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From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
To: brauner@kernel.org
Cc: stgraber@stgraber.org,
	tycho@tycho.pizza,
	cyphar@cyphar.com,
	linux-kernel@vger.kernel.org,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Subject: [PATCH v1 2/2] tests/pid_namespace: add pid_max tests
Date: Thu, 22 Feb 2024 17:09:15 +0100
Message-Id: <20240222160915.315255-3-aleksandr.mikhalitsyn@canonical.com>
In-Reply-To: <20240222160915.315255-1-aleksandr.mikhalitsyn@canonical.com>
References: <20240222160915.315255-1-aleksandr.mikhalitsyn@canonical.com>
Precedence: bulk
MIME-Version: 1.0
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From: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
 .../selftests/pid_namespace/.gitignore        |   1 +
 .../testing/selftests/pid_namespace/Makefile  |   2 +-
 .../testing/selftests/pid_namespace/pid_max.c | 358 ++++++++++++++++++
 3 files changed, 360 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/pid_namespace/pid_max.c

diff --git a/tools/testing/selftests/pid_namespace/.gitignore b/tools/testing/selftests/pid_namespace/.gitignore
index 93ab9d7e5b7e..5118f0f3edf4 100644
--- a/tools/testing/selftests/pid_namespace/.gitignore
+++ b/tools/testing/selftests/pid_namespace/.gitignore
@@ -1 +1,2 @@
+pid_max
 regression_enomem
diff --git a/tools/testing/selftests/pid_namespace/Makefile b/tools/testing/selftests/pid_namespace/Makefile
index 9286a1d22cd3..b972f55d07ae 100644
--- a/tools/testing/selftests/pid_namespace/Makefile
+++ b/tools/testing/selftests/pid_namespace/Makefile
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -g $(KHDR_INCLUDES)
 
-TEST_GEN_PROGS = regression_enomem
+TEST_GEN_PROGS = regression_enomem pid_max
 
 LOCAL_HDRS += $(selfdir)/pidfd/pidfd.h
 
diff --git a/tools/testing/selftests/pid_namespace/pid_max.c b/tools/testing/selftests/pid_namespace/pid_max.c
new file mode 100644
index 000000000000..51c414faabb0
--- /dev/null
+++ b/tools/testing/selftests/pid_namespace/pid_max.c
@@ -0,0 +1,358 @@
+/* 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 "../kselftest_harness.h"
+#include "../pidfd/pidfd.h"
+
+#define __STACK_SIZE (8 * 1024 * 1024)
+static pid_t do_clone(int (*fn)(void *), void *arg, int flags)
+{
+	char *stack;
+	pid_t ret;
+
+	stack = malloc(__STACK_SIZE);
+	if (!stack)
+		return -ENOMEM;
+
+#ifdef __ia64__
+	ret = __clone2(fn, stack, __STACK_SIZE, flags | SIGCHLD, arg);
+#else
+	ret = clone(fn, stack + __STACK_SIZE, flags | SIGCHLD, arg);
+#endif
+	free(stack);
+	return ret;
+}
+
+static int pid_max_cb(void *data)
+{
+	int fd, ret;
+	pid_t pid;
+
+	ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to make rootfs private mount\n");
+		return -1;
+	}
+
+	umount2("/proc", MNT_DETACH);
+
+	ret = mount("proc", "/proc", "proc", 0, NULL);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to mount proc\n");
+		return -1;
+	}
+
+	fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY);
+	if (fd < 0) {
+		fprintf(stderr, "%m - Failed to open pid_max\n");
+		return -1;
+	}
+
+	ret = write(fd, "500", sizeof("500") - 1);
+	if (ret < 0) {
+		fprintf(stderr, "%m - Failed to write pid_max\n");
+		return -1;
+	}
+
+	for (int i = 0; i < 501; i++) {
+		pid = fork();
+		if (pid == 0)
+			exit(EXIT_SUCCESS);
+		wait_for_pid(pid);
+		if (pid > 500) {
+			fprintf(stderr, "Managed to create pid number beyond limit\n");
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+static int pid_max_nested_inner(void *data)
+{
+	int fret = -1;
+	pid_t pids[2];
+	int fd, i, ret;
+
+	ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to make rootfs private mount\n");
+		return fret;
+	}
+
+	umount2("/proc", MNT_DETACH);
+
+	ret = mount("proc", "/proc", "proc", 0, NULL);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to mount proc\n");
+		return fret;
+	}
+
+	fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY);
+	if (fd < 0) {
+		fprintf(stderr, "%m - Failed to open pid_max\n");
+		return fret;
+	}
+
+	ret = write(fd, "500", sizeof("500") - 1);
+	close(fd);
+	if (ret < 0) {
+		fprintf(stderr, "%m - Failed to write pid_max\n");
+		return fret;
+	}
+
+	pids[0] = fork();
+	if (pids[0] < 0) {
+		fprintf(stderr, "Failed to create first new process\n");
+		return fret;
+	}
+
+	if (pids[0] == 0)
+		exit(EXIT_SUCCESS);
+
+	pids[1] = fork();
+	wait_for_pid(pids[0]);
+	if (pids[1] >= 0) {
+		if (pids[1] == 0)
+			exit(EXIT_SUCCESS);
+		wait_for_pid(pids[1]);
+
+		fprintf(stderr, "Managed to create process even though ancestor pid namespace had a limit\n");
+		return fret;
+	}
+
+	/* Now make sure that we wrap pids at 400. */
+	for (i = 0; i < 510; i++) {
+		pid_t pid;
+
+		pid = fork();
+		if (pid < 0)
+			return fret;
+
+		if (pid == 0)
+			exit(EXIT_SUCCESS);
+
+		wait_for_pid(pid);
+		if (pid >= 500) {
+			fprintf(stderr, "Managed to create process with pid %d beyond configured limit\n", pid);
+			return fret;
+		}
+	}
+
+	return 0;
+}
+
+static int pid_max_nested_outer(void *data)
+{
+	int fret = -1, nr_procs = 400;
+	pid_t pids[1000];
+	int fd, i, ret;
+	pid_t pid;
+
+	ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to make rootfs private mount\n");
+		return fret;
+	}
+
+	umount2("/proc", MNT_DETACH);
+
+	ret = mount("proc", "/proc", "proc", 0, NULL);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to mount proc\n");
+		return fret;
+	}
+
+	fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY);
+	if (fd < 0) {
+		fprintf(stderr, "%m - Failed to open pid_max\n");
+		return fret;
+	}
+
+	ret = write(fd, "400", sizeof("400") - 1);
+	close(fd);
+	if (ret < 0) {
+		fprintf(stderr, "%m - Failed to write pid_max\n");
+		return fret;
+	}
+
+	/*
+	 * Create 397 processes. This leaves room for do_clone() (398) and
+	 * one more 399. So creating another process needs to fail.
+	 */
+	for (nr_procs = 0; nr_procs < 396; nr_procs++) {
+		pid = fork();
+		if (pid < 0)
+			goto reap;
+
+		if (pid == 0)
+			exit(EXIT_SUCCESS);
+
+		pids[nr_procs] = pid;
+	}
+
+	pid = do_clone(pid_max_nested_inner, NULL, CLONE_NEWPID | CLONE_NEWNS);
+	if (pid < 0) {
+		fprintf(stderr, "%m - Failed to clone nested pidns\n");
+		goto reap;
+	}
+
+	if (wait_for_pid(pid)) {
+		fprintf(stderr, "%m - Nested pid_max failed\n");
+		goto reap;
+	}
+
+	fret = 0;
+
+reap:
+	for (int i = 0; i < nr_procs; i++)
+		wait_for_pid(pids[i]);
+
+	return fret;
+}
+
+static int pid_max_nested_limit_inner(void *data)
+{
+	int fret = -1, nr_procs = 400;
+	int fd, ret;
+	pid_t pid;
+	pid_t pids[1000];
+
+	ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to make rootfs private mount\n");
+		return fret;
+	}
+
+	umount2("/proc", MNT_DETACH);
+
+	ret = mount("proc", "/proc", "proc", 0, NULL);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to mount proc\n");
+		return fret;
+	}
+
+	fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY);
+	if (fd < 0) {
+		fprintf(stderr, "%m - Failed to open pid_max\n");
+		return fret;
+	}
+
+	ret = write(fd, "500", sizeof("500") - 1);
+	close(fd);
+	if (ret < 0) {
+		fprintf(stderr, "%m - Failed to write pid_max\n");
+		return fret;
+	}
+
+	for (nr_procs = 0; nr_procs < 500; nr_procs++) {
+		pid = fork();
+		if (pid < 0)
+			break;
+
+		if (pid == 0)
+			exit(EXIT_SUCCESS);
+
+		pids[nr_procs] = pid;
+	}
+
+	if (nr_procs >= 400) {
+		fprintf(stderr, "Managed to create processes beyond the configured outer limit\n");
+		goto reap;
+	}
+
+	fret = 0;
+
+reap:
+	for (int i = 0; i < nr_procs; i++)
+		wait_for_pid(pids[i]);
+
+	return fret;
+}
+
+static int pid_max_nested_limit_outer(void *data)
+{
+	int fd, ret;
+	pid_t pid;
+
+	ret = mount("", "/", NULL, MS_PRIVATE | MS_REC, 0);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to make rootfs private mount\n");
+		return -1;
+	}
+
+	umount2("/proc", MNT_DETACH);
+
+	ret = mount("proc", "/proc", "proc", 0, NULL);
+	if (ret) {
+		fprintf(stderr, "%m - Failed to mount proc\n");
+		return -1;
+	}
+
+	fd = open("/proc/sys/kernel/pid_max", O_RDWR | O_CLOEXEC | O_NOCTTY);
+	if (fd < 0) {
+		fprintf(stderr, "%m - Failed to open pid_max\n");
+		return -1;
+	}
+
+	ret = write(fd, "400", sizeof("400") - 1);
+	close(fd);
+	if (ret < 0) {
+		fprintf(stderr, "%m - Failed to write pid_max\n");
+		return -1;
+	}
+
+	pid = do_clone(pid_max_nested_limit_inner, NULL, CLONE_NEWPID | CLONE_NEWNS);
+	if (pid < 0) {
+		fprintf(stderr, "%m - Failed to clone nested pidns\n");
+		return -1;
+	}
+
+	if (wait_for_pid(pid)) {
+		fprintf(stderr, "%m - Nested pid_max failed\n");
+		return -1;
+	}
+
+	return 0;
+}
+
+TEST(pid_max_simple)
+{
+	pid_t pid;
+
+
+	pid = do_clone(pid_max_cb, NULL, CLONE_NEWPID | CLONE_NEWNS);
+	ASSERT_GT(pid, 0);
+	ASSERT_EQ(0, wait_for_pid(pid));
+}
+
+TEST(pid_max_nested_limit)
+{
+	pid_t pid;
+
+	pid = do_clone(pid_max_nested_limit_outer, NULL, CLONE_NEWPID | CLONE_NEWNS);
+	ASSERT_GT(pid, 0);
+	ASSERT_EQ(0, wait_for_pid(pid));
+}
+
+TEST(pid_max_nested)
+{
+	pid_t pid;
+
+	pid = do_clone(pid_max_nested_outer, NULL, CLONE_NEWPID | CLONE_NEWNS);
+	ASSERT_GT(pid, 0);
+	ASSERT_EQ(0, wait_for_pid(pid));
+}
+
+TEST_HARNESS_MAIN
-- 
2.34.1