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lightningd: another gossip transition corner case.
Public commit record
81/100 · Strong
What the developer wrote
Authored by Rusty Russell
lightningd: another gossip transition corner case.
If we see a close tx at the same time we see the channel reach announce depth (here, 104x1x0 confirms
and we process blocks 109 and 110), we see it go from:
CGOSSIP_WAITING_FOR_ANNOUNCE_DEPTH->CGOSSIP_CHANNEL_UNANNOUNCED_DYING (Channel closing before 6 confirms)
Then:
CGOSSIP_CHANNEL_UNANNOUNCED_DYING->CGOSSIP_CHANNEL_ANNOUNCED_DEAD
```
INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: State changed from CHANNELD_NORMAL to CHANNELD_SHUTTING_DOWN
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: gossip state: CGOSSIP_WAITING_FOR_ANNOUNCE_DEPTH->CGOSSIP_CHANNEL_UNANNOUNCED_DYING (Channel closing before 6 confirms)
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: billboard: Channel ready for use. They've sent shutdown, waiting for ours
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: Trying commit
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: Can't send commit: nothing to send, feechange not wanted ({ RCVD_ADD_ACK_REVOCATION:3755 }) blockheight not wanted ({ RCVD_ADD_ACK_REVOCATION:109 })
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: peer_out WIRE_SHUTDOWN
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: billboard: Channel ready for use. Shutdown messages exchanged.
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: pid 35692, msgfd 86
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-channeld-chan#2: Status closed, but not exited. Killing
INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: State changed from CHANNELD_SHUTTING_DOWN to CLOSINGD_SIGEXCHANGE
DEBUG hsmd: new_client: 2
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: Expected closing weight = 772, fee 2895sat (min 1447sat, max 1006268sat)
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: out = 506268sat/500000sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: dustlimit = 546sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: fee = 2895sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: fee negotiation step = 50%
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: billboard perm: Negotiating closing fee between 1447sat and 1006268sat satoshi (ideal 2895sat) using step 50%
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: billboard: Waiting for their initial closing fee offer
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: peer_in WIRE_CLOSING_SIGNED
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: Making close tx at = 506268sat/500000sat fee 2895sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: Received fee offer 2895sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: ...offer is reasonable
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: Their actual closing tx fee is 2895sat vs previous 4220sat: weight is 772
INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: performing quickclose in range 1447sat-8492sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: Making close tx at = 506268sat/500000sat fee 2895sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-hsmd: Got WIRE_HSMD_SIGN_MUTUAL_CLOSE_TX
DEBUG hsmd: Client: Received message 21 from client
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: sending fee offer 2895sat
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: peer_out WIRE_CLOSING_SIGNED
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-closingd-chan#2: billboard perm: We agreed on a closing fee of 2895 satoshi for tx:7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce
INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: State changed from CLOSINGD_SIGEXCHANGE to CLOSINGD_COMPLETE
DEBUG wallet: Owning output 1 506268sat (p2tr) txid 7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: We have 1 anchor points to use
DEBUG lightningd: Broadcasting txid 7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce
DEBUG lightningd: sendrawtransaction: 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
DEBUG lightningd: Adding block 108: 4e6ba3059c6890797a29acd306e82d6f4e85ad62a6aa6d0ee5bc6ead3e6329cd
DEBUG hsmd: Client: Received message 5 from client
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-connectd: peer_downgrade
DEBUG plugin-bcli: sendrawtx exit 0 (bitcoin-cli -regtest -datadir=/tmp/ltests-laf51vlg/test_buy_liquidity_ad_check_bookkeeping_1/lightning-2/ -rpcclienttimeout=60 -rpcport=41847 -rpcuser=... -stdinrpcpass sendrawtransaction 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)
DEBUG lightningd: Adding block 109: 540a47d6b316aec8d1b56efca22ffb384403659e3b29cddd3d68f87df72065a6
DEBUG lightningd: Adding block 110: 1931e9ea62324d0fb50188df525e84ee7021e1910cf3534b343db05cc4639851
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: Got UTXO spend for beff505170fbccbbc8f72ae16f07b3a99dcf1460de9d71ed8224bf1a48e5506f:0: 7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce
UNUSUAL 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: Peer permanent failure in CLOSINGD_COMPLETE: Funding transaction spent: onchain txid 7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce (reason=unknown)
UNUSUAL 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: Not dropping our unilateral close onchain since we already saw 7685256e6e4632bd601f42bb85b6f22b7a0db8d55c468dfbb1703c3ab2e4d9ce confirm.
INFO 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: State changed from CLOSINGD_COMPLETE to FUNDING_SPEND_SEEN
**BROKEN** 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-chan#2: Illegal gossip state transition: CGOSSIP_CHANNEL_UNANNOUNCED_DYING->CGOSSIP_CHANNEL_ANNOUNCED_DEAD
DEBUG 0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518-onchaind-chan#2: pid 35721, msgfd 86
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Links an issue, advisory, or supporting reference
What changed, and why it matters
This commit fixes a rare internal state-machine error in Core Lightning that could occur when a channel was closing at exactly the same moment it would normally be announced to the network. Previously, the code did not allow the transition from 'unannounced and dying' directly to 'announced and dead,' causing a 'BROKEN' log error. The patch simply adds that missing allowed transition. It is a bug fix for a corner case, not a security vulnerability that an attacker can exploit.
Recommended action
Treat as a routine bug-fix patch. No urgent security action required. Users should upgrade in normal course if affected by the logged BROKEN state transition, but there is no evidence of remote exploitability or funds at risk.
Security signals we found
01
Fixes an internal state-machine crash/corner-case (BROKEN log)
02
No external input validation, cryptographic, or authorization change
03
No memory safety, overflow, or injection pattern
04
Change is defensive hardening of gossip state transitions
Evidence from the diff
The patch adds one allowed state transition in lightningd/channel_gossip.c: CGOSSIP_CHANNEL_UNANNOUNCED_DYING -> CGOSSIP_CHANNEL_ANNOUNCED_DEAD. This handles the race where a channel reaches the gossip announce depth and its funding output is spent in the same block processing window. Without this transition, the code logs ‘Illegal gossip state transition’ and aborts the state change. The fix is a two-line addition to the allowed_transitions table.
Changed components
lightningd/channel_gossip.cchannel gossip state machineInspect captured patch +2 / −0
diff --git a/lightningd/channel_gossip.c b/lightningd/channel_gossip.c
index d7d5374..d00627a 100644
--- a/lightningd/channel_gossip.c
+++ b/lightningd/channel_gossip.c
@@ -118,6 +118,8 @@ static struct state_transition allowed_transitions[] = {
"Unannounced channel closed onchain." },
{ CGOSSIP_CHANNEL_UNANNOUNCED_DYING, CGOSSIP_CHANNEL_ANNOUNCED_DYING,
"Unannounced closing channel reached announce depth." },
+ { CGOSSIP_CHANNEL_UNANNOUNCED_DYING, CGOSSIP_CHANNEL_ANNOUNCED_DEAD,
+ "Unannounced closing channel reached announce depth and was closed in same block." },
{ CGOSSIP_WAITING_FOR_ANNOUNCE_DEPTH, CGOSSIP_ANNOUNCED,
"Channel fully announced" },
{ CGOSSIP_WAITING_FOR_MATCHING_PEER_SIGS, CGOSSIP_ANNOUNCED,
Risk score
Our methodology →Why this scored 19/100
Human-validated context
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