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/*
* Copyright (C) 2018 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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "switch_root.h"
#include <fcntl.h>
#include <mntent.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <unistd.h>
#include <android-base/logging.h>
#include <android-base/strings.h>
using android::base::StartsWith;
using namespace std::literals;
namespace android {
namespace init {
namespace {
std::vector<std::string> GetMounts(const std::string& new_root) {
auto fp = std::unique_ptr<std::FILE, decltype(&endmntent)>{setmntent("/proc/mounts", "re"),
endmntent};
if (fp == nullptr) {
PLOG(FATAL) << "Failed to open /proc/mounts";
}
std::vector<std::string> result;
mntent* mentry;
while ((mentry = getmntent(fp.get())) != nullptr) {
// We won't try to move rootfs.
if (mentry->mnt_dir == "/"s) {
continue;
}
// The new root mount is handled separately.
if (mentry->mnt_dir == new_root) {
continue;
}
// Move operates on subtrees, so do not try to move children of other mounts.
if (std::find_if(result.begin(), result.end(), [&mentry](const auto& older_mount) {
return StartsWith(mentry->mnt_dir, older_mount);
}) != result.end()) {
continue;
}
result.emplace_back(mentry->mnt_dir);
}
return result;
}
} // namespace
void SwitchRoot(const std::string& new_root) {
auto mounts = GetMounts(new_root);
LOG(INFO) << "Switching root to '" << new_root << "'";
for (const auto& mount_path : mounts) {
auto new_mount_path = new_root + mount_path;
mkdir(new_mount_path.c_str(), 0755);
if (mount(mount_path.c_str(), new_mount_path.c_str(), nullptr, MS_MOVE, nullptr) != 0) {
PLOG(FATAL) << "Unable to move mount at '" << mount_path << "' to "
<< "'" << new_mount_path << "'";
}
}
if (chdir(new_root.c_str()) != 0) {
PLOG(FATAL) << "Could not chdir to new_root, '" << new_root << "'";
}
if (mount(new_root.c_str(), "/", nullptr, MS_MOVE, nullptr) != 0) {
PLOG(FATAL) << "Unable to move root mount to new_root, '" << new_root << "'";
}
if (chroot(".") != 0) {
PLOG(FATAL) << "Unable to chroot to new root";
}
}
} // namespace init
} // namespace android
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