p2p: Drop unsolicited CMPCTBLOCK from non-HB peer #32606

1. 
   davidgumberg commented at 9:58 pm on May 23, 2025: contributor

   Processing unsolicited CMPCTBLOCK’s from a peer that has not been marked high bandwidth is not well-specified behavior in BIP-0152, in fact the BIP seems to imply that it is not permitted:

   “[…] method is not useful for compact blocks because cmpctblock blocks can be sent unsolicitedly in high-bandwidth mode”

   See https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki#separate-version-for-segregated-witness

   This partially mitigates a mempool leak described in #28272, making it only possible for peers selected as high bandwidth to discover a node’s mempool.

2. p2p: Drop unsolicited CMPCTBLOCK from non-HB peer

   Processing unsolicited CMPCTBLOCK's from a peer that has not been marked
   high bandwidth is not well-specified behavior in BIP-0152, in fact the
   BIP seems to imply that it is not permitted:
   
   "[...] method is not useful for compact blocks because `cmpctblock`
   blocks can be sent unsolicitedly in high-bandwidth mode"
   
   See https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki#separate-version-for-segregated-witness
   
   This partially mitigates a mempool leak described in
   [#28272](https://github.com/bitcoin/bitcoin/issues/28272), making it
   only possible for peers selected as high bandwidth to discover a node's
   mempool.

   13ca017017
3. test: p2p: Nodes ignore unsolicited CMPCTBLOCK's 28086e7b99
4. 
   DrahtBot commented at 9:58 pm on May 23, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32606.

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   Concept ACK	jonatack

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   LLM Linter (✨ experimental)

   Possible typos and grammar issues:

   • high-bandwidth sent -> high-bandwidth, sent [Missing comma creates a grammatically invalid phrase, impacting comprehension of the sentence structure.]

   drahtbot_id_0520

5. DrahtBot added the label P2P on May 23, 2025
6. in test/functional/p2p_compactblocks.py:779 in 13ca017017 outdated

   775@@ -763,6 +776,7 @@ def announce_cmpct_block(node, peer):
   776                 assert "getblocktxn" in peer.last_message
   777             return block, cmpct_block
   778 
   779+
   

   ---

   ---

   

   davidgumberg commented at 10:10 pm on May 23, 2025:

   I’ll delete this on next rebase.
7. 
   jonatack commented at 10:16 pm on May 23, 2025: member

   Concept ACK. BIP152 is marked as Final but perhaps could be clarified on this point.

Contributors
davidgumberg DrahtBot jonatack

Labels
P2P