fix(security): bound vault and asset decimals to MAX_DECIMALS (closes #84)

src/generated/ERC4626Words.pointers.sol

@@ -10,7 +10,7 @@ pragma solidity ^0.8.25;
 // file needs the contract to exist so that it can be compiled.
 
 /// @dev Hash of the known bytecode.
-bytes32 constant BYTECODE_HASH = bytes32(0x9905f7f79bbbbea0cde049efb56d1aed955479c30db2ee9b6eeae543e3b33bfb);
+bytes32 constant BYTECODE_HASH = bytes32(0x742585ed2b4e04325a26604e90eabd1cbe7552a83e9ccec3d894bfce1ae1fcbf);
 
 /// @dev The hash of the meta that describes the contract.
 bytes32 constant DESCRIBED_BY_META_HASH = bytes32(0xdde475220ea06da58884f3f7abbfc091637e02cb924b8b9a8a9d20dbd4ae703a);

src/lib/erc4626/LibERC4626.sol

@@ -19,6 +19,16 @@ interface IERC20MetadataMinimal {
     function decimals() external view returns (uint8);
 }
 
+/// @dev Upper bound on decimals accepted from vault and asset contracts. Values
+/// above this would cause toFixedDecimalLossless to overflow uint256 for any
+/// non-trivial Float, enabling denial-of-service by a malicious vault.
+uint8 constant MAX_DECIMALS = 36;
+
+/// Thrown when a vault or asset reports more decimals than MAX_DECIMALS.
+/// @param token The vault or asset address that reported the excessive decimals.
+/// @param decimals The reported decimals value.
+error UnsupportedDecimals(address token, uint8 decimals);
+
 /// @title LibERC4626
 /// @notice Core library for interacting with ERC-4626 tokenised vaults on-chain.
 /// Takes the vault as a typed contract reference and handles conversion of the
@@ -28,12 +38,16 @@ library LibERC4626 {
     /// Reads the share and underlying-asset decimal scales from the vault:
     /// vault.decimals() then vault.asset() then assetToken.decimals(), giving
     /// both conversion functions a single, symmetric read path.
+    /// Reverts with UnsupportedDecimals if either reported value exceeds MAX_DECIMALS.
     /// @param vault The ERC-4626 vault contract.
     /// @return shareDecimals The decimal precision of the vault share token.
     /// @return assetDecimals The decimal precision of the underlying asset token.
     function _vaultScales(IERC4626Minimal vault) private view returns (uint8 shareDecimals, uint8 assetDecimals) {
         shareDecimals = vault.decimals();
-        assetDecimals = IERC20MetadataMinimal(vault.asset()).decimals();
+        if (shareDecimals > MAX_DECIMALS) revert UnsupportedDecimals(address(vault), shareDecimals);
+        address assetAddr = vault.asset();
+        assetDecimals = IERC20MetadataMinimal(assetAddr).decimals();
+        if (assetDecimals > MAX_DECIMALS) revert UnsupportedDecimals(assetAddr, assetDecimals);
     }
 
     /// @notice Converts vault shares to underlying assets via ERC-4626 convertToAssets.

test/src/lib/erc4626/LibERC4626.t.sol

@@ -3,10 +3,11 @@
 pragma solidity =0.8.25;
 
 import {Test} from "forge-std-1.16.1/src/Test.sol";
-import {LibERC4626, IERC4626Minimal} from "../../../../src/lib/erc4626/LibERC4626.sol";
+import {LibERC4626, IERC4626Minimal, UnsupportedDecimals} from "../../../../src/lib/erc4626/LibERC4626.sol";
 import {LibDecimalFloat, Float} from "rain-math-float-0.1.1/src/lib/LibDecimalFloat.sol";
 import {MockERC4626} from "../../../utils/MockERC4626.sol";
 import {MockERC20} from "../../../utils/MockERC20.sol";
+import {MaliciousERC4626} from "../../../utils/MaliciousERC4626.sol";
 
 contract LibERC4626Test is Test {
     MockERC20 internal asset;
@@ -196,6 +197,48 @@ contract LibERC4626Test is Test {
         assertEq(LibDecimalFloat.toFixedDecimalLossless(sharesFloat, 18), 0, "0 assets must yield 0 shares");
     }
 
+    /// A vault reporting decimals() > MAX_DECIMALS must revert UnsupportedDecimals
+    /// for convertToAssets. Mutation: remove the shareDecimals guard → expectRevert fails.
+    function testShareDecimalsAboveMaxRevertsConvertToAssets() external {
+        MaliciousERC4626 malVault = new MaliciousERC4626(255, address(asset));
+        Float sharesFloat = LibDecimalFloat.packLossless(1, 0);
+
+        vm.expectRevert(abi.encodeWithSelector(UnsupportedDecimals.selector, address(malVault), uint8(255)));
+        this._convertToAssets(IERC4626Minimal(address(malVault)), sharesFloat);
+    }
+
+    /// A vault reporting decimals() > MAX_DECIMALS must revert UnsupportedDecimals
+    /// for convertToShares. Mutation: remove the shareDecimals guard → expectRevert fails.
+    function testShareDecimalsAboveMaxRevertsConvertToShares() external {
+        MaliciousERC4626 malVault = new MaliciousERC4626(255, address(asset));
+        Float assetsFloat = LibDecimalFloat.packLossless(1, 0);
+
+        vm.expectRevert(abi.encodeWithSelector(UnsupportedDecimals.selector, address(malVault), uint8(255)));
+        this._convertToShares(IERC4626Minimal(address(malVault)), assetsFloat);
+    }
+
+    /// An asset reporting decimals() > MAX_DECIMALS must revert UnsupportedDecimals
+    /// for convertToAssets. Mutation: remove the assetDecimals guard → expectRevert fails.
+    function testAssetDecimalsAboveMaxRevertsConvertToAssets() external {
+        MockERC20 malAsset = new MockERC20(255);
+        MockERC4626 normalVault = new MockERC4626(18, address(malAsset), 1e18);
+        Float sharesFloat = LibDecimalFloat.packLossless(1, 0);
+
+        vm.expectRevert(abi.encodeWithSelector(UnsupportedDecimals.selector, address(malAsset), uint8(255)));
+        this._convertToAssets(IERC4626Minimal(address(normalVault)), sharesFloat);
+    }
+
+    /// An asset reporting decimals() > MAX_DECIMALS must revert UnsupportedDecimals
+    /// for convertToShares. Mutation: remove the assetDecimals guard → expectRevert fails.
+    function testAssetDecimalsAboveMaxRevertsConvertToShares() external {
+        MockERC20 malAsset = new MockERC20(255);
+        MockERC4626 normalVault = new MockERC4626(18, address(malAsset), 1e18);
+        Float assetsFloat = LibDecimalFloat.packLossless(1, 0);
+
+        vm.expectRevert(abi.encodeWithSelector(UnsupportedDecimals.selector, address(malAsset), uint8(255)));
+        this._convertToShares(IERC4626Minimal(address(normalVault)), assetsFloat);
+    }
+
     function testConvertToAssetsLargeInput() external view {
         IERC4626Minimal typedVault = IERC4626Minimal(address(vault));
         // 1e9 whole shares: well within int64 range, exercises large fixed-point packing.