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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 <dirent.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 {
void FreeRamdisk(DIR* dir, dev_t dev) {
int dfd = dirfd(dir);
dirent* de;
while ((de = readdir(dir)) != nullptr) {
if (de->d_name == "."s || de->d_name == ".."s) {
continue;
}
bool is_dir = false;
if (de->d_type == DT_DIR || de->d_type == DT_UNKNOWN) {
struct stat info;
if (fstatat(dfd, de->d_name, &info, AT_SYMLINK_NOFOLLOW) != 0) {
continue;
}
if (info.st_dev != dev) {
continue;
}
if (S_ISDIR(info.st_mode)) {
is_dir = true;
auto fd = openat(dfd, de->d_name, O_RDONLY | O_DIRECTORY);
if (fd >= 0) {
auto subdir =
std::unique_ptr<DIR, decltype(&closedir)>{fdopendir(fd), closedir};
if (subdir) {
FreeRamdisk(subdir.get(), dev);
} else {
close(fd);
}
}
}
}
unlinkat(dfd, de->d_name, is_dir ? AT_REMOVEDIR : 0);
}
}
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);
for (const auto& mount_path : mounts) {
auto new_mount_path = new_root + mount_path;
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 << "'";
}
}
auto old_root_dir = std::unique_ptr<DIR, decltype(&closedir)>{opendir("/"), closedir};
if (!old_root_dir) {
PLOG(ERROR) << "Could not opendir(\"/\"), not freeing ramdisk";
}
struct stat old_root_info;
if (stat("/", &old_root_info) != 0) {
PLOG(ERROR) << "Could not stat(\"/\"), not freeing ramdisk";
old_root_dir.reset();
}
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";
}
if (old_root_dir) {
FreeRamdisk(old_root_dir.get(), old_root_info.st_dev);
}
}
} // namespace init
} // namespace android
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