Improve nested path detection across app

ts/test/util/isPathInside_test.ts

@@ -0,0 +1,42 @@
+import { assert } from 'chai';
+
+import { isPathInside } from '../../util/isPathInside';
+
+describe('isPathInside', () => {
+  it('returns false if the child path is not inside the parent path', () => {
+    assert.isFalse(isPathInside('x', 'a/b'));
+    assert.isFalse(isPathInside('a/b', '/a/b'));
+    assert.isFalse(isPathInside('/a/b', 'a/b'));
+    assert.isFalse(isPathInside('/x', '/a/b'));
+    assert.isFalse(isPathInside('/x/y', '/a/b'));
+    assert.isFalse(isPathInside('/a/x', '/a/b'));
+    assert.isFalse(isPathInside('/a/bad', '/a/b'));
+    assert.isFalse(isPathInside('/a/x', '/a/b'));
+    assert.isFalse(isPathInside('/a/b', '/a/b'));
+    assert.isFalse(isPathInside('/a/b/c/..', '/a/b'));
+    assert.isFalse(isPathInside('/', '/'));
+    assert.isFalse(isPathInside('/x/..', '/'));
+
+    if (process.platform === 'win32') {
+      assert.isFalse(isPathInside('C:\\a\\x\\y', 'C:\\a\\b'));
+      assert.isFalse(isPathInside('D:\\a\\b\\c', 'C:\\a\\b'));
+    }
+  });
+
+  it('returns true if the child path is inside the parent path', () => {
+    assert.isTrue(isPathInside('a/b/c', 'a/b'));
+    assert.isTrue(isPathInside('a/b/c/d', 'a/b'));
+    assert.isTrue(isPathInside('/a/b/c', '/a/b'));
+    assert.isTrue(isPathInside('/a/b/c', '/a/b/'));
+    assert.isTrue(isPathInside('/a/b/c/', '/a/b'));
+    assert.isTrue(isPathInside('/a/b/c/', '/a/b/'));
+    assert.isTrue(isPathInside('/a/b/c/d', '/a/b'));
+    assert.isTrue(isPathInside('/a/b/c/d/..', '/a/b'));
+    assert.isTrue(isPathInside('/x/y/z/z/y', '/'));
+    assert.isTrue(isPathInside('x/y/z/z/y', '/'));
+
+    if (process.platform === 'win32') {
+      assert.isTrue(isPathInside('C:\\a\\b\\c', 'C:\\a\\b'));
+    }
+  });
+});

ts/updater/common.ts

@@ -26,6 +26,7 @@ import { Dialogs } from '../types/Dialogs';
 // @ts-ignore
 import * as packageJson from '../../package.json';
 import { getSignatureFileName } from './signature';
+import { isPathInside } from '../util/isPathInside';
 
 import { LocaleType } from '../types/I18N';
 import { LoggerType } from '../types/Logging';
@@ -71,7 +72,7 @@ export async function checkForUpdates(
 export function validatePath(basePath: string, targetPath: string) {
   const normalized = normalize(targetPath);
 
-  if (!normalized.startsWith(basePath)) {
+  if (!isPathInside(normalized, basePath)) {
     throw new Error(
       `validatePath: Path ${normalized} is not under base path ${basePath}`
     );
@@ -352,7 +353,7 @@ export async function deleteTempDir(targetDir: string) {
   }
 
   const baseTempDir = getBaseTempDir();
-  if (!targetDir.startsWith(baseTempDir)) {
+  if (!isPathInside(targetDir, baseTempDir)) {
     throw new Error(
       `deleteTempDir: Cannot delete path '${targetDir}' since it is not within base temp dir`
     );

ts/util/isPathInside.ts

@@ -0,0 +1,16 @@
+// This is inspired by the `is-path-inside` module on npm.
+import * as path from 'path';
+
+export function isPathInside(childPath: string, parentPath: string): boolean {
+  const childPathResolved = path.resolve(childPath);
+
+  let parentPathResolved = path.resolve(parentPath);
+  if (!parentPathResolved.endsWith(path.sep)) {
+    parentPathResolved += path.sep;
+  }
+
+  return (
+    childPathResolved !== parentPathResolved &&
+    childPathResolved.startsWith(parentPathResolved)
+  );
+}