Commit message: Prevent heap OOB error in `MaxPoolGrad`

PiperOrigin-RevId: 372424854
Change-Id: Idac0f23867ad8b0601cafbaaa52d5e64269e63a7
CVE: CVE-2021-29579
CWE: CWE-787
Vulnerability description: TensorFlow is an end-to-end open source platform for machine learning. The implementation of `tf.raw_ops.MaxPoolGrad` is vulnerable to a heap buffer overflow. The implementation(https://github.com/tensorflow/tensorflow/blob/ab1e644b48c82cb71493f4362b4dd38f4577a1cf/tensorflow/core/kernels/maxpooling_op.cc#L194-L203) fails to validate that indices used to access elements of input/output arrays are valid. Whereas accesses to `input_backprop_flat` are guarded by `FastBoundsCheck`, the indexing in `out_backprop_flat` can result in OOB access. The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, as these are also affected and still in supported range.

Project: tensorflow
File: maxpooling_op.cc

static void SpatialMaxPoolWithArgMaxHelper(
    OpKernelContext* context, Tensor* output, Tensor* output_arg_max,
    Tensor* input_backprop, const Tensor& tensor_in, const Tensor& out_backprop,
    const PoolParameters& params, const bool include_batch_in_index) {
  if (input_backprop != nullptr) {
    OP_REQUIRES(
        context, include_batch_in_index,
        errors::Internal(
            "SpatialMaxPoolWithArgMaxHelper requires include_batch_in_index "
            "to be True when input_backprop != nullptr"));
    OP_REQUIRES(
        context, (std::is_same<Targmax, int64>::value),
        errors::Internal("SpatialMaxPoolWithArgMaxHelper requires Targmax "
                         "to be int64 when input_backprop != nullptr"));
  }

  typedef Eigen::Map<const Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>>
      ConstEigenMatrixMap;
  typedef Eigen::Map<Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>>
      EigenMatrixMap;
  typedef Eigen::Map<Eigen::Matrix<Targmax, Eigen::Dynamic, Eigen::Dynamic>>
      EigenIndexMatrixMap;

  ConstEigenMatrixMap in_mat(
      tensor_in.flat<T>().data(), params.depth,
      params.tensor_in_cols * params.tensor_in_rows * params.tensor_in_batch);
  EigenMatrixMap out_mat(
      output->flat<T>().data(), params.depth,
      params.out_width * params.out_height * params.tensor_in_batch);
  EigenIndexMatrixMap out_arg_max_mat(
      output_arg_max->flat<Targmax>().data(), params.depth,
      params.out_width * params.out_height * params.tensor_in_batch);

  const DeviceBase::CpuWorkerThreads& worker_threads =
      *(context->device()->tensorflow_cpu_worker_threads());

  // The following code basically does the following:
  // 1. Flattens the input and output tensors into two dimensional arrays.
  //    tensor_in_as_matrix:
  //      depth by (tensor_in_cols * tensor_in_rows * tensor_in_batch)
  //    output_as_matrix:
  //      depth by (out_width * out_height * tensor_in_batch)
  //
  // 2. Walks through the set of columns in the flattened tensor_in_as_matrix,
  //    and updates the corresponding column(s) in output_as_matrix with the
  //    max value.
  auto shard = [&params, &in_mat, &out_mat, &out_arg_max_mat, &input_backprop,
                &output_arg_max, &out_backprop,
                include_batch_in_index](int64 start, int64 limit) {
    const int32 depth = params.depth;
    const int32 in_rows = params.tensor_in_rows;
    const int32 in_cols = params.tensor_in_cols;
    const int32 pad_top = params.pad_top;
    const int32 pad_left = params.pad_left;
    const int32 window_rows = params.window_rows;
    const int32 window_cols = params.window_cols;
    const int32 row_stride = params.row_stride;
    const int32 col_stride = params.col_stride;
    const int32 out_height = params.out_height;
    const int32 out_width = params.out_width;

    {
      // Initializes the output tensor with MIN<T>.
      const int32 output_image_size = out_height * out_width * depth;
      EigenMatrixMap out_shard(out_mat.data() + start * output_image_size, 1,
                               (limit - start) * output_image_size);
      out_shard.setConstant(Eigen::NumTraits<T>::lowest());
      EigenIndexMatrixMap out_arg_max_shard(
          out_arg_max_mat.data() + start * output_image_size, 1,
          (limit - start) * output_image_size);
      out_arg_max_shard.setConstant(kInvalidMaxPoolingIndex);
    }

    for (int64 b = start; b < limit; ++b) {
      for (int h = 0; h < in_rows; ++h) {
        for (int w = 0; w < in_cols; ++w) {
          // (h_start, h_end) * (w_start, w_end) is the range that the input
          // vector projects to.
          const int hpad = h + pad_top;
          const int wpad = w + pad_left;
          const int h_start =
              (hpad < window_rows) ? 0 : (hpad - window_rows) / row_stride + 1;
          const int h_end = std::min(hpad / row_stride + 1, out_height);
          const int w_start =
              (wpad < window_cols) ? 0 : (wpad - window_cols) / col_stride + 1;
          const int w_end = std::min(wpad / col_stride + 1, out_width);
          // compute elementwise max
          const int64 in_index = (b * in_rows + h) * in_cols + w;
          for (int ph = h_start; ph < h_end; ++ph) {
            const int64 out_index_base = (b * out_height + ph) * out_width;
            for (int pw = w_start; pw < w_end; ++pw) {
              const int64 out_index = out_index_base + pw;
              /// NOTES(zhengxq): not using the eigen matrix operation for
              /// now.
              for (int d = 0; d < depth; ++d) {
                const T& input_ref = in_mat.coeffRef(d, in_index);
                T& output_ref = out_mat.coeffRef(d, out_index);
                Targmax& out_arg_max_ref =
                    out_arg_max_mat.coeffRef(d, out_index);
                if (output_ref < input_ref ||
                    out_arg_max_ref == kInvalidMaxPoolingIndex) {
                  output_ref = input_ref;
                  if (include_batch_in_index) {
                    out_arg_max_ref = in_index * depth + d;
                  } else {
                    out_arg_max_ref = (h * in_cols + w) * depth + d;
                  }
                }
              }
            }
          }
        }
      }
    }

    if (input_backprop != nullptr) {
      auto input_backprop_flat = input_backprop->flat<T>();
      auto out_arg_max_flat = output_arg_max->flat<int64>();
      auto out_backprop_flat = out_backprop.flat<T>();

      // Initialize output to 0.
      const int64 in_size = in_rows * in_cols * depth;
      const int64 in_start = start * in_size;
      const int64 in_end = limit * in_size;
      EigenMatrixMap in_shard(input_backprop_flat.data() + in_start, 1,
                              in_end - in_start);
      in_shard.setConstant(T(0));

      // Backpropagate.
      const int out_size = out_height * out_width * depth;
      const int out_start = start * out_size;
      const int out_end = limit * out_size;
      for (int index = out_start; index < out_end; ++index) {
        int input_backprop_index = out_arg_max_flat(index);
        // Although this check is in the inner loop, it is worth its value
        // so we don't end up with memory corruptions. Our benchmark shows that
        // the performance impact is quite small
        // CHECK(input_backprop_index >= in_start && input_backprop_index <
        // in_end)
        FastBoundsCheck(input_backprop_index - in_start, in_end - in_start);
        input_backprop_flat(input_backprop_index) += out_backprop_flat(index);
      }
    }
  };

  const int64 shard_cost = params.tensor_in_rows * params.tensor_in_cols *
                           params.depth * params.window_rows *
                           params.window_cols;
  Shard(worker_threads.num_threads, worker_threads.workers,
        params.tensor_in_batch, shard_cost, shard);
}