track double spending in the txpool

Transactions in the txpool are marked when another transaction
is seen double spending one or more of its inputs.
This is then exposed wherever appropriate.

Note that being marked with this "double spend seen" flag does
NOT mean this transaction IS a double spend and will never be
mined: it just means that the network has seen at least another
transaction spending at least one of the same inputs, so care
should be taken to wait for a few confirmations before acting
upon that transaction (ie, mostly of use for merchants wanting
to accept unconfirmed transactions).

1 files changed, 47 insertions, 1 deletions

diff --git a/src/cryptonote_core/tx_pool.cpp b/src/cryptonote_core/tx_pool.cpp
index 9071c330c..40691f6a3 100644
--- a/src/cryptonote_core/tx_pool.cpp
+++ b/src/cryptonote_core/tx_pool.cpp
@@ -187,6 +187,7 @@ namespace cryptonote
     {
       if(have_tx_keyimges_as_spent(tx))
       {
+        mark_double_spend(tx);
         LOG_PRINT_L1("Transaction with id= "<< id << " used already spent key images");
         tvc.m_verifivation_failed = true;
         tvc.m_double_spend = true;
@@ -228,6 +229,7 @@ namespace cryptonote
         meta.last_relayed_time = time(NULL);
         meta.relayed = relayed;
         meta.do_not_relay = do_not_relay;
+        meta.double_spend_seen = have_tx_keyimges_as_spent(tx);
         memset(meta.padding, 0, sizeof(meta.padding));
         try
         {
@@ -266,6 +268,7 @@ namespace cryptonote
       meta.last_relayed_time = time(NULL);
       meta.relayed = relayed;
       meta.do_not_relay = do_not_relay;
+      meta.double_spend_seen = false;
       memset(meta.padding, 0, sizeof(meta.padding));
 
       try
@@ -354,7 +357,7 @@ namespace cryptonote
     return true;
   }
   //---------------------------------------------------------------------------------
-  bool tx_memory_pool::take_tx(const crypto::hash &id, transaction &tx, size_t& blob_size, uint64_t& fee, bool &relayed, bool &do_not_relay)
+  bool tx_memory_pool::take_tx(const crypto::hash &id, transaction &tx, size_t& blob_size, uint64_t& fee, bool &relayed, bool &do_not_relay, bool &double_spend_seen)
   {
     CRITICAL_REGION_LOCAL(m_transactions_lock);
     CRITICAL_REGION_LOCAL1(m_blockchain);
@@ -377,6 +380,7 @@ namespace cryptonote
       fee = meta.fee;
       relayed = meta.relayed;
       do_not_relay = meta.do_not_relay;
+      double_spend_seen = meta.double_spend_seen;
 
       // remove first, in case this throws, so key images aren't removed
       m_blockchain.remove_txpool_tx(id);
@@ -594,6 +598,8 @@ namespace cryptonote
       uint64_t age = now - meta.receive_time + (now == meta.receive_time);
       agebytes[age].txs++;
       agebytes[age].bytes += meta.blob_size;
+      if (meta.double_spend_seen)
+        ++stats.num_double_spends;
       return true;
     });
     stats.bytes_med = epee::misc_utils::median(sizes);
@@ -649,6 +655,7 @@ namespace cryptonote
     m_blockchain.for_all_txpool_txes([&tx_infos, key_image_infos](const crypto::hash &txid, const txpool_tx_meta_t &meta, const cryptonote::blobdata *bd){
       tx_info txi;
       txi.id_hash = epee::string_tools::pod_to_hex(txid);
+      txi.tx_blob = *bd;
       transaction tx;
       if (!parse_and_validate_tx_from_blob(*bd, tx))
       {
@@ -668,6 +675,7 @@ namespace cryptonote
       txi.relayed = meta.relayed;
       txi.last_relayed_time = meta.last_relayed_time;
       txi.do_not_relay = meta.do_not_relay;
+      txi.double_spend_seen = meta.double_spend_seen;
       tx_infos.push_back(txi);
       return true;
     }, true);
@@ -712,6 +720,7 @@ namespace cryptonote
       txi.relayed = meta.relayed;
       txi.last_relayed_time = meta.last_relayed_time;
       txi.do_not_relay = meta.do_not_relay;
+      txi.double_spend_seen = meta.double_spend_seen;
       tx_infos.push_back(txi);
       return true;
     }, true);
@@ -843,7 +852,10 @@ namespace cryptonote
     }
     //if we here, transaction seems valid, but, anyway, check for key_images collisions with blockchain, just to be sure
     if(m_blockchain.have_tx_keyimges_as_spent(tx))
+    {
+      txd.double_spend_seen = true;
       return false;
+    }
 
     //transaction is ok.
     return true;
@@ -871,6 +883,39 @@ namespace cryptonote
     return true;
   }
   //---------------------------------------------------------------------------------
+  void tx_memory_pool::mark_double_spend(const transaction &tx)
+  {
+    CRITICAL_REGION_LOCAL(m_transactions_lock);
+    CRITICAL_REGION_LOCAL1(m_blockchain);
+    LockedTXN lock(m_blockchain);
+    for(size_t i = 0; i!= tx.vin.size(); i++)
+    {
+      CHECKED_GET_SPECIFIC_VARIANT(tx.vin[i], const txin_to_key, itk, void());
+      const key_images_container::const_iterator it = m_spent_key_images.find(itk.k_image);
+      if (it != m_spent_key_images.end())
+      {
+        for (const crypto::hash &txid: it->second)
+        {
+          txpool_tx_meta_t meta = m_blockchain.get_txpool_tx_meta(txid);
+          if (!meta.double_spend_seen)
+          {
+            MDEBUG("Marking " << txid << " as double spending " << itk.k_image);
+            meta.double_spend_seen = true;
+            try
+            {
+              m_blockchain.update_txpool_tx(txid, meta);
+            }
+            catch (const std::exception &e)
+            {
+              MERROR("Failed to update tx meta: " << e.what());
+              // continue, not fatal
+            }
+          }
+        }
+      }
+    }
+  }
+  //---------------------------------------------------------------------------------
   std::string tx_memory_pool::print_pool(bool short_format) const
   {
     std::stringstream ss;
@@ -890,6 +935,7 @@ namespace cryptonote
       ss << "blob_size: " << meta.blob_size << std::endl
         << "fee: " << print_money(meta.fee) << std::endl
         << "kept_by_block: " << (meta.kept_by_block ? 'T' : 'F') << std::endl
+        << "double_spend_seen: " << (meta.double_spend_seen ? 'T' : 'F') << std::endl
         << "max_used_block_height: " << meta.max_used_block_height << std::endl
         << "max_used_block_id: " << meta.max_used_block_id << std::endl
         << "last_failed_height: " << meta.last_failed_height << std::endl