Limit formspec fields to 640K (#13380)

Fixes an issue where long inputs could cause issues when dealing with formspecs.
The expected data is usually below 1 KiB, however that's not a technical limit.

1 files changed, 36 insertions, 20 deletions

diff --git a/src/network/serverpackethandler.cpp b/src/network/serverpackethandler.cpp
index 89e2e2a1c..237c7805c 100644
--- a/src/network/serverpackethandler.cpp
+++ b/src/network/serverpackethandler.cpp
@@ -1342,21 +1342,26 @@ void Server::handleCommand_RemovedSounds(NetworkPacket* pkt)
 	}
 }
 
-void Server::handleCommand_NodeMetaFields(NetworkPacket* pkt)
+static bool pkt_read_formspec_fields(NetworkPacket *pkt, StringMap &fields)
 {
-	v3s16 p;
-	std::string formname;
-	u16 num;
-
-	*pkt >> p >> formname >> num;
+	u16 field_count;
+	*pkt >> field_count;
 
-	StringMap fields;
-	for (u16 k = 0; k < num; k++) {
+	u64 length = 0;
+	for (u16 k = 0; k < field_count; k++) {
 		std::string fieldname;
 		*pkt >> fieldname;
 		fields[fieldname] = pkt->readLongString();
+
+		length += fieldname.size();
+		length += fields[fieldname].size();
 	}
+	// 640K ought to be enough for anyone
+	return length < 640 * 1024;
+}
 
+void Server::handleCommand_NodeMetaFields(NetworkPacket* pkt)
+{
 	session_t peer_id = pkt->getPeerId();
 	RemotePlayer *player = m_env->getPlayer(peer_id);
 
@@ -1377,6 +1382,18 @@ void Server::handleCommand_NodeMetaFields(NetworkPacket* pkt)
 		return;
 	}
 
+	v3s16 p;
+	std::string formname;
+	StringMap fields;
+
+	*pkt >> p >> formname;
+
+	if (!pkt_read_formspec_fields(pkt, fields)) {
+		warningstream << "Too large formspec fields! Ignoring for pos="
+			<< PP(p) << ", player=" << player->getName() << std::endl;
+		return;
+	}
+
 	// If something goes wrong, this player is to blame
 	RollbackScopeActor rollback_scope(m_rollback,
 			std::string("player:")+player->getName());
@@ -1397,18 +1414,6 @@ void Server::handleCommand_NodeMetaFields(NetworkPacket* pkt)
 
 void Server::handleCommand_InventoryFields(NetworkPacket* pkt)
 {
-	std::string client_formspec_name;
-	u16 num;
-
-	*pkt >> client_formspec_name >> num;
-
-	StringMap fields;
-	for (u16 k = 0; k < num; k++) {
-		std::string fieldname;
-		*pkt >> fieldname;
-		fields[fieldname] = pkt->readLongString();
-	}
-
 	session_t peer_id = pkt->getPeerId();
 	RemotePlayer *player = m_env->getPlayer(peer_id);
 
@@ -1429,6 +1434,17 @@ void Server::handleCommand_InventoryFields(NetworkPacket* pkt)
 		return;
 	}
 
+	std::string client_formspec_name;
+	StringMap fields;
+
+	*pkt >> client_formspec_name;
+
+	if (!pkt_read_formspec_fields(pkt, fields)) {
+		warningstream << "Too large formspec fields! Ignoring for formname=\""
+			<< client_formspec_name << "\", player=" << player->getName() << std::endl;
+		return;
+	}
+
 	if (client_formspec_name.empty()) { // pass through inventory submits
 		m_script->on_playerReceiveFields(playersao, client_formspec_name, fields);
 		return;