JohnSmith - Function `convertToUnderlying(uint256 s)` does not follow EIP5095

[sherlock-admin]

JohnSmith

medium

Function convertToUnderlying(uint256 s) does not follow EIP5095

Summary

The convertToUnderlying function does not follow EIP5095 standard, when called before maturity

Vulnerability Detail

according to https://eips.ethereum.org/EIPS/eip-5095 convertToUnderlying

Before maturity, the amount of underlying returned is as if the PTs would be at maturity.

in illuminate docs stateв that

upon maturity, may redeem the underlying at a 1:1 ratio

when block.timestamp < maturity we call previewRedeem(s)

src/tokens/ERC5095.sol
64:         if (block.timestamp < maturity) {
65:             return previewRedeem(s);
66:         }

which will lead to IYield(pool).buyBasePreview(Cast.u128(a)); Such implementation will result in not having 1:1

Impact

Users, who view this as implementation of EIP5095 will get not expected results, which may lead to some value loss.

Code Snippet

https://github.com/sherlock-audit/2022-10-illuminate/blob/main/src/tokens/ERC5095.sol#L64-L66

Tool used

Manual Review

Recommendation

Always return promised 1:1

src/tokens/ERC5095.sol
58:     function convertToUnderlying(uint256 s)
59:         external
60:         view
61:         override
62:         returns (uint256)
63:     {
- 64:         if (block.timestamp < maturity) {
- 65:             return previewRedeem(s);//@audit breaking EIP5095, should return s anyway
- 66:         }
67:         return s;
68:     }

If user wants to see what they can get before maturity, they should call previewRedeem(uint256)