Sablier

Summary

In manual tranche stream creation (with broker fee), it is possible that some specific tranche deposits would be impossible to craft due to _checkTranches reverting.

Vulnerability Details

Imagine the following: stream sender has 200 tokens (with 18 decimals so 200e18) to stream to recipient via 2 equivalent tranches (100, 100), broker is also involved, brokerFee = 10%. According to the natspec, the stream creator is responsible for accounting for all due sums in the params.totalAmount (tranche amounts sum + broker fee). If the sender intends to stream 200e18 (after fee) then we calculate the params.totalAmount (before fee) as 200e18 / (1 - brokerFee) = 222,222222e18. With this input, checkAndCalculateBrokerFee will calculate createAmounts.deposit as 222,222222e18 - 222,222222e18 * brokerFee = 199,999998e18. This amount is further checked in Helpers._checkTranches and will cause a revert since it does not amount to the intended 200 tokens stream.

Sender would be unable to stream their initially intended (and presumably owed to recipient) 200 token amount with the given parameters.

Impact

Unexpected behavior, broken core functionality

Tools Used

Manual Review

Recommendations

Instead of reverting the transaction, cover the difference between depositAmount and trancheAmountSum from the brokerFee when handling periodic numbers.