【智能合约审计】———

合约地址：https://etherscan.io/address/0x80fB784B7eD66730e8b1DBd9820aFD29931aab03#code

pragma solidity ^0.4.16;contract SafeMath {function safeMul(uint a, uint b) internal returns (uint) {uint c = a * b;assert(a == 0 || c / a == b);return c;}function safeSub(uint a, uint b) internal returns (uint) {assert(b <= a);return a - b;}function safeAdd(uint a, uint b) internal returns (uint) {uint c = a + b;assert(c>=a && c>=b);return c;}
}// Standard token interface (ERC 20)
// https://github.com/ethereum/EIPs/issues/20
contract Token is SafeMath {// Functions:/// @return total amount of tokensfunction totalSupply() constant returns (uint256 supply);/// @param _owner The address from which the balance will be retrieved/// @return The balancefunction balanceOf(address _owner) constant returns (uint256 balance);/// @notice send `_value` token to `_to` from `msg.sender`/// @param _to The address of the recipient/// @param _value The amount of token to be transferredfunction transfer(address _to, uint256 _value) returns(bool);/// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`/// @param _from The address of the sender/// @param _to The address of the recipient/// @param _value The amount of token to be transferred/// @return Whether the transfer was successful or notfunction transferFrom(address _from, address _to, uint256 _value) returns(bool);/// @notice `msg.sender` approves `_addr` to spend `_value` tokens/// @param _spender The address of the account able to transfer the tokens/// @param _value The amount of wei to be approved for transfer/// @return Whether the approval was successful or notfunction approve(address _spender, uint256 _value) returns (bool success);/// @param _owner The address of the account owning tokens/// @param _spender The address of the account able to transfer the tokens/// @return Amount of remaining tokens allowed to spentfunction allowance(address _owner, address _spender) constant returns (uint256 remaining);// Events:event Transfer(address indexed _from, address indexed _to, uint256 _value);event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}contract StdToken is Token {// Fields:mapping(address => uint256) balances;mapping (address => mapping (address => uint256)) allowed;uint public supply = 0;// Functions:function transfer(address _to, uint256 _value) returns(bool) {require(balances[msg.sender] >= _value);require(balances[_to] + _value > balances[_to]);balances[msg.sender] = safeSub(balances[msg.sender],_value);balances[_to] = safeAdd(balances[_to],_value);Transfer(msg.sender, _to, _value);return true;}function transferFrom(address _from, address _to, uint256 _value) returns(bool){require(balances[_from] >= _value);require(allowed[_from][msg.sender] >= _value);require(balances[_to] + _value > balances[_to]);balances[_to] = safeAdd(balances[_to],_value);balances[_from] = safeSub(balances[_from],_value);allowed[_from][msg.sender] = safeSub(allowed[_from][msg.sender],_value);Transfer(_from, _to, _value);return true;}function totalSupply() constant returns (uint256) {return supply;}function balanceOf(address _owner) constant returns (uint256) {return balances[_owner];}function approve(address _spender, uint256 _value) returns (bool) {// To change the approve amount you first have to reduce the addresses`//  allowance to zero by calling `approve(_spender, 0)` if it is not//  already 0 to mitigate the race condition described here://  https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729require((_value == 0) || (allowed[msg.sender][_spender] == 0));allowed[msg.sender][_spender] = _value;Approval(msg.sender, _spender, _value);return true;}function allowance(address _owner, address _spender) constant returns (uint256) {return allowed[_owner][_spender];}
}contract EthLendToken is StdToken
{
/// Fields:string public constant name = "EthLend Token";string public constant symbol = "LEND";uint public constant decimals = 18;// this includes DEVELOPERS_BONUSuint public constant TOTAL_SUPPLY = 1300000000 * (1 ether / 1 wei);uint public constant DEVELOPERS_BONUS = 300000000 * (1 ether / 1 wei);uint public constant PRESALE_PRICE = 30000;  // per 1 Etheruint public constant PRESALE_MAX_ETH = 2000;// 60 mln tokens sold during presaleuint public constant PRESALE_TOKEN_SUPPLY_LIMIT = PRESALE_PRICE * PRESALE_MAX_ETH * (1 ether / 1 wei);uint public constant ICO_PRICE1 = 27500;     // per 1 Etheruint public constant ICO_PRICE2 = 26250;     // per 1 Etheruint public constant ICO_PRICE3 = 25000;     // per 1 Ether// 1bln - this includes presale tokensuint public constant TOTAL_SOLD_TOKEN_SUPPLY_LIMIT = 1000000000* (1 ether / 1 wei);enum State{Init,Paused,PresaleRunning,PresaleFinished,ICORunning,ICOFinished}State public currentState = State.Init;bool public enableTransfers = false;address public teamTokenBonus = 0;// Gathered funds can be withdrawn only to escrow's address.address public escrow = 0;// Token manager has exclusive priveleges to call administrative// functions on this contract.address public tokenManager = 0;uint public presaleSoldTokens = 0;uint public icoSoldTokens = 0;uint public totalSoldTokens = 0;/// Modifiers:modifier onlyTokenManager(){require(msg.sender==tokenManager); _; }modifier onlyInState(State state){require(state==currentState); _; }/// Events:event LogBuy(address indexed owner, uint value);event LogBurn(address indexed owner, uint value);/// Functions:/// @dev Constructor/// @param _tokenManager Token manager address.function EthLendToken(address _tokenManager, address _escrow, address _teamTokenBonus) {tokenManager = _tokenManager;teamTokenBonus = _teamTokenBonus;escrow = _escrow;// send team bonus immediatelyuint teamBonus = DEVELOPERS_BONUS;balances[_teamTokenBonus] += teamBonus;supply+= teamBonus;assert(PRESALE_TOKEN_SUPPLY_LIMIT==60000000 * (1 ether / 1 wei));assert(TOTAL_SOLD_TOKEN_SUPPLY_LIMIT==1000000000 * (1 ether / 1 wei));}function buyTokens() public payable{require(currentState==State.PresaleRunning || currentState==State.ICORunning);if(currentState==State.PresaleRunning){return buyTokensPresale();}else{return buyTokensICO();}}function buyTokensPresale() public payable onlyInState(State.PresaleRunning){// min - 1 ETHrequire(msg.value >= (1 ether / 1 wei));uint newTokens = msg.value * PRESALE_PRICE;require(presaleSoldTokens + newTokens <= PRESALE_TOKEN_SUPPLY_LIMIT);balances[msg.sender] += newTokens;supply+= newTokens;presaleSoldTokens+= newTokens;totalSoldTokens+= newTokens;LogBuy(msg.sender, newTokens);}function buyTokensICO() public payable onlyInState(State.ICORunning){// min - 0.01 ETHrequire(msg.value >= ((1 ether / 1 wei) / 100));uint newTokens = msg.value * getPrice();require(totalSoldTokens + newTokens <= TOTAL_SOLD_TOKEN_SUPPLY_LIMIT);balances[msg.sender] += newTokens;supply+= newTokens;icoSoldTokens+= newTokens;totalSoldTokens+= newTokens;LogBuy(msg.sender, newTokens);}function getPrice()constant returns(uint){if(currentState==State.ICORunning){if(icoSoldTokens<(200000000 * (1 ether / 1 wei))){return ICO_PRICE1;}if(icoSoldTokens<(300000000 * (1 ether / 1 wei))){return ICO_PRICE2;}return ICO_PRICE3;}else{return PRESALE_PRICE;}}function setState(State _nextState) public onlyTokenManager{//setState() method call shouldn't be entertained after ICOFinishedrequire(currentState != State.ICOFinished);currentState = _nextState;// enable/disable transfers//enable transfers only after ICOFinished, disable otherwiseenableTransfers = (currentState==State.ICOFinished);}function withdrawEther() public onlyTokenManager{if(this.balance > 0) {require(escrow.send(this.balance));}}/// Overrides:function transfer(address _to, uint256 _value) returns(bool){require(enableTransfers);return super.transfer(_to,_value);}function transferFrom(address _from, address _to, uint256 _value) returns(bool){require(enableTransfers);return super.transferFrom(_from,_to,_value);}function approve(address _spender, uint256 _value) returns (bool) {require(enableTransfers);return super.approve(_spender,_value);}/// Setters/gettersfunction setTokenManager(address _mgr) public onlyTokenManager{tokenManager = _mgr;}// Default fallback functionfunction() payable {buyTokens();}
}

问题：

概述：买家如果拥有足够多的ETH，可以通过发送大量token制造溢出，从而绕过ICO发币上限，达到超额购币。

漏洞攻击效果：调用者绕过合约中规定ICO的token容量上限，获得了超额购币；

漏洞原理：一个极大的_newTokens可以使得算数加法运算totalSoldTokens + newTokens发生整数溢出，变为一个极小值，从而绕过L236的检测。

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