cros-disks/archive_manager.cc

// Copyright (c) 2012 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 "cros-disks/archive_manager.h"

#include <sys/mount.h>

#include <memory>

#include <base/files/file_path.h>
#include <base/files/file_util.h>
#include <base/logging.h>
#include <base/strings/string_util.h>
#include <base/strings/stringprintf.h>
#include <brillo/cryptohome.h>

#include "cros-disks/error_logger.h"
#include "cros-disks/fuse_helper.h"
#include "cros-disks/fuse_mounter.h"
#include "cros-disks/metrics.h"
#include "cros-disks/mount_info.h"
#include "cros-disks/mount_options.h"
#include "cros-disks/platform.h"
#include "cros-disks/quote.h"
#include "cros-disks/system_mounter.h"

// TODO(benchan): Remove entire archive manager after deprecating the rar
// support (see chromium:707327).

namespace cros_disks {
namespace {

// Mapping from a base path to its corresponding path inside the AVFS mount.
struct AVFSPathMapping {
  const char* const base_path;
  const char* const avfs_path;
};

const char kAVFSMountGroup[] = "chronos-access";
const char kAVFSMountUser[] = "avfs";
// TODO(wad,benchan): Revisit the location of policy files once more system
// daemons are sandboxed with seccomp filters.
const char kAVFSSeccompFilterPolicyFile[] =
    "/usr/share/policy/avfsd-seccomp.policy";
const char kAVFSMountProgram[] = "/usr/bin/avfsd";
const char kAVFSRootDirectory[] = "/run/avfsroot";
const mode_t kAVFSDirectoryPermissions = 0770;  // rwx by avfs user and group
const char kAVFSLogFile[] = "/run/avfsroot/avfs.log";
const char kAVFSMediaDirectory[] = "/run/avfsroot/media";
const char kAVFSUsersDirectory[] = "/run/avfsroot/users";
const char kMediaDirectory[] = "/media";
const char kUserRootDirectory[] = "/home/chronos";
const AVFSPathMapping kAVFSPathMapping[] = {
    {kMediaDirectory, kAVFSMediaDirectory},
    {kUserRootDirectory, kAVFSUsersDirectory},
};
const char kAVFSModulesOption[] = "modules=subdir";
const char kAVFSSubdirOptionPrefix[] = "subdir=";

}  // namespace

ArchiveManager::ArchiveManager(const std::string& mount_root,
                               Platform* platform,
                               Metrics* metrics,
                               brillo::ProcessReaper* process_reaper)
    : MountManager(mount_root, platform, metrics, process_reaper),
      avfs_started_(false) {}

ArchiveManager::~ArchiveManager() {
  // StopAVFS() unmounts all mounted archives as well as AVFS mount points.
  StopAVFS();
}

bool ArchiveManager::Initialize() {
  RegisterDefaultFileExtensions();
  return MountManager::Initialize();
}

bool ArchiveManager::StopSession() {
  return StopAVFS();
}

bool ArchiveManager::CanMount(const std::string& source_path) const {
  // The following paths can be mounted:
  //     /home/chronos/u-<user-id>/Downloads/...<file>
  //     /home/chronos/u-<user-id>/MyFiles/...<file>
  //     /home/chronos/u-<user-id>/GCache/...<file>
  //     /media/<dir>/<dir>/...<file>
  //
  base::FilePath file_path(source_path);
  if (base::FilePath(kUserRootDirectory).IsParent(file_path)) {
    std::vector<std::string> components;
    file_path.StripTrailingSeparators().GetComponents(&components);
    // The file path of an archive file under a user's Downloads or GCache
    // directory path is split into the following components:
    //   '/', 'home', 'chronos', 'u-<userid>', 'Downloads', ..., 'doc.zip'
    //   '/', 'home', 'chronos', 'u-<userid>', 'GCache', ..., 'doc.zip'
    if (components.size() > 5 &&
        (base::StartsWith(components[3], "u-",
                          base::CompareCase::INSENSITIVE_ASCII) &&
         brillo::cryptohome::home::IsSanitizedUserName(
             components[3].substr(2))) &&
        (components[4] == "Downloads" || components[4] == "GCache" ||
         components[4] == "MyFiles")) {
      return true;
    }
  }

  if (base::FilePath(kMediaDirectory).IsParent(file_path)) {
    std::vector<std::string> components;
    file_path.StripTrailingSeparators().GetComponents(&components);
    // A mount directory is always created under /media/<sub type>/<mount dir>,
    // so the file path of an archive file under a mount directory is split
    // into more than 4 components:
    //   '/', 'media', 'removable', 'usb', ..., 'doc.zip'
    if (components.size() > 4)
      return true;
  }
  return false;
}

MountErrorType ArchiveManager::DoMount(const std::string& source_path,
                                       const std::string& source_format,
                                       const std::vector<std::string>& options,
                                       const std::string& mount_path,
                                       MountOptions* applied_options) {
  CHECK(!source_path.empty()) << "Invalid source path argument";
  CHECK(!mount_path.empty()) << "Invalid mount path argument";

  std::string extension = GetFileExtension(source_format);
  if (extension.empty())
    extension = GetFileExtension(source_path);

  metrics()->RecordArchiveType(extension);

  std::string avfs_path = GetAVFSPath(source_path, extension);
  if (avfs_path.empty()) {
    LOG(ERROR) << "Path " << quote(source_path)
               << " is not a supported archive";
    return MOUNT_ERROR_UNSUPPORTED_ARCHIVE;
  }

  MountErrorType avfs_start_error = StartAVFS();
  if (avfs_start_error != MOUNT_ERROR_NONE) {
    LOG(ERROR) << "Failed to start AVFS mounts: " << avfs_start_error;
    return avfs_start_error;
  }

  // Perform a bind mount from the archive path under the AVFS mount
  // to /media/archive/<archive name>.
  std::vector<std::string> extended_options = options;
  extended_options.push_back(MountOptions::kOptionBind);
  MountOptions mount_options;
  mount_options.WhitelistOption(MountOptions::kOptionNoSymFollow);
  mount_options.Initialize(extended_options, false, "", "");
  MounterCompat mounter(std::make_unique<SystemMounter>("", platform()),
                        avfs_path, base::FilePath(mount_path), mount_options);

  MountErrorType error_type = mounter.Mount();
  if (error_type != MOUNT_ERROR_NONE) {
    return error_type;
  }

  AddMountVirtualPath(mount_path, avfs_path);
  return MOUNT_ERROR_NONE;
}

MountErrorType ArchiveManager::DoUnmount(const std::string& path) {
  CHECK(!path.empty()) << "Invalid path argument";

  // Since all archives are read-only, always use lazy unmount.
  const MountErrorType error = platform()->Unmount(path, MNT_DETACH);
  if (error != MOUNT_ERROR_NONE) {
    return error;
  }

  // DoUnmount() is always called with |path| being the mount path.
  RemoveMountVirtualPath(path);
  return MOUNT_ERROR_NONE;
}

std::string ArchiveManager::SuggestMountPath(
    const std::string& source_path) const {
  // Use the archive name to name the mount directory.
  base::FilePath base_name = base::FilePath(source_path).BaseName();
  return base::FilePath(mount_root()).Append(base_name).value();
}

void ArchiveManager::RegisterDefaultFileExtensions() {
  // Different archive formats can now be supported via an extension (built-in
  // or installed by user) using the chrome.fileSystemProvider API. Thus, zip,
  // tar, and gzip/bzip2 compressed tar formats are no longer supported here.

  // rar is still supported until there is a replacement using a built-in
  // extension.
  RegisterFileExtension("rar", "#urar");
}

void ArchiveManager::RegisterFileExtension(const std::string& extension,
                                           const std::string& avfs_handler) {
  extension_handlers_[extension] = avfs_handler;
}

std::string ArchiveManager::GetFileExtension(const std::string& path) const {
  base::FilePath file_path(path);
  std::string extension = file_path.Extension();
  if (!extension.empty()) {
    // Strip the leading dot and convert the extension to lower case.
    extension.erase(0, 1);
    extension = base::ToLowerASCII(extension);
  }
  return extension;
}

std::string ArchiveManager::GetAVFSPath(const std::string& path,
                                        const std::string& extension) const {
  // When mounting an archive within another mounted archive, we need to
  // resolve the virtual path of the inner archive to the "unfolded"
  // form within the AVFS mount, such as
  //   "/run/avfsroot/media/layer2.zip#/test/doc/layer1.zip#"
  // instead of the "nested" form, such as
  //   "/run/avfsroot/media/archive/layer2.zip/test/doc/layer1.zip#"
  // where "/media/archive/layer2.zip" is a mount point to the virtual
  // path "/run/avfsroot/media/layer2.zip#".
  //
  // Mounting the inner archive using the nested form may cause problems
  // reading files from the inner archive. To avoid that, we first try to
  // find the longest parent path of |path| that is an existing mount
  // point to a virtual path within the AVFS mount. If such a parent path
  // is found, we construct the virtual path of |path| within the AVFS
  // mount as a subpath of its parent's virtual path.
  //
  // e.g. Given |path| is "/media/archive/layer2.zip/test/doc/layer1.zip",
  //      and "/media/archive/layer2.zip" is a mount point to the virtual
  //      path "/run/avfsroot/media/layer2.zip#" within the AVFS mount.
  //      The following code should return the virtual path of |path| as
  //      "/run/avfsroot/media/layer2.zip#/test/doc/layer1.zip#".
  std::map<std::string, std::string>::const_iterator handler_iterator =
      extension_handlers_.find(extension);
  if (handler_iterator == extension_handlers_.end())
    return std::string();

  base::FilePath file_path(path);
  base::FilePath current_path = file_path.DirName();
  base::FilePath parent_path = current_path.DirName();
  while (current_path != parent_path) {  // Search till the root
    VirtualPathMap::const_iterator path_iterator =
        virtual_paths_.find(current_path.value());
    if (path_iterator != virtual_paths_.end()) {
      base::FilePath avfs_path(path_iterator->second);
      // As current_path is a parent of file_path, AppendRelativePath()
      // should return true here.
      CHECK(current_path.AppendRelativePath(file_path, &avfs_path));
      return avfs_path.value() + handler_iterator->second;
    }
    current_path = parent_path;
    parent_path = parent_path.DirName();
  }

  // If no parent path is a mounted via AVFS, we are not mounting a nested
  // archive and thus construct the virtual path of the archive based on a
  // corresponding AVFS mount path.
  for (const auto& mapping : kAVFSPathMapping) {
    base::FilePath base_path(mapping.base_path);
    base::FilePath avfs_path(mapping.avfs_path);
    if (base_path.AppendRelativePath(file_path, &avfs_path)) {
      return avfs_path.value() + handler_iterator->second;
    }
  }
  return std::string();
}

MountErrorType ArchiveManager::StartAVFS() {
  if (avfs_started_)
    return MOUNT_ERROR_NONE;

  // As cros-disks is now a non-privileged process, the directory tree under
  // |kAVFSRootDirectory| is created by the pre-start script of the cros-disks
  // upstart job. We simply check to make sure the directory tree is created
  // with the expected file ownership and permissions.
  uid_t avfs_user_id, dir_user_id;
  gid_t avfs_group_id, dir_group_id;
  mode_t dir_mode;
  if (!platform()->PathExists(kAVFSRootDirectory) ||
      !platform()->GetUserAndGroupId(kAVFSMountUser, &avfs_user_id,
                                     &avfs_group_id) ||
      !platform()->GetOwnership(kAVFSRootDirectory, &dir_user_id,
                                &dir_group_id) ||
      !platform()->GetPermissions(kAVFSRootDirectory, &dir_mode) ||
      (dir_user_id != avfs_user_id) || (dir_group_id != avfs_group_id) ||
      ((dir_mode & 07777) != kAVFSDirectoryPermissions)) {
    LOG(ERROR) << kAVFSRootDirectory << " isn't created properly";
    return MOUNT_ERROR_INTERNAL;
  }

  // Set the AVFS_LOGFILE environment variable so that the AVFS daemon
  // writes log messages to a file instead of syslog. Otherwise, writing
  // to syslog may trigger the socket/connect/send system calls, which are
  // disabled by the seccomp filters policy file. This only affects the
  // child processes spawned by cros-disks and does not persist after
  // cros-disks restarts.
  setenv("AVFS_LOGFILE", kAVFSLogFile, 1);

  avfs_started_ = true;
  for (const auto& mapping : kAVFSPathMapping) {
    MountErrorType mount_error =
        MountAVFSPath(mapping.base_path, mapping.avfs_path);
    if (mount_error != MOUNT_ERROR_NONE) {
      LOG(ERROR) << "Cannot mount AVFS path " << quote(mapping.avfs_path)
                 << ": " << mount_error;
      StopAVFS();
      return mount_error;
    }
  }
  return MOUNT_ERROR_NONE;
}

bool ArchiveManager::StopAVFS() {
  if (!avfs_started_)
    return true;

  avfs_started_ = false;
  // Unmounts all mounted archives before unmounting AVFS mounts.
  bool all_unmounted = UnmountAll();
  for (const auto& mapping : kAVFSPathMapping) {
    const std::string& path = mapping.avfs_path;
    if (!platform()->PathExists(path))
      continue;

    const MountErrorType error = platform()->Unmount(path, 0);
    if (error != MOUNT_ERROR_NONE)
      all_unmounted = false;
  }

  return all_unmounted;
}

bool ArchiveManager::CreateMountDirectory(const std::string& path) const {
  // If an empty directory was left behind for any reason, remove it first.
  if (platform()->DirectoryExists(path) &&
      !platform()->RemoveEmptyDirectory(path)) {
    return false;
  }

  // Create directory. This works because /run/avfsroot is owned by avfs:avfs,
  // and cros-disks is in the avfs group.
  if (!platform()->CreateDirectory(path)) {
    return false;
  }

  uid_t uid;
  gid_t gid;

  // Set directory's permissions and owner.
  if (!platform()->SetPermissions(path, kAVFSDirectoryPermissions) ||
      !platform()->GetUserAndGroupId(kAVFSMountUser, &uid, &gid) ||
      !platform()->SetOwnership(path, uid, gid)) {
    // Remove directory in case of error.
    platform()->RemoveEmptyDirectory(path);
    return false;
  }

  return true;
}

MountErrorType ArchiveManager::MountAVFSPath(
    const std::string& base_path, const std::string& avfs_path) const {
  MountInfo mount_info;
  if (!mount_info.RetrieveFromCurrentProcess())
    return MOUNT_ERROR_INTERNAL;

  if (mount_info.HasMountPath(avfs_path)) {
    LOG(WARNING) << "Path " << quote(avfs_path) << " is already mounted";
    // Not using MOUNT_ERROR_PATH_ALREADY_MOUNTED here because that implies an
    // error on the user-requested mount. The error here is for the avfsd
    // daemon.
    return MOUNT_ERROR_INTERNAL;
  }

  // Create avfs_path with the right uid, gid and permissions.
  if (!CreateMountDirectory(avfs_path)) {
    LOG(ERROR) << "Cannot create mount directory " << quote(avfs_path);
    return MOUNT_ERROR_INTERNAL;
  }

  MountOptions mount_options;
  mount_options.WhitelistOption(FUSEHelper::kOptionAllowOther);
  mount_options.WhitelistOption(kAVFSModulesOption);
  mount_options.WhitelistOptionPrefix(kAVFSSubdirOptionPrefix);
  std::vector<std::string> options = {
      MountOptions::kOptionReadOnly,
      kAVFSModulesOption,
      kAVFSSubdirOptionPrefix + base_path,
  };
  mount_options.Initialize(options, false, "", "");

  std::unique_ptr<FUSEMounter> fuse_mounter = std::make_unique<FUSEMounter>(
      "", avfs_path, "avfs", mount_options, platform(), process_reaper(),
      kAVFSMountProgram, kAVFSMountUser, kAVFSSeccompFilterPolicyFile,
      std::vector<FUSEMounter::BindPath>({
          // This needs to be recursively bind mounted so that any external
          // media (mounted under /media) or user (under /home/chronos) mounts
          // are visible to AVFS.
          {base_path, false /* writable*/, true /* recursive */},
      }),
      false /* permit_network_access */, kAVFSMountGroup);

  MountErrorType mount_error = fuse_mounter->Mount();
  if (mount_error != MOUNT_ERROR_NONE) {
    return mount_error;
  }

  if (!mount_info.RetrieveFromCurrentProcess() ||
      !mount_info.HasMountPath(avfs_path)) {
    LOG(WARNING) << "Cannot mount " << quote(base_path) << " to "
                 << quote(avfs_path) << " via AVFS";
    return MOUNT_ERROR_INTERNAL;
  }

  LOG(INFO) << "Mounted " << quote(base_path) << " to " << quote(avfs_path)
            << " via AVFS";
  return MOUNT_ERROR_NONE;
}

void ArchiveManager::AddMountVirtualPath(const std::string& mount_path,
                                         const std::string& virtual_path) {
  virtual_paths_[mount_path] = virtual_path;
}

void ArchiveManager::RemoveMountVirtualPath(const std::string& mount_path) {
  virtual_paths_.erase(mount_path);
}

}  // namespace cros_disks