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* Copyright (C) 2019 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "mount_namespace.h"
#include <sys/mount.h>
#include <string>
#include <vector>
#include <ApexProperties.sysprop.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <android-base/result.h>
#include <android-base/unique_fd.h>
#include "util.h"
#ifndef RECOVERY
#include <apex_manifest.pb.h>
#include <com_android_apex.h>
#include <selinux/android.h>
namespace android {
namespace init {
namespace {
static bool BindMount(const std::string& source, const std::string& mount_point) {
if (mount(source.c_str(), mount_point.c_str(), nullptr, MS_BIND | MS_REC, nullptr) == -1) {
PLOG(ERROR) << "Failed to bind mount " << source;
return false;
return true;
static bool ChangeMount(const std::string& mount_point, unsigned long mountflags) {
if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
PLOG(ERROR) << "Failed to remount " << mount_point << " as " << std::hex << mountflags;
return false;
return true;
static int OpenMountNamespace() {
int fd = open("/proc/self/ns/mnt", O_RDONLY | O_CLOEXEC);
if (fd < 0) {
PLOG(ERROR) << "Cannot open fd for current mount namespace";
return fd;
static std::string GetMountNamespaceId() {
std::string ret;
if (!android::base::Readlink("/proc/self/ns/mnt", &ret)) {
PLOG(ERROR) << "Failed to read namespace ID";
return "";
return ret;
static bool IsApexUpdatable() {
static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
return updatable;
// In case we have two sets of APEXes (non-updatable, updatable), we need two separate mount
// namespaces.
static bool NeedsTwoMountNamespaces() {
if (!IsApexUpdatable()) return false;
if (IsRecoveryMode()) return false;
// In microdroid, there's only one set of APEXes in built-in directories include block devices.
if (IsMicrodroid()) return false;
return true;
static android::base::unique_fd bootstrap_ns_fd;
static android::base::unique_fd default_ns_fd;
static std::string bootstrap_ns_id;
static std::string default_ns_id;
} // namespace
bool SetupMountNamespaces() {
// Set the propagation type of / as shared so that any mounting event (e.g.
// /data) is by default visible to all processes. When private mounting is
// needed for /foo/bar, then we will make /foo/bar as a mount point (by
// bind-mounting by to itself) and set the propagation type of the mount
// point to private.
if (!ChangeMount("/", MS_SHARED | MS_REC)) return false;
// /apex is a private mountpoint to give different sets of APEXes for
// the bootstrap and default mount namespaces. The processes running with
// the bootstrap namespace get APEXes from the read-only partition.
if (!(ChangeMount("/apex", MS_PRIVATE))) return false;
// /linkerconfig is a private mountpoint to give a different linker configuration
// based on the mount namespace. Subdirectory will be bind-mounted based on current mount
// namespace
if (!(ChangeMount("/linkerconfig", MS_PRIVATE))) return false;
// The two mount namespaces present challenges for scoped storage, because
// vold, which is responsible for most of the mounting, lives in the
// bootstrap mount namespace, whereas most other daemons and all apps live
// in the default namespace. Scoped storage has a need for a
// /mnt/installer view that is a slave bind mount of /mnt/user - in other
// words, all mounts under /mnt/user should automatically show up under
// /mnt/installer. However, additional mounts done under /mnt/installer
// should not propagate back to /mnt/user. In a single mount namespace
// this is easy to achieve, by simply marking the /mnt/installer a slave
// bind mount. Unfortunately, if /mnt/installer is only created and
// bind mounted after the two namespaces are created below, we end up
// with the following situation:
// /mnt/user and /mnt/installer share the same peer group in both the
// bootstrap and default namespaces. Marking /mnt/installer slave in either
// namespace means that it won't propagate events to the /mnt/installer in
// the other namespace, which is still something we require - vold is the
// one doing the mounting under /mnt/installer, and those mounts should
// show up in the default namespace as well.
// The simplest solution is to do the bind mount before the two namespaces
// are created: the effect is that in both namespaces, /mnt/installer is a
// slave to the /mnt/user mount, and at the same time /mnt/installer in the
// bootstrap namespace shares a peer group with /mnt/installer in the
// default namespace.
// /mnt/androidwritable is similar to /mnt/installer but serves for
if (!mkdir_recursive("/mnt/user", 0755)) return false;
if (!mkdir_recursive("/mnt/installer", 0755)) return false;
if (!mkdir_recursive("/mnt/androidwritable", 0755)) return false;
if (!(BindMount("/mnt/user", "/mnt/installer"))) return false;
if (!(BindMount("/mnt/user", "/mnt/androidwritable"))) return false;
// First, make /mnt/installer and /mnt/androidwritable a slave bind mount
if (!(ChangeMount("/mnt/installer", MS_SLAVE))) return false;
if (!(ChangeMount("/mnt/androidwritable", MS_SLAVE))) return false;
// Then, make it shared again - effectively creating a new peer group, that
// will be inherited by new mount namespaces.
if (!(ChangeMount("/mnt/installer", MS_SHARED))) return false;
if (!(ChangeMount("/mnt/androidwritable", MS_SHARED))) return false;
bootstrap_ns_id = GetMountNamespaceId();
// When APEXes are updatable (e.g. not-flattened), we create separate mount
// namespaces for processes that are started before and after the APEX is
// activated by apexd. In the namespace for pre-apexd processes, small
// number of essential APEXes (e.g. are activated.
// In the namespace for post-apexd processes, all APEXes are activated.
bool success = true;
if (NeedsTwoMountNamespaces()) {
// Creating a new namespace by cloning, saving, and switching back to
// the original namespace.
if (unshare(CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Cannot create mount namespace";
return false;
default_ns_id = GetMountNamespaceId();
if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Cannot switch back to bootstrap mount namespace";
return false;
} else {
// Otherwise, default == bootstrap
default_ns_id = GetMountNamespaceId();
LOG(INFO) << "SetupMountNamespaces done";
return success;
Result<void> SwitchToMountNamespaceIfNeeded(MountNamespace target_mount_namespace) {
if (IsRecoveryMode() || !IsApexUpdatable()) {
// we don't have multiple namespaces in recovery mode or if apex is not updatable
return {};
const auto& ns_id = target_mount_namespace == NS_BOOTSTRAP ? bootstrap_ns_id : default_ns_id;
const auto& ns_fd = target_mount_namespace == NS_BOOTSTRAP ? bootstrap_ns_fd : default_ns_fd;
const auto& ns_name = target_mount_namespace == NS_BOOTSTRAP ? "bootstrap" : "default";
if (ns_id != GetMountNamespaceId() && ns_fd.get() != -1) {
if (setns(ns_fd.get(), CLONE_NEWNS) == -1) {
return ErrnoError() << "Failed to switch to " << ns_name << " mount namespace.";
return {};
base::Result<MountNamespace> GetCurrentMountNamespace() {
std::string current_namespace_id = GetMountNamespaceId();
if (current_namespace_id == "") {
return Error() << "Failed to get current mount namespace ID";
if (current_namespace_id == bootstrap_ns_id) {
} else if (current_namespace_id == default_ns_id) {
return NS_DEFAULT;
return Error() << "Failed to find current mount namespace";
} // namespace init
} // namespace android