[validation/refactor] store precomputed txdata in workspace

We want to be able to re-use the precomputed transaction data between
PolicyScriptChecks and ConsensusScriptChecks in
AcceptMultipleTransactions.

Author: glozow

src/validation.cpp

@@ -513,6 +513,9 @@ class MemPoolAccept
         const CTransactionRef& m_ptx;
         const uint256& m_hash;
         TxValidationState m_state;
+        /** A temporary cache containing serialized transaction data for signature verification.
+         * Reused across PolicyScriptChecks and ConsensusScriptChecks. */
+        PrecomputedTransactionData m_precomputed_txdata;
     };
 
     // Run the policy checks on a given transaction, excluding any script checks.
@@ -523,13 +526,13 @@ class MemPoolAccept
 
     // Run the script checks using our policy flags. As this can be slow, we should
     // only invoke this on transactions that have otherwise passed policy checks.
-    bool PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
+    bool PolicyScriptChecks(const ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
 
     // Re-run the script checks, using consensus flags, and try to cache the
     // result in the scriptcache. This should be done after
     // PolicyScriptChecks(). This requires that all inputs either be in our
     // utxo set or in the mempool.
-    bool ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData &txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
+    bool ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws) EXCLUSIVE_LOCKS_REQUIRED(cs_main, m_pool.cs);
 
     // Try to add the transaction to the mempool, removing any conflicts first.
     // Returns true if the transaction is in the mempool after any size
@@ -842,7 +845,7 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     return true;
 }
 
-bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
+bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws)
 {
     const CTransaction& tx = *ws.m_ptx;
     TxValidationState& state = ws.m_state;
@@ -851,13 +854,13 @@ bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, Prec
 
     // Check input scripts and signatures.
     // This is done last to help prevent CPU exhaustion denial-of-service attacks.
-    if (!CheckInputScripts(tx, state, m_view, scriptVerifyFlags, true, false, txdata)) {
+    if (!CheckInputScripts(tx, state, m_view, scriptVerifyFlags, true, false, ws.m_precomputed_txdata)) {
         // SCRIPT_VERIFY_CLEANSTACK requires SCRIPT_VERIFY_WITNESS, so we
         // need to turn both off, and compare against just turning off CLEANSTACK
         // to see if the failure is specifically due to witness validation.
         TxValidationState state_dummy; // Want reported failures to be from first CheckInputScripts
-        if (!tx.HasWitness() && CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, txdata) &&
-                !CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, txdata)) {
+        if (!tx.HasWitness() && CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~(SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_CLEANSTACK), true, false, ws.m_precomputed_txdata) &&
+                !CheckInputScripts(tx, state_dummy, m_view, scriptVerifyFlags & ~SCRIPT_VERIFY_CLEANSTACK, true, false, ws.m_precomputed_txdata)) {
             // Only the witness is missing, so the transaction itself may be fine.
             state.Invalid(TxValidationResult::TX_WITNESS_STRIPPED,
                     state.GetRejectReason(), state.GetDebugMessage());
@@ -868,7 +871,7 @@ bool MemPoolAccept::PolicyScriptChecks(const ATMPArgs& args, Workspace& ws, Prec
     return true;
 }
 
-bool MemPoolAccept::ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws, PrecomputedTransactionData& txdata)
+bool MemPoolAccept::ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws)
 {
     const CTransaction& tx = *ws.m_ptx;
     const uint256& hash = ws.m_hash;
@@ -891,7 +894,8 @@ bool MemPoolAccept::ConsensusScriptChecks(const ATMPArgs& args, Workspace& ws, P
     // invalid blocks (using TestBlockValidity), however allowing such
     // transactions into the mempool can be exploited as a DoS attack.
     unsigned int currentBlockScriptVerifyFlags = GetBlockScriptFlags(m_active_chainstate.m_chain.Tip(), chainparams.GetConsensus());
-    if (!CheckInputsFromMempoolAndCache(tx, state, m_view, m_pool, currentBlockScriptVerifyFlags, txdata, m_active_chainstate.CoinsTip())) {
+    if (!CheckInputsFromMempoolAndCache(tx, state, m_view, m_pool, currentBlockScriptVerifyFlags,
+                                        ws.m_precomputed_txdata, m_active_chainstate.CoinsTip())) {
         return error("%s: BUG! PLEASE REPORT THIS! CheckInputScripts failed against latest-block but not STANDARD flags %s, %s",
                 __func__, hash.ToString(), state.ToString());
     }
@@ -952,15 +956,11 @@ MempoolAcceptResult MemPoolAccept::AcceptSingleTransaction(const CTransactionRef
 
     if (!PreChecks(args, ws)) return MempoolAcceptResult::Failure(ws.m_state);
 
-    // Only compute the precomputed transaction data if we need to verify
-    // scripts (ie, other policy checks pass). We perform the inexpensive
-    // checks first and avoid hashing and signature verification unless those
-    // checks pass, to mitigate CPU exhaustion denial-of-service attacks.
-    PrecomputedTransactionData txdata;
+    // Perform the inexpensive checks first and avoid hashing and signature verification unless
+    // those checks pass, to mitigate CPU exhaustion denial-of-service attacks.
+    if (!PolicyScriptChecks(args, ws)) return MempoolAcceptResult::Failure(ws.m_state);
 
-    if (!PolicyScriptChecks(args, ws, txdata)) return MempoolAcceptResult::Failure(ws.m_state);
-
-    if (!ConsensusScriptChecks(args, ws, txdata)) return MempoolAcceptResult::Failure(ws.m_state);
+    if (!ConsensusScriptChecks(args, ws)) return MempoolAcceptResult::Failure(ws.m_state);
 
     // Tx was accepted, but not added
     if (args.m_test_accept) {
@@ -1020,8 +1020,7 @@ PackageMempoolAcceptResult MemPoolAccept::AcceptMultipleTransactions(const std::
     }
 
     for (Workspace& ws : workspaces) {
-        PrecomputedTransactionData txdata;
-        if (!PolicyScriptChecks(args, ws, txdata)) {
+        if (!PolicyScriptChecks(args, ws)) {
             // Exit early to avoid doing pointless work. Update the failed tx result; the rest are unfinished.
             package_state.Invalid(PackageValidationResult::PCKG_TX, "transaction failed");
             results.emplace(ws.m_ptx->GetWitnessHash(), MempoolAcceptResult::Failure(ws.m_state));