protocol: drop peers that decrease claimed height

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -328,6 +328,11 @@ namespace cryptonote
       }
     }
 
+    if (hshd.current_height < context.m_remote_blockchain_height)
+    {
+      MINFO(context << "Claims " << hshd.current_height << ", claimed " << context.m_remote_blockchain_height << " before");
+      hit_score(context, 1);
+    }
     context.m_remote_blockchain_height = hshd.current_height;
     context.m_pruning_seed = hshd.pruning_seed;
 #ifdef CRYPTONOTE_PRUNING_DEBUG_SPOOF_SEED
@@ -1112,6 +1117,11 @@ namespace cryptonote
       return 1;
     }
 
+    if (arg.current_blockchain_height < context.m_remote_blockchain_height)
+    {
+      MINFO(context << "Claims " << arg.current_blockchain_height << ", claimed " << context.m_remote_blockchain_height << " before");
+      hit_score(context, 1);
+    }
     context.m_remote_blockchain_height = arg.current_blockchain_height;
     if (context.m_remote_blockchain_height > m_core.get_target_blockchain_height())
       m_core.set_target_blockchain_height(context.m_remote_blockchain_height);
@@ -2345,7 +2355,7 @@ skip:
       }
       else
       {
-        MINFO(context << " we've reached this peer's blockchain height");
+        MINFO(context << " we've reached this peer's blockchain height (theirs " << context.m_remote_blockchain_height << ", our target " << m_core.get_target_blockchain_height());
       }
     }
     return true;
@@ -2472,6 +2482,11 @@ skip:
       drop_connection(context, false, false);
       return 1;
     }
+    if (arg.total_height < context.m_remote_blockchain_height)
+    {
+      MINFO(context << "Claims " << arg.total_height << ", claimed " << context.m_remote_blockchain_height << " before");
+      hit_score(context, 1);
+    }
     context.m_remote_blockchain_height = arg.total_height;
     context.m_last_response_height = arg.start_height + arg.m_block_ids.size()-1;
     if(context.m_last_response_height > context.m_remote_blockchain_height)