Fix null pointer dereference in MrpRelay when hasStp is false

MrpRelay::isForwardingInterface() and handleLowerPacket() dereferenced
MrpInterfaceData and Ieee8021dInterfaceData pointers without null checks.
When hasMrp=true but hasStp=false (e.g. MrpSwitch), Ieee8021dInterfaceData
is not added to interfaces, causing a segfault (signal 139).

Added null checks following the base class Ieee8021dRelay pattern: treat
missing protocol data as forwarding (the protocol is not active, so it
does not block the port).

Author: ZoltanBojthe

src/inet/linklayer/mrp/MrpRelay.cc

@@ -64,8 +64,8 @@ void MrpRelay::handleLowerPacket(Packet *incomingPacket)
                    << EV_FIELD(incomingPacket) << EV_ENDL;
     updatePeerAddress(incomingInterface, sourceAddress, vlanId);
 
-    const auto &stpData = incomingInterface->findProtocolData<Ieee8021dInterfaceData>();
-    const auto &mrpInterfaceData = incomingInterface->findProtocolData<MrpInterfaceData>();
+    const auto* stpData = incomingInterface->findProtocolData<Ieee8021dInterfaceData>();
+    const auto* mrpInterfaceData = incomingInterface->findProtocolData<MrpInterfaceData>();
 
     auto outgoingPacket = incomingPacket->dup();
     outgoingPacket->trim();
@@ -79,7 +79,7 @@ void MrpRelay::handleLowerPacket(Packet *incomingPacket)
     macAddressReq->setSrcAddress(sourceAddress);
     macAddressReq->setDestAddress(destinationAddress);
 
-    if (mrpInterfaceData->getRole() != MrpInterfaceData::NOTASSIGNED
+    if ((!mrpInterfaceData || (mrpInterfaceData->getRole() != MrpInterfaceData::NOTASSIGNED))
             && isMrpMulticast(destinationAddress)) {
         //Mrp-Multicast Handling, forwarding to RingPort according to MrpFilteringDatabase in case incoming interface is not filtering, send up if registered
         auto outgoingInterfaceIds = mrpMacForwardingTable->getMrpForwardingInterfaces(destinationAddress, vlanId);
@@ -206,14 +206,11 @@ void MrpRelay::handleLowerPacket(Packet *incomingPacket)
 
 bool MrpRelay::isForwardingInterface(NetworkInterface *networkInterface) const
 {
-    const auto &MrpData = networkInterface->findProtocolData<MrpInterfaceData>();
-    const auto &Ieee8021dData = networkInterface->findProtocolData<Ieee8021dInterfaceData>();
     if (networkInterface->isLoopback() || !networkInterface->isBroadcast())
         return false;
-    else if (!MrpData->isForwarding() || !Ieee8021dData->isForwarding())
-        return false;
-    else
-        return true;
+    const auto* mrpData = networkInterface->findProtocolData<MrpInterfaceData>();
+    const auto* ieee8021dData = networkInterface->findProtocolData<Ieee8021dInterfaceData>();
+    return (!mrpData || mrpData->isForwarding()) && (!ieee8021dData || ieee8021dData->isForwarding());
 }
 
 int MrpRelay::getCcmLevel(Packet *packet)