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fix invalid tensors #950

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fix invalid tensors #950

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5 changes: 5 additions & 0 deletions src/torchcodec/_core/Encoder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,11 @@ torch::Tensor validateSamples(const torch::Tensor& samples) {
samples.dim() == 2,
"samples must have 2 dimensions, got ",
samples.dim());
TORCH_CHECK(
samples.numel() == 0 || samples.data_ptr() != nullptr,
"Samples tensor has null data pointer but non-zero numel. ",
"This indicates an invalid tensor state.");

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@NicolasHug NicolasHug Oct 9, 2025

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Thanks for the PR @pipitochka . Can you please share more details about how the fuzzer managed to create a tensor with numel() > 0 and data_ptr() == nullptr ?

I wonder how it's even possible to end up with such tensors through normal torch operations.

Note for myself: right now if we pass an a tensor with numel == 0 we get a decent error message:

E RuntimeError: Desired number of channels (0) is not supported by the encoder. Supported number of channels are: 1, 2.

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@pipitochka pipitochka Oct 9, 2025

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I done it by torch::load(input_data, dir)

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@pipitochka pipitochka Oct 9, 2025 •
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My function to fuzzing

    char name[] = "/tmp/torch-fuzz-XXXXXX";
    char *dir = mktemp(name);
    std::ofstream fp;
    fp.open(dir, std::ios::out | std::ios::binary);
    fp.write((char *)data, size);
    fp.close();

    if (size <= 0) {
        unlink(dir);
        return 0;
    }

    try {
        torch::Tensor input_data;
        torch::load(input_data, dir);

        int mode = (int)data[0] % 5;
        facebook::torchcodec::AudioStreamOptions aso;
        aso.bitRate = mode;
        aso.numChannels = 1;
        aso.sampleRate = 1;
        std::string fileName = "tmp";

        facebook::torchcodec::AudioEncoder encoder = facebook::torchcodec::AudioEncoder(
        input_data, mode, fileName, aso);

        auto result = encoder.encodeToTensor();

    } catch (const c10::Error &e) {

    } catch (const torch::jit::ErrorReport &e) {

    } catch (const std::runtime_error &e) {

    }

    unlink(dir);
    return 0;


// We enforce this, but if we get user reports we should investigate whether
// that's actually needed.
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