
+	pid_t pid;
+
+	uid_t uid = getuid();
+
+	test_clone3_supported();
+	ksft_print_header();
+	ksft_set_plan(17);
+
+	/* Just a simple clone3() should return 0.*/
+	test_clone3(0, 0, 0, CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() in a new PID NS.*/
+	if (uid == 0)
+		test_clone3(CLONE_NEWPID, 0, 0, CLONE3_ARGS_NO_TEST);
+	else
+		ksft_test_result_skip("Skipping clone3() with CLONE_NEWPID\n");
+
+	/* Do a clone3() with CLONE3_ARGS_SIZE_V0. */
+	test_clone3(0, CLONE3_ARGS_SIZE_V0, 0, CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() with CLONE3_ARGS_SIZE_V0 - 8 */
+	test_clone3(0, CLONE3_ARGS_SIZE_V0 - 8, -EINVAL, CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() with sizeof(struct clone_args) + 8 */
+	test_clone3(0, sizeof(struct clone_args) + 8, 0, CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() with exit_signal having highest 32 bits non-zero */
+	test_clone3(0, 0, -EINVAL, CLONE3_ARGS_INVAL_EXIT_SIGNAL_BIG);
+
+	/* Do a clone3() with negative 32-bit exit_signal */
+	test_clone3(0, 0, -EINVAL, CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG);
+
+	/* Do a clone3() with exit_signal not fitting into CSIGNAL mask */
+	test_clone3(0, 0, -EINVAL, CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG);
+
+	/* Do a clone3() with NSIG < exit_signal < CSIG */
+	test_clone3(0, 0, -EINVAL, CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG);
+
+	test_clone3(0, sizeof(struct clone_args) + 8, 0, CLONE3_ARGS_ALL_0);
+
+	test_clone3(0, sizeof(struct clone_args) + 16, -E2BIG,
+			CLONE3_ARGS_ALL_0);
+
+	test_clone3(0, sizeof(struct clone_args) * 2, -E2BIG,
+			CLONE3_ARGS_ALL_0);
+
+	/* Do a clone3() with > page size */
+	test_clone3(0, getpagesize() + 8, -E2BIG, CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() with CLONE3_ARGS_SIZE_V0 in a new PID NS. */
+	if (uid == 0)
+		test_clone3(CLONE_NEWPID, CLONE3_ARGS_SIZE_V0, 0,
+				CLONE3_ARGS_NO_TEST);
+	else
+		ksft_test_result_skip("Skipping clone3() with CLONE_NEWPID\n");
+
+	/* Do a clone3() with CLONE3_ARGS_SIZE_V0 - 8 in a new PID NS */
+	test_clone3(CLONE_NEWPID, CLONE3_ARGS_SIZE_V0 - 8, -EINVAL,
+			CLONE3_ARGS_NO_TEST);
+
+	/* Do a clone3() with sizeof(struct clone_args) + 8 in a new PID NS */
+	if (uid == 0)
+		test_clone3(CLONE_NEWPID, sizeof(struct clone_args) + 8, 0,
+				CLONE3_ARGS_NO_TEST);
+	else
+		ksft_test_result_skip("Skipping clone3() with CLONE_NEWPID\n");
+
+	/* Do a clone3() with > page size in a new PID NS */
+	test_clone3(CLONE_NEWPID, getpagesize() + 8, -E2BIG,
+			CLONE3_ARGS_NO_TEST);
+
+	return !ksft_get_fail_cnt() ? ksft_exit_pass() : ksft_exit_fail();
+}
diff --git a/tools/testing/selftests/clone3/clone3_clear_sighand.c b/tools/testing/selftests/clone3/clone3_clear_sighand.c
new file mode 100644
index 000000000000..9e1af8aa7698
--- /dev/null
+++ b/tools/testing/selftests/clone3/clone3_clear_sighand.c
@@ -0,0 +1,129 @@
+/* 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"
+#include "clone3_selftests.h"
+
+#ifndef CLONE_CLEAR_SIGHAND
+#define CLONE_CLEAR_SIGHAND 0x100000000ULL
+#endif
+
+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();
+	test_clone3_supported();
+
+	ksft_set_plan(1);
+
+	test_clone3_clear_sighand();
+
+	return ksft_exit_pass();
+}
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
new file mode 100644
index 000000000000..a3f2c8ad8bcc
--- /dev/null
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _CLONE3_SELFTESTS_H
+#define _CLONE3_SELFTESTS_H
+
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdint.h>
+#include <syscall.h>
+#include <linux/types.h>
+
+#define ptr_to_u64(ptr) ((__u64)((uintptr_t)(ptr)))
+
+#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;
+	__aligned_u64 set_tid;
+	__aligned_u64 set_tid_size;
+};
+#endif
+
+static pid_t sys_clone3(struct clone_args *args, size_t size)
+{
+	fflush(stdout);
+	fflush(stderr);
+	return syscall(__NR_clone3, args, size);
+}
+
+static inline 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");
+}
+
+#endif /* _CLONE3_SELFTESTS_H */
diff --git a/tools/testing/selftests/clone3/clone3_set_tid.c b/tools/testing/selftests/clone3/clone3_set_tid.c
new file mode 100644
index 000000000000..25beb22f35b5
--- /dev/null
+++ b/tools/testing/selftests/clone3/clone3_set_tid.c
@@ -0,0 +1,397 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Based on Christian Brauner's clone3() example.
+ * These tests are assuming to be running in the host's
+ * PID namespace.
+ */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <sched.h>
+
+#include "../kselftest.h"
+#include "clone3_selftests.h"
+
+#ifndef MAX_PID_NS_LEVEL
+#define MAX_PID_NS_LEVEL 32
+#endif
+
+static int pipe_1[2];
+static int pipe_2[2];
+
+static void child_exit(int ret)
+{
+	fflush(stdout);
+	fflush(stderr);
+	_exit(ret);
+}
+
+static int call_clone3_set_tid(pid_t *set_tid,
+			       size_t set_tid_size,
+			       int flags,
+			       int expected_pid,
+			       bool wait_for_it)
+{
+	int status;
+	pid_t pid = -1;
+
+	struct clone_args args = {
+		.flags = flags,
+		.exit_signal = SIGCHLD,
+		.set_tid = ptr_to_u64(set_tid),
+		.set_tid_size = set_tid_size,
+	};
+
+	pid = sys_clone3(&args, sizeof(struct clone_args));
+	if (pid < 0) {
+		ksft_print_msg("%s - Failed to create new process\n",
+			       strerror(errno));
+		return -errno;
+	}
+
+	if (pid == 0) {
+		int ret;
+		char tmp = 0;
+		int exit_code = EXIT_SUCCESS;
+
+		ksft_print_msg("I am the child, my PID is %d (expected %d)\n",
+			       getpid(), set_tid[0]);
+		if (wait_for_it) {
+			ksft_print_msg("[%d] Child is ready and waiting\n",
+				       getpid());
+
+			/* Signal the parent that the child is ready */
+			close(pipe_1[0]);
+			ret = write(pipe_1[1], &tmp, 1);
+			if (ret != 1) {
+				ksft_print_msg(
+					"Writing to pipe returned %d", ret);
+				exit_code = EXIT_FAILURE;
+			}
+			close(pipe_1[1]);
+			close(pipe_2[1]);
+			ret = read(pipe_2[0], &tmp, 1);
+			if (ret != 1) {
+				ksft_print_msg(
+					"Reading from pipe returned %d", ret);
+				exit_code = EXIT_FAILURE;
+			}
+			close(pipe_2[0]);
+		}
+
+		if (set_tid[0] != getpid())
+			child_exit(EXIT_FAILURE);
+		child_exit(exit_code);
+	}
+
+	if (expected_pid == 0 || expected_pid == pid) {
+		ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
+			       getpid(), pid);
+	} else {
+		ksft_print_msg(
+			"Expected child pid %d does not match actual pid %d\n",
+			expected_pid, pid);
+		return -1;
+	}
+
+	if (waitpid(pid, &status, 0) < 0) {
+		ksft_print_msg("Child returned %s\n", strerror(errno));
+		return -errno;
+	}
+
+	if (!WIFEXITED(status))
+		return -1;
+
+	return WEXITSTATUS(status);
+}
+
+static void test_clone3_set_tid(pid_t *set_tid,
+				size_t set_tid_size,
+				int flags,
+				int expected,
+				int expected_pid,
+				bool wait_for_it)
+{
+	int ret;
+
+	ksft_print_msg(
+		"[%d] Trying clone3() with CLONE_SET_TID to %d and 0x%x\n",
+		getpid(), set_tid[0], flags);
+	ret = call_clone3_set_tid(set_tid, set_tid_size, flags, expected_pid,
+				  wait_for_it);
+	ksft_print_msg(
+		"[%d] clone3() with CLONE_SET_TID %d says :%d - expected %d\n",
+		getpid(), set_tid[0], ret, expected);
+	if (ret != expected)
+		ksft_test_result_fail(
+			"[%d] Result (%d) is different than expected (%d)\n",
+			getpid(), ret, expected);
+	else
+		ksft_test_result_pass(
+			"[%d] Result (%d) matches expectation (%d)\n",
+			getpid(), ret, expected);
+}
+int main(int argc, char *argv[])
+{
+	FILE *f;
+	char buf;
+	char *line;
+	int status;
+	int ret = -1;
+	size_t len = 0;
+	int pid_max = 0;
+	uid_t uid = getuid();
+	char proc_path[100] = {0};
+	pid_t pid, ns1, ns2, ns3, ns_pid;
+	pid_t set_tid[MAX_PID_NS_LEVEL * 2];
+
+	ksft_print_header();
+	test_clone3_supported();
+	ksft_set_plan(29);
+
+	if (pipe(pipe_1) < 0 || pipe(pipe_2) < 0)
+		ksft_exit_fail_msg("pipe() failed\n");
+
+	f = fopen("/proc/sys/kernel/pid_max", "r");
+	if (f == NULL)
+		ksft_exit_fail_msg(
+			"%s - Could not open /proc/sys/kernel/pid_max\n",
+			strerror(errno));
+	fscanf(f, "%d", &pid_max);
+	fclose(f);
+	ksft_print_msg("/proc/sys/kernel/pid_max %d\n", pid_max);
+
+	/* Try invalid settings */
+	memset(&set_tid, 0, sizeof(set_tid));
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL + 1, 0, -EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 2, 0, -EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 2 + 1, 0,
+			-EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 42, 0, -EINVAL, 0, 0);
+
+	/*
+	 * This can actually work if this test running in a MAX_PID_NS_LEVEL - 1
+	 * nested PID namespace.
+	 */
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL - 1, 0, -EINVAL, 0, 0);
+
+	memset(&set_tid, 0xff, sizeof(set_tid));
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL + 1, 0, -EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 2, 0, -EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 2 + 1, 0,
+			-EINVAL, 0, 0);
+
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL * 42, 0, -EINVAL, 0, 0);
+
+	/*
+	 * This can actually work if this test running in a MAX_PID_NS_LEVEL - 1
+	 * nested PID namespace.
+	 */
+	test_clone3_set_tid(set_tid, MAX_PID_NS_LEVEL - 1, 0, -EINVAL, 0, 0);
+
+	memset(&set_tid, 0, sizeof(set_tid));
+	/* Try with an invalid PID */
+	set_tid[0] = 0;
+	test_clone3_set_tid(set_tid, 1, 0, -EINVAL, 0, 0);
+
+	set_tid[0] = -1;
+	test_clone3_set_tid(set_tid, 1, 0, -EINVAL, 0, 0);
+
+	/* Claim that the set_tid array actually contains 2 elements. */
+	test_clone3_set_tid(set_tid, 2, 0, -EINVAL, 0, 0);
+
+	/* Try it in a new PID namespace */
+	if (uid == 0)
+		test_clone3_set_tid(set_tid, 1, CLONE_NEWPID, -EINVAL, 0, 0);
+	else
+		ksft_test_result_skip("Clone3() with set_tid requires root\n");
+
+	/* Try with a valid PID (1) this should return -EEXIST. */
+	set_tid[0] = 1;
+	if (uid == 0)
+		test_clone3_set_tid(set_tid, 1, 0, -EEXIST, 0, 0);
+	else
+		ksft_test_result_skip("Clone3() with set_tid requires root\n");
+
+	/* Try it in a new PID namespace */
+	if (uid == 0)
+		test_clone3_set_tid(set_tid, 1, CLONE_NEWPID, 0, 0, 0);
+	else
+		ksft_test_result_skip("Clone3() with set_tid requires root\n");
+
+	/* pid_max should fail everywhere */
+	set_tid[0] = pid_max;
+	test_clone3_set_tid(set_tid, 1, 0, -EINVAL, 0, 0);
+
+	if (uid == 0)
+		test_clone3_set_tid(set_tid, 1, CLONE_NEWPID, -EINVAL, 0, 0);
+	else
+		ksft_test_result_skip("Clone3() with set_tid requires root\n");
+
+	if (uid != 0) {
+		/*
+		 * All remaining tests require root. Tell the framework
+		 * that all those tests are skipped as non-root.
+		 */
+		ksft_cnt.ksft_xskip += ksft_plan - ksft_test_num();
+		goto out;
+	}
+
+	/* Find the current active PID */
+	pid = fork();
+	if (pid == 0) {
+		ksft_print_msg("Child has PID %d\n", getpid());
+		child_exit(EXIT_SUCCESS);
+	}
+	if (waitpid(pid, &status, 0) < 0)
+		ksft_exit_fail_msg("Waiting for child %d failed", pid);
+
+	/* After the child has finished, its PID should be free. */
+	set_tid[0] = pid;
+	test_clone3_set_tid(set_tid, 1, 0, 0, 0, 0);
+
+	/* This should fail as there is no PID 1 in that namespace */
+	test_clone3_set_tid(set_tid, 1, CLONE_NEWPID, -EINVAL, 0, 0);
+
+	/*
+	 * Creating a process with PID 1 in the newly created most nested
+	 * PID namespace and PID 'pid' in the parent PID namespace. This
+	 * needs to work.
+	 */
+	set_tid[0] = 1;
+	set_tid[1] = pid;
+	test_clone3_set_tid(set_tid, 2, CLONE_NEWPID, 0, pid, 0);
+
+	ksft_print_msg("unshare PID namespace\n");
+	if (unshare(CLONE_NEWPID) == -1)
+		ksft_exit_fail_msg("unshare(CLONE_NEWPID) failed: %s\n",
+				strerror(errno));
+
+	set_tid[0] = pid;
+
+	/* This should fail as there is no PID 1 in that namespace */
+	test_clone3_set_tid(set_tid, 1, 0, -EINVAL, 0, 0);
+
+	/* Let's create a PID 1 */
+	ns_pid = fork();
+	if (ns_pid == 0) {
+		/*
+		 * This and the next test cases check that all pid-s are
+		 * released on error paths.
+		 */
+		set_tid[0] = 43;
+		set_tid[1] = -1;
+		test_clone3_set_tid(set_tid, 2, 0, -EINVAL, 0, 0);
+
+		set_tid[0] = 43;
+		set_tid[1] = pid;
+		test_clone3_set_tid(set_tid, 2, 0, 0, 43, 0);
+
+		ksft_print_msg("Child in PID namespace has PID %d\n", getpid());
+		set_tid[0] = 2;
+		test_clone3_set_tid(set_tid, 1, 0, 0, 2, 0);
+
+		set_tid[0] = 1;
+		set_tid[1] = -1;
+		set_tid[2] = pid;
+		/* This should fail as there is invalid PID at level '1'. */
+		test_clone3_set_tid(set_tid, 3, CLONE_NEWPID, -EINVAL, 0, 0);
+
+		set_tid[0] = 1;
+		set_tid[1] = 42;
+		set_tid[2] = pid;
+		/*
+		 * This should fail as there are not enough active PID
+		 * namespaces. Again assuming this is running in the host's
+		 * PID namespace. Not yet nested.
+		 */
+		test_clone3_set_tid(set_tid, 4, CLONE_NEWPID, -EINVAL, 0, 0);
+
+		/*
+		 * This should work and from the parent we should see
+		 * something like 'NSpid:	pid	42	1'.
+		 */
+		test_clone3_set_tid(set_tid, 3, CLONE_NEWPID, 0, 42, true);
+
+		child_exit(ksft_cnt.ksft_fail);
+	}
+
+	close(pipe_1[1]);
+	close(pipe_2[0]);
+	while (read(pipe_1[0], &buf, 1) > 0) {
+		ksft_print_msg("[%d] Child is ready and waiting\n", getpid());
+		break;
+	}
+
+	snprintf(proc_path, sizeof(proc_path), "/proc/%d/status", pid);
+	f = fopen(proc_path, "r");
+	if (f == NULL)
+		ksft_exit_fail_msg(
+			"%s - Could not open %s\n",
+			strerror(errno), proc_path);
+
+	while (getline(&line, &len, f) != -1) {
+		if (strstr(line, "NSpid")) {
+			int i;
+
+			/* Verify that all generated PIDs are as expected. */
+			i = sscanf(line, "NSpid:\t%d\t%d\t%d",
+				   &ns3, &ns2, &ns1);
+			if (i != 3) {
+				ksft_print_msg(
+					"Unexpected 'NSPid:' entry: %s",
+					line);
+				ns1 = ns2 = ns3 = 0;
+			}
+			break;
+		}
+	}
+	fclose(f);
+	free(line);
+	close(pipe_2[0]);
+
+	/* Tell the clone3()'d child to finish. */
+	write(pipe_2[1], &buf, 1);
+	close(pipe_2[1]);
+
+	if (waitpid(ns_pid, &status, 0) < 0) {
+		ksft_print_msg("Child returned %s\n", strerror(errno));
+		ret = -errno;
+		goto out;
+	}
+
+	if (!WIFEXITED(status))
+		ksft_test_result_fail("Child error\n");
+
+	ksft_cnt.ksft_pass += 6 - (ksft_cnt.ksft_fail - WEXITSTATUS(status));
+	ksft_cnt.ksft_fail = WEXITSTATUS(status);
+
+	if (ns3 == pid && ns2 == 42 && ns1 == 1)
+		ksft_test_result_pass(
+			"PIDs in all namespaces as expected (%d,%d,%d)\n",
+			ns3, ns2, ns1);
+	else
+		ksft_test_result_fail(
+			"PIDs in all namespaces not as expected (%d,%d,%d)\n",
+			ns3, ns2, ns1);
+out:
+	ret = 0;
+
+	return !ret ? ksft_exit_pass() : ksft_exit_fail();
+}
diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
index 7550f08822a3..43db1b98e845 100644
--- a/tools/testing/selftests/pidfd/Makefile
+++ b/tools/testing/selftests/pidfd/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -g -I../../../../usr/include/ -pthread
 
-TEST_GEN_PROGS := pidfd_test pidfd_open_test pidfd_poll_test pidfd_wait
+TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test pidfd_poll_test pidfd_wait
 
 include ../lib.mk
 
diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
new file mode 100644
index 000000000000..22558524f71c
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
@@ -0,0 +1,296 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/types.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syscall.h>
+#include <sys/wait.h>
+
+#include "pidfd.h"
+#include "../kselftest.h"
+
+struct error {
+	int  code;
+	char msg[512];
+};
+
+static int error_set(struct error *err, int code, const char *fmt, ...)
+{
+	va_list args;
+	int r;
+
+	if (code == PIDFD_PASS || !err || err->code != PIDFD_PASS)
+		return code;
+
+	err->code = code;
+	va_start(args, fmt);
+	r = vsnprintf(err->msg, sizeof(err->msg), fmt, args);
+	assert((size_t)r < sizeof(err->msg));
+	va_end(args);
+
+	return code;
+}
+
+static void error_report(struct error *err, const char *test_name)
+{
+	switch (err->code) {
+	case PIDFD_ERROR:
+		ksft_exit_fail_msg("%s test: Fatal: %s\n", test_name, err->msg);
+		break;
+
+	case PIDFD_FAIL:
+		/* will be: not ok %d # error %s test: %s */
+		ksft_test_result_error("%s test: %s\n", test_name, err->msg);
+		break;
+
+	case PIDFD_SKIP:
+		/* will be: not ok %d # SKIP %s test: %s */
+		ksft_test_result_skip("%s test: %s\n", test_name, err->msg);
+		break;
+
+	case PIDFD_XFAIL:
+		ksft_test_result_pass("%s test: Expected failure: %s\n",
+				      test_name, err->msg);
+		break;
+
+	case PIDFD_PASS:
+		ksft_test_result_pass("%s test: Passed\n");
+		break;
+
+	default:
+		ksft_exit_fail_msg("%s test: Unknown code: %d %s\n",
+				   test_name, err->code, err->msg);
+		break;
+	}
+}
+
+static inline int error_check(struct error *err, const char *test_name)
+{
+	/* In case of error we bail out and terminate the test program */
+	if (err->code == PIDFD_ERROR)
+		error_report(err, test_name);
+
+	return err->code;
+}
+
+struct child {
+	pid_t pid;
+	int   fd;
+};
+
+static struct child clone_newns(int (*fn)(void *), void *args,
+				struct error *err)
+{
+	static int flags = CLONE_PIDFD | CLONE_NEWPID | CLONE_NEWNS | SIGCHLD;
+	size_t stack_size = 1024;
+	char *stack[1024] = { 0 };
+	struct child ret;
+
+	if (!(flags & CLONE_NEWUSER) && geteuid() != 0)
+		flags |= CLONE_NEWUSER;
+
+#ifdef __ia64__
+	ret.pid = __clone2(fn, stack, stack_size, flags, args, &ret.fd);
+#else
+	ret.pid = clone(fn, stack + stack_size, flags, args, &ret.fd);
+#endif
+
+	if (ret.pid < 0) {
+		error_set(err, PIDFD_ERROR, "clone failed (ret %d, errno %d)",
+			  ret.fd, errno);
+		return ret;
+	}
+
+	ksft_print_msg("New child: %d, fd: %d\n", ret.pid, ret.fd);
+
+	return ret;
+}
+
+static inline void child_close(struct child *child)
+{
+	close(child->fd);
+}
+
+static inline int child_join(struct child *child, struct error *err)
+{
+	int r;
+
+	r = wait_for_pid(child->pid);
+	if (r < 0)
+		error_set(err, PIDFD_ERROR, "waitpid failed (ret %d, errno %d)",
+			  r, errno);
+	else if (r > 0)
+		error_set(err, r, "child %d reported: %d", child->pid, r);
+
+	return r;
+}
+
+static inline int child_join_close(struct child *child, struct error *err)
+{
+	child_close(child);
+	return child_join(child, err);
+}
+
+static inline void trim_newline(char *str)
+{
+	char *pos = strrchr(str, '\n');
+
+	if (pos)
+		*pos = '\0';
+}
+
+static int verify_fdinfo(int pidfd, struct error *err, const char *prefix,
+			 size_t prefix_len, const char *expect, ...)
+{
+	char buffer[512] = {0, };
+	char path[512] = {0, };
+	va_list args;
+	FILE *f;
+	char *line = NULL;
+	size_t n = 0;
+	int found = 0;
+	int r;
+
+	va_start(args, expect);
+	r = vsnprintf(buffer, sizeof(buffer), expect, args);
+	assert((size_t)r < sizeof(buffer));
+	va_end(args);
+
+	snprintf(path, sizeof(path), "/proc/self/fdinfo/%d", pidfd);
+	f = fopen(path, "re");
+	if (!f)
+		return error_set(err, PIDFD_ERROR, "fdinfo open failed for %d",
+				 pidfd);
+
+	while (getline(&line, &n, f) != -1) {
+		char *val;
+
+		if (strncmp(line, prefix, prefix_len))
+			continue;
+
+		found = 1;
+
+		val = line + prefix_len;
+		r = strcmp(val, buffer);
+		if (r != 0) {
+			trim_newline(line);
+			trim_newline(buffer);
+			error_set(err, PIDFD_FAIL, "%s '%s' != '%s'",
+				  prefix, val, buffer);
+		}
+		break;
+	}
+
+	free(line);
+	fclose(f);
+
+	if (found == 0)
+		return error_set(err, PIDFD_FAIL, "%s not found for fd %d",
+				 prefix, pidfd);
+
+	return PIDFD_PASS;
+}
+
+static int child_fdinfo_nspid_test(void *args)
+{
+	struct error err;
+	int pidfd;
+	int r;
+
+	/* if we got no fd for the sibling, we are done */
+	if (!args)
+		return PIDFD_PASS;
+
+	/* verify that we can not resolve the pidfd for a process
+	 * in a sibling pid namespace, i.e. a pid namespace it is
+	 * not in our or a descended namespace
+	 */
+	r = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
+	if (r < 0) {
+		ksft_print_msg("Failed to remount / private\n");
+		return PIDFD_ERROR;
+	}
+
+	(void)umount2("/proc", MNT_DETACH);
+	r = mount("proc", "/proc", "proc", 0, NULL);
+	if (r < 0) {
+		ksft_print_msg("Failed to remount /proc\n");
+		return PIDFD_ERROR;
+	}
+
+	pidfd = *(int *)args;
+	r = verify_fdinfo(pidfd, &err, "NSpid:", 6, "\t0\n");
+
+	if (r != PIDFD_PASS)
+		ksft_print_msg("NSpid fdinfo check failed: %s\n", err.msg);
+
+	return r;
+}
+
+static void test_pidfd_fdinfo_nspid(void)
+{
+	struct child a, b;
+	struct error err = {0, };
+	const char *test_name = "pidfd check for NSpid in fdinfo";
+
+	/* Create a new child in a new pid and mount namespace */
+	a = clone_newns(child_fdinfo_nspid_test, NULL, &err);
+	error_check(&err, test_name);
+
+	/* Pass the pidfd representing the first child to the
+	 * second child, which will be in a sibling pid namespace,
+	 * which means that the fdinfo NSpid entry for the pidfd
+	 * should only contain '0'.
+	 */
+	b = clone_newns(child_fdinfo_nspid_test, &a.fd, &err);
+	error_check(&err, test_name);
+
+	/* The children will have pid 1 in the new pid namespace,
+	 * so the line must be 'NSPid:\t<pid>\t1'.
+	 */
+	verify_fdinfo(a.fd, &err, "NSpid:", 6, "\t%d\t%d\n", a.pid, 1);
+	verify_fdinfo(b.fd, &err, "NSpid:", 6, "\t%d\t%d\n", b.pid, 1);
+
+	/* wait for the process, check the exit status and set
+	 * 'err' accordingly, if it is not already set.
+	 */
+	child_join_close(&a, &err);
+	child_join_close(&b, &err);
+
+	error_report(&err, test_name);
+}
+
+static void test_pidfd_dead_fdinfo(void)
+{
+	struct child a;
+	struct error err = {0, };
+	const char *test_name = "pidfd check fdinfo for dead process";
+
+	/* Create a new child in a new pid and mount namespace */
+	a = clone_newns(child_fdinfo_nspid_test, NULL, &err);
+	error_check(&err, test_name);
+	child_join(&a, &err);
+
+	verify_fdinfo(a.fd, &err, "Pid:", 4, "\t-1\n");
+	verify_fdinfo(a.fd, &err, "NSpid:", 6, "\t-1\n");
+	child_close(&a);
+	error_report(&err, test_name);
+}
+
+int main(int argc, char **argv)
+{
+	ksft_print_header();
+	ksft_set_plan(2);
+
+	test_pidfd_fdinfo_nspid();
+	test_pidfd_dead_fdinfo();
+
+	return ksft_exit_pass();
+}