fix(ethexe/malachite): saturate Fin sequence to avoid overflow in StreamState

[grishasobol]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical vulnerability where a maliciously crafted or extreme sequence value in a Fin message could cause the engine to panic in debug mode or enter an inconsistent state in release mode. By switching to saturating arithmetic, the system now gracefully handles these edge cases, ensuring stability in the stream processing logic.

Highlights

• Arithmetic Overflow Fix: Updated the sequence calculation in StreamState to use saturating_add(1) instead of a standard addition, preventing potential panics or integer wrapping when a peer sends a sequence value of u64::MAX.
• Regression Testing: Added a new test case, fin_at_u64_max_sequence_does_not_panic, to ensure that receiving a Fin message with the maximum possible sequence value does not crash the engine.

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[gemini-code-assist]

Code Review

This pull request addresses a potential panic and overflow vulnerability in the streaming module by replacing unchecked addition with saturating addition when calculating total messages from a peer-controlled sequence number. A regression test has been added to ensure that a sequence number of u64::MAX does not cause a crash. The review feedback correctly identifies that the 'as usize' cast remains a risk on 32-bit platforms where truncation could occur, and suggests using a safer try_into conversion with context as per repository standards.

[gemini-code-assist]

Code Review

This pull request prevents panics or silent wrapping of total_messages in StreamState when receiving a peer-controlled Fin message with a sequence number of u64::MAX by replacing the unchecked addition with saturating_add(1). It also adds a regression test for this scenario. The reviewer suggested using try_into() instead of a direct as usize cast to prevent silent truncation on 32-bit targets.