From b301141dd36b0dc5d7289ffe504e17cf4c2921e1 Mon Sep 17 00:00:00 2001
From: Freeyorp <TheFreeYorp+git@gmail.com>
Date: Sat, 20 Apr 2024 18:35:55 +0000
Subject: npc: Deregister events with `ev_db` on free
In serverdata@c3b7fe59a, `magic-knuckles` made use of temporary copies of the
spell NPC via `puppet`/`destroy` to provide additional functionality. This
implementation was correct with respect to tmwa behaviour as documented.
However, `puppet` and `destroy` doesn't quite return the server to a clean
prior state. In `builtin_puppet`, events with the fresh new copy of NPC are
registered into the global `ev_db` map to track named events, such as
`OnDischarge`, which might be triggered later. However, these registrations
are not reversed with `destroy`, leaving `ev_db` to retain references to now
invalid and destroyed NPCs.
serverdata@c3b7fe59a revealed this oversight through an intersection of rare
conditions:
- An NPC that is routinely cloned and destroyed
- Having a variety of events
- Including one that can be triggered during a search for the event over ALL
NPCs when `#discharge` is cast.
To reproduce, compile with `-fsanitize=address -fsanitize=undefined` to more
reliably catch use of invalid memory, cast `magic-knuckles`, log out the
character which cast `magic-knuckles` to destroy the NPC, log back in, then
cast `#discharge`. The server will then crash.
Special thanks to SystemError for testing out this theory. Currently lacking
a test environment of my own, this would not have been possible without his
patience and diligence.
---
src/map/npc.cpp | 12 ++++++++++++
1 file changed, 12 insertions(+)
(limited to 'src')
diff --git a/src/map/npc.cpp b/src/map/npc.cpp
index ee2f30c..efb2ba3 100644
--- a/src/map/npc.cpp
+++ b/src/map/npc.cpp
@@ -1050,6 +1050,18 @@ void npc_free_internal(dumb_ptr<npc_data> nd_)
nd_->bl_m->npc[nd_->n] = nullptr;
}
+ // Also clean up any events we registered to the global ev_db
+ if (auto nd = nd_->is_script())
+ {
+ for (auto& pair : ev_db)
+ {
+ if (pair.second.nd == nd)
+ {
+ ev_db.erase(pair.first);
+ }
+ }
+ }
+
nd_.delete_();
}
--
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