cros-disks/rar_manager.cc

// Copyright 2020 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/rar_manager.h"

#include <algorithm>
#include <memory>
#include <utility>

#include <base/files/file_path.h>
#include <base/files/file_util.h>
#include <base/logging.h>
#include <base/strings/string_number_conversions.h>
#include <base/strings/string_util.h>
#include <brillo/scoped_mount_namespace.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_options.h"
#include "cros-disks/platform.h"
#include "cros-disks/quote.h"

namespace cros_disks {
namespace {

const char kExtension[] = ".rar";

}  // namespace

RarManager::~RarManager() {
  UnmountAll();
}

bool RarManager::CanMount(const std::string& source_path) const {
  // Check for expected file extension.
  return base::EndsWith(source_path, kExtension,
                        base::CompareCase::INSENSITIVE_ASCII) &&
         IsInAllowedFolder(source_path);
}

std::unique_ptr<MountPoint> RarManager::DoMount(
    const std::string& source_path,
    const std::string& /*filesystem_type*/,
    const std::vector<std::string>& options,
    const base::FilePath& mount_path,
    MountOptions* const applied_options,
    MountErrorType* const error) {
  DCHECK(applied_options);
  DCHECK(error);

  metrics()->RecordArchiveType("rar");

  FUSEMounter::Params params{
      .filesystem_type = "rarfs",
      .metrics = metrics(),
      .metrics_name = "Rar2fs",
      .mount_group = FUSEHelper::kFilesGroup,
      .mount_program = "/usr/bin/rar2fs",
      .mount_user = "fuse-rar2fs",
      .platform = platform(),
      .process_reaper = process_reaper(),
      .seccomp_policy = "/usr/share/policy/rar2fs-seccomp.policy",
  };

  // Prepare FUSE mount options.
  {
    uid_t uid;
    gid_t gid;
    if (!platform()->GetUserAndGroupId(FUSEHelper::kFilesUser, &uid, nullptr) ||
        !platform()->GetGroupId(FUSEHelper::kFilesGroup, &gid)) {
      *error = MOUNT_ERROR_INTERNAL;
      return nullptr;
    }

    params.mount_options.WhitelistOptionPrefix("locale=");
    params.mount_options.WhitelistOptionPrefix("umask=");
    params.mount_options.Initialize(
        {"locale=en_US.UTF8", "umask=0222", MountOptions::kOptionReadOnly},
        true, base::NumberToString(uid), base::NumberToString(gid));

    *applied_options = params.mount_options;
  }

  // Determine which mount namespace to use.
  {
    // Attempt to enter the Chrome mount namespace, if it exists.
    auto guard = brillo::ScopedMountNamespace::CreateFromPath(
        base::FilePath(kChromeMountNamespacePath));

    // Check if the source path exists in Chrome's mount namespace.
    if (guard && base::PathExists(base::FilePath(source_path))) {
      // The source path exists in Chrome's mount namespace.
      params.mount_namespace = kChromeMountNamespacePath;
    } else {
      // Use the default mount namespace.
      guard.reset();
    }

    params.bind_paths = GetBindPaths(source_path);
  }

  // To access Play Files.
  {
    gid_t gid;
    if (params.platform->GetGroupId("android-everybody", &gid))
      params.supplementary_groups.push_back(gid);
  }

  // Run rar2fs.
  const FUSEMounter mounter(std::move(params));
  return mounter.Mount(source_path, mount_path, options, error);
}

bool RarManager::Increment(const std::string::iterator begin,
                           std::string::iterator end) {
  while (true) {
    if (begin == end) {
      // Overflow.
      return false;
    }

    char& c = *--end;

    if (c == '9') {
      // Roll 9 to 0.
      c = '0';
    } else if (c == 'z') {
      // Roll z to a.
      c = 'a';
    } else if (c == 'Z') {
      // Roll Z to A.
      c = 'A';
    } else {
      // Increment any other character and done.
      ++c;
      return true;
    }
  }
}

RarManager::IndexRange RarManager::ParseDigits(base::StringPiece path) {
  const base::StringPiece extension = kExtension;

  if (!base::EndsWith(path, extension, base::CompareCase::INSENSITIVE_ASCII))
    return {};

  path.remove_suffix(extension.size());
  const size_t end = path.size();

  while (!path.empty() && base::IsAsciiDigit(path.back()))
    path.remove_suffix(1);

  if (!base::EndsWith(path, ".part", base::CompareCase::INSENSITIVE_ASCII))
    return {};

  return {path.size(), end};
}

void RarManager::AddPathsWithOldNamingScheme(
    FUSEMounter::BindPaths* const bind_paths,
    const base::StringPiece original_path) const {
  DCHECK(bind_paths);

  // Is the extension right?
  if (!base::EndsWith(original_path, kExtension,
                      base::CompareCase::INSENSITIVE_ASCII))
    return;

  // Prepare candidate path.
  std::string candidate_path(original_path);
  const std::string::iterator end = candidate_path.end();

  // Set the last 2 characters to '0', so that extension '.rar' becomes '.r00'
  // and extension '.RAR' becomes '.R00'.
  std::fill(end - 2, end, '0');

  // Is there at least the first supplementary file of the multipart archive?
  if (!platform()->PathExists(candidate_path))
    return;

  bind_paths->push_back({candidate_path});

  // Iterate by incrementing the last 3 characters of the extension:
  // '.r00' -> '.r01' -> ... -> '.r99' -> '.s00' -> ... -> '.z99'
  // or
  // '.R00' -> '.R01' -> ... -> '.R99' -> '.S00' -> ... -> '.Z99'
  while (Increment(end - 3, end) && platform()->PathExists(candidate_path))
    bind_paths->push_back({candidate_path});
}

void RarManager::AddPathsWithNewNamingScheme(
    FUSEMounter::BindPaths* const bind_paths,
    const base::StringPiece original_path,
    const IndexRange& digits) const {
  DCHECK(bind_paths);
  DCHECK_LT(digits.begin, digits.end);
  DCHECK_LE(digits.end, original_path.size());

  // Prepare candidate path.
  std::string candidate_path(original_path);

  // [begin, end) is the digit range to increment.
  const std::string::iterator begin = candidate_path.begin() + digits.begin;
  const std::string::iterator end = candidate_path.begin() + digits.end;

  // Fill the digit range with zeros.
  std::fill(begin, end, '0');

  // Find all the files making the multipart archive.
  while (Increment(begin, end) && platform()->PathExists(candidate_path)) {
    if (candidate_path != original_path)
      bind_paths->push_back({candidate_path});
  }
}

FUSEMounter::BindPaths RarManager::GetBindPaths(
    const base::StringPiece original_path) const {
  FUSEMounter::BindPaths bind_paths = {{std::string(original_path)}};

  // Delimit the digit range assuming original_path uses the new naming scheme.
  const IndexRange digits = ParseDigits(original_path);
  if (digits.empty()) {
    // Use the old naming scheme.
    AddPathsWithOldNamingScheme(&bind_paths, original_path);
  } else {
    // Use the new naming scheme.
    AddPathsWithNewNamingScheme(&bind_paths, original_path, digits);
  }

  return bind_paths;
}

}  // namespace cros_disks