fix: chain: Do not update message info cache until after message validation

[gammazero]

Related Issues

The sequence number used for replay detection was being updated before message validation confirmed that the message originated from the correct host. This would allow one host A to create a message with the ID of another host B that could then update the cached sequence number for B. While the message from A would fail validation and be ignored, the cached sequence number for B would get updated. This would lead to a temporary DoS for host B as its messages were incorrectly rejected as replays.

Host A would need to be authorized to send messages on the network, so this issue could only be caused by an authorized host.

Proposed Changes

This fixes the issue by setting the cached sequence number after message validation.

A unit test is included that demonstrates the issue is fixed. It fails with the previous code and works with the fixed code.

Additional Info

Checklist

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[arajasek]

LGTM, thank you!