config/lua: fix dispatcher shapes to not be callable (#14268)

this would only lead to abuse, explicitly forbid it

1 files changed, 144 insertions, 0 deletions

diff --git a/src/config/lua/bindings/LuaBindingsDispatcherUtils.cpp b/src/config/lua/bindings/LuaBindingsDispatcherUtils.cpp
new file mode 100644
index 00000000..a55dfc65
--- /dev/null
+++ b/src/config/lua/bindings/LuaBindingsDispatcherUtils.cpp
@@ -0,0 +1,144 @@
+#include "LuaBindingsInternal.hpp"
+
+using namespace Config::Lua::Bindings;
+
+static constexpr const char* DISPATCHER_MT = "HL.Dispatcher";
+static char                  DISPATCHER_TABLES_REGISTRY_KEY;
+
+namespace {
+    struct SDispatcherRef {
+        int ref = LUA_NOREF;
+    };
+}
+
+static int dispatcherGc(lua_State* L) {
+    auto* dispatcher = sc<SDispatcherRef*>(luaL_checkudata(L, 1, DISPATCHER_MT));
+    if (dispatcher->ref != LUA_NOREF) {
+        luaL_unref(L, LUA_REGISTRYINDEX, dispatcher->ref);
+        dispatcher->ref = LUA_NOREF;
+    }
+
+    return 0;
+}
+
+static int dispatcherCall(lua_State* L) {
+    return Internal::configError(L, "dispatcher objects cannot be called directly; use hl.dispatch(dispatcher)");
+}
+
+static int dispatcherToString(lua_State* L) {
+    lua_pushstring(L, "HL.Dispatcher");
+    return 1;
+}
+
+static void ensureDispatcherMetatable(lua_State* L) {
+    if (luaL_newmetatable(L, DISPATCHER_MT)) {
+        lua_pushcfunction(L, dispatcherGc);
+        lua_setfield(L, -2, "__gc");
+        lua_pushcfunction(L, dispatcherCall);
+        lua_setfield(L, -2, "__call");
+        lua_pushcfunction(L, dispatcherToString);
+        lua_setfield(L, -2, "__tostring");
+
+        lua_pushstring(L, DISPATCHER_MT);
+        lua_setfield(L, -2, "__metatable");
+    }
+
+    lua_pop(L, 1);
+}
+
+static bool isDispatcherTable(lua_State* L, int idx) {
+    if (!lua_istable(L, idx))
+        return false;
+
+    idx = lua_absindex(L, idx);
+    lua_pushlightuserdata(L, &DISPATCHER_TABLES_REGISTRY_KEY);
+    lua_rawget(L, LUA_REGISTRYINDEX);
+
+    if (!lua_istable(L, -1)) {
+        lua_pop(L, 1);
+        return false;
+    }
+
+    lua_pushvalue(L, idx);
+    lua_rawget(L, -2);
+    const bool result = lua_toboolean(L, -1);
+    lua_pop(L, 2);
+    return result;
+}
+
+static int dispatcherFactory(lua_State* L) {
+    const int nargs = lua_gettop(L);
+
+    lua_pushvalue(L, lua_upvalueindex(1));
+    lua_insert(L, 1);
+    lua_call(L, nargs, LUA_MULTRET);
+
+    const int nresults = lua_gettop(L);
+    if (nresults == 1 && lua_isfunction(L, -1))
+        return Internal::wrapDispatcher(L);
+
+    return nresults;
+}
+
+void Internal::setFn(lua_State* L, const char* name, lua_CFunction fn) {
+    if (isDispatcherTable(L, -1)) {
+        lua_pushcfunction(L, fn);
+        lua_pushcclosure(L, dispatcherFactory, 1);
+    } else
+        lua_pushcfunction(L, fn);
+
+    lua_setfield(L, -2, name);
+}
+
+void Internal::markDispatcherTable(lua_State* L) {
+    if (!lua_istable(L, -1))
+        return;
+
+    lua_pushlightuserdata(L, &DISPATCHER_TABLES_REGISTRY_KEY);
+    lua_rawget(L, LUA_REGISTRYINDEX);
+
+    if (!lua_istable(L, -1)) {
+        lua_pop(L, 1);
+        lua_newtable(L);
+        lua_pushlightuserdata(L, &DISPATCHER_TABLES_REGISTRY_KEY);
+        lua_pushvalue(L, -2);
+        lua_rawset(L, LUA_REGISTRYINDEX);
+    }
+
+    lua_pushvalue(L, -2);
+    lua_pushboolean(L, true);
+    lua_rawset(L, -3);
+    lua_pop(L, 1);
+}
+
+int Internal::wrapDispatcher(lua_State* L) {
+    luaL_checktype(L, -1, LUA_TFUNCTION);
+
+    const int ref = luaL_ref(L, LUA_REGISTRYINDEX);
+
+    new (lua_newuserdata(L, sizeof(SDispatcherRef))) SDispatcherRef{.ref = ref};
+
+    ensureDispatcherMetatable(L);
+    luaL_getmetatable(L, DISPATCHER_MT);
+    lua_setmetatable(L, -2);
+
+    return 1;
+}
+
+bool Internal::pushDispatcherFunction(lua_State* L, int idx) {
+    if (lua_isfunction(L, idx)) {
+        lua_pushvalue(L, idx);
+        return true;
+    }
+
+    auto* dispatcher = sc<SDispatcherRef*>(luaL_testudata(L, idx, DISPATCHER_MT));
+    if (!dispatcher || dispatcher->ref == LUA_NOREF)
+        return false;
+
+    lua_rawgeti(L, LUA_REGISTRYINDEX, dispatcher->ref);
+    if (lua_isfunction(L, -1))
+        return true;
+
+    lua_pop(L, 1);
+    return false;
+}