openingd: check upfront shutdown script.

The spec doesn't say to do this, but it makes sense, otherwise
they'll never be able to mutually close the channel.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

openingd/Makefile

@@ -75,6 +75,7 @@ OPENINGD_COMMON_OBJS :=				\
 	common/pseudorand.o			\
 	common/read_peer_msg.o			\
 	common/setup.o				\
+	common/shutdown_scriptpubkey.o		\
 	common/status.o				\
 	common/status_wire.o			\
 	common/subdaemon.o			\

openingd/openingd.c

@@ -34,6 +34,7 @@
 #include <common/peer_status_wiregen.h>
 #include <common/penalty_base.h>
 #include <common/read_peer_msg.h>
+#include <common/shutdown_scriptpubkey.h>
 #include <common/status.h>
 #include <common/subdaemon.h>
 #include <common/type_to_string.h>
@@ -321,6 +322,20 @@ static bool setup_channel_funder(struct state *state)
 	return true;
 }
 
+static void set_remote_upfront_shutdown(struct state *state,
+					u8 *shutdown_scriptpubkey STEALS)
+{
+	state->upfront_shutdown_script[REMOTE]
+		= tal_steal(state, shutdown_scriptpubkey);
+
+	if (shutdown_scriptpubkey
+	    && !valid_shutdown_scriptpubkey(shutdown_scriptpubkey))
+		peer_failed_err(state->pps,
+				&state->channel_id,
+				"Unacceptable upfront_shutdown_script %s",
+				tal_hex(tmpctx, shutdown_scriptpubkey));
+}
+
 /* We start the 'open a channel' negotation with the supplied peer, but
  * stop when we get to the part where we need the funding txid */
 static u8 *funder_channel_start(struct state *state, u8 channel_flags)
@@ -404,8 +419,7 @@ static u8 *funder_channel_start(struct state *state, u8 channel_flags)
 				&state->channel_id,
 				"Parsing accept_channel %s", tal_hex(msg, msg));
 	}
-	state->upfront_shutdown_script[REMOTE]
+	set_remote_upfront_shutdown(state, accept_tlvs->upfront_shutdown_script);
-		= tal_steal(state, accept_tlvs->upfront_shutdown_script);
 
 	/* BOLT #2:
 	 *
@@ -764,8 +778,7 @@ static u8 *fundee_channel(struct state *state, const u8 *open_channel_msg)
 		    peer_failed_err(state->pps,
 				    &state->channel_id,
 				    "Parsing open_channel %s", tal_hex(tmpctx, open_channel_msg));
-	state->upfront_shutdown_script[REMOTE]
+	set_remote_upfront_shutdown(state, open_tlvs->upfront_shutdown_script);
-		= tal_steal(state, open_tlvs->upfront_shutdown_script);
 
 	/* BOLT #2:
 	 *

tests/test_closing.py

@@ -2594,3 +2594,18 @@ def test_option_upfront_shutdown_script(node_factory, bitcoind, executor):
     l1.rpc.fundchannel(l2.info['id'], 1000000)
     l1.rpc.close(l2.info['id'])
     wait_for(lambda: sorted([c['state'] for c in only_one(l1.rpc.listpeers()['peers'])['channels']]) == ['CLOSINGD_COMPLETE', 'ONCHAIN', 'ONCHAIN'])
+
+
+@unittest.skipIf(not DEVELOPER, "needs to set upfront_shutdown_script")
+def test_invalid_upfront_shutdown_script(node_factory, bitcoind, executor):
+    l1, l2 = node_factory.line_graph(2, fundchannel=False)
+
+    l1 = node_factory.get_node(start=False, allow_warning=True)
+    # Insist on upfront script we're not going to match.
+    l1.daemon.env["DEV_OPENINGD_UPFRONT_SHUTDOWN_SCRIPT"] = "76a91404b61f7dc1ea0dc99424464cc4064dc564d91e8988ac00"
+    l1.start()
+
+    l2 = node_factory.get_node()
+    l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
+    with pytest.raises(RpcError, match=r'Unacceptable upfront_shutdown_script'):
+        l1.fundchannel(l2, 1000000, False)