contractcourt: Taproot Channel Bugfixes #8879

ProofOfKeags · 2024-06-28T19:49:34Z

Change Description

This PR fixes two bugs with Taproot Channel closures. These bugs never had corresponding issue documentation so they will be described here:

The first bug is an issue wherein we only identified a coop close transaction as one that had the finalized squence number. Since taproot channels use the new RBF coop close process, they will have the max RBF-able sequence number instead. Right now we do not correctly identify this RBF coop close transaction for taproot channels.

SOLUTION: include the max RBF sequence number in the heuristic for identifying coop close transactions.

The second bug is an issue wherein we fail to properly identify whether the commitment transaction was broadcast by the local or remote party because we use a broken heuristic when analyzing the output script. Right now we check if the final byte of the script is an OP_DROP. However both the local and remote outputs of the commitment transaction will end with an OP_DROP.

SOLUTION: check the signing key of the resolver and compare it to the channel config to see if we are using the delay key or the non-delay key.

Steps to Test

I'm unsure what our testing strategy should be here. Open to suggestions.

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coderabbitai · 2024-06-28T19:49:39Z

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contractcourt/chain_watcher.go

contractcourt/commit_sweep_resolver.go

lightninglabs-deploy · 2024-07-10T23:03:51Z

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

yyforyongyu

Thanks for the fix! Looking good, just a few questions.

contractcourt/commit_sweep_resolver.go

yyforyongyu · 2024-07-16T22:10:19Z

contractcourt/commit_sweep_resolver.go

-		isLocalCommitTx = signDesc.WitnessScript[scriptLen-1] ==
-			txscript.OP_DROP
+		delayKey := *c.localChanCfg.DelayBasePoint.PubKey
+		nonDelayKey := *c.localChanCfg.PaymentBasePoint.PubKey


looks like nonDelayKey provides little utility but sanity checking an impossible case?

If we allow ourselves to assume that the signing key MUST be one of these two keys, then all we need is for one of them to be there as we can infer that if it isn't one, then it is the other. I chose this approach for thoroughness but we can trim it down if you'd rather this either/or assumption to be documented in the comments rather than explicitly checked in the control logic.

Roasbeef

LGTM 🧲

As mentioned elsewhere, things end up working as is since the witness scripts are identical. We also have some added confidence with the various sweeping scenarios in the itest.

One potential follow up here would be to extract the routine that determines isLocalCommitTx into a new function. Then we can write a unit test that directly calls NewUnilateralCloseSummary with a realistic set of arguments to further bind the assumption we're making here re SelfOutputSignDesc.KeyDesc.PubKey (that it's always set, and non-nil, etc).

contractcourt/commit_sweep_resolver.go

This commit fixes an issue where we did not properly detect and therefore record the coop close transaction if it used the newer RBF coop close v2 scheme. This only affects coop closes of taproot channels today.

This commit fixes the heuristic we use for identifying the party that broadcast a Simple Taproot Channel commitment transaction. Prior to this change we checked if the last script element was an OP_DROP. However, both the local and remote commitment outputs have an OP_DROP at the end. The new approach checks the resolver's SignDescriptor and compares that key to the keys in the channel's local ChannelConfig. If the key is the delay key, we know that it is our commitment transaction.

yyforyongyu

LGTM🦾

Found this new flake,

--- FAIL: TestChanStatusManagerStateMachine (0.00s)
    --- FAIL: TestChanStatusManagerStateMachine/add_new_channels (4.05s)
        chan_status_manager_test.go:765: received update for unexpected short chan id: 0:0:144
FAIL

Don't think it's related to this PR tho.

contractcourt/commit_sweep_resolver.go

ProofOfKeags added bug Unintended code behaviour taproot chans labels Jun 28, 2024

ProofOfKeags added this to the v0.18.2 milestone Jun 28, 2024

ProofOfKeags requested a review from Roasbeef June 28, 2024 19:49

ProofOfKeags self-assigned this Jun 28, 2024

ProofOfKeags requested a review from yyforyongyu June 28, 2024 19:52

Roasbeef requested changes Jun 28, 2024

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yyforyongyu reviewed Jul 2, 2024

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ProofOfKeags force-pushed the bugfix/taproot-coop-sequence branch 3 times, most recently from 5ff3516 to ba465c8 Compare July 3, 2024 22:10

dstadulis added the llm-review add to a PR to have an LLM bot review it label Jul 8, 2024

ProofOfKeags requested review from Roasbeef and yyforyongyu July 11, 2024 19:34

yyforyongyu reviewed Jul 16, 2024

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Roasbeef approved these changes Jul 17, 2024

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contractcourt: properly detect RBF coop close transactions

31d4575

This commit fixes an issue where we did not properly detect and therefore record the coop close transaction if it used the newer RBF coop close v2 scheme. This only affects coop closes of taproot channels today.

ProofOfKeags force-pushed the bugfix/taproot-coop-sequence branch from ba465c8 to fc3aa5d Compare July 17, 2024 21:51

ProofOfKeags force-pushed the bugfix/taproot-coop-sequence branch from fc3aa5d to 09f5e08 Compare July 17, 2024 21:57

ProofOfKeags requested a review from yyforyongyu July 17, 2024 23:23

ProofOfKeags mentioned this pull request Jul 18, 2024

Define isLocalCommitTx and refactor contractcourt to use it #8920

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yyforyongyu approved these changes Jul 18, 2024

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Roasbeef added the no-changelog label Jul 18, 2024

Roasbeef merged commit 6dea864 into lightningnetwork:master Jul 18, 2024
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contractcourt: Taproot Channel Bugfixes #8879

contractcourt: Taproot Channel Bugfixes #8879

ProofOfKeags commented Jun 28, 2024 •

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contractcourt: Taproot Channel Bugfixes #8879

contractcourt: Taproot Channel Bugfixes #8879

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ProofOfKeags commented Jun 28, 2024 • edited Loading

Change Description

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ProofOfKeags commented Jun 28, 2024 •

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