First Flight #2: Puppy Raffle
First Flight #2
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100 EXP
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Submission Details
Severity: medium
Invalid

The selectWinner function iterates through the players array to select a winner. As the number of players increases, this function may run out of gas, making it impossible to select a winner.

0xVinylDavyl

Summary

The selectWinner function iterates through the players array to select a winner. As the number of players increases, this function may run out of gas, making it impossible to select a winner.

Vulnerability Details

In the selectWinner function, the contract uses a loop to iterate through the players array to select a winner. While this approach works with a moderate number of players, it becomes inefficient and may encounter gas limitations as the number of players increases.

function selectWinner() external {
// ...
​
uint256 winnerIndex =
uint256(keccak256(abi.encodePacked(msg.sender, block.timestamp, block.difficulty))) % players.length;
address winner = players[winnerIndex];
​
// ...
}

The gas limitation is a significant concern as Ethereum imposes a block gas limit that can be exceeded if the players array becomes very large, preventing the function from completing its execution.

Impact

If the gas limit is exceeded in the selectWinner function, it will become impossible to select a winner. As a result, the raffle may stall, causing inconvenience to participants and potentially affecting the contract's integrity.

Tools Used

Manual

Recommendations

To mitigate the potential gas limitation issue in the selectWinner function, consider optimizing the selection process by reducing the reliance on gas-consuming operations. Here are some recommendations:

  1. Use a Random Number Generator: Instead of iterating through the players array, consider using a more efficient and gas-friendly random number generator. This can be implemented using external services like Chainlink VRF or other provably fair random number generation mechanisms. This approach ensures fairness and efficiency.

  2. Limit the Number of Players: If using a more efficient random number generator is not feasible, consider imposing a limit on the number of players allowed in a single raffle. This can help manage gas consumption and ensure the function remains efficient.

  3. Implement Batching: If the number of players is expected to be very large, consider implementing a batch processing approach, where the selection of multiple winners occurs over several iterations to stay within gas limits.

Now using Chainlink VRF to obtain a secure and gas-efficient random number, which can be used to select the winner without relying on gas-consuming iterations. This approach significantly improves the contract's scalability and efficiency in handling larger numbers of participants.

Example of an optimized approach using Chainlink VRF:

import "@chainlink/contracts/src/v0.8/VRFConsumerBase.sol";
​
contract PuppyRaffle is ERC721, Ownable, VRFConsumerBase {
// ...
​
constructor(uint256 _entranceFee, address _feeAddress, uint256 _raffleDuration, address _vrfCoordinator, address _linkToken)
ERC721("Puppy Raffle", "PR")
VRFConsumerBase(_vrfCoordinator, _linkToken)
{
// Initialize the contract
// ...
}
​
function selectWinner() external onlyOwner {
require(block.timestamp >= raffleStartTime + raffleDuration, "PuppyRaffle: Raffle not over");
require(players.length >= 4, "PuppyRaffle: Need at least 4 players");
// Use Chainlink VRF to get a random number for selecting the winner
requestRandomness(); // Implement this function to use Chainlink VRF
// ...
}
// Implement the Chainlink VRF callback to select the winner
function fulfillRandomness(uint256 requestId, uint256 randomness) internal override {
uint256 winnerIndex = randomness % players.length;
address winner = players[winnerIndex];
// ...
}
// ...
}
Updates

Lead Judging Commences

Hamiltonite Lead Judge almost 2 years ago
Submission Judgement Published
Invalidated
Reason: Other

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