discovery: enforce strict validation of peer gossip messages

[NishantBansal2003]

While fuzzing the gossip state machine, I found that LND does not validate the chain hash in ReplyChannelRange, ReplyShortChanIDsEnd and GossipTimestampRange messages. It would be safer to enforce strict validation on these messages to prevent malformed responses from being processed. I verified that CLN performs chain hash validation for these message types.

[gemini-code-assist]

Summary of Changes

Hello @NishantBansal2003, 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 significantly enhances the robustness of the gossip state machine by introducing strict validation for incoming peer gossip messages. Specifically, it ensures that ReplyChannelRange, ReplyShortChanIDsEnd, and GossipTimestampRange messages contain the correct chain hash, preventing the processing of messages intended for different networks. Additionally, ReplyChannelRange messages now undergo a defensive check to confirm that the number of provided timestamps aligns with the number of short channel IDs, mitigating potential panics. These changes improve the network's resilience against malformed or malicious gossip data.

Highlights

• Strict Chain Hash Validation: Implemented strict chain hash validation for ReplyChannelRange, ReplyShortChanIDsEnd, and GossipTimestampRange messages to prevent processing malformed responses from peers and ensure messages pertain to the correct blockchain network.
• Defensive Timestamp Validation: Added validation to ReplyChannelRange messages to ensure that if timestamps are provided, their count matches the number of Short Channel IDs, enhancing defensive safety against potential panics.
• Code Refactoring and Test Coverage: Refactored the processing of ReplyShortChanIDsEnd messages into a dedicated function and introduced comprehensive unit tests to cover the new validation logic for malformed gossip messages.

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Changelog

• discovery/syncer.go
  • Updated a log message from 'query' to 'reply' for channel range processing.
  • Introduced a new function processScidEndReply to handle ReplyShortChanIDsEnd messages, including chain hash validation.
  • Modified the main channelGraphSyncer loop to call processScidEndReply for ReplyShortChanIDsEnd messages.
  • Added chain hash validation to processChanRangeReply.
  • Implemented a check in processChanRangeReply to ensure the count of timestamps matches the count of short channel IDs.
  • Added chain hash validation to ApplyGossipFilter for GossipTimestampRange messages.
• discovery/syncer_test.go
  • Initialized chainHash in newTestSyncer configuration.
  • Added ChainHash field to GossipTimestampRange messages in TestGossipSyncerApplyNoHistoricalGossipFilter, TestGossipSyncerApplyGossipFilter, and TestGossipSyncerSyncTransitions tests.
  • Added ChainHash field to ChannelAnnouncement1 and ChannelUpdate1 messages in TestGossipSyncerReplyShortChanIDs.
  • Added ChainHash field to QueryShortChanIDs messages in TestGossipSyncerReplyShortChanIDs.
  • Added ChainHash field to QueryChannelRange messages in TestGossipSyncerReplyChanRangeQuery, TestGossipSyncerReplyChanRangeQueryBlockRange, TestGossipSyncerReplyChanRangeQueryNoNewChans, and TestGossipSyncerHistoricalSync tests.
  • Added ChainHash field to ReplyChannelRange messages in testGossipSyncerProcessChanRangeReply.
  • Introduced TestGossipSyncerProcessMalformedChanRangeReply to verify rejection of ReplyChannelRange messages with incorrect chain hash or mismatched timestamp/SCID counts.
  • Introduced TestGossipSyncerProcessMalformedShortChanIDsEndReply to verify rejection of ReplyShortChanIDsEnd messages with incorrect chain hash.
  • Introduced TestGossipSyncerProcessMalformedGossipTimestampRange to verify rejection of GossipTimestampRange messages with incorrect chain hash.

Activity

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[gemini-code-assist]

Code Review

This is a solid pull request that hardens the gossip message processing by adding strict validation for the chain hash in ReplyChannelRange, ReplyShortChanIDsEnd, and GossipTimestampRange messages. The defensive check for timestamp consistency in ReplyChannelRange is also a good addition for robustness.

The changes are well-implemented and follow existing patterns in the codebase. The refactoring to introduce processScidEndReply improves the structure of the channelGraphSyncer. The new tests for malformed messages are comprehensive and directly verify the new validation logic.

Overall, this is a high-quality contribution that improves the security and stability of the gossip syncer. I have no further recommendations.

[lightninglabs-deploy]

@NishantBansal2003, remember to re-request review from reviewers when ready