Replace MAX_PACKAGE_SIZE with MAX_PACKAGE_WEIGHT to avoid vbyte confusion

While allowing submitted packages to be slightly larger than what
may be allowed in the mempool to allow simpler reasoning
about contextual-less checks vs chain limits.

Author: instagibbs

doc/policy/packages.md

@@ -18,16 +18,19 @@ tip or some preceding transaction in the package.
 
 The following rules are enforced for all packages:
 
-* Packages cannot exceed `MAX_PACKAGE_COUNT=25` count and `MAX_PACKAGE_SIZE=101KvB` total size
+* Packages cannot exceed `MAX_PACKAGE_COUNT=25` count and `MAX_PACKAGE_WEIGHT=404000` total weight
    (#20833)
 
-   - *Rationale*: This is already enforced as mempool ancestor/descendant limits. If
-     transactions in a package are all related, exceeding this limit would mean that the package
-     can either be split up or it wouldn't pass individual mempool policy.
+   - *Rationale*: We want package size to be as small as possible to mitigate DoS via package
+     validation. However, we want to make sure that the limit does not restrict ancestor
+     packages that would be allowed if submitted individually.
 
    - Note that, if these mempool limits change, package limits should be reconsidered. Users may
      also configure their mempool limits differently.
 
+   - Note that the this is transaction weight, not "virtual" size as with other limits to allow
+     simpler context-less checks.
+
 * Packages must be topologically sorted. (#20833)
 
 * Packages cannot have conflicting transactions, i.e. no two transactions in a package can spend

src/policy/packages.cpp

@@ -23,10 +23,10 @@ bool CheckPackage(const Package& txns, PackageValidationState& state)
         return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-too-many-transactions");
     }
 
-    const int64_t total_size = std::accumulate(txns.cbegin(), txns.cend(), 0,
-                               [](int64_t sum, const auto& tx) { return sum + GetVirtualTransactionSize(*tx); });
-    // If the package only contains 1 tx, it's better to report the policy violation on individual tx size.
-    if (package_count > 1 && total_size > MAX_PACKAGE_SIZE * 1000) {
+    const int64_t total_weight = std::accumulate(txns.cbegin(), txns.cend(), 0,
+                               [](int64_t sum, const auto& tx) { return sum + GetTransactionWeight(*tx); });
+    // If the package only contains 1 tx, it's better to report the policy violation on individual tx weight.
+    if (package_count > 1 && total_weight > MAX_PACKAGE_WEIGHT) {
         return state.Invalid(PackageValidationResult::PCKG_POLICY, "package-too-large");
     }
 

src/policy/packages.h

@@ -15,18 +15,22 @@
 
 /** Default maximum number of transactions in a package. */
 static constexpr uint32_t MAX_PACKAGE_COUNT{25};
-/** Default maximum total virtual size of transactions in a package in KvB. */
-static constexpr uint32_t MAX_PACKAGE_SIZE{101};
-static_assert(MAX_PACKAGE_SIZE * WITNESS_SCALE_FACTOR * 1000 >= MAX_STANDARD_TX_WEIGHT);
+/** Default maximum total weight of transactions in a package in weight
+    to allow for context-less checks. This must allow a superset of sigops
+    weighted vsize limited transactions to not disallow transactions we would
+    have otherwise accepted individually. */
+static constexpr uint32_t MAX_PACKAGE_WEIGHT = 404'000;
+static_assert(MAX_PACKAGE_WEIGHT >= MAX_STANDARD_TX_WEIGHT);
 
-// If a package is submitted, it must be within the mempool's ancestor/descendant limits. Since a
-// submitted package must be child-with-unconfirmed-parents (all of the transactions are an ancestor
+// If a package is to be evaluated, it must be at least as large as the mempool's ancestor/descendant limits,
+// otherwise transactions that would be individually accepted may be rejected in a package erroneously.
+// Since a submitted package must be child-with-unconfirmed-parents (all of the transactions are an ancestor
 // of the child), package limits are ultimately bounded by mempool package limits. Ensure that the
 // defaults reflect this constraint.
 static_assert(DEFAULT_DESCENDANT_LIMIT >= MAX_PACKAGE_COUNT);
 static_assert(DEFAULT_ANCESTOR_LIMIT >= MAX_PACKAGE_COUNT);
-static_assert(DEFAULT_ANCESTOR_SIZE_LIMIT_KVB >= MAX_PACKAGE_SIZE);
-static_assert(DEFAULT_DESCENDANT_SIZE_LIMIT_KVB >= MAX_PACKAGE_SIZE);
+static_assert(MAX_PACKAGE_WEIGHT >= DEFAULT_ANCESTOR_SIZE_LIMIT_KVB * WITNESS_SCALE_FACTOR * 1000);
+static_assert(MAX_PACKAGE_WEIGHT >= DEFAULT_DESCENDANT_SIZE_LIMIT_KVB * WITNESS_SCALE_FACTOR * 1000);
 
 /** A "reason" why a package was invalid. It may be that one or more of the included
  * transactions is invalid or the package itself violates our rules.
@@ -47,7 +51,7 @@ class PackageValidationState : public ValidationState<PackageValidationResult> {
 
 /** Context-free package policy checks:
  * 1. The number of transactions cannot exceed MAX_PACKAGE_COUNT.
- * 2. The total virtual size cannot exceed MAX_PACKAGE_SIZE.
+ * 2. The total weight cannot exceed MAX_PACKAGE_WEIGHT.
  * 3. If any dependencies exist between transactions, parents must appear before children.
  * 4. Transactions cannot conflict, i.e., spend the same inputs.
  */

src/test/txpackage_tests.cpp

@@ -51,14 +51,14 @@ BOOST_FIXTURE_TEST_CASE(package_sanitization_tests, TestChain100Setup)
     BOOST_CHECK_EQUAL(state_too_many.GetResult(), PackageValidationResult::PCKG_POLICY);
     BOOST_CHECK_EQUAL(state_too_many.GetRejectReason(), "package-too-many-transactions");
 
-    // Packages can't have a total size of more than 101KvB.
+    // Packages can't have a total weight of more than 404'000WU.
     CTransactionRef large_ptx = create_placeholder_tx(150, 150);
     Package package_too_large;
-    auto size_large = GetVirtualTransactionSize(*large_ptx);
-    size_t total_size{0};
-    while (total_size <= MAX_PACKAGE_SIZE * 1000) {
+    auto size_large = GetTransactionWeight(*large_ptx);
+    size_t total_weight{0};
+    while (total_weight <= MAX_PACKAGE_WEIGHT) {
         package_too_large.push_back(large_ptx);
-        total_size += size_large;
+        total_weight += size_large;
     }
     BOOST_CHECK(package_too_large.size() <= MAX_PACKAGE_COUNT);
     PackageValidationState state_too_large;
@@ -122,7 +122,7 @@ BOOST_FIXTURE_TEST_CASE(package_validation_tests, TestChain100Setup)
 
     // A single, giant transaction submitted through ProcessNewPackage fails on single tx policy.
     CTransactionRef giant_ptx = create_placeholder_tx(999, 999);
-    BOOST_CHECK(GetVirtualTransactionSize(*giant_ptx) > MAX_PACKAGE_SIZE * 1000);
+    BOOST_CHECK(GetVirtualTransactionSize(*giant_ptx) > DEFAULT_ANCESTOR_SIZE_LIMIT_KVB * 1000);
     auto result_single_large = ProcessNewPackage(m_node.chainman->ActiveChainstate(), *m_node.mempool, {giant_ptx}, /*test_accept=*/true);
     BOOST_CHECK(result_single_large.m_state.IsInvalid());
     BOOST_CHECK_EQUAL(result_single_large.m_state.GetResult(), PackageValidationResult::PCKG_TX);