permission: fix Uint8Array path traversal

Previous security patches addressed path traversal vulnerabilities for
string and Buffer inputs, but ignored Uint8Array inputs. This commit
fixes the existing logic to account for the latter.

The previous implementation would silently ignore unexpected inputs,
whereas this commit introduces an explicit assertion to prevent that
unsafe behavior.

PR-URL: nodejs-private/node-private#456
Reviewed-By: Rafael Gonzaga <[email protected]>
CVE-ID: CVE-2023-39332

Author: tniessen

lib/internal/fs/utils.js

@@ -22,6 +22,7 @@ const {
   Symbol,
   TypedArrayPrototypeAt,
   TypedArrayPrototypeIncludes,
+  uncurryThis,
 } = primordials;
 
 const permission = require('internal/process/permission');
@@ -709,13 +710,16 @@ const validatePath = hideStackFrames((path, propName = 'path') => {
 // See: https://github.com/nodejs/node/pull/44004#discussion_r930958420
 // The permission model needs the absolute path for the fs_permission
 const resolvePath = pathModule.resolve;
+const { isBuffer: BufferIsBuffer, from: BufferFrom } = Buffer;
+const BufferToString = uncurryThis(Buffer.prototype.toString);
 function possiblyTransformPath(path) {
   if (permission.isEnabled()) {
     if (typeof path === 'string') {
       return resolvePath(path);
-    } else if (Buffer.isBuffer(path)) {
-      return Buffer.from(resolvePath(path.toString()));
     }
+    assert(isUint8Array(path));
+    if (!BufferIsBuffer(path)) path = BufferFrom(path);
+    return BufferFrom(resolvePath(BufferToString(path)));
   }
   return path;
 }

test/fixtures/permission/fs-traversal.js

@@ -15,6 +15,7 @@ const allowedFolder = process.env.ALLOWEDFOLDER;
 const traversalPath = allowedFolder + '../file.md';
 const traversalFolderPath = allowedFolder + '../folder';
 const bufferTraversalPath = Buffer.from(allowedFolder + '../file.md');
+const uint8ArrayTraversalPath = new TextEncoder().encode(traversalPath);
 
 {
   assert.ok(process.permission.has('fs.read', allowedFolder));
@@ -83,6 +84,18 @@ const bufferTraversalPath = Buffer.from(allowedFolder + '../file.md');
   }));
 }
 
+{
+  assert.throws(() => {
+    fs.readFile(uint8ArrayTraversalPath, (error) => {
+      assert.ifError(error);
+    });
+  }, common.expectsError({
+    code: 'ERR_ACCESS_DENIED',
+    permission: 'FileSystemRead',
+    resource: resolve(traversalPath),
+  }));
+}
+
 {
   assert.ok(!process.permission.has('fs.read', traversalPath));
   assert.ok(!process.permission.has('fs.write', traversalPath));