CSM restrictions: Make 'LOAD_CLIENT_MODS' disable loading of 'builtin' (#8000)

Previously, when the CSM restriction 'LOAD_CLIENT_MODS' was used a
client was still able to add CSM code to 'builtin' to bypass that
restriction, because 'builtin' is not yet verified.

Until server-sent CSM and verifying of 'builtin' are complete, make
'LOAD_CLIENT_MODS' disable the loading of builtin.

Clarify code comments and messages to distinguish between client-side
modding and client-side scripting. 'Scripting' includes 'builtin',
'modding' does not.

4 files changed, 38 insertions, 16 deletions

diff --git a/builtin/settingtypes.txt b/builtin/settingtypes.txt
index d8d9ec3ab..c312bdcf6 100644
--- a/builtin/settingtypes.txt
+++ b/builtin/settingtypes.txt
@@ -1189,14 +1189,16 @@ block_send_optimize_distance (Block send optimize distance) int 4 2
 #    so that the utility of noclip mode is reduced.
 server_side_occlusion_culling (Server side occlusion culling) bool true
 
-#    Restricts the access of certain client-side functions on servers
-#    Combine these byteflags below to restrict client-side features:
-#    LOAD_CLIENT_MODS: 1 (disable client mods loading)
+#    Restricts the access of certain client-side functions on servers.
+#    Combine the byteflags below to restrict client-side features, or set to 0
+#    for no restrictions:
+#    LOAD_CLIENT_MODS: 1 (disable loading client-provided mods)
 #    CHAT_MESSAGES: 2 (disable send_chat_message call client-side)
 #    READ_ITEMDEFS: 4 (disable get_item_def call client-side)
 #    READ_NODEDEFS: 8 (disable get_node_def call client-side)
 #    LOOKUP_NODES_LIMIT: 16 (limits get_node call client-side to
 #    csm_restriction_noderange)
+#    READ_PLAYERINFO: 32 (disable get_player_names call client-side)
 csm_restriction_flags (Client side modding restrictions) int 62
 
 #   If the CSM restriction for node range is enabled, get_node calls are limited
diff --git a/src/client/client.cpp b/src/client/client.cpp
index 17ee3a10a..3ba69333a 100644
--- a/src/client/client.cpp
+++ b/src/client/client.cpp
@@ -110,7 +110,8 @@ Client::Client(
 	m_cache_save_interval = g_settings->getU16("server_map_save_interval");
 
 	m_modding_enabled = g_settings->getBool("enable_client_modding");
-	// Only create the client script environment if client modding is enabled
+	// Only create the client script environment if client scripting is enabled by the
+	// client.
 	if (m_modding_enabled) {
 		m_script = new ClientScripting(this);
 		m_env.setScript(m_script);
@@ -125,10 +126,22 @@ void Client::loadMods()
 		return;
 	}
 
-	// If client modding is not enabled, don't load client-provided CSM mods or
-	// builtin.
+	// If client scripting is disabled by the client, don't load builtin or
+	// client-provided mods.
 	if (!m_modding_enabled) {
-		warningstream << "Client side mods are disabled by configuration." << std::endl;
+		warningstream << "Client side scripting is disabled by client." << std::endl;
+		return;
+	}
+
+	// If client scripting is disabled by the server, don't load builtin or
+	// client-provided mods.
+	// TODO Delete this code block when server-sent CSM and verifying of builtin are
+	// complete.
+	if (checkCSMRestrictionFlag(CSMRestrictionFlags::CSM_RF_LOAD_CLIENT_MODS)) {
+		warningstream << "Client-provided mod loading is disabled by server." <<
+			std::endl;
+		// This line is needed because builtin is not loaded
+		m_modding_enabled = false;
 		return;
 	}
 
@@ -136,16 +149,19 @@ void Client::loadMods()
 	scanModIntoMemory(BUILTIN_MOD_NAME, getBuiltinLuaPath());
 	m_script->loadModFromMemory(BUILTIN_MOD_NAME);
 
-	// If the server has disabled client-provided CSM mod loading, don't load
-	// client-provided CSM mods. Builtin is loaded so needs verfying.
+	// TODO Uncomment when server-sent CSM and verifying of builtin are complete
+	/*
+	// Don't load client-provided mods if disabled by server
 	if (checkCSMRestrictionFlag(CSMRestrictionFlags::CSM_RF_LOAD_CLIENT_MODS)) {
-		warningstream << "Client side mods are disabled by server." << std::endl;
+		warningstream << "Client-provided mod loading is disabled by server." <<
+			std::endl;
 		// If builtin integrity is wrong, disconnect user
 		if (!checkBuiltinIntegrity()) {
-			// @TODO disconnect user
+			// TODO disconnect user
 		}
 		return;
 	}
+	*/
 
 	ClientModConfiguration modconf(getClientModsLuaPath());
 	m_mods = modconf.getMods();
@@ -155,7 +171,7 @@ void Client::loadMods()
 	}
 
 	// Print mods
-	infostream << "Client Loading mods: ";
+	infostream << "Client loading mods: ";
 	for (const ModSpec &mod : m_mods)
 		infostream << mod.name << " ";
 	infostream << std::endl;
@@ -181,7 +197,7 @@ void Client::loadMods()
 
 bool Client::checkBuiltinIntegrity()
 {
-	// @TODO
+	// TODO
 	return true;
 }
 
diff --git a/src/client/game.cpp b/src/client/game.cpp
index bd37bd58a..28f6a90ed 100644
--- a/src/client/game.cpp
+++ b/src/client/game.cpp
@@ -1891,7 +1891,7 @@ void Game::processKeyInput()
 		if (client->moddingEnabled())
 			openConsole(0.2, L".");
 		else
-			m_game_ui->showStatusText(wgettext("CSM is disabled"));
+			m_game_ui->showStatusText(wgettext("Client side scripting is disabled"));
 	} else if (wasKeyDown(KeyType::CONSOLE)) {
 		openConsole(core::clamp(g_settings->getFloat("console_height"), 0.1f, 1.0f));
 	} else if (wasKeyDown(KeyType::FREEMOVE)) {
@@ -2554,7 +2554,7 @@ void Game::handleClientEvent_PlayerForceMove(ClientEvent *event, CameraOrientati
 
 void Game::handleClientEvent_Deathscreen(ClientEvent *event, CameraOrientation *cam)
 {
-	// If CSM enabled, deathscreen is handled by CSM code in
+	// If client scripting is enabled, deathscreen is handled by CSM code in
 	// builtin/client/init.lua
 	if (client->moddingEnabled())
 		client->getScript()->on_death();
diff --git a/src/network/networkprotocol.h b/src/network/networkprotocol.h
index 6d6708482..96dfbe44f 100644
--- a/src/network/networkprotocol.h
+++ b/src/network/networkprotocol.h
@@ -947,7 +947,11 @@ enum PlayerListModifer: u8
 
 enum CSMRestrictionFlags : u64 {
 	CSM_RF_NONE = 0x00000000,
-	CSM_RF_LOAD_CLIENT_MODS = 0x00000001, // Disable mods provided by clients
+	// Until server-sent CSM and verifying of builtin are complete,
+	// 'CSM_RF_LOAD_CLIENT_MODS' also disables loading 'builtin'.
+	// When those are complete, this should return to only being a restriction on the
+	// loading of client mods.
+	CSM_RF_LOAD_CLIENT_MODS = 0x00000001, // Don't load client-provided mods or 'builtin'
 	CSM_RF_CHAT_MESSAGES = 0x00000002, // Disable chat message sending from CSM
 	CSM_RF_READ_ITEMDEFS = 0x00000004, // Disable itemdef lookups
 	CSM_RF_READ_NODEDEFS = 0x00000008, // Disable nodedef lookups