Minimal Forwarder

contracts/metatx/MinimalForwarder.sol

@@ -47,6 +47,11 @@ contract MinimalForwarder is EIP712, Nonces {
      */
     error MinimalForwaderMismatchedValue(uint256 msgValue, uint256 value);
 
+    /**
+     * @dev The list of requests length doesn't match with the list of signatures length.
+     */
+    error MinimalForwaderInvalidBatchLength(uint256 requestsLength, uint256 signaturesLength);
+
     /**
      * @dev The request `deadline` has expired.
      */
@@ -87,13 +92,21 @@ contract MinimalForwarder is EIP712, Nonces {
 
         _useCheckedNonce(request.from, request.nonce);
 
+        // As a consequence of EIP-150, the maximum gas forwarded to a call is 63/64 of the remaining gas. So:
+        // - At most `gasleft() - floor(gasleft() / 64)` is passed.
+        // - At least `floor(gasleft() / 64)` is kept in the caller.
+        // The current gas available is saved for later checking.
+        uint256 gasBefore = gasleft();
         (bool success, bytes memory returndata) = request.to.call{gas: request.gas, value: request.value}(
             abi.encodePacked(request.data, request.from)
         );
 
-        // Validate that the relayer has sent enough gas for the call.
-        // See https://ronan.eth.limo/blog/ethereum-gas-dangers/
-        if (gasleft() <= request.gas / 63) {
+        // To avoid gas griefing attacks, as referenced in https://ronan.eth.limo/blog/ethereum-gas-dangers/
+        // A malicious relayer can attempt to manipulate the gas forwarded so that the underlying call reverts and
+        // the top-level call still passes.
+        // Such manipulation can be prevented by checking if `gasleft() < floor(gasBefore / 64)`. If so, we
+        // can assume an out of gas error was forced in the subcall. There's no need to process such transactions.
+        if (gasleft() < gasBefore / 64) {
             // We explicitly trigger invalid opcode to consume all gas and bubble-up the effects, since
             // neither revert or assert consume all gas since Solidity 0.8.0
             // https://docs.soliditylang.org/en/v0.8.0/control-structures.html#panic-via-assert-and-error-via-require
@@ -110,9 +123,9 @@ contract MinimalForwarder is EIP712, Nonces {
      * @dev Validates if the provided request can be executed at `blockNumber` with `signature`.
      */
     function _validateAt(
+        uint256 blockNumber,
         ForwardRequest calldata request,
-        bytes calldata signature,
-        uint256 blockNumber
+        bytes calldata signature
     ) internal view virtual returns (bool alive, bool signerMatch, bool nonceMatch) {
         address signer = _recoverForwardRequestSigner(request, signature);
         return (request.deadline >= blockNumber, signer == request.from, nonces(request.from) == request.nonce);
@@ -125,7 +138,7 @@ contract MinimalForwarder is EIP712, Nonces {
         ForwardRequest calldata request,
         bytes calldata signature
     ) internal view virtual returns (bool alive, bool signerMatch, bool nonceMatch) {
-        return _validateAt(request, signature, block.number);
+        return _validateAt(block.number, request, signature);
     }
 
     /**