akovalenko/lnd.xprv
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Merge pull request #2855 from Roasbeef/output-based-force-close-detection

Browse Source 
contractcourt: detect local force closes based on commitment outputs
This commit is contained in:
Olaoluwa Osuntokun 2019-04-30 15:39:41 -07:00 committed by GitHub
commit 1acd38e48c
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 282 additions and 45 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

143
contractcourt/chain_watcher.go
View File

@ -1,6 +1,7 @@
package contractcourt
import (
"bytes"
"fmt"
"sync"
"sync/atomic"
@ -16,6 +17,7 @@ import (
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/lightningnetwork/lnd/shachain"
)
const (
@ -271,6 +273,74 @@ func (c *chainWatcher) SubscribeChannelEvents() *ChainEventSubscription {
return sub
}
// isOurCommitment returns true if the passed commitSpend is a spend of the
// funding transaction using our commitment transaction (a local force close).
// In order to do this in a state agnostic manner, we'll make our decisions
// based off of only the set of outputs included.
func isOurCommitment(localChanCfg, remoteChanCfg channeldb.ChannelConfig,
commitSpend *chainntnfs.SpendDetail, broadcastStateNum uint64,
revocationProducer shachain.Producer) (bool, error) {
// First, we'll re-derive our commitment point for this state since
// this is what we use to randomize each of the keys for this state.
commitSecret, err := revocationProducer.AtIndex(broadcastStateNum)
if err != nil {
return false, err
}
commitPoint := input.ComputeCommitmentPoint(commitSecret[:])
// Now that we have the commit point, we'll derive the tweaked local
// and remote keys for this state. We use our point as only we can
// revoke our own commitment.
localDelayBasePoint := localChanCfg.DelayBasePoint.PubKey
localDelayKey := input.TweakPubKey(localDelayBasePoint, commitPoint)
remoteNonDelayPoint := remoteChanCfg.PaymentBasePoint.PubKey
remotePayKey := input.TweakPubKey(remoteNonDelayPoint, commitPoint)
// With the keys derived, we'll construct the remote script that'll be
// present if they have a non-dust balance on the commitment.
remotePkScript, err := input.CommitScriptUnencumbered(remotePayKey)
if err != nil {
return false, err
}
// Next, we'll derive our script that includes the revocation base for
// the remote party allowing them to claim this output before the CSV
// delay if we breach.
revocationKey := input.DeriveRevocationPubkey(
remoteChanCfg.RevocationBasePoint.PubKey, commitPoint,
)
localScript, err := input.CommitScriptToSelf(
uint32(localChanCfg.CsvDelay), localDelayKey, revocationKey,
)
if err != nil {
return false, err
}
localPkScript, err := input.WitnessScriptHash(localScript)
if err != nil {
return false, err
}
// With all our scripts assembled, we'll examine the outputs of the
// commitment transaction to determine if this is a local force close
// or not.
for _, output := range commitSpend.SpendingTx.TxOut {
pkScript := output.PkScript
switch {
case bytes.Equal(localPkScript, pkScript):
return true, nil
case bytes.Equal(remotePkScript, pkScript):
return true, nil
}
}
// If neither of these scripts are present, then it isn't a local force
// close.
return false, nil
}
// closeObserver is a dedicated goroutine that will watch for any closes of the
// channel that it's watching on chain. In the event of an on-chain event, the
// close observer will assembled the proper materials required to claim the
@ -320,35 +390,40 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
return
}
// If this channel has been recovered, then we'll modify our
// behavior as it isn't possible for us to close out the
// channel off-chain ourselves. It can only be the remote party
// force closing, or a cooperative closure we signed off on
// before losing data getting confirmed in the chain.
isRecoveredChan := c.cfg.chanState.HasChanStatus(
channeldb.ChanStatusRestored,
// Decode the state hint encoded within the commitment
// transaction to determine if this is a revoked state or not.
obfuscator := c.stateHintObfuscator
broadcastStateNum := c.cfg.extractStateNumHint(
commitTxBroadcast, obfuscator,
)
// If we're not recovering this channel, and this is our
// commitment transaction, then we can exit here as we don't
// have any further processing we need to do (we can't cheat
// ourselves :p).
if !isRecoveredChan {
commitmentHash := localCommit.CommitTx.TxHash()
isOurCommitment := commitSpend.SpenderTxHash.IsEqual(
&commitmentHash,
)
// Based on the output scripts within this commitment, we'll
// determine if this is our commitment transaction or not (a
// self force close).
isOurCommit, err := isOurCommitment(
c.cfg.chanState.LocalChanCfg,
c.cfg.chanState.RemoteChanCfg, commitSpend,
broadcastStateNum, c.cfg.chanState.RevocationProducer,
)
if err != nil {
log.Errorf("unable to determine self commit for "+
"chan_point=%v: %v",
c.cfg.chanState.FundingOutpoint, err)
return
}
if isOurCommitment {
if err := c.dispatchLocalForceClose(
commitSpend, *localCommit,
); err != nil {
log.Errorf("unable to handle local"+
"close for chan_point=%v: %v",
c.cfg.chanState.FundingOutpoint, err)
}
return
// If this is our commitment transaction, then we can exit here
// as we don't have any further processing we need to do (we
// can't cheat ourselves :p).
if isOurCommit {
if err := c.dispatchLocalForceClose(
commitSpend, *localCommit,
); err != nil {
log.Errorf("unable to handle local"+
"close for chan_point=%v: %v",
c.cfg.chanState.FundingOutpoint, err)
}
return
}
// Next, we'll check to see if this is a cooperative channel
@ -369,14 +444,9 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
log.Warnf("Unprompted commitment broadcast for "+
"ChannelPoint(%v) ", c.cfg.chanState.FundingOutpoint)
// Decode the state hint encoded within the commitment
// transaction to determine if this is a revoked state or not.
obfuscator := c.stateHintObfuscator
broadcastStateNum := c.cfg.extractStateNumHint(
commitTxBroadcast, obfuscator,
)
// Fetch the current known commit height for the remote party,
// and their pending commitment chain tip if it exist.
remoteStateNum := remoteCommit.CommitHeight
remoteChainTip, err := c.cfg.chanState.RemoteCommitChainTip()
if err != nil && err != channeldb.ErrNoPendingCommit {
log.Errorf("unable to obtain chain tip for "+
@ -385,6 +455,15 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
return
}
// If this channel has been recovered, then we'll modify our
// behavior as it isn't possible for us to close out the
// channel off-chain ourselves. It can only be the remote party
// force closing, or a cooperative closure we signed off on
// before losing data getting confirmed in the chain.
isRecoveredChan := c.cfg.chanState.HasChanStatus(
channeldb.ChanStatusRestored,
)
switch {
// If state number spending transaction matches the current
// latest state, then they've initiated a unilateral close. So

184
contractcourt/chain_watcher_test.go
View File

@ -234,6 +234,24 @@ type dlpTestCase struct {
NumUpdates uint8
}
func executeStateTransitions(t *testing.T, htlcAmount lnwire.MilliSatoshi,
aliceChannel, bobChannel *lnwallet.LightningChannel,
numUpdates uint8) error {
for i := 0; i < int(numUpdates); i++ {
addFakeHTLC(
t, htlcAmount, uint64(i), aliceChannel, bobChannel,
)
err := lnwallet.ForceStateTransition(aliceChannel, bobChannel)
if err != nil {
return err
}
}
return nil
}
// TestChainWatcherDataLossProtect tests that if we've lost data (and are
// behind the remote node), then we'll properly detect this case and dispatch a
// remote force close using the obtained data loss commitment point.
@ -291,19 +309,13 @@ func TestChainWatcherDataLossProtect(t *testing.T) {
// new HTLC to add to the commitment, and then lock in a state
// transition.
const htlcAmt = 1000
for i := 0; i < int(testCase.NumUpdates); i++ {
addFakeHTLC(
t, 1000, uint64(i), aliceChannel, bobChannel,
)
err := lnwallet.ForceStateTransition(
aliceChannel, bobChannel,
)
if err != nil {
t.Errorf("unable to trigger state "+
"transition: %v", err)
return false
}
err = executeStateTransitions(
t, htlcAmt, aliceChannel, bobChannel, testCase.NumUpdates,
)
if err != nil {
t.Errorf("unable to trigger state "+
"transition: %v", err)
return false
}
// We'll request a new channel event subscription from Alice's
@ -412,3 +424,149 @@ func TestChainWatcherDataLossProtect(t *testing.T) {
})
}
}
// TestChainWatcherLocalForceCloseDetect tests we're able to always detect our
// commitment output based on only the outputs present on the transaction.
func TestChainWatcherLocalForceCloseDetect(t *testing.T) {
t.Parallel()
// localForceCloseScenario is the primary test we'll use to execut eout
// table driven tests. We'll assert that for any number of state
// updates, and if the commitment transaction has our output or not,
// we're able to properly detect a local force close.
localForceCloseScenario := func(t *testing.T, numUpdates uint8,
remoteOutputOnly, localOutputOnly bool) bool {
// First, we'll create two channels which already have
// established a commitment contract between themselves.
aliceChannel, bobChannel, cleanUp, err := lnwallet.CreateTestChannels()
if err != nil {
t.Fatalf("unable to create test channels: %v", err)
}
defer cleanUp()
// With the channels created, we'll now create a chain watcher
// instance which will be watching for any closes of Alice's
// channel.
aliceNotifier := &mockNotifier{
spendChan: make(chan *chainntnfs.SpendDetail),
}
aliceChainWatcher, err := newChainWatcher(chainWatcherConfig{
chanState: aliceChannel.State(),
notifier: aliceNotifier,
signer: aliceChannel.Signer,
extractStateNumHint: lnwallet.GetStateNumHint,
})
if err != nil {
t.Fatalf("unable to create chain watcher: %v", err)
}
if err := aliceChainWatcher.Start(); err != nil {
t.Fatalf("unable to start chain watcher: %v", err)
}
defer aliceChainWatcher.Stop()
// We'll execute a number of state transitions based on the
// randomly selected number from testing/quick. We do this to
// get more coverage of various state hint encodings beyond 0
// and 1.
const htlcAmt = 1000
err = executeStateTransitions(
t, htlcAmt, aliceChannel, bobChannel, numUpdates,
)
if err != nil {
t.Errorf("unable to trigger state "+
"transition: %v", err)
return false
}
// We'll request a new channel event subscription from Alice's
// chain watcher so we can be notified of our fake close below.
chanEvents := aliceChainWatcher.SubscribeChannelEvents()
// Next, we'll obtain Alice's commitment transaction and
// trigger a force close. This should cause her to detect a
// local force close, and dispatch a local close event.
aliceCommit := aliceChannel.State().LocalCommitment.CommitTx
// Since this is Alice's commitment, her output is always first
// since she's the one creating the HTLCs (lower balance). In
// order to simulate the commitment only having the remote
// party's output, we'll remove Alice's output.
if remoteOutputOnly {
aliceCommit.TxOut = aliceCommit.TxOut[1:]
}
if localOutputOnly {
aliceCommit.TxOut = aliceCommit.TxOut[:1]
}
aliceTxHash := aliceCommit.TxHash()
aliceSpend := &chainntnfs.SpendDetail{
SpenderTxHash: &aliceTxHash,
SpendingTx: aliceCommit,
}
aliceNotifier.spendChan <- aliceSpend
// We should get a local force close event from Alice as she
// should be able to detect the close based on the commitment
// outputs.
select {
case <-chanEvents.LocalUnilateralClosure:
return true
case <-time.After(time.Second * 5):
t.Errorf("didn't get local for close for state #%v",
numUpdates)
return false
}
}
// For our test cases, we'll ensure that we test having a remote output
// present and absent with non or some number of updates in the channel.
testCases := []struct {
numUpdates uint8
remoteOutputOnly bool
localOutputOnly bool
}{
{
numUpdates: 0,
remoteOutputOnly: true,
},
{
numUpdates: 0,
remoteOutputOnly: false,
},
{
numUpdates: 0,
localOutputOnly: true,
},
{
numUpdates: 20,
remoteOutputOnly: false,
},
{
numUpdates: 20,
remoteOutputOnly: true,
},
{
numUpdates: 20,
localOutputOnly: true,
},
}
for _, testCase := range testCases {
testName := fmt.Sprintf(
"num_updates=%v,remote_output=%v,local_output=%v",
testCase.numUpdates, testCase.remoteOutputOnly,
testCase.localOutputOnly,
)
testCase := testCase
t.Run(testName, func(t *testing.T) {
t.Parallel()
localForceCloseScenario(
t, testCase.numUpdates, testCase.remoteOutputOnly,
testCase.localOutputOnly,
)
})
}
}