298 lines
12 KiB
C++
298 lines
12 KiB
C++
/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "mount_namespace.h"
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#include <sys/mount.h>
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#include <string>
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#include <vector>
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#include <ApexProperties.sysprop.h>
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#include <android-base/file.h>
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#include <android-base/logging.h>
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#include <android-base/properties.h>
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#include <android-base/result.h>
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#include <android-base/unique_fd.h>
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#include "util.h"
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#ifndef RECOVERY
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#define ACTIVATE_FLATTENED_APEX 1
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#endif
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#ifdef ACTIVATE_FLATTENED_APEX
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#include <apex_manifest.pb.h>
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#include <com_android_apex.h>
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#include <selinux/android.h>
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#endif // ACTIVATE_FLATTENED_APEX
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namespace android {
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namespace init {
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namespace {
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static bool BindMount(const std::string& source, const std::string& mount_point) {
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if (mount(source.c_str(), mount_point.c_str(), nullptr, MS_BIND | MS_REC, nullptr) == -1) {
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PLOG(ERROR) << "Failed to bind mount " << source;
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return false;
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}
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return true;
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}
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static bool ChangeMount(const std::string& mount_point, unsigned long mountflags) {
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if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
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PLOG(ERROR) << "Failed to remount " << mount_point << " as " << std::hex << mountflags;
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return false;
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}
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return true;
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}
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static int OpenMountNamespace() {
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int fd = open("/proc/self/ns/mnt", O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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PLOG(ERROR) << "Cannot open fd for current mount namespace";
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}
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return fd;
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}
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static std::string GetMountNamespaceId() {
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std::string ret;
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if (!android::base::Readlink("/proc/self/ns/mnt", &ret)) {
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PLOG(ERROR) << "Failed to read namespace ID";
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return "";
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}
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return ret;
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}
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static bool IsApexUpdatable() {
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static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
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return updatable;
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}
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#ifdef ACTIVATE_FLATTENED_APEX
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static Result<void> MountDir(const std::string& path, const std::string& mount_path) {
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if (int ret = mkdir(mount_path.c_str(), 0755); ret != 0 && errno != EEXIST) {
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return ErrnoError() << "Could not create mount point " << mount_path;
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}
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if (mount(path.c_str(), mount_path.c_str(), nullptr, MS_BIND, nullptr) != 0) {
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return ErrnoError() << "Could not bind mount " << path << " to " << mount_path;
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}
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return {};
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}
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static Result<apex::proto::ApexManifest> GetApexManifest(const std::string& apex_dir) {
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const std::string manifest_path = apex_dir + "/apex_manifest.pb";
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std::string content;
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if (!android::base::ReadFileToString(manifest_path, &content)) {
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return Error() << "Failed to read manifest file: " << manifest_path;
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}
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apex::proto::ApexManifest manifest;
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if (!manifest.ParseFromString(content)) {
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return Error() << "Can't parse manifest file: " << manifest_path;
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}
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return manifest;
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}
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template <typename Fn>
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static Result<void> ActivateFlattenedApexesFrom(const std::string& from_dir,
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const std::string& to_dir, Fn on_activate) {
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std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(from_dir.c_str()), closedir);
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if (!dir) {
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return {};
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}
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dirent* entry;
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while ((entry = readdir(dir.get())) != nullptr) {
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if (entry->d_name[0] == '.') continue;
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if (entry->d_type == DT_DIR) {
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const std::string apex_path = from_dir + "/" + entry->d_name;
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const auto apex_manifest = GetApexManifest(apex_path);
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if (!apex_manifest.ok()) {
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LOG(ERROR) << apex_path << " is not an APEX directory: " << apex_manifest.error();
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continue;
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}
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const std::string mount_path = to_dir + "/" + apex_manifest->name();
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if (auto result = MountDir(apex_path, mount_path); !result.ok()) {
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return result;
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}
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on_activate(apex_path, *apex_manifest);
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}
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}
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return {};
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}
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static bool ActivateFlattenedApexesIfPossible() {
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if (IsRecoveryMode() || IsApexUpdatable()) {
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return true;
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}
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const std::string kApexTop = "/apex";
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const std::vector<std::string> kBuiltinDirsForApexes = {
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"/system/apex",
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"/system_ext/apex",
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"/product/apex",
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"/vendor/apex",
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};
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std::vector<com::android::apex::ApexInfo> apex_infos;
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auto on_activate = [&](const std::string& apex_path,
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const apex::proto::ApexManifest& apex_manifest) {
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apex_infos.emplace_back(apex_manifest.name(), apex_path, apex_path, apex_manifest.version(),
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apex_manifest.versionname(), /*isFactory=*/true, /*isActive=*/true);
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};
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for (const auto& dir : kBuiltinDirsForApexes) {
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if (auto result = ActivateFlattenedApexesFrom(dir, kApexTop, on_activate); !result.ok()) {
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LOG(ERROR) << result.error();
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return false;
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}
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}
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std::ostringstream oss;
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com::android::apex::ApexInfoList apex_info_list(apex_infos);
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com::android::apex::write(oss, apex_info_list);
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const std::string kApexInfoList = kApexTop + "/apex-info-list.xml";
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if (!android::base::WriteStringToFile(oss.str(), kApexInfoList)) {
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PLOG(ERROR) << "Failed to write " << kApexInfoList;
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return false;
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}
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if (selinux_android_restorecon(kApexInfoList.c_str(), 0) != 0) {
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PLOG(ERROR) << "selinux_android_restorecon(" << kApexInfoList << ") failed";
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}
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return true;
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}
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#endif // ACTIVATE_FLATTENED_APEX
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static android::base::unique_fd bootstrap_ns_fd;
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static android::base::unique_fd default_ns_fd;
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static std::string bootstrap_ns_id;
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static std::string default_ns_id;
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} // namespace
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bool SetupMountNamespaces() {
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// Set the propagation type of / as shared so that any mounting event (e.g.
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// /data) is by default visible to all processes. When private mounting is
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// needed for /foo/bar, then we will make /foo/bar as a mount point (by
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// bind-mounting by to itself) and set the propagation type of the mount
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// point to private.
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if (!ChangeMount("/", MS_SHARED | MS_REC)) return false;
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// /apex is a private mountpoint to give different sets of APEXes for
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// the bootstrap and default mount namespaces. The processes running with
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// the bootstrap namespace get APEXes from the read-only partition.
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if (!(ChangeMount("/apex", MS_PRIVATE))) return false;
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// /linkerconfig is a private mountpoint to give a different linker configuration
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// based on the mount namespace. Subdirectory will be bind-mounted based on current mount
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// namespace
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if (!(ChangeMount("/linkerconfig", MS_PRIVATE))) return false;
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// The two mount namespaces present challenges for scoped storage, because
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// vold, which is responsible for most of the mounting, lives in the
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// bootstrap mount namespace, whereas most other daemons and all apps live
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// in the default namespace. Scoped storage has a need for a
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// /mnt/installer view that is a slave bind mount of /mnt/user - in other
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// words, all mounts under /mnt/user should automatically show up under
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// /mnt/installer. However, additional mounts done under /mnt/installer
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// should not propagate back to /mnt/user. In a single mount namespace
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// this is easy to achieve, by simply marking the /mnt/installer a slave
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// bind mount. Unfortunately, if /mnt/installer is only created and
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// bind mounted after the two namespaces are created below, we end up
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// with the following situation:
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// /mnt/user and /mnt/installer share the same peer group in both the
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// bootstrap and default namespaces. Marking /mnt/installer slave in either
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// namespace means that it won't propagate events to the /mnt/installer in
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// the other namespace, which is still something we require - vold is the
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// one doing the mounting under /mnt/installer, and those mounts should
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// show up in the default namespace as well.
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//
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// The simplest solution is to do the bind mount before the two namespaces
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// are created: the effect is that in both namespaces, /mnt/installer is a
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// slave to the /mnt/user mount, and at the same time /mnt/installer in the
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// bootstrap namespace shares a peer group with /mnt/installer in the
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// default namespace.
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// /mnt/androidwritable is similar to /mnt/installer but serves for
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// MOUNT_EXTERNAL_ANDROID_WRITABLE apps.
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if (!mkdir_recursive("/mnt/user", 0755)) return false;
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if (!mkdir_recursive("/mnt/installer", 0755)) return false;
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if (!mkdir_recursive("/mnt/androidwritable", 0755)) return false;
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if (!(BindMount("/mnt/user", "/mnt/installer"))) return false;
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if (!(BindMount("/mnt/user", "/mnt/androidwritable"))) return false;
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// First, make /mnt/installer and /mnt/androidwritable a slave bind mount
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if (!(ChangeMount("/mnt/installer", MS_SLAVE))) return false;
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if (!(ChangeMount("/mnt/androidwritable", MS_SLAVE))) return false;
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// Then, make it shared again - effectively creating a new peer group, that
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// will be inherited by new mount namespaces.
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if (!(ChangeMount("/mnt/installer", MS_SHARED))) return false;
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if (!(ChangeMount("/mnt/androidwritable", MS_SHARED))) return false;
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bootstrap_ns_fd.reset(OpenMountNamespace());
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bootstrap_ns_id = GetMountNamespaceId();
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// When APEXes are updatable (e.g. not-flattened), we create separate mount
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// namespaces for processes that are started before and after the APEX is
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// activated by apexd. In the namespace for pre-apexd processes, small
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// number of essential APEXes (e.g. com.android.runtime) are activated.
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// In the namespace for post-apexd processes, all APEXes are activated.
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bool success = true;
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if (IsApexUpdatable() && !IsRecoveryMode()) {
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// Creating a new namespace by cloning, saving, and switching back to
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// the original namespace.
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if (unshare(CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Cannot create mount namespace";
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return false;
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}
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default_ns_fd.reset(OpenMountNamespace());
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default_ns_id = GetMountNamespaceId();
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if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Cannot switch back to bootstrap mount namespace";
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return false;
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}
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} else {
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// Otherwise, default == bootstrap
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default_ns_fd.reset(OpenMountNamespace());
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default_ns_id = GetMountNamespaceId();
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}
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#ifdef ACTIVATE_FLATTENED_APEX
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success &= ActivateFlattenedApexesIfPossible();
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#endif
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LOG(INFO) << "SetupMountNamespaces done";
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return success;
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}
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Result<void> SwitchToMountNamespaceIfNeeded(MountNamespace target_mount_namespace) {
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if (IsRecoveryMode() || !IsApexUpdatable()) {
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// we don't have multiple namespaces in recovery mode or if apex is not updatable
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return {};
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}
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const auto& ns_id = target_mount_namespace == NS_BOOTSTRAP ? bootstrap_ns_id : default_ns_id;
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const auto& ns_fd = target_mount_namespace == NS_BOOTSTRAP ? bootstrap_ns_fd : default_ns_fd;
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const auto& ns_name = target_mount_namespace == NS_BOOTSTRAP ? "bootstrap" : "default";
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if (ns_id != GetMountNamespaceId() && ns_fd.get() != -1) {
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if (setns(ns_fd.get(), CLONE_NEWNS) == -1) {
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return ErrnoError() << "Failed to switch to " << ns_name << " mount namespace.";
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}
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}
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return {};
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}
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} // namespace init
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} // namespace android
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