Merge pull request #252 from euler-xyz/test-stealth-donation

LEND-184/Test stealth donation

test/unit/evault/modules/Vault/deposit.t.sol

@@ -11,6 +11,8 @@ import {IEVC} from "ethereum-vault-connector/interfaces/IEthereumVaultConnector.
 
 import "../../../../../src/EVault/shared/types/Types.sol";
 
+import "forge-std/Test.sol";
+
 contract VaultTest_Deposit is EVaultTestBase {
     using TypesLib for uint256;
 
@@ -32,11 +34,11 @@ contract VaultTest_Deposit is EVaultTestBase {
         user = vm.addr(userPK);
         user1 = makeAddr("user1");
 
-        assetTST.mint(user1, type(uint256).max);
+        assetTST.mint(user1, type(uint256).max / 4);
         hoax(user1);
         assetTST.approve(address(eTST), type(uint256).max);
 
-        assetTST.mint(user, type(uint256).max);
+        assetTST.mint(user, type(uint256).max / 4);
         startHoax(user);
         assetTST.approve(address(eTST), type(uint256).max);
     }
@@ -368,4 +370,63 @@ contract VaultTest_Deposit is EVaultTestBase {
         assertEq(eTST.totalSupply(), 2 * amount);
         assertEq(eTST.totalAssets(), 2 * amount);
     }
+
+    function test_deposit_stealthDonation() public {
+        startHoax(address(this));
+        oracle.setPrice(address(assetTST), unitOfAccount, 1e18);
+        oracle.setPrice(address(assetTST2), unitOfAccount, 1e18);
+        eTST.setLTV(address(eTST2), 0.9e4, 0.9e4, 0);
+
+        startHoax(user1);
+        assetTST.mint(user1, 10e18);
+        assetTST.approve(address(eTST), type(uint256).max);
+        assetTST2.mint(user1, 100e18);
+        assetTST2.approve(address(eTST2), type(uint256).max);
+        eTST2.deposit(10e18, user1);
+        evc.enableController(user1, address(eTST));
+        evc.enableCollateral(user1, address(eTST2));
+
+        // attacker deposits 1 wei from one account
+        startHoax(user);
+        eTST.deposit(1, user);
+
+        // borrows it from a second for 1 second
+        startHoax(user1);
+        eTST.borrow(1, user1);
+        skip(1);
+
+        // 1 wei of debt accrued
+        assertEq(eTST.debtOf(user1), 2);
+        eTST.repay(type(uint256).max, user1);
+        eTST.disableController();
+
+        // and exchange rate is pushed above 1
+        assertEq(1.000000999999e18, eTST.convertToAssets(1e18)); // ~= 1.000001
+
+        assertEq(eTST.totalAssets(), 2); // 1 deposited + 1 interest repaid
+        assertEq(eTST.cash(), 2);
+        assertEq(eTST.totalSupply(), 1); // 1 deposited initially
+
+        // in a loop deposit max assets to create 1 share but not enough for 2. The rounding remainder is a stealth
+        // donation
+        for (uint256 i; i < 1000; i++) {
+            eTST.deposit(2, user1);
+            // 2 were deposited, but they round down to 1 share
+            assertEq(eTST.balanceOf(user1), 1);
+            // which is redeemable for 1 asset, the rest is donated
+            assertEq(eTST.maxWithdraw(user1), 1);
+
+            // reset account
+            eTST.withdraw(1, user1, user1);
+            assertEq(eTST.balanceOf(user1), 0);
+        }
+
+        // after 1000 iterations, 1000 assets were stealth donated
+        assertEq(eTST.totalAssets(), 1002);
+        assertEq(eTST.cash(), 1002);
+        assertEq(eTST.totalSupply(), 1);
+
+        // it will take 1e6 loops to reach exchange rate of 2
+        assertEq(1.001000998999001e18, eTST.convertToAssets(1e18)); // ~= 1.001
+    }
 }