Message-Id: <20250721-procfs-pidns-api-v1-4-5cd9007e512d@cyphar.com>
Date: Mon, 21 Jul 2025 18:44:14 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 linux-api@...r.kernel.org, linux-doc@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>
Subject: [PATCH RFC 4/4] selftests/proc: add tests for new pidns APIs

Signed-off-by: Aleksa Sarai <cyphar@...har.com>
---
 tools/testing/selftests/proc/.gitignore   |   1 +
 tools/testing/selftests/proc/Makefile     |   1 +
 tools/testing/selftests/proc/proc-pidns.c | 286 ++++++++++++++++++++++++++++++
 3 files changed, 288 insertions(+)

diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore
index 973968f45bba..2dced03e9e0e 100644
--- a/tools/testing/selftests/proc/.gitignore
+++ b/tools/testing/selftests/proc/.gitignore
@@ -17,6 +17,7 @@
 /proc-tid0
 /proc-uptime-001
 /proc-uptime-002
+/proc-pidns
 /read
 /self
 /setns-dcache
diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile
index b12921b9794b..c6f7046b9860 100644
--- a/tools/testing/selftests/proc/Makefile
+++ b/tools/testing/selftests/proc/Makefile
@@ -27,5 +27,6 @@ TEST_GEN_PROGS += setns-sysvipc
 TEST_GEN_PROGS += thread-self
 TEST_GEN_PROGS += proc-multiple-procfs
 TEST_GEN_PROGS += proc-fsconfig-hidepid
+TEST_GEN_PROGS += proc-pidns
 
 include ../lib.mk
diff --git a/tools/testing/selftests/proc/proc-pidns.c b/tools/testing/selftests/proc/proc-pidns.c
new file mode 100644
index 000000000000..e7e34c78d383
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-pidns.c
@@ -0,0 +1,286 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Author: Aleksa Sarai <cyphar@...har.com>
+ * Copyright (C) 2025 SUSE LLC.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <sys/prctl.h>
+
+#include "../kselftest_harness.h"
+
+#define bail(fmt, ...)							\
+	do {								\
+		fprintf(stderr, fmt ": %m", __VA_ARGS__);		\
+		exit(1);						\
+	} while (0)
+
+#define ASSERT_SUCCESS	ASSERT_FALSE
+#define ASSERT_FAIL	ASSERT_TRUE
+
+int touch(char *path)
+{
+	int fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC, 0644);
+	if (fd < 0 || close(fd) < 0)
+		return -errno;
+	return 0;
+}
+
+FIXTURE(ns)
+{
+	int host_mntns, host_pidns;
+	int dummy_pidns;
+};
+
+FIXTURE_SETUP(ns)
+{
+	/* Stash the old mntns. */
+	self->host_mntns = open("/proc/self/ns/mnt", O_RDONLY|O_CLOEXEC);
+	ASSERT_GE(self->host_mntns, 0);
+
+	/* Create a new mount namespace and make it private. */
+	ASSERT_SUCCESS(unshare(CLONE_NEWNS));
+	ASSERT_SUCCESS(mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL));
+
+	/*
+	 * Create a proper tmpfs that we can use and will disappear once we
+	 * leave this mntns.
+	 */
+	ASSERT_SUCCESS(mount("tmpfs", "/tmp", "tmpfs", 0, NULL));
+
+	/*
+	 * Create a pidns we can use for later tests. We need to fork off a
+	 * child so that we get a usable nsfd that we can bind-mount and open.
+	 */
+	ASSERT_SUCCESS(touch("/tmp/dummy-pidns"));
+
+	self->host_pidns = open("/proc/self/ns/pid", O_RDONLY|O_CLOEXEC);
+	ASSERT_GE(self->host_pidns, 0);
+	ASSERT_SUCCESS(unshare(CLONE_NEWPID));
+
+	pid_t pid = fork();
+	ASSERT_GE(pid, 0);
+	if (!pid) {
+		prctl(PR_SET_PDEATHSIG, SIGKILL);
+		ASSERT_SUCCESS(mount("/proc/self/ns/pid", "/tmp/dummy-pidns", NULL, MS_BIND, 0));
+		exit(0);
+	}
+
+	int wstatus;
+	ASSERT_EQ(waitpid(pid, &wstatus, 0), pid);
+	ASSERT_TRUE(WIFEXITED(wstatus));
+	ASSERT_EQ(WEXITSTATUS(wstatus), 0);
+
+	ASSERT_SUCCESS(setns(self->host_pidns, CLONE_NEWPID));
+
+	self->dummy_pidns = open("/tmp/dummy-pidns", O_RDONLY|O_CLOEXEC);
+	ASSERT_GE(self->dummy_pidns, 0);
+}
+
+FIXTURE_TEARDOWN(ns)
+{
+	ASSERT_SUCCESS(setns(self->host_mntns, CLONE_NEWNS));
+	ASSERT_SUCCESS(close(self->host_mntns));
+
+	ASSERT_SUCCESS(close(self->host_pidns));
+	ASSERT_SUCCESS(close(self->dummy_pidns));
+}
+
+TEST_F(ns, pidns_mount_string_path)
+{
+	ASSERT_SUCCESS(mkdir("/tmp/proc-host", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc-host", "proc", 0, "pidns=/proc/self/ns/pid"));
+	ASSERT_SUCCESS(access("/tmp/proc-host/self/", X_OK));
+
+	ASSERT_SUCCESS(mkdir("/tmp/proc-dummy", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc-dummy", "proc", 0, "pidns=/tmp/dummy-pidns"));
+	ASSERT_FAIL(access("/tmp/proc-dummy/1/", X_OK));
+	ASSERT_FAIL(access("/tmp/proc-dummy/self/", X_OK));
+}
+
+TEST_F(ns, pidns_fsconfig_string_path)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy-pidns", 0));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	ASSERT_FAIL(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_FAIL(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_fsconfig_fd)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	ASSERT_FAIL(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_FAIL(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_reconfigure_remount)
+{
+	ASSERT_SUCCESS(mkdir("/tmp/proc", 0755));
+	ASSERT_SUCCESS(mount("proc", "/tmp/proc", "proc", 0, ""));
+	ASSERT_SUCCESS(access("/tmp/proc/self/", X_OK));
+
+	ASSERT_SUCCESS(mount(NULL, "/tmp/proc", NULL, MS_REMOUNT, "pidns=/tmp/dummy-pidns"));
+	ASSERT_FAIL(access("/tmp/proc/self/", X_OK));
+}
+
+TEST_F(ns, pidns_reconfigure_fsconfig_string_path)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy-pidns", 0));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0));
+
+	ASSERT_FAIL(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_FAIL(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+TEST_F(ns, pidns_reconfigure_fsconfig_fd)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	ASSERT_SUCCESS(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_SUCCESS(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0));
+
+	ASSERT_FAIL(faccessat(mountfd, "1/", X_OK, 0));
+	ASSERT_FAIL(faccessat(mountfd, "self/", X_OK, 0));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(mountfd));
+}
+
+int is_same_inode(int fd1, int fd2)
+{
+	struct stat stat1, stat2;
+
+	assert(fstat(fd1, &stat1) == 0);
+	assert(fstat(fd2, &stat2) == 0);
+
+	return stat1.st_ino == stat2.st_ino && stat1.st_dev == stat2.st_dev;
+}
+
+#define PROCFS_IOCTL_MAGIC 'f'
+#define PROCFS_GET_PID_NAMESPACE	_IO(PROCFS_IOCTL_MAGIC, 1)
+
+TEST_F(ns, get_pidns_ioctl)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_FD, "pidns", NULL, self->dummy_pidns));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	/* fsmount returns an O_PATH, which ioctl(2) doesn't accept. */
+	int new_mountfd = openat(mountfd, ".", O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+	ASSERT_GE(new_mountfd, 0);
+
+	ASSERT_SUCCESS(close(mountfd));
+	mountfd = -EBADF;
+
+	int procfs_pidns = ioctl(new_mountfd, PROCFS_GET_PID_NAMESPACE);
+	ASSERT_GE(procfs_pidns, 0);
+
+	ASSERT_NE(self->dummy_pidns, procfs_pidns);
+	ASSERT_FALSE(is_same_inode(self->host_pidns, procfs_pidns));
+	ASSERT_TRUE(is_same_inode(self->dummy_pidns, procfs_pidns));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(new_mountfd));
+	ASSERT_SUCCESS(close(procfs_pidns));
+}
+
+TEST_F(ns, reconfigure_get_pidns_ioctl)
+{
+	int fsfd = fsopen("proc", FSOPEN_CLOEXEC);
+	ASSERT_GE(fsfd, 0);
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0));
+
+	int mountfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0);
+	ASSERT_GE(mountfd, 0);
+
+	/* fsmount returns an O_PATH, which ioctl(2) doesn't accept. */
+	int new_mountfd = openat(mountfd, ".", O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+	ASSERT_GE(new_mountfd, 0);
+
+	ASSERT_SUCCESS(close(mountfd));
+	mountfd = -EBADF;
+
+	int procfs_pidns1 = ioctl(new_mountfd, PROCFS_GET_PID_NAMESPACE);
+	ASSERT_GE(procfs_pidns1, 0);
+
+	ASSERT_NE(self->dummy_pidns, procfs_pidns1);
+	ASSERT_TRUE(is_same_inode(self->host_pidns, procfs_pidns1));
+	ASSERT_FALSE(is_same_inode(self->dummy_pidns, procfs_pidns1));
+
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_SET_STRING, "pidns", "/tmp/dummy-pidns", 0));
+	ASSERT_SUCCESS(fsconfig(fsfd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0));
+
+	int procfs_pidns2 = ioctl(new_mountfd, PROCFS_GET_PID_NAMESPACE);
+	ASSERT_GE(procfs_pidns2, 0);
+
+	ASSERT_NE(self->dummy_pidns, procfs_pidns2);
+	ASSERT_FALSE(is_same_inode(self->host_pidns, procfs_pidns2));
+	ASSERT_TRUE(is_same_inode(self->dummy_pidns, procfs_pidns2));
+
+	ASSERT_SUCCESS(close(fsfd));
+	ASSERT_SUCCESS(close(new_mountfd));
+	ASSERT_SUCCESS(close(procfs_pidns1));
+	ASSERT_SUCCESS(close(procfs_pidns2));
+}
+
+TEST_HARNESS_MAIN

-- 
2.50.0

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