Saurabh_Singh - UnderFlow revert in the amirX::swap function because of (fBalance - iBalance) substraction.

[sherlock-admin2]

Saurabh_Singh

Medium

UnderFlow revert in the amirX::swap function because of (fBalance - iBalance) substraction.

summary

The amirX::swap function will revert each time when the value of fBalance is less then iBalance since a swap is performed.

Vulnerability Detail

Since a swap is performed the value of token of a address can be increase or decreased depend on swap.
if the balance decreased (fBalance < IBalance) the below line will cause a underflow revert, becasue the value of a variable cannot be less then 0 in solidity.

https://github.com/sherlock-audit/2024-11-telcoin/blob/main/telcoin-audit/contracts/swap/AmirX.sol#L93

##Impact
The underflow revert will cause the contract to not perfrom the intended task of swap function.

##Recommendation

 function swap(
        address wallet,
        bool directional,
        StablecoinSwap memory ss,
        DefiSwap memory defi
    ) external payable onlyRole(SWAPPER_ROLE) whenNotPaused {
        // checks if it will fail
        if (ss.destination != address(0)) _verifyStablecoinSwap(wallet, ss);
        if (defi.walletData.length != 0) _verifyDefiSwap(wallet, defi);

        if (directional) {
            // if only defi swap
            if (ss.destination == address(0)) _defiSwap(wallet, defi);
            else {
                // if defi then stablecoin swap
                //check balance to adjust second swap
                uint256 iBalance = ERC20(ss.origin).balanceOf(wallet);
                if (defi.walletData.length != 0) _defiSwap(wallet, defi);
                uint256 fBalance = ERC20(ss.origin).balanceOf(wallet);
                //change balance to reflect change
-               if (fBalance - iBalance != 0) ss.oAmount = fBalance - iBalance;
+              if (fBalance - iBalance != 0){
+                 ss.oAmount = (fBalance >= iBalance ) ? (fBalance - iBalance) : iBalance - fBalance;
+                }
                _stablecoinSwap(wallet, ss);
            }
        } else {
            // if stablecoin swap
            _stablecoinSwap(wallet, ss);
            // if only stablecoin swap
            if (defi.walletData.length != 0) _defiSwap(wallet, defi);
        }
    }