From e11bab8bbb20d461488881f5bf6d0069a7260946 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Wed, 7 Aug 2024 11:19:52 +0930
Subject: [PATCH] gossmap: don't process channel_announcement until amount is
 present.

This simplifies the callers significantly: all channel_announcements now
have an amount, so gossmap_chan_get_capacity() only fails on a local
modification.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 common/gossmap.c | 21 +++++++++++++++------
 common/gossmap.h |  2 +-
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/common/gossmap.c b/common/gossmap.c
index ac88d3152..068a25c41 100644
--- a/common/gossmap.c
+++ b/common/gossmap.c
@@ -444,7 +444,8 @@ void gossmap_remove_node(struct gossmap *map, struct gossmap_node *node)
  *     * [`point`:`node_id_2`]
  */
 static struct gossmap_chan *add_channel(struct gossmap *map,
-					size_t cannounce_off)
+					size_t cannounce_off,
+					size_t msglen)
 {
 	/* Note that first two bytes are message type */
 	const size_t feature_len_off = 2 + (64 + 64 + 64 + 64);
@@ -473,6 +474,12 @@ static struct gossmap_chan *add_channel(struct gossmap *map,
 		return NULL;
 	}
 
+	/* gossipd writes WIRE_GOSSIP_STORE_CHANNEL_AMOUNT after this (not for
+	 * local channels), so ignore channel_announcement until that appears */
+	if (msglen
+	    && (map->map_size < cannounce_off + msglen + sizeof(struct gossip_hdr) + sizeof(u16) + sizeof(u64)))
+		return NULL;
+
 	/* We carefully map pointers to indexes, since new_node can move them! */
 	n[0] = gossmap_find_node(map, &node_id[0]);
 	if (n[0])
@@ -668,9 +675,11 @@ static bool map_catchup(struct gossmap *map, bool *changed)
 
 		off = map->map_end + sizeof(ghdr);
 		type = map_be16(map, off);
-		if (type == WIRE_CHANNEL_ANNOUNCEMENT)
-			add_channel(map, off);
-		else if (type == WIRE_CHANNEL_UPDATE)
+		if (type == WIRE_CHANNEL_ANNOUNCEMENT) {
+			/* Don't read yet if amount field is not there! */
+			if (!add_channel(map, off, be16_to_cpu(ghdr.len)))
+				break;
+		} else if (type == WIRE_CHANNEL_UPDATE)
 			update_channel(map, off);
 		else if (type == WIRE_GOSSIP_STORE_DELETE_CHAN)
 			remove_channel_by_deletemsg(map, off);
@@ -944,7 +953,7 @@ void gossmap_apply_localmods(struct gossmap *map,
 				continue;
 
 			/* Create new channel, pointing into local. */
-			chan = add_channel(map, map->map_size + mod->local_off);
+			chan = add_channel(map, map->map_size + mod->local_off, 0);
 		}
 
 		/* Save old, overwrite (keep nodeidx) */
@@ -1144,7 +1153,7 @@ bool gossmap_chan_get_capacity(const struct gossmap *map,
 	off += sizeof(ghdr) + be16_to_cpu(ghdr.len);
 
 	/* Partial write, this can happen. */
-	if (off + sizeof(ghdr) + 2 > map->map_size)
+	if (off + sizeof(ghdr) + sizeof(u16) + sizeof(u64) > map->map_size)
 		return false;
 
 	/* Get type of next field. */
diff --git a/common/gossmap.h b/common/gossmap.h
index f4fbc883a..61ed2bbbb 100644
--- a/common/gossmap.h
+++ b/common/gossmap.h
@@ -161,7 +161,7 @@ static inline bool gossmap_chan_set(const struct gossmap_chan *chan, int dir)
 	return chan->cupdate_off[dir] != 0;
 }
 
-/* Return capacity if it's known (fails only on race condition, or a local mod) */
+/* Return capacity if it's known (fails on a local mod) */
 bool gossmap_chan_get_capacity(const struct gossmap *map,
 			       const struct gossmap_chan *c,
 			       struct amount_sat *amount);