core/jni/fd_utils.h

/*
 * Copyright (C) 2016 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.
 */

#ifndef FRAMEWORKS_BASE_CORE_JNI_FD_UTILS_H_
#define FRAMEWORKS_BASE_CORE_JNI_FD_UTILS_H_

#include <set>
#include <string>
#include <unordered_map>
#include <vector>

#include <dirent.h>
#include <inttypes.h>
#include <sys/stat.h>

#include <android-base/macros.h>

class FileDescriptorInfo;

// This type is duplicated in com_android_internal_os_Zygote.cpp
typedef const std::function<void(std::string)>& fail_fn_t;

// Allowlist of open paths that the zygote is allowed to keep open.
//
// In addition to the paths listed in kPathAllowlist in file_utils.cpp, and
// paths dynamically added with Allow(), all files ending with ".jar"
// under /system/framework" are allowlisted. See IsAllowed() for the canonical
// definition.
//
// If the allowlisted path is associated with a regular file or a
// character device, the file is reopened after a fork with the same
// offset and mode. If the allowlisted path is associated with a
// AF_UNIX socket, the socket will refer to /dev/null after each
// fork, and all operations on it will fail.
class FileDescriptorAllowlist {
public:
    // Lazily creates the global allowlist.
    static FileDescriptorAllowlist* Get();

    // Adds a path to the allowlist.
    void Allow(const std::string& path) { allowlist_.push_back(path); }

    // Returns true iff. a given path is allowlisted. A path is allowlisted
    // if it belongs to the allowlist (see kPathAllowlist) or if it's a path
    // under /system/framework that ends with ".jar" or if it is a system
    // framework overlay.
    bool IsAllowed(const std::string& path) const;

private:
    FileDescriptorAllowlist();

    static FileDescriptorAllowlist* instance_;

    std::vector<std::string> allowlist_;

    DISALLOW_COPY_AND_ASSIGN(FileDescriptorAllowlist);
};

// Returns the set of file descriptors currently open by the process.
std::unique_ptr<std::set<int>> GetOpenFds(fail_fn_t fail_fn);

// A FileDescriptorTable is a collection of FileDescriptorInfo objects
// keyed by their FDs.
class FileDescriptorTable {
 public:
  // Creates a new FileDescriptorTable. This function scans
  // /proc/self/fd for the list of open file descriptors and collects
  // information about them. Returns NULL if an error occurs.
  static FileDescriptorTable* Create(const std::vector<int>& fds_to_ignore,
                                     fail_fn_t fail_fn);

  ~FileDescriptorTable();

  // Checks that the currently open FDs did not change their metadata from
  // stat(2), readlink(2) etc. Ignores FDs from |fds_to_ignore|.
  //
  // Temporary: allows newly open FDs if they pass the same checks as in
  // Create(). This will be further restricted. See TODOs in the
  // implementation.
  void Restat(const std::vector<int>& fds_to_ignore, fail_fn_t fail_fn);

  // Reopens all file descriptors that are contained in the table. Returns true
  // if all descriptors were successfully re-opened or detached, and false if an
  // error occurred.
  void ReopenOrDetach(fail_fn_t fail_fn);

 private:
  explicit FileDescriptorTable(const std::unordered_map<int, FileDescriptorInfo*>& map);

  void RestatInternal(std::set<int>& open_fds, fail_fn_t fail_fn);

  // Invariant: All values in this unordered_map are non-NULL.
  std::unordered_map<int, FileDescriptorInfo*> open_fd_map_;

  DISALLOW_COPY_AND_ASSIGN(FileDescriptorTable);
};

#endif  // FRAMEWORKS_BASE_CORE_JNI_FD_UTILS_H_