Fix gossip announce address binding

src/network/gossip.rs

@@ -79,6 +79,8 @@ enum GossipReject {
     BadSignature,
     /// Timestamp outside the freshness window — stale (replay) or implausibly future.
     OutOfWindow,
+    /// A signed Announce advertised an address for a different node id.
+    AnnounceAddressMismatch,
 }
 
 /// Authenticate a received payload against the room topic and local clock. The
@@ -99,6 +101,10 @@ fn verify_gossip(
     if now_ms.abs_diff(payload.ts) > window_ms {
         return Err(GossipReject::OutOfWindow);
     }
+    if let GossipMessage::Announce(state) = &payload.msg
+        && state.addr.id != payload.author {
+        return Err(GossipReject::AnnounceAddressMismatch);
+    }
     Ok(())
 }
 
@@ -490,10 +496,8 @@ mod tests {
     use crate::network::PeerState;
     use iroh::SecretKey;
 
-    fn sample_peer_state() -> PeerState {
+    fn sample_peer_state_for(id: EndpointId) -> PeerState {
-        let secret = SecretKey::generate();
+        let addr = iroh::EndpointAddr::from(id);
-        let public = secret.public();
-        let addr = iroh::EndpointAddr::from(public);
         PeerState {
             name: "TestPeerGossip".to_string(),
             is_muted: true,
@@ -563,7 +567,7 @@ mod tests {
     fn test_gossip_payload_announce_round_trip() {
         let secret = SecretKey::generate();
         let topic = [9u8; 32];
-        let peer_state = sample_peer_state();
+        let peer_state = sample_peer_state_for(secret.public());
         let payload = sign_gossip(&secret, &topic, 1000, GossipMessage::Announce(peer_state.clone()));
 
         let serialized = serde_json::to_string(&payload).unwrap();
@@ -732,5 +736,18 @@ mod tests {
         // Within the window (clock skew tolerance) → accepted.
         assert!(verify_gossip(&p, &topic, 1_000_000 + GOSSIP_FRESHNESS_MS - 1, GOSSIP_FRESHNESS_MS).is_ok());
     }
-}
 
+    #[test]
+    fn verify_rejects_announce_with_address_for_another_identity() {
+        let signer = SecretKey::generate();
+        let advertised = SecretKey::generate();
+        let topic = [6u8; 32];
+        let state = sample_peer_state_for(advertised.public());
+        let p = sign_gossip(&signer, &topic, 5_000, GossipMessage::Announce(state));
+
+        assert_eq!(
+            verify_gossip(&p, &topic, 5_000, GOSSIP_FRESHNESS_MS),
+            Err(GossipReject::AnnounceAddressMismatch)
+        );
+    }
+}