fix(multiplayer): Race Condition during Packet Discovery

src/core/hle/service/ldn/lan_discovery.cpp

@@ -77,6 +77,8 @@ void LANDiscovery::SetState(State new_state) {
 }
 
 Result LANDiscovery::GetNetworkInfo(NetworkInfo& out_network) const {
+    // Lock must be held while copying to prevent the Network thread from corrupting the copy
+    std::scoped_lock lock{packet_mutex};
     if (state == State::AccessPointCreated || state == State::StationConnected) {
         std::memcpy(&out_network, &network_info, sizeof(network_info));
         return ResultSuccess;
@@ -117,7 +119,7 @@ Result LANDiscovery::Scan(std::span<NetworkInfo> out_networks, s16& out_count,
     }
 
     LOG_INFO(Service_LDN, "Waiting for scan replies");
-    std::this_thread::sleep_for(std::chrono::seconds(1));
+    std::this_thread::sleep_for(std::chrono::milliseconds(100));
 
     std::scoped_lock lock{packet_mutex};
     for (const auto& [key, info] : scan_results) {
@@ -567,10 +569,19 @@ void LANDiscovery::ReceivePacket(const Network::LDNPacket& packet) {
     }
     case Network::LDNPacketType::SyncNetwork: {
         if (state == State::StationOpened || state == State::StationConnected) {
-            LOG_INFO(Frontend, "SyncNetwork packet received!");
+            if (packet.data.size() < sizeof(NetworkInfo)) {
+                LOG_ERROR(Service_LDN, "SyncNetwork packet too small!");
+                break;
+            }
+
             NetworkInfo info{};
             std::memcpy(&info, packet.data.data(), sizeof(NetworkInfo));
 
+            if (info.ldn.node_count == 0) {
+                LOG_ERROR(Service_LDN, "SyncNetwork reported 0 nodes! Ignoring to prevent SDK crash.");
+                break;
+            }
+
             OnSyncNetwork(info);
         } else {
             LOG_INFO(Frontend, "SyncNetwork packet received but in wrong State!");

src/core/hle/service/ldn/lan_discovery.h

@@ -112,7 +112,7 @@ protected:
     static constexpr Ssid fake_ssid{"CitronFakeSsidForLdn"};
 
     bool inited{};
-    std::mutex packet_mutex;
+    mutable std::mutex packet_mutex;
     std::array<LanStation, StationCountMax> stations;
     std::array<NodeLatestUpdate, NodeCountMax> node_changes{};
     std::array<u8, NodeCountMax> node_last_states{};