fix contract

contracts/ytLending/Lending.sol

@@ -543,8 +543,9 @@ contract Lending is
 
     function getBalance(address account) external view override returns (int256) {
         int104 principal = userBasic[account].principal;
-        // 使用 supplyIndex 计算实际余额（含利息）
-        return LendingMath.principalToBalance(principal, supplyIndex);
+        // 根据余额正负使用对应的索引：正余额用supplyIndex，负余额用borrowIndex
+        uint256 index = principal >= 0 ? supplyIndex : borrowIndex;
+        return LendingMath.principalToBalance(principal, index);
     }
     
     function supplyBalanceOf(address account) external view override returns (uint256) {

contracts/ytLending/LendingPriceFeed.sol

@@ -9,10 +9,14 @@ import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/shared/interf
 contract LendingPriceFeed is OwnableUpgradeable, UUPSUpgradeable {
     address public usdcAddress;
     AggregatorV3Interface internal usdcPriceFeed;
+    
+    /// @notice 价格过期阈值（秒）
+    uint256 public priceStalenesThreshold;
 
     error InvalidUsdcAddress();
     error InvalidUsdcPriceFeedAddress();
     error InvalidChainlinkPrice();
+    error StalePrice();
 
     /// @custom:oz-upgrades-unsafe-allow constructor
     constructor() {
@@ -26,6 +30,7 @@ contract LendingPriceFeed is OwnableUpgradeable, UUPSUpgradeable {
         if (_usdcPriceFeed == address(0)) revert InvalidUsdcPriceFeedAddress();
         usdcAddress = _usdcAddress;   
         usdcPriceFeed = AggregatorV3Interface(_usdcPriceFeed);
+        priceStalenesThreshold = 3600; // 默认1小时
     }
 
     function _authorizeUpgrade(address newImplementation) internal override onlyOwner {}
@@ -35,6 +40,15 @@ contract LendingPriceFeed is OwnableUpgradeable, UUPSUpgradeable {
         usdcAddress = _usdcAddress;
     }
     
+    /**
+     * @notice 设置价格过期阈值
+     * @param _threshold 阈值（秒），例如：3600 = 1小时，86400 = 24小时
+     */
+    function setPriceStalenessThreshold(uint256 _threshold) external onlyOwner {
+        require(_threshold > 0 && _threshold <= 7 days, "Invalid threshold");
+        priceStalenesThreshold = _threshold;
+    }
+    
     function getPrice(address _token) external view returns (uint256) {
         if (_token == usdcAddress) {
             return _getUSDCPrice();
@@ -44,15 +58,21 @@ contract LendingPriceFeed is OwnableUpgradeable, UUPSUpgradeable {
 
     function _getUSDCPrice() internal view returns (uint256) {
         (
-            /* uint80 roundId */,
+            uint80 roundId,
             int256 price,
             /* uint256 startedAt */,
-            /* uint256 updatedAt */,
-            /* uint80 answeredInRound */
+            uint256 updatedAt,
+            uint80 answeredInRound
         ) = usdcPriceFeed.latestRoundData();
         
+        // 价格有效性检查
         if (price <= 0) revert InvalidChainlinkPrice();
         
+        // 新鲜度检查：确保价格数据不过期
+        if (updatedAt == 0) revert StalePrice();
+        if (answeredInRound < roundId) revert StalePrice();
+        if (block.timestamp - updatedAt > priceStalenesThreshold) revert StalePrice();
+        
         return uint256(price) * 1e22; // 1e22 = 10^(30-8)
     }
 }