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Refactor Paymaster to Use Precharge + Refund Model #127

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Nov 22, 2023
Merged

Refactor Paymaster to Use Precharge + Refund Model #127

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32 changes: 19 additions & 13 deletions contracts/paymaster/ERC20Paymaster.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,9 @@ contract ERC20Paymaster is BasePaymaster {
uint256 public constant PRICE_DENOMINATOR = 1e6;
// calculated cost of the postOp
uint256 public constant COST_OF_POST = 40000;
// This is the threshold check in the active wallet constructor for the maximum sponsor fund.
// It prevents a malicious user from draining the Paymaster's deposit in a single user operation.
uint256 public constant MAX_ALLOW_SPONSOR_FUND_ACTIVE_WALLET = 0.1 ether;

// Trusted token approve gas cost
uint256 private constant _SAFE_APPROVE_GAS_COST = 50000;
Expand Down Expand Up @@ -85,7 +88,6 @@ contract ERC20Paymaster is BasePaymaster {

function _validatePaymasterUserOp(UserOperation calldata userOp, bytes32, uint256 requiredPreFund)
internal
view
override
returns (bytes memory context, uint256 validationResult)
{
Expand All @@ -94,6 +96,8 @@ contract ERC20Paymaster is BasePaymaster {
address sender = userOp.getSender();

// paymasterAndData: [paymaster, token, maxCost]
// The length check prevents the user from add exceeding calldata, which could drain paymaster deposits in entrypoint
require(userOp.paymasterAndData.length == 84, "invalid data length");
(address token, uint256 maxCost) = abi.decode(userOp.paymasterAndData[20:], (address, uint256));
require(isSupportToken(token), "Paymaster: token not support");
IERC20Metadata ERC20Token = IERC20Metadata(token);
Expand All @@ -112,16 +116,17 @@ contract ERC20Paymaster is BasePaymaster {
require(tokenRequiredPreFund <= maxCost, "Paymaster: maxCost too low");

if (userOp.initCode.length != 0) {
// This operation prevents a malicious user from draining the Paymaster's deposit in a single active wallet user operation.
// However, it doesn't prevent a user from sending multiple active wallet user operations to drain the Paymaster's deposit.
// It does, however, add overhead for the attacker.
require(requiredPreFund < MAX_ALLOW_SPONSOR_FUND_ACTIVE_WALLET, "Paymaster: maxCost too high");
require(ERC20Token.balanceOf(sender) >= tokenRequiredPreFund, "Paymaster: not enough balance");
_validateConstructor(userOp, token, tokenRequiredPreFund);
} else {
require(
ERC20Token.allowance(sender, address(this)) >= tokenRequiredPreFund, "Paymaster: not enough allowance"
);
ERC20Token.safeTransferFrom(sender, address(this), tokenRequiredPreFund);
}

require(ERC20Token.balanceOf(sender) >= tokenRequiredPreFund, "Paymaster: not enough balance");

return (abi.encode(sender, token, costOfPost, exchangeRate), 0);
return (abi.encode(sender, token, costOfPost, exchangeRate, tokenRequiredPreFund), 0);
}

/*
Expand Down Expand Up @@ -152,11 +157,10 @@ contract ERC20Paymaster is BasePaymaster {
}

require(dest.length == func.length, "Paymaster: invalid callData length");
address _destAddress = address(0);
require(isSupportToken(token), "Paymaster: token not support");
bool checkAllowance = false;
for (uint256 i = 0; i < dest.length; i++) {
address destAddr = dest[i];
require(isSupportToken(token), "Paymaster: token not support");
// check it contains approve operation, 0x095ea7b3 approve(address,uint256)
if (destAddr == token && bytes4(func[i]) == bytes4(0x095ea7b3)) {
(address spender, uint256 amount) = _decodeApprove(func[i]);
Expand Down Expand Up @@ -185,12 +189,14 @@ contract ERC20Paymaster is BasePaymaster {
if (mode == PostOpMode.postOpReverted) {
return; // Do nothing here to not revert the whole bundle and harm reputation
}
(address sender, address payable token, uint256 costOfPost, uint256 exchangeRate) =
abi.decode(context, (address, address, uint256, uint256));
(address sender, address payable token, uint256 costOfPost, uint256 exchangeRate, uint256 tokenRequiredPreFund)
= abi.decode(context, (address, address, uint256, uint256, uint256));
uint256 tokenRequiredFund =
(actualGasCost + costOfPost) * supportedToken[token].priceMarkup * exchangeRate / (1e18 * PRICE_DENOMINATOR);

IERC20Metadata(token).safeTransferFrom(sender, address(this), tokenRequiredFund);
// refund unsed precharge token
if (tokenRequiredPreFund > tokenRequiredFund) {
IERC20Metadata(token).safeTransfer(sender, tokenRequiredPreFund - tokenRequiredFund);
}
// update oracle
uint192 lasestTokenPrice = fetchPrice(supportedToken[token].tokenOracle);
supportedToken[token].previousPrice = lasestTokenPrice;
Expand Down