Is Integer Overflow and Underflow possible in any scenerio in Solidity ^0.8.0

Question

I came across a tweet which tells there are few scenarios in which Integer Overflow/Underflow are possible in Solidity ^0.8.0? Do you know how?

Does this answer your question? Revert reason for arithmetic overflows in Solidity v0.8 — Paul Razvan Berg, Sep 05 '22 at 12:57

score 2 · Accepted Answer · answered Sep 05 '22 at 12:46

Well, yes. If you use assembly or the unchecked keyword you can get an overflow/underflow.

Check this simple code I created:

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract Counter {
mapping(address =&gt; uint256) public balances;

constructor() {
    balances[msg.sender] = 0;
}

function underflow_assembly() public pure returns(uint256) {
    uint256 n = 0;
    assembly {
        n := sub(n, 1)
    }
    // n now is equal to 115792089237316195423570985008687907853269984665640564039457584007913129639935
    return n;
}

function underflow_unchecked() public pure returns(uint256) {
    uint256 n = 0;
    unchecked {
        n--;
    }
    // n now is equal to 115792089237316195423570985008687907853269984665640564039457584007913129639935
    return n;
}

// reverts
function no_underflow() public pure returns(uint256) {
    uint256 n = 0;
    n--;
    return n;
}

// reverts
function balanceUnderflow() public {
    balances[msg.sender] -= 1;
}


}

With Solidity version ^0.8.0, you cannot get underflow/overflow unless you use the unchecked keyword or use assembly.

Is Integer Overflow and Underflow possible in any scenerio in Solidity ^0.8.0

1 Answers1