imageloader/helper_process_receiver.cc

// Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "imageloader/helper_process_receiver.h"

#include <string>
#include <utility>
#include <vector>

#include <fcntl.h>
#include <libminijail.h>
#include <scoped_minijail.h>
#include <sys/capability.h>
#include <sys/socket.h>
#include <unistd.h>

#include <base/bind.h>
#include <base/files/file_path.h>
#include <base/logging.h>
#include <base/posix/eintr_wrapper.h>
#include <base/time/time.h>

#include "imageloader/imageloader.h"
#include "imageloader/verity_mounter.h"

namespace imageloader {

namespace {
constexpr char kSeccompFilterPath[] =
    "/usr/share/policy/imageloader-helper-seccomp.policy";
}  // namespace

HelperProcessReceiver::HelperProcessReceiver(base::ScopedFD control_fd)
    : control_fd_(std::move(control_fd)), pending_fd_(-1), mounter_() {}

int HelperProcessReceiver::OnInit() {
  // Prevent the main process from sending us any signals.
  // errno can be EPERM if the process is already the group leader.
  if (setsid() < 0 && errno != EPERM)
    PLOG(FATAL) << "setsid failed";

  // Run with minimal privileges.
  ScopedMinijail jail(minijail_new());
  minijail_no_new_privs(jail.get());
  minijail_use_seccomp_filter(jail.get());
  minijail_parse_seccomp_filters(jail.get(), kSeccompFilterPath);
  minijail_reset_signal_mask(jail.get());
  minijail_namespace_net(jail.get());
  minijail_skip_remount_private(jail.get());
  minijail_enter(jail.get());

  controller_ = base::FileDescriptorWatcher::WatchReadable(
      control_fd_.get(),
      base::BindRepeating(&HelperProcessReceiver::OnCommandReady,
                          base::Unretained(this)));
  return Daemon::OnInit();
}

void HelperProcessReceiver::OnCommandReady() {
  std::vector<char> buffer(4096 * 4);

  struct msghdr msg = {0};
  struct iovec iov[1];

  iov[0].iov_base = buffer.data();
  iov[0].iov_len = buffer.size();

  msg.msg_iov = iov;
  msg.msg_iovlen = sizeof(iov) / sizeof(iov[0]);

  char c_buffer[256];
  msg.msg_control = c_buffer;
  msg.msg_controllen = sizeof(c_buffer);

  ssize_t bytes = HANDLE_EINTR(recvmsg(control_fd_.get(), &msg, 0));
  if (bytes < 0)
    PLOG(FATAL) << "recvmsg failed";
  // Per recvmsg(2), the return value will be 0 when the peer has performed an
  // orderly shutdown.
  if (bytes == 0)
    _exit(0);

  struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);

  ImageCommand command;
  if (!command.ParseFromArray(buffer.data(), bytes))
    LOG(FATAL) << "error parsing protobuf";

  // Handle the command to mount the image.
  CommandResponse response = HandleCommand(command, cmsg);
  // Reply to the parent process with the success or failure.
  SendResponse(response);
}

CommandResponse HelperProcessReceiver::HandleCommand(
    const ImageCommand& image_command, struct cmsghdr* cmsg) {
  CommandResponse response;
  if (image_command.has_mount_command()) {
    MountCommand command = image_command.mount_command();
    if (cmsg == nullptr)
      LOG(FATAL) << "no cmsg";

    if (cmsg->cmsg_level != SOL_SOCKET || cmsg->cmsg_type != SCM_RIGHTS)
      LOG(FATAL) << "cmsg is wrong type";

    memmove(&pending_fd_, CMSG_DATA(cmsg), sizeof(pending_fd_));

    // Convert the fs type to a string.
    std::string fs_type;
    switch (command.fs_type()) {
      case MountCommand::EXT4:
        fs_type = "ext4";
        break;
      case MountCommand::SQUASH:
        fs_type = "squashfs";
        break;
      default:
        LOG(FATAL) << "unknown filesystem type";
    }

    bool status = mounter_.Mount(base::ScopedFD(pending_fd_),
                                 base::FilePath(command.mount_path()), fs_type,
                                 command.table());
    if (!status)
      LOG(ERROR) << "mount failed";

    response.set_success(status);
  } else if (image_command.has_unmount_all_command()) {
    UnmountAllCommand command = image_command.unmount_all_command();
    std::vector<base::FilePath> paths;
    const base::FilePath root_dir(command.unmount_rootpath());
    response.set_success(
        mounter_.CleanupAll(command.dry_run(), root_dir, &paths));
    for (const auto& path : paths) {
      const std::string path_(path.value());
      response.add_paths(path_);
    }
  } else if (image_command.has_unmount_command()) {
    UnmountCommand command = image_command.unmount_command();
    const base::FilePath path(command.unmount_path());
    response.set_success(mounter_.Cleanup(path));
  } else {
    LOG(FATAL) << "unknown operations";
  }
  return response;
}

void HelperProcessReceiver::SendResponse(const CommandResponse& response) {
  if (!response.SerializeToFileDescriptor(control_fd_.get()))
    LOG(FATAL) << "failed to serialize protobuf";
}

}  // namespace imageloader