Coverity fixes

[embhorn]

Coverity flagged the return values of the network read functions as potentially overflowed. Each returns a byte count derived from a socket read, and the checker models that count as unbounded.

Clamp the returned value to the requested length on the success path, right before it is returned:

• MqttPacket_Read: reject a socket read that exceeds remain_read.
• MqttSocket_Read: clamp rc to buf_len.
• NetRead_ex and the FreeRTOS NetRead variant: clamp rc to buf_len.

These bounds are already guaranteed by the read logic; the explicit clamps make them local to each return so the analysis can prove no overflow occurs.

[Copilot]

Pull request overview

This PR addresses Coverity findings around potentially unbounded return values from network read functions by adding explicit bounds checks/clamps so return values cannot exceed the requested read length.

Changes:

• Clamp MqttSocket_Read’s returned byte count to buf_len on the success path.
• In MqttPacket_Read, reject socket reads that return more bytes than requested (remain_read).
• Clamp the example network read implementations’ returned byte count to buf_len.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/mqtt_socket.c	Adds a final success-path clamp to keep MqttSocket_Read’s return value bounded by the requested length.
src/mqtt_packet.c	Adds a defensive check that rejects oversized socket reads before using the result.
examples/mqttnet.c	Adds success-path clamps to example NetRead/NetRead_ex return values for static-analysis friendliness.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #562

Scan targets checked: wolfmqtt-bugs, wolfmqtt-src

No new issues found in the changed files. ✅