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100 lines
2.9 KiB
100 lines
2.9 KiB
/*
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* Copyright (C) 2018 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 "switch_root.h"
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#include <fcntl.h>
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#include <mntent.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <android-base/logging.h>
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#include <android-base/strings.h>
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using android::base::StartsWith;
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using namespace std::literals;
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namespace android {
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namespace init {
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namespace {
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std::vector<std::string> GetMounts(const std::string& new_root) {
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auto fp = std::unique_ptr<std::FILE, decltype(&endmntent)>{setmntent("/proc/mounts", "re"),
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endmntent};
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if (fp == nullptr) {
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PLOG(FATAL) << "Failed to open /proc/mounts";
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}
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std::vector<std::string> result;
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mntent* mentry;
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while ((mentry = getmntent(fp.get())) != nullptr) {
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// We won't try to move rootfs.
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if (mentry->mnt_dir == "/"s) {
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continue;
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}
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// The new root mount is handled separately.
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if (mentry->mnt_dir == new_root) {
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continue;
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}
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// Move operates on subtrees, so do not try to move children of other mounts.
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if (std::find_if(result.begin(), result.end(), [&mentry](const auto& older_mount) {
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return StartsWith(mentry->mnt_dir, older_mount);
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}) != result.end()) {
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continue;
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}
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result.emplace_back(mentry->mnt_dir);
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}
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return result;
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}
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} // namespace
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void SwitchRoot(const std::string& new_root) {
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auto mounts = GetMounts(new_root);
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LOG(INFO) << "Switching root to '" << new_root << "'";
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for (const auto& mount_path : mounts) {
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auto new_mount_path = new_root + mount_path;
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mkdir(new_mount_path.c_str(), 0755);
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if (mount(mount_path.c_str(), new_mount_path.c_str(), nullptr, MS_MOVE, nullptr) != 0) {
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PLOG(FATAL) << "Unable to move mount at '" << mount_path << "'";
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}
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}
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if (chdir(new_root.c_str()) != 0) {
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PLOG(FATAL) << "Could not chdir to new_root, '" << new_root << "'";
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}
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if (mount(new_root.c_str(), "/", nullptr, MS_MOVE, nullptr) != 0) {
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PLOG(FATAL) << "Unable to move root mount to new_root, '" << new_root << "'";
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}
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if (chroot(".") != 0) {
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PLOG(FATAL) << "Unable to chroot to new root";
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}
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}
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} // namespace init
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} // namespace android
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