Don't apply monitor updates after watch_channel PermFail

The full stack fuzzer found an unreachable panic where we receive a
FundingSigned with a duplicate channel outpoint.

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index ac2297f86aeab74651b7f2f86ba2f903870be565..ef16af455adc6f02f4c8131d680f994b8af176ae 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -3352,7 +3352,16 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
                                                Err(e) => try_chan_entry!(self, Err(e), channel_state, chan),
                                        };
                                        if let Err(e) = self.chain_monitor.watch_channel(chan.get().get_funding_txo().unwrap(), monitor) {
-                                               return_monitor_err!(self, e, channel_state, chan, RAACommitmentOrder::RevokeAndACKFirst, false, false);
+                                               let mut res = handle_monitor_err!(self, e, channel_state, chan, RAACommitmentOrder::RevokeAndACKFirst, false, false);
+                                               if let Err(MsgHandleErrInternal { ref mut shutdown_finish, .. }) = res {
+                                                       // We weren't able to watch the channel to begin with, so no updates should be made on
+                                                       // it. Previously, full_stack_target found an (unreachable) panic when the
+                                                       // monitor update contained within `shutdown_finish` was applied.
+                                                       if let Some((ref mut shutdown_finish, _)) = shutdown_finish {
+                                                               shutdown_finish.0.take();
+                                                       }
+                                               }
+                                               return res
                                        }
                                        funding_tx
                                },