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lnwallet: ensure we re-sign retransmitted commits for taproot channels

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In this commit, we fix an existing bug with the taproot channel type
that can cause force closes if a peer disconnects while attempting to
send the commitment signature.

Before this commit, since the `PartialSig` we send is never committed to
disk, the version read wouldn't contain the musig2 partial sig. We never
write these signatures to disk, as each time we make a new session, we
need to generate fresh nonces to avoid nonce-reuse.

Due to the above interaction, if we went to re-send a signature after a
disconnection, the `CommitSig` message we sent wouldn't actually contain
a `PartialSigWithNonce`, causing a protocol error.
This commit is contained in:
Olaoluwa Osuntokun 2024-08-28 18:23:14 -05:00
parent e8c5e7d5ce
commit 69a1cf4f23
No known key found for this signature in database
GPG Key ID: 3BBD59E99B280306
1 changed files with 35 additions and 3 deletions
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38
lnwallet/channel.go
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@ -4151,6 +4151,27 @@ func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
}, nil
}
// resignMusigCommit is used to resign a commitment transaction for taproot
// channels when we need to retransmit a signature after a channel reestablish
// message. Taproot channels use musig2, which means we must use fresh nonces
// each time. After we receive the channel reestablish message, we learn the
// nonce we need to use for the remote party. As a result, we need to generate
// the partial signature again with the new nonce.
func (lc *LightningChannel) resignMusigCommit(commitTx *wire.MsgTx,
) (lnwire.OptPartialSigWithNonceTLV, error) {
remoteSession := lc.musigSessions.RemoteSession
musig, err := remoteSession.SignCommit(commitTx)
if err != nil {
var none lnwire.OptPartialSigWithNonceTLV
return none, err
}
partialSig := lnwire.MaybePartialSigWithNonce(musig.ToWireSig())
return partialSig, nil
}
// ProcessChanSyncMsg processes a ChannelReestablish message sent by the remote
// connection upon re establishment of our connection with them. This method
// will return a single message if we are currently out of sync, otherwise a
@ -4428,12 +4449,23 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
commitUpdates = append(commitUpdates, logUpdate.UpdateMsg)
}
// If this is a taproot channel, then we need to regenerate the
// musig2 signature for the remote party, using their fresh
// nonce.
if lc.channelState.ChanType.IsTaproot() {
partialSig, err := lc.resignMusigCommit(
commitDiff.Commitment.CommitTx,
)
if err != nil {
return nil, nil, nil, err
}
commitDiff.CommitSig.PartialSig = partialSig
}
// With the batch of updates accumulated, we'll now re-send the
// original CommitSig message required to re-sync their remote
// commitment chain with our local version of their chain.
//
// TODO(roasbeef): need to re-sign commitment states w/
// fresh nonce
commitUpdates = append(commitUpdates, commitDiff.CommitSig)
// NOTE: If a revocation is not owed, then updates is empty.