Add proxy for ethereum global (MetaMask#1087)

* Add proxy for ethereum global * Test access to ethereum public props
ShadowCloud01 · Dec 19, 2022 · ddffcf5 · ddffcf5
1 parent 8966739
commit ddffcf5
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Showing 3 changed files with 124 additions and 6 deletions.
diff --git a/packages/snaps-execution-environments/jest.config.js b/packages/snaps-execution-environments/jest.config.js
@@ -6,10 +6,10 @@ module.exports = deepmerge(baseConfig, {
   coveragePathIgnorePatterns: ['./src/index.ts', '.ava.test.ts'],
   coverageThreshold: {
     global: {
-      branches: 83.68,
-      functions: 92.19,
-      lines: 87.11,
-      statements: 87.22,
+      branches: 83.93,
+      functions: 92.25,
+      lines: 87.07,
+      statements: 87.18,
     },
   },
   testEnvironment: '<rootDir>/jest.environment.js',

diff --git a/packages/snaps-execution-environments/src/common/BaseSnapExecutor.test.ts b/packages/snaps-execution-environments/src/common/BaseSnapExecutor.test.ts
@@ -642,6 +642,111 @@ describe('BaseSnapExecutor', () => {
     });
   });
 
+  it('allows direct access to ethereum public properties', async () => {
+    const CODE = `
+      module.exports.onRpcRequest = () => {
+        const listener = () => undefined;
+        ethereum.on('accountsChanged', listener);
+        ethereum.removeListener('accountsChanged', listener);
+        return ethereum.request({ method: 'eth_blockNumber', params: [] }) };
+    `;
+    const executor = new TestSnapExecutor();
+
+    await executor.executeSnap(1, FAKE_SNAP_NAME, CODE, ['ethereum']);
+
+    expect(await executor.readCommand()).toStrictEqual({
+      jsonrpc: '2.0',
+      id: 1,
+      result: 'OK',
+    });
+
+    await executor.writeCommand({
+      jsonrpc: '2.0',
+      id: 2,
+      method: 'snapRpc',
+      params: [
+        FAKE_SNAP_NAME,
+        ON_RPC_REQUEST,
+        FAKE_ORIGIN,
+        { jsonrpc: '2.0', method: '', params: [] },
+      ],
+    });
+
+    expect(await executor.readCommand()).toStrictEqual({
+      jsonrpc: '2.0',
+      method: 'OutboundRequest',
+    });
+
+    const blockNumRequest = await executor.readRpc();
+    expect(blockNumRequest).toStrictEqual({
+      name: 'metamask-provider',
+      data: {
+        id: expect.any(Number),
+        jsonrpc: '2.0',
+        method: 'eth_blockNumber',
+        params: [],
+      },
+    });
+
+    await executor.writeRpc({
+      name: 'metamask-provider',
+      data: {
+        jsonrpc: '2.0',
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        id: blockNumRequest.data.id!,
+        result: '0xa70e77',
+      },
+    });
+
+    expect(await executor.readCommand()).toStrictEqual({
+      jsonrpc: '2.0',
+      method: 'OutboundResponse',
+    });
+
+    expect(await executor.readCommand()).toStrictEqual({
+      id: 2,
+      jsonrpc: '2.0',
+      result: '0xa70e77',
+    });
+  });
+
+  it("doesn't allow direct access to ethereum internals", async () => {
+    const CODE = `
+      module.exports.onRpcRequest = () => ethereum._rpcEngine.handle({ method: 'snap_confirm', params: [] });
+    `;
+    const executor = new TestSnapExecutor();
+
+    await executor.executeSnap(1, FAKE_SNAP_NAME, CODE, ['ethereum']);
+
+    expect(await executor.readCommand()).toStrictEqual({
+      jsonrpc: '2.0',
+      id: 1,
+      result: 'OK',
+    });
+
+    await executor.writeCommand({
+      jsonrpc: '2.0',
+      id: 2,
+      method: 'snapRpc',
+      params: [
+        FAKE_SNAP_NAME,
+        ON_RPC_REQUEST,
+        FAKE_ORIGIN,
+        { jsonrpc: '2.0', method: '', params: [] },
+      ],
+    });
+
+    expect(await executor.readCommand()).toStrictEqual({
+      jsonrpc: '2.0',
+      error: {
+        code: -32603,
+        message: "Cannot read properties of undefined (reading 'handle')",
+        data: expect.any(Object),
+      },
+      id: 2,
+    });
+  });
+
   it('only allows certain methods in snap API', async () => {
     const CODE = `
       module.exports.onRpcRequest = () => snap.request({ method: 'eth_blockNumber', params: [] });

diff --git a/packages/snaps-execution-environments/src/common/BaseSnapExecutor.ts b/packages/snaps-execution-environments/src/common/BaseSnapExecutor.ts
@@ -411,7 +411,7 @@ export class BaseSnapExecutor {
   private createEIP1193Provider(provider: StreamProvider): StreamProvider {
     const originalRequest = provider.request.bind(provider);
 
-    provider.request = async (args) => {
+    const request = async (args: RequestArguments) => {
       assert(
         !args.method.startsWith('snap_'),
         ethErrors.rpc.methodNotFound({
@@ -428,7 +428,20 @@ export class BaseSnapExecutor {
       }
     };
 
-    return provider;
+    // To harden and limit access to internals, we use a proxy.
+    const proxy = new Proxy(provider, {
+      get(target, prop: keyof StreamProvider) {
+        if (prop === 'request') {
+          return request;
+        } else if (['on', 'removeListener'].includes(prop)) {
+          return target[prop];
+        }
+
+        return undefined;
+      },
+    });
+
+    return proxy;
   }
 
   /**