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Workaround for LND to cause a force-close on our channel #8213

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a64c5f0
Workaround for LND to cause a force-close on our channel
adi2011 Apr 5, 2025
92fc59b
tests: Fix test_emergencyrecover to check for ChannelReestablish
adi2011 Apr 5, 2025
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26 changes: 26 additions & 0 deletions lightningd/peer_control.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1383,6 +1383,32 @@ static void connect_activate_subd(struct lightningd *ld, struct channel *channel
send_error:
log_debug(channel->log, "Telling connectd to send error %s",
tal_hex(tmpctx, error));

/* LND does not respond to errors with a unilateral close
* (https://github.com/lightningnetwork/lnd/blob/abb1e3463f3a83bbb843d5c399869dbe930ad94f/htlcswitch/link.go#L2119).
* We fix this by sending a `ChannelReestablish` msg with `0` commitment numbers and an
* invalid `your_last_per_commitment_secret`. */
if (is_stub_scid(*channel->scid)) {
struct secret your_last_per_commit_secret;
memset(&your_last_per_commit_secret, 1,
sizeof(your_last_per_commit_secret));

const u8 *msg = towire_channel_reestablish(tmpctx, &channel->cid,
0,
0,
&your_last_per_commit_secret,
&channel->channel_info.remote_per_commit,
NULL);

log_debug(channel->log, "Sending a bogus channel_reestablish message to make the peer "
"unilaterally close the channel.");

subd_send_msg(ld->connectd,
take(towire_connectd_peer_send_msg(NULL, &channel->peer->id,
channel->peer->connectd_counter,
msg)));
}

/* Get connectd to send error and close. */
subd_send_msg(ld->connectd,
take(towire_connectd_peer_send_msg(NULL, &channel->peer->id,
Expand Down
7 changes: 7 additions & 0 deletions tests/test_misc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2974,6 +2974,7 @@ def test_emergencyrecoverpenaltytxn(node_factory, bitcoind):
stubs = l1.rpc.emergencyrecover()["stubs"]
assert len(stubs) == 1
assert stubs[0] == _["channel_id"]
l1.daemon.wait_for_log('Sending a bogus channel_reestablish message to make the peer unilaterally close the channel.')
l1.daemon.wait_for_log('peer_out WIRE_ERROR')

# Restarting so that L1
Expand Down Expand Up @@ -3021,7 +3022,10 @@ def test_emergencyrecover(node_factory, bitcoind):
listfunds = l1.rpc.listfunds()["channels"][0]
assert listfunds["short_channel_id"] == "1x1x1"

l1.daemon.wait_for_log('Sending a bogus channel_reestablish message to make the peer unilaterally close the channel.')
l1.daemon.wait_for_log('peer_out WIRE_ERROR')

l2.daemon.wait_for_log('bad reestablish commitment_number: 0')
l2.daemon.wait_for_log('State changed from CHANNELD_NORMAL to AWAITING_UNILATERAL')

bitcoind.generate_block(5, wait_for_mempool=1)
Expand Down Expand Up @@ -3140,7 +3144,10 @@ def test_restorefrompeer(node_factory, bitcoind):

assert l1.rpc.restorefrompeer()['stubs'][0] == _['channel_id']

l1.daemon.wait_for_log('Sending a bogus channel_reestablish message to make the peer unilaterally close the channel.')
l1.daemon.wait_for_log('peer_out WIRE_ERROR')

l2.daemon.wait_for_log('bad reestablish commitment_number: 0')
l2.daemon.wait_for_log('State changed from CHANNELD_NORMAL to AWAITING_UNILATERAL')

bitcoind.generate_block(5, wait_for_mempool=1)
Expand Down
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