utsav - setStartBlock doesn't update the lastRewardBlock

[sherlock-admin4]

utsav

medium

setStartBlock doesn't update the lastRewardBlock

Summary

setStartBlock doesn't update the lastRewardBlock and this can lead to wrong reward calculation

Vulnerability Detail

Owner can update the startBlock before farming started

    function setStartBlock(uint256 _startBlock) public onlyOwner {
        if (_startBlock == 0 || (endBlock != 0 && _startBlock >= endBlock)) {
            revert InvalidStartBlock();
        }
        if (getBlockNumber() > startBlock) {
            revert FarmingIsStarted();
        }
        startBlock = _startBlock;
    }

But the issue is setStartBlock doesn't update lastRewardBlock of pools. As a result pool will be started earlier or later but reward will be calculated based on old lastRewardBlock

Impact

User can get less/more reward than expected

Code Snippet

https://github.com/sherlock-audit/2024-05-sophon/blob/main/farming-contracts/contracts/farm/SophonFarming.sol#L272C1-L280C6

Tool used

Manual Review + VS code

Recommendation

Update the lastRewardBlock while updating startBlock

Duplicate of #108

[sherlock-admin2]

1 comment(s) were left on this issue during the judging contest.

0xmystery commented:

valid because lastRewardBlock for each pool should indeed sync with the latest startBlock

[mystery0x]

This report should be valid as it described both scenarios 1 and 2 (albeit in a simpler way) of #108.