SWC-125/不正确的继承顺序
Solidity支持多重继承,这意味着一个合约可以继承多个合约。多重继承引入了称为Diamond Problem的歧义问题: 如果两个或多个基础合约定义了相同的函数,则在子合约中应调用哪个?Solidity通过使用反向C3线性化 来解决这种歧义,该线性化设置了基础合约之间的优先级。
这样,基础合约具有不同的优先级,因此继承顺序很重要。忽略继承顺序可能导致意外行为。
CWE漏洞分类
整改方案
在继承多个合约时,尤其是在它们具有相同函数的情况下,开发人员应按正确的顺序仔细指定继承。 经验法则是将合约从更通用到更有针对性地继承。
参考文献
示例合约
MDTCrowdsale.sol
/*
* @source: https://github.com/Arachnid/uscc/blob/master/submissions-2017/philipdaian/MDTCrowdsale.sol
* @author: Philip Daian
*/
pragma solidity ^0.4.25;
//import "https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/math/SafeMath.sol";
/**
* @title SafeMath
* @dev Math operations with safety checks that revert on error
*/
library SafeMath {
/**
* @dev Multiplies two numbers, reverts on overflow.
*/
function mul(uint256 a, uint256 b) internal pure returns (uint256) {
// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
// benefit is lost if 'b' is also tested.
// See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
if (a == 0) {
return 0;
}
uint256 c = a * b;
require(c / a == b);
return c;
}
/**
* @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
*/
function div(uint256 a, uint256 b) internal pure returns (uint256) {
// Solidity only automatically asserts when dividing by 0
require(b > 0);
uint256 c = a / b;
// assert(a == b * c + a % b); // There is no case in which this doesn't hold
return c;
}
/**
* @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
*/
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
require(b <= a);
uint256 c = a - b;
return c;
}
/**
* @dev Adds two numbers, reverts on overflow.
*/
function add(uint256 a, uint256 b) internal pure returns (uint256) {
uint256 c = a + b;
require(c >= a);
return c;
}
/**
* @dev Divides two numbers and returns the remainder (unsigned integer modulo),
* reverts when dividing by zero.
*/
function mod(uint256 a, uint256 b) internal pure returns (uint256) {
require(b != 0);
return a % b;
}
}
//import "https://github.com/OpenZeppelin/openzeppelin-solidity/contracts/token/ERC20/ERC20Mintable.sol";
/**
* @title ERC20 interface
* @dev see https://github.com/ethereum/EIPs/issues/20
*/
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address who) external view returns (uint256);
function allowance(address owner, address spender) external view returns (uint256);
function transfer(address to, uint256 value) external returns (bool);
function approve(address spender, uint256 value) external returns (bool);
function transferFrom(address from, address to, uint256 value) external returns (bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(address indexed owner, address indexed spender, uint256 value);
}
/**
* @title Standard ERC20 token
*
* @dev Implementation of the basic standard token.
* https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
* Originally based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
*
* This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
* all accounts just by listening to said events. Note that this isn't required by the specification, and other
* compliant implementations may not do it.
*/
contract ERC20 is IERC20 {
using SafeMath for uint256;
mapping (address => uint256) private _balances;
mapping (address => mapping (address => uint256)) private _allowed;
uint256 private _totalSupply;
/**
* @dev Total number of tokens in existence
*/
function totalSupply() public view returns (uint256) {
return _totalSupply;
}
/**
* @dev Gets the balance of the specified address.
* @param owner The address to query the balance of.
* @return An uint256 representing the amount owned by the passed address.
*/
function balanceOf(address owner) public view returns (uint256) {
return _balances[owner];
}
/**
* @dev Function to check the amount of tokens that an owner allowed to a spender.
* @param owner address The address which owns the funds.
* @param spender address The address which will spend the funds.
* @return A uint256 specifying the amount of tokens still available for the spender.
*/
function allowance(address owner, address spender) public view returns (uint256) {
return _allowed[owner][spender];
}
/**
* @dev Transfer token for a specified address
* @param to The address to transfer to.
* @param value The amount to be transferred.
*/
function transfer(address to, uint256 value) public returns (bool) {
_transfer(msg.sender, to, value);
return true;
}
/**
* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
* Beware that changing an allowance with this method brings the risk that someone may use both the old
* and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
* race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
* @param spender The address which will spend the funds.
* @param value The amount of tokens to be spent.
*/
function approve(address spender, uint256 value) public returns (bool) {
require(spender != address(0));
_allowed[msg.sender][spender] = value;
emit Approval(msg.sender, spender, value);
return true;
}
/**
* @dev Transfer tokens from one address to another.
* Note that while this function emits an Approval event, this is not required as per the specification,
* and other compliant implementations may not emit the event.
* @param from address The address which you want to send tokens from
* @param to address The address which you want to transfer to
* @param value uint256 the amount of tokens to be transferred
*/
function transferFrom(address from, address to, uint256 value) public returns (bool) {
_allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
_transfer(from, to, value);
emit Approval(from, msg.sender, _allowed[from][msg.sender]);
return true;
}
/**
* @dev Increase the amount of tokens that an owner allowed to a spender.
* approve should be called when allowed_[_spender] == 0. To increment
* allowed value is better to use this function to avoid 2 calls (and wait until
* the first transaction is mined)
* From MonolithDAO Token.sol
* Emits an Approval event.
* @param spender The address which will spend the funds.
* @param addedValue The amount of tokens to increase the allowance by.
*/
function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
require(spender != address(0));
_allowed[msg.sender][spender] = _allowed[msg.sender][spender].add(addedValue);
emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
return true;
}
/**
* @dev Decrease the amount of tokens that an owner allowed to a spender.
* approve should be called when allowed_[_spender] == 0. To decrement
* allowed value is better to use this function to avoid 2 calls (and wait until
* the first transaction is mined)
* From MonolithDAO Token.sol
* Emits an Approval event.
* @param spender The address which will spend the funds.
* @param subtractedValue The amount of tokens to decrease the allowance by.
*/
function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
require(spender != address(0));
_allowed[msg.sender][spender] = _allowed[msg.sender][spender].sub(subtractedValue);
emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
return true;
}
/**
* @dev Transfer token for a specified addresses
* @param from The address to transfer from.
* @param to The address to transfer to.
* @param value The amount to be transferred.
*/
function _transfer(address from, address to, uint256 value) internal {
require(to != address(0));
_balances[from] = _balances[from].sub(value);
_balances[to] = _balances[to].add(value);
emit Transfer(from, to, value);
}
/**
* @dev Internal function that mints an amount of the token and assigns it to
* an account. This encapsulates the modification of balances such that the
* proper events are emitted.
* @param account The account that will receive the created tokens.
* @param value The amount that will be created.
*/
function _mint(address account, uint256 value) internal {
require(account != address(0));
_totalSupply = _totalSupply.add(value);
_balances[account] = _balances[account].add(value);
emit Transfer(address(0), account, value);
}
/**
* @dev Internal function that burns an amount of the token of a given
* account.
* @param account The account whose tokens will be burnt.
* @param value The amount that will be burnt.
*/
function _burn(address account, uint256 value) internal {
require(account != address(0));
_totalSupply = _totalSupply.sub(value);
_balances[account] = _balances[account].sub(value);
emit Transfer(account, address(0), value);
}
/**
* @dev Internal function that burns an amount of the token of a given
* account, deducting from the sender's allowance for said account. Uses the
* internal burn function.
* Emits an Approval event (reflecting the reduced allowance).
* @param account The account whose tokens will be burnt.
* @param value The amount that will be burnt.
*/
function _burnFrom(address account, uint256 value) internal {
_allowed[account][msg.sender] = _allowed[account][msg.sender].sub(value);
_burn(account, value);
emit Approval(account, msg.sender, _allowed[account][msg.sender]);
}
}
/**
* @title Roles
* @dev Library for managing addresses assigned to a Role.
*/
library Roles {
struct Role {
mapping (address => bool) bearer;
}
/**
* @dev give an account access to this role
*/
function add(Role storage role, address account) internal {
require(account != address(0));
require(!has(role, account));
role.bearer[account] = true;
}
/**
* @dev remove an account's access to this role
*/
function remove(Role storage role, address account) internal {
require(account != address(0));
require(has(role, account));
role.bearer[account] = false;
}
/**
* @dev check if an account has this role
* @return bool
*/
function has(Role storage role, address account) internal view returns (bool) {
require(account != address(0));
return role.bearer[account];
}
}
contract MinterRole {
using Roles for Roles.Role;
event MinterAdded(address indexed account);
event MinterRemoved(address indexed account);
Roles.Role private _minters;
constructor () internal {
_addMinter(msg.sender);
}
modifier onlyMinter() {
require(isMinter(msg.sender));
_;
}
function isMinter(address account) public view returns (bool) {
return _minters.has(account);
}
function addMinter(address account) public onlyMinter {
_addMinter(account);
}
function renounceMinter() public {
_removeMinter(msg.sender);
}
function _addMinter(address account) internal {
_minters.add(account);
emit MinterAdded(account);
}
function _removeMinter(address account) internal {
_minters.remove(account);
emit MinterRemoved(account);
}
}
/**
* @title ERC20Mintable
* @dev ERC20 minting logic
*/
contract ERC20Mintable is ERC20, MinterRole {
/**
* @dev Function to mint tokens
* @param to The address that will receive the minted tokens.
* @param value The amount of tokens to mint.
* @return A boolean that indicates if the operation was successful.
*/
function mint(address to, uint256 value) public onlyMinter returns (bool) {
_mint(to, value);
return true;
}
}
/**
* @title Crowdsale
* @dev Crowdsale is a base contract for managing a token crowdsale.
* Crowdsales have a start and end block, where investors can make
* token purchases and the crowdsale will assign them tokens based
* on a token per ETH rate. Funds collected are forwarded to a wallet
* as they arrive.
*/
contract Crowdsale {
using SafeMath for uint256;
// The token being sold
ERC20Mintable public token;
// start and end block where investments are allowed (both inclusive)
uint256 public startBlock;
uint256 public endBlock;
// address where funds are collected
address public wallet;
// how many token units a buyer gets per wei
uint256 public rate;
// amount of raised money in wei
uint256 public weiRaised;
/**
* event for token purchase logging
* @param purchaser who paid for the tokens
* @param beneficiary who got the tokens
* @param value weis paid for purchase
* @param amount amount of tokens purchased
*/
event TokenPurchase(address indexed purchaser, address indexed beneficiary, uint256 value, uint256 amount);
function Crowdsale(uint256 _startBlock, uint256 _endBlock, uint256 _rate, address _wallet) {
require(_startBlock >= block.number);
require(_endBlock >= _startBlock);
require(_rate > 0);
require(_wallet != 0x0);
token = createTokenContract();
startBlock = _startBlock;
endBlock = _endBlock;
rate = _rate;
wallet = _wallet;
}
// creates the token to be sold.
// override this method to have crowdsale of a specific mintable token.
function createTokenContract() internal returns (ERC20Mintable) {
return new ERC20Mintable();
}
// fallback function can be used to buy tokens
function () payable {
buyTokens(msg.sender);
}
// low level token purchase function
function buyTokens(address beneficiary) payable {
require(beneficiary != 0x0);
require(validPurchase());
uint256 weiAmount = msg.value;
// calculate token amount to be created
uint256 tokens = weiAmount.mul(rate);
// update state
weiRaised = weiRaised.add(weiAmount);
token.mint(beneficiary, tokens);
TokenPurchase(msg.sender, beneficiary, weiAmount, tokens);
forwardFunds();
}
// send ether to the fund collection wallet
// override to create custom fund forwarding mechanisms
function forwardFunds() internal {
wallet.transfer(msg.value);
}
// @return true if the transaction can buy tokens
function validPurchase() internal constant returns (bool) {
uint256 current = block.number;
bool withinPeriod = current >= startBlock && current <= endBlock;
bool nonZeroPurchase = msg.value != 0;
return withinPeriod && nonZeroPurchase;
}
// @return true if crowdsale event has ended
function hasEnded() public constant returns (bool) {
return block.number > endBlock;
}
}
/**
* @title CappedCrowdsale
* @dev Extension of Crowsdale with a max amount of funds raised
*/
contract CappedCrowdsale is Crowdsale {
using SafeMath for uint256;
uint256 public cap;
function CappedCrowdsale(uint256 _cap) {
require(_cap > 0);
cap = _cap;
}
// overriding Crowdsale#validPurchase to add extra cap logic
// @return true if investors can buy at the moment
function validPurchase() internal constant returns (bool) {
bool withinCap = weiRaised.add(msg.value) <= cap;
return super.validPurchase() && withinCap;
}
// overriding Crowdsale#hasEnded to add cap logic
// @return true if crowdsale event has ended
function hasEnded() public constant returns (bool) {
bool capReached = weiRaised >= cap;
return super.hasEnded() || capReached;
}
}
/**
* @title WhitelistedCrowdsale
* @dev Extension of Crowsdale with a whitelist of investors that
* can buy before the start block
*/
contract WhitelistedCrowdsale is Crowdsale {
using SafeMath for uint256;
mapping (address => bool) public whitelist;
function addToWhitelist(address addr) {
require(msg.sender != address(this));
whitelist[addr] = true;
}
// overriding Crowdsale#validPurchase to add extra whitelit logic
// @return true if investors can buy at the moment
function validPurchase() internal constant returns (bool) {
return super.validPurchase() || (whitelist[msg.sender] && !hasEnded());
}
}
contract MDTCrowdsale is CappedCrowdsale, WhitelistedCrowdsale {
function MDTCrowdsale()
CappedCrowdsale(50000000000000000000000)
Crowdsale(block.number, block.number + 100000, 1, msg.sender) { // Wallet is the contract creator, to whom funds will be sent
addToWhitelist(msg.sender);
addToWhitelist(0x0d5bda9db5dd36278c6a40683960ba58cac0149b);
addToWhitelist(0x1b6ddc637c24305b354d7c337f9126f68aad4886);
}
}
MDTCrowdsale.yaml
description: Incorrect inheritance order
issues:
- id: SWC-125
count: 1
locations:
- bytecode_offsets: {}
line_numbers:
MDTCrowdsale.sol: [162]