Sigvex
EVMRemediation2 min read

Batch Operation Atomicity Remediation

How to make batch functions behave predictably: choose all-or-nothing or per-item isolation deliberately, and never silently skip.

evmdenial-of-service

Batch Operation Atomicity Remediation

Overview

Related Detector: Batch Operation Atomicity

A function that processes an array of operations has to decide what happens when one element fails. Reverting the whole batch lets a single poisoned element grief everyone; silently skipping failed items causes fund loss and inconsistent state. The remediation is to pick a policy deliberately — atomic all-or-nothing, or isolated per-item with explicit success reporting — and never let a failure pass unrecorded.

Before (Vulnerable — one bad element decides for all, silently)

function batchTransfer(address[] calldata to, uint256[] calldata amt) external {
    for (uint256 i; i < to.length; ++i) {
        token.transfer(to[i], amt[i]);   // a failing transfer reverts everything (or is ignored)
    }
}

After (Fixed — isolate per item and report outcomes)

event ItemResult(uint256 indexed index, bool success);

function batchTransfer(address[] calldata to, uint256[] calldata amt) external {
    require(to.length == amt.length, "Length mismatch");
    for (uint256 i; i < to.length; ++i) {
        try token.transfer(to[i], amt[i]) returns (bool ok) {
            emit ItemResult(i, ok);          // record every outcome
        } catch {
            emit ItemResult(i, false);       // failure is explicit, not silent
        }
    }
}

If the batch must be atomic (e.g. an accounting invariant spans items), keep the plain revert-on-failure form and document it. The key is that the choice is intentional and observable.

Common Mistakes

  • Catching failures and continuing without emitting or recording them, so callers believe every item succeeded.
  • Using an atomic batch for user-supplied recipient lists, letting one hostile recipient block the whole operation.
  • Leaving partial state (some items applied, some not) with no way to reconcile which succeeded.

References