gossip: Make sure timestamp does not change while creating sig

If the HSM is slow it might happen that the timestamp has changed the
second time we come around, so we generate the timestamp externally
and pass it in so we're sure it won't change between calls.

Reported-by: Rusty Russell
Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/peer_control.c

@@ -1431,11 +1431,15 @@ static void opening_got_hsm_funding_sig(struct funding_channel *fc,
 
 /* Create a node_announcement with the given signature. It may be NULL
  * in the case we need to create a provisional announcement for the
- * HSM to sign. */
+ * HSM to sign. This is typically called twice: once with the dummy
+ * signature to get it signed and a second time to build the full
+ * packet with the signature. The timestamp is handed in since that is
+ * the only thing that may change between the dummy creation and the
+ * call with a signature.*/
 static u8 *create_node_announcement(const tal_t *ctx, struct lightningd *ld,
-				    secp256k1_ecdsa_signature *sig)
+				    secp256k1_ecdsa_signature *sig,
+				    u32 timestamp)
 {
-	u32 timestamp = time_now().ts.tv_sec;
 	u8 rgb[3] = {0x77, 0x88, 0x99};
 	u8 alias[32];
 	u8 *features = NULL;
@@ -1465,6 +1469,7 @@ static int peer_channel_announced(struct peer *peer, const u8 *msg)
 	tal_t *tmpctx = tal_tmpctx(peer);
 	secp256k1_ecdsa_signature sig;
 	u8 *announcement, *wrappedmsg;
+	u32 timestamp = time_now().ts.tv_sec;
 
 	if (!fromwire_channel_announced(msg, NULL)) {
 		peer_internal_error(peer, "bad fromwire_channel_announced %s",
@@ -1473,7 +1478,7 @@ static int peer_channel_announced(struct peer *peer, const u8 *msg)
 	}
 
 	msg = towire_hsmctl_node_announcement_sig_req(
-		tmpctx, create_node_announcement(tmpctx, ld, NULL));
+		tmpctx, create_node_announcement(tmpctx, ld, NULL, timestamp));
 
 	if (!wire_sync_write(ld->hsm_fd, take(msg)))
 		fatal("Could not write to HSM: %s", strerror(errno));
@@ -1485,7 +1490,7 @@ static int peer_channel_announced(struct peer *peer, const u8 *msg)
 	/* We got the signature for out provisional node_announcement back
 	 * from the HSM, create the real announcement and forward it to
 	 * gossipd so it can take care of forwarding it. */
-	announcement = create_node_announcement(tmpctx, ld, &sig);
+	announcement = create_node_announcement(tmpctx, ld, &sig, timestamp);
 	wrappedmsg = towire_gossip_forwarded_msg(tmpctx, announcement);
 	subd_send_msg(ld->gossip, take(wrappedmsg));
 	tal_free(tmpctx);