0xaliyah - infinite approval will always revert for some ERC20 compliant tokens

[sherlock-admin2]

0xaliyah

Medium

infinite approval will always revert for some ERC20 compliant tokens

Summary

    /**
     * @notice Approves `grantee` to spend infinite tokens from the caller
     * @dev Uses `approve` rather than `safeApprove` since the race condition
     *      in safeApprove does not apply when going to an infinite approval
     * @param self Token to grant approval
     * @param self Token to grant approval
     * @param grantee Address to allow spending
     */

Vulnerability Detail

1. #revert-on-large-approvals--transfers

Impact

1. Some tokens (e.g. UNI, COMP) revert if the value passed to approve or transfer is larger than uint96.

Code Snippet

1. TokenOrEther18.sol
2. Token6.sol
3. Token18.sol

Tool used

Manual Review

Recommendation

[sabatha7]

Quirks in the COMP token itself
The COMP token that the rewards contract distributes does not store balances as a uint256 like most ERC 20 tokens do, but rather as a uint96.

COMP token balances mapping

If you try to transfer or approve an amount greater than the uint96 maximum value, the transaction will revert.