Block malicious users who generated syntax errors

Author: Seonpyo Kim

core/src/miner/miner.rs

@@ -270,6 +270,12 @@ impl Miner {
             .into_iter()
             .map(|tx| {
                 let hash = tx.hash();
+                let signer_public = tx.recover_public()?;
+
+                if self.malicious_users.read().contains(&signer_public) {
+                    // FIXME: just to skip, think about another way.
+                    return Ok(())
+                }
                 if client.transaction_block(&TransactionId::Hash(hash)).is_some() {
                     cdebug!(MINER, "Rejected transaction {:?}: already in the blockchain", hash);
                     return Err(HistoryError::TransactionAlreadyImported.into())
@@ -283,12 +289,29 @@ impl Miner {
                     .and_then(|_| self.engine.verify_transaction_unordered(tx, &best_block_header))
                 {
                     Err(e) => {
+                        match e {
+                            Error::Syntax(_) if !self.mem_pool.read().is_local_transaction(hash) => {
+                                self.malicious_users.write().insert(signer_public);
+                            }
+                            _ => {}
+                        }
                         cdebug!(MINER, "Rejected transaction {:?} with invalid signature: {:?}", hash, e);
                         Err(e)
                     }
                     Ok(tx) => {
                         // This check goes here because verify_transaction takes SignedTransaction parameter
-                        self.engine.machine().verify_transaction(&tx, &best_block_header, client, false)?;
+                        self.engine.machine().verify_transaction(&tx, &best_block_header, client, false).map_err(
+                            |e| {
+                                match e {
+                                    Error::Syntax(_) if !self.mem_pool.read().is_local_transaction(hash) => {
+                                        self.malicious_users.write().insert(tx.signer_public());
+                                    }
+                                    _ => {}
+                                };
+                                e
+                            },
+                        )?;
+
 
                         let origin = self
                             .accounts