Rounding error in Aave Lending Pool

Summary

The aave lending pool produces rounding errors when calling PreDepositVault::earn().

Vulnerability Detail

These errors were found to be negligible, being at most 1 wei, and they can either increase or decrease totalAssets() by 1. It shouldn't be exploitable but it's good to know.

Impact

totalPrincipal will be under/overestimated by 1 wei. For example, earning 1000 in PreDepositVault::earn():

1. If it rounds up, totalPrincipal is 1000 but there will already be 1 profit, as we get 1001 aTokens
2. If it rounds down, totalPrincipal is 1000 but we only have 999 aTokens. Due to decimals in the assets, this isn't impactful. 1 wei is at most 1e-8 wbtc.

Code Snippet

https://github.com/sherlock-audit/2025-03-gaib/blob/main/pre-vaults/contracts/pre-vaults/gpdWBTC.sol#L56-L62

Tool Used

Manual Review

Recommendation

Rounding error is very small so no fix is needed.