Fix reentrancy effort-limit bypass in FlowTransactionScheduler - #618
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Address review feedback: extract self.config.priorityEffortLimit[txData.priority]! into a local variable used by both the assert condition and its message. make generate for the embedded contract assets.
Adds a test-only ReentrantHandler whose resolveView() attempts to reenter schedule() while the outer schedule() call is still in flight, trying to stuff two 9000-effort high-priority transactions into a 15000-effort slot. With the checks-effects-interactions fix, the outer call reserves its slot capacity before the handler callback runs, so the nested schedule fails the effort estimate and the whole transaction is rolled back atomically. Verified that this test fails against the pre-fix contract. - test-only ReentrantHandler in TestFlowScheduledTransactionHandler - schedule_transaction_reentrant.cdc test transaction - testScheduleReentrancy asserting failure and full slot rollback - make generate for the embedded assets
turbolent
approved these changes
Aug 4, 2026
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Fix a reentrancy vector in
schedule()where slot capacity was only reservedafter the handler callback ran. A handler's
resolveView()could reenterschedule()and fit additional transactions into a slot whose capacity wasalready spoken for, bypassing the per-priority effort limit.
This ports the fix already deployed via onflow/flow-core-contracts-internal#7.
Changes
addTransaction) before invoking the handler callbackin
schedule(), following checks-effects-interactionsaddTransaction()that the per-priority slottotal never exceeds the configured effort limit
testScheduleReentrancy) with a test-onlyReentrantHandlerthat attempts to nest aschedule()call; verified tofail against the pre-fix contract
Related: onflow/flow-core-contracts-internal#7