SPDM - enhance the payload size check upon receiving

[IntelCaisui]

Enhance the payload size check in SPDM receive function to prevent
buffer overflow and interger overflow.

Fix problem 2 of issue #603

[jyao1]

Please don't lock() twice.

The above check should be put below the lock().

[IntelCaisui]

Updated. sorry for such incautious problem.

[Copilot]

Pull Request Overview

This PR enhances payload size validation in the SPDM receive function to prevent buffer overflow and integer overflow vulnerabilities. The changes add an early buffer size check and refactor the payload size comparison to avoid potential integer underflow.

• Added early validation to ensure the buffer can accommodate the SPDM message header
• Refactored payload size comparison to prevent integer underflow when buffer length is smaller than header size

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

This check can still underflow if buffer.len() is less than VMCALL_SPDM_MESSAGE_HEADER_SIZE. While the early check at line 65 prevents this for the initial buffer lock, the buffer reference at line 69 is a new mutable lock that could potentially have a different length. Consider using checked_sub() or restructuring to use the result from the early check: if payload_size > buffer.len().saturating_sub(VMCALL_SPDM_MESSAGE_HEADER_SIZE)

Suggested change

	if payload_size > buffer.len() - VMCALL_SPDM_MESSAGE_HEADER_SIZE {
	if payload_size > buffer.len().saturating_sub(VMCALL_SPDM_MESSAGE_HEADER_SIZE) {

[IntelCaisui]

updated.