Gate identity learning on signature in NodeDB::updateUser (#11084)

src/mesh/NodeDB.cpp

@@ -3310,13 +3310,20 @@ void NodeDB::addFromContact(meshtastic_SharedContact contact)
 
 /** Update user info and channel for this node based on received user data
  */
-bool NodeDB::updateUser(uint32_t nodeId, meshtastic_User &p, uint8_t channelIndex)
+bool NodeDB::updateUser(uint32_t nodeId, meshtastic_User &p, uint8_t channelIndex, bool xeddsaSigned)
 {
     meshtastic_NodeInfoLite *info = getOrCreateMeshNode(nodeId);
     if (!info) {
         return false;
     }
 
+    // Once a node has proven it signs, only a signed update may change its identity. The public-key guard
+    // below is no help - an attacker can replay the victim's real (public) key. Our own record is exempt.
+    if (nodeId != getNodeNum() && nodeInfoLiteHasXeddsaSigned(info) && !xeddsaSigned) {
+        LOG_WARN("Refusing unsigned identity update for node 0x%08x that previously signed", nodeId);
+        return false;
+    }
+
 #if !(MESHTASTIC_EXCLUDE_PKI)
     if (p.public_key.size == 32 && nodeId != nodeDB->getNodeNum()) {
         printBytes("Incoming Pubkey: ", p.public_key.bytes, 32);

src/mesh/NodeDB.h

@@ -255,9 +255,9 @@ class NodeDB
      */
     void updateTelemetry(uint32_t nodeId, const meshtastic_Telemetry &t, RxSource src = RX_SRC_RADIO);
 
-    /** Update user info and channel for this node based on received user data
-     */
-    bool updateUser(uint32_t nodeId, meshtastic_User &p, uint8_t channelIndex = 0);
+    /** Update user info and channel for this node based on received user data.
+     * A known signer's identity is only learned when xeddsaSigned; defaults false so callers fail closed. */
+    bool updateUser(uint32_t nodeId, meshtastic_User &p, uint8_t channelIndex = 0, bool xeddsaSigned = false);
 
     /*
      * Sets a node either favorite or unfavorite. Returns true if the node ends

src/modules/NodeInfoModule.cpp

@@ -61,7 +61,9 @@ bool NodeInfoModule::handleReceivedProtobuf(const meshtastic_MeshPacket &mp, mes
     // Coerce user.id to be derived from the node number
     snprintf(p.id, sizeof(p.id), "!%08x", getFrom(&mp));
 
-    bool hasChanged = nodeDB->updateUser(getFrom(&mp), p, mp.channel);
+    // updateUser() refuses the identity write for a known signer sending unsigned (all unicast
+    // NodeInfo), so the exchange above still proceeds but cannot spoof the stored name.
+    bool hasChanged = nodeDB->updateUser(getFrom(&mp), p, mp.channel, mp.xeddsa_signed);
 
     bool wasBroadcast = isBroadcast(mp.to);
 

src/modules/TrafficManagementModule.cpp

@@ -734,7 +734,7 @@ ProcessMessage TrafficManagementModule::handleReceived(const meshtastic_MeshPack
             meshtastic_User requester = meshtastic_User_init_zero;
             if (!unauthenticatedSigner &&
                 pb_decode_from_bytes(mp.decoded.payload.bytes, mp.decoded.payload.size, &meshtastic_User_msg, &requester)) {
-                nodeDB->updateUser(getFrom(&mp), requester, mp.channel);
+                nodeDB->updateUser(getFrom(&mp), requester, mp.channel, mp.xeddsa_signed);
             }
             logAction("respond", &mp, "nodeinfo-cache");
             incrementStat(&stats.nodeinfo_cache_hits);