fix(modem): handle nullptr in DTE constructors to prevent invalid access (IDFGH-14688)

[deodatomatheus]

Description

The issue can be reproduced by setting a timeout for waiting for a USB connection (esp_modem_usb_term_config.timeou_ms). When the timeout occurs, the value of primary_term becomes null.

If either primary_term or secondary_term is nullptr, the set_command_callbacks function attempts to access invalid values. For example, in the first line of the function, primary_term->set_read_cb([this](uint8_t *data, size_t len), the program tries to dereference primary_term, leading to a LoadProhibited exception and crashing the application.

To address this, I added a validation check in the DTE constructor to ensure the values are valid. Additionally, I handled the exception in the standard exception handler.

Related

Testing

I test the changes in a ESP32S3.

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[CLAassistant]

All committers have signed the CLA.

[david-cermak]

Thanks for the fix, LGTM!

Could you please just update the commit message prefix -> fix(modem): ...?
(or install the pre-commit hook)

[david-cermak]

@deodatomatheus Please check also the CI failures, above,
we support a build with exception disabled, as well.

[deodatomatheus]

@david-cermak i changed the code to use ESP_MODEM_THROW_IF_FALSE(...) instead of throw std::invalid_argument(...) to support building with exceptions disabled.

[david-cermak]

Thanks for the updates, LGTM!