protocol: drop nodes if they claim new data but only give stale data

Some joker is spending time actually doing this

src/cryptonote_basic/connection_context.h

@@ -44,7 +44,7 @@ namespace cryptonote
     cryptonote_connection_context(): m_state(state_before_handshake), m_remote_blockchain_height(0), m_last_response_height(0),
         m_last_request_time(boost::date_time::not_a_date_time), m_callback_request_count(0),
         m_last_known_hash(crypto::null_hash), m_pruning_seed(0), m_rpc_port(0), m_rpc_credits_per_hash(0), m_anchor(false), m_score(0),
-        m_expect_response(0) {}
+        m_expect_response(0), m_num_requested(0)  {}
 
     enum state
     {
@@ -70,6 +70,7 @@ namespace cryptonote
     int32_t m_score;
     int m_expect_response;
     uint64_t m_expect_height;
+    size_t m_num_requested;
   };
 
   inline std::string get_protocol_state_string(cryptonote_connection_context::state s)

src/cryptonote_protocol/cryptonote_protocol_handler.h

@@ -150,7 +150,7 @@ namespace cryptonote
     bool update_sync_search();
     int try_add_next_blocks(cryptonote_connection_context &context);
     void notify_new_stripe(cryptonote_connection_context &context, uint32_t stripe);
-    void skip_unneeded_hashes(cryptonote_connection_context& context, bool check_block_queue) const;
+    size_t skip_unneeded_hashes(cryptonote_connection_context& context, bool check_block_queue) const;
     bool request_txpool_complement(cryptonote_connection_context &context);
     void hit_score(cryptonote_connection_context &context, int32_t score);
 

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -409,6 +409,7 @@ namespace cryptonote
     ++context.m_callback_request_count;
     m_p2p->request_callback(context);
     MLOG_PEER_STATE("requesting callback");
+    context.m_num_requested = 0;
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------
@@ -1990,7 +1991,7 @@ skip:
   }
   //------------------------------------------------------------------------------------------------------------------------
   template<class t_core>
-  void t_cryptonote_protocol_handler<t_core>::skip_unneeded_hashes(cryptonote_connection_context& context, bool check_block_queue) const
+  size_t t_cryptonote_protocol_handler<t_core>::skip_unneeded_hashes(cryptonote_connection_context& context, bool check_block_queue) const
   {
     // take out blocks we already have
     size_t skip = 0;
@@ -2007,6 +2008,7 @@ skip:
       MDEBUG(context << "skipping " << skip << "/" << context.m_needed_objects.size() << " blocks");
       context.m_needed_objects = std::vector<std::pair<crypto::hash, uint64_t>>(context.m_needed_objects.begin() + skip, context.m_needed_objects.end());
     }
+    return skip;
   }
   //------------------------------------------------------------------------------------------------------------------------
   template<class t_core>
@@ -2060,7 +2062,11 @@ skip:
         const size_t block_queue_size_threshold = m_block_download_max_size ? m_block_download_max_size : BLOCK_QUEUE_SIZE_THRESHOLD;
         bool queue_proceed = nspans < BLOCK_QUEUE_NSPANS_THRESHOLD || size < block_queue_size_threshold;
         // get rid of blocks we already requested, or already have
-        skip_unneeded_hashes(context, true);
+        if (skip_unneeded_hashes(context, true) && context.m_needed_objects.empty() && context.m_num_requested == 0)
+        {
+          MERROR(context << "Nothing we can request from this peer, and we did not request anything previously");
+          return false;
+        }
         uint64_t next_needed_height = m_block_queue.get_next_needed_height(bc_height);
         uint64_t next_block_height;
         if (context.m_needed_objects.empty())
@@ -2196,7 +2202,11 @@ skip:
           context.m_last_response_height = 0;
           goto skip;
         }
-        skip_unneeded_hashes(context, false);
+        if (skip_unneeded_hashes(context, false) && context.m_needed_objects.empty() && context.m_num_requested == 0)
+        {
+          MERROR(context << "Nothing we can request from this peer, and we did not request anything previously");
+          return false;
+        }
 
         const uint64_t first_block_height = context.m_last_response_height - context.m_needed_objects.size() + 1;
         static const uint64_t bp_fork_height = m_core.get_earliest_ideal_height_for_version(8);
@@ -2293,6 +2303,7 @@ skip:
           << "/" << tools::get_pruning_stripe(span.first + span.second - 1, context.m_remote_blockchain_height, CRYPTONOTE_PRUNING_LOG_STRIPES)
           << ", ours " << tools::get_pruning_stripe(m_core.get_blockchain_pruning_seed()) << ", peer stripe " << tools::get_pruning_stripe(context.m_pruning_seed));
 
+        context.m_num_requested += req.blocks.size();
         post_notify<NOTIFY_REQUEST_GET_OBJECTS>(req, context);
         MLOG_PEER_STATE("requesting objects");
         return true;
@@ -2608,6 +2619,7 @@ skip:
     if (arg.total_height > m_core.get_target_blockchain_height())
       m_core.set_target_blockchain_height(arg.total_height);
 
+    context.m_num_requested = 0;
     return 1;
   }
   //------------------------------------------------------------------------------------------------------------------------