login_manager/secret_util.cc

// Copyright 2019 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 "login_manager/secret_util.h"

#include <utility>

#include <base/file_descriptor_posix.h>
#include <base/files/file_util.h>
#include <base/files/scoped_file.h>
#include <base/memory/shared_memory_handle.h>
#include <base/memory/shared_memory.h>
#include <base/process/process_handle.h>
#include <base/strings/string_number_conversions.h>
#include <crypto/sha2.h>
#include <gmock/gmock.h>
#include <gtest/gtest.h>

namespace login_manager {
namespace secret_util {

namespace {

// Maximum amount of data that can be sent through the pipe using |secret_util|
// methods.
// 64k of data, minus 64 bits for a preceding size. This number was chosen to
// fit all the data in a single pipe buffer and avoid blocking on write.
// (http://man7.org/linux/man-pages/man7/pipe.7.html)
const size_t kPipeSecretSizeLimit = 1024 * 64 - sizeof(size_t);

// Reads |data_size| from the pipe. Returns 'false' if it couldn't read
// |data_size| or if |data_size| was incorrect.
bool GetSecretDataSizeFromPipe(int in_secret_fd, size_t* data_size_out) {
  if (!base::ReadFromFD(in_secret_fd, reinterpret_cast<char*>(data_size_out),
                        sizeof(size_t))) {
    PLOG(ERROR) << "Could not read secret size from file.";
    return false;
  }

  if (*data_size_out == 0 || *data_size_out > kPipeSecretSizeLimit) {
    LOG(ERROR) << "Invalid data size read from file descriptor. Size read: "
               << *data_size_out;
    return false;
  }

  return true;
}

}  // namespace

// Limiting data size to 10MB here because it covers the current use cases,
// it can be increased if needed up to an operating system limit (man 1 lsipc).
const size_t kSharedMemorySecretSizeLimit = 10 * 1024 * 1024;

SharedMemoryUtil::~SharedMemoryUtil() = default;

base::ScopedFD SharedMemoryUtil::WriteDataToSharedMemory(
    const std::vector<uint8_t>& data) {
  size_t data_size = data.size();
  CHECK_LE(data_size, kSharedMemorySecretSizeLimit);
  base::SharedMemory shared_memory;
  base::SharedMemoryCreateOptions options;
  options.size = data.size();
  options.share_read_only = true;
  if (!shared_memory.Create(options) || !shared_memory.Map(data.size()))
    return base::ScopedFD();
  memcpy(shared_memory.memory(), data.data(), data.size());
  base::SharedMemoryHandle read_only_handle = shared_memory.GetReadOnlyHandle();
  if (!read_only_handle.IsValid())
    return base::ScopedFD();
  return base::ScopedFD(read_only_handle.Release());
}

bool SharedMemoryUtil::ReadDataFromSharedMemory(
    const base::ScopedFD& in_data_fd,
    size_t data_size,
    std::vector<uint8_t>* out_data) {
  // |shared_memory.TakeHandle()| must be called before leaving this function,
  // otherwise the file descriptor will be closed twice (once here and once by
  // session manager).
  base::SharedMemory shared_memory(
      base::SharedMemoryHandle::ImportHandle(in_data_fd.get(), data_size),
      /*read_only=*/true);
  if (!shared_memory.Map(data_size)) {
    shared_memory.TakeHandle();
    return false;
  }
  out_data->assign(
      reinterpret_cast<uint8_t*>(shared_memory.memory()),
      reinterpret_cast<uint8_t*>(shared_memory.memory()) + data_size);
  shared_memory.Unmap();
  shared_memory.TakeHandle();
  return true;
}

base::ScopedFD WriteSizeAndDataToPipe(const std::vector<uint8_t>& data) {
  size_t data_size = data.size();
  CHECK_LE(data_size, kPipeSecretSizeLimit);

  int fds[2];
  base::CreateLocalNonBlockingPipe(fds);
  base::ScopedFD read_dbus_fd(fds[0]);
  base::ScopedFD write_scoped_fd(fds[1]);

  base::WriteFileDescriptor(write_scoped_fd.get(),
                            reinterpret_cast<const char*>(&data_size),
                            sizeof(size_t));
  base::WriteFileDescriptor(write_scoped_fd.get(),
                            reinterpret_cast<const char*>(data.data()),
                            data_size);
  return read_dbus_fd;
}

bool SaveSecretFromPipe(password_provider::PasswordProviderInterface* provider,
                        const base::ScopedFD& in_secret_fd) {
  size_t data_size = 0;
  if (!GetSecretDataSizeFromPipe(in_secret_fd.get(), &data_size))
    return false;

  auto secret = password_provider::Password::CreateFromFileDescriptor(
      in_secret_fd.get(), data_size);

  if (!secret) {
    LOG(ERROR) << "Could not create secret from file descriptor.";
    return false;
  }

  if (!provider->SavePassword(*secret)) {
    LOG(ERROR) << "Could not save secret.";
    return false;
  }

  return true;
}

base::FilePath StringToSafeFilename(std::string data) {
  std::string sha256hash = crypto::SHA256HashString(data);
  return base::FilePath(base::HexEncode(sha256hash.data(), sha256hash.size()));
}

}  // namespace secret_util
}  // namespace login_manager