BBA/BuiltIn: Make network interface consistent

Source/Core/Core/HW/EXI/BBA/BuiltIn.cpp

@@ -68,6 +68,8 @@ bool CEXIETHERNET::BuiltInBBAInterface::Activate()
     buf.reserve(2048);
 
   // Workaround to get the host IP (might not be accurate)
+  // TODO: Fix the JNI crash and use GetSystemDefaultInterface()
+  //  - https://pastebin.com/BFpmnxby (see https://dolp.in/pr10920)
   const u32 ip = m_local_ip.empty() ? sf::IpAddress::getLocalAddress().toInteger() :
                                       sf::IpAddress(m_local_ip).toInteger();
   m_current_ip = htonl(ip);
@@ -334,7 +336,7 @@ void CEXIETHERNET::BuiltInBBAInterface::HandleTCPFrame(const Common::TCPPacket&
 
     ref->seq_num++;
     target = sf::IpAddress(ntohl(destination_ip));
-    ref->tcp_socket.connect(target, ntohs(tcp_header.destination_port));
+    ref->tcp_socket.Connect(target, ntohs(tcp_header.destination_port), m_current_ip);
     ref->ready = false;
     ref->ip = Common::BitCast<u32>(ip_header.destination_addr);
 
@@ -420,7 +422,7 @@ void CEXIETHERNET::BuiltInBBAInterface::InitUDPPort(u16 port)
   ref->to.sin_addr.s_addr = m_current_ip;
   ref->to.sin_port = htons(port);
   ref->udp_socket.setBlocking(false);
-  if (ref->udp_socket.bind(port) != sf::Socket::Done)
+  if (ref->udp_socket.Bind(port, m_current_ip) != sf::Socket::Done)
   {
     ERROR_LOG_FMT(SP1, "Couldn't open UDP socket");
     PanicAlertFmt("Could't open port {:x}, this game might not work proprely in LAN mode.", port);
@@ -450,12 +452,12 @@ void CEXIETHERNET::BuiltInBBAInterface::HandleUDPFrame(const Common::UDPPacket&
     ref->to.sin_addr.s_addr = Common::BitCast<u32>(ip_header.source_addr);
     ref->to.sin_port = udp_header.source_port;
     ref->udp_socket.setBlocking(false);
-    if (ref->udp_socket.bind(ntohs(udp_header.source_port)) != sf::Socket::Done)
+    if (ref->udp_socket.Bind(ntohs(udp_header.source_port), m_current_ip) != sf::Socket::Done)
     {
       PanicAlertFmt(
           "Port {:x} is already in use, this game might not work as intented in LAN Mode.",
           htons(udp_header.source_port));
-      if (ref->udp_socket.bind(sf::Socket::AnyPort) != sf::Socket::Done)
+      if (ref->udp_socket.Bind(sf::Socket::AnyPort, m_current_ip) != sf::Socket::Done)
       {
         ERROR_LOG_FMT(SP1, "Couldn't open UDP socket");
         return;
@@ -710,3 +712,22 @@ void CEXIETHERNET::BuiltInBBAInterface::RecvStop()
   m_queue_write = 0;
 }
 }  // namespace ExpansionInterface
+
+BbaTcpSocket::BbaTcpSocket() = default;
+
+sf::Socket::Status BbaTcpSocket::Connect(const sf::IpAddress& dest, u16 port, u32 net_ip)
+{
+  sockaddr_in addr;
+  addr.sin_addr.s_addr = net_ip;
+  addr.sin_family = AF_INET;
+  addr.sin_port = 0;
+  ::bind(getHandle(), reinterpret_cast<sockaddr*>(&addr), sizeof(addr));
+  return this->connect(dest, port);
+}
+
+BbaUdpSocket::BbaUdpSocket() = default;
+
+sf::Socket::Status BbaUdpSocket::Bind(u16 port, u32 net_ip)
+{
+  return this->bind(port, sf::IpAddress(ntohl(net_ip)));
+}

Source/Core/Core/HW/EXI/BBA/BuiltIn.h

@@ -34,6 +34,27 @@ struct TcpBuffer
   std::vector<u8> data;
 };
 
+// Socket helper classes to ensure network interface consistency.
+//
+// If the socket isn't bound, the system will pick the interface to use automatically.
+// This might result in the source IP address changing when talking to the same peer
+// and multiple interfaces/IP addresses can reach the socket's peer.
+class BbaTcpSocket : public sf::TcpSocket
+{
+public:
+  BbaTcpSocket();
+
+  sf::Socket::Status Connect(const sf::IpAddress& dest, u16 port, u32 net_ip);
+};
+
+class BbaUdpSocket : public sf::UdpSocket
+{
+public:
+  BbaUdpSocket();
+
+  sf::Socket::Status Bind(u16 port, u32 net_ip);
+};
+
 struct StackRef
 {
   u32 ip;
@@ -52,7 +73,7 @@ struct StackRef
   sockaddr_in to;
   Common::MACAddress bba_mac{};
   Common::MACAddress my_mac{};
-  sf::UdpSocket udp_socket;
+  BbaUdpSocket udp_socket;
-  sf::TcpSocket tcp_socket;
+  BbaTcpSocket tcp_socket;
   u64 poke_time;
 };