reject path traversal in files.read and files.ls (T-78)

Both handlers concatenated the request path onto the workspace root without validating containment, letting `path: "../../../etc/passwd"` escape the workspace. resolveUnderRoot normalizes the path and checks containment under root.absolute.path before any filesystem access. Co-Authored-By: Claude <noreply@anthropic.com>
2026-05-05 15:02:30 +02:00
parent b99548a900
commit 816e60d028
5 changed files with 148 additions and 4 deletions
@@ -0,0 +1,51 @@
+/// Workspace-relative path validation. Rejects paths that resolve
+/// outside the workspace root (path traversal via `..`, absolute
+/// paths, symlink-out attempts).
+library;
+
+import 'dart:io';
+
+class PathOutsideRoot implements Exception {
+  PathOutsideRoot(this.requested, this.resolved, this.root);
+  final String requested;
+  final String resolved;
+  final String root;
+
+  @override
+  String toString() => 'path outside workspace root: $requested → $resolved (root: $root)';
+}
+
+/// Resolve [relative] against [root] and verify the result is
+/// contained within [root]. Returns the absolute, normalized path.
+/// Throws [PathOutsideRoot] on traversal attempts.
+String resolveUnderRoot(Directory root, String relative) {
+  final rootPath = _normalize(root.absolute.path);
+  final joined = _normalize('$rootPath${Platform.pathSeparator}$relative');
+
+  // Containment check: joined must equal rootPath, or start with
+  // rootPath + separator. Equality covers `relative == ''` (the
+  // root itself); the separator check prevents `/repo` matching
+  // `/repository`.
+  if (joined != rootPath && !joined.startsWith('$rootPath${Platform.pathSeparator}')) {
+    throw PathOutsideRoot(relative, joined, rootPath);
+  }
+  return joined;
+}
+
+String _normalize(String path) {
+  // Use Uri to collapse `..` and `.` segments without hitting the
+  // filesystem (Directory(...).resolveSymbolicLinksSync would also
+  // resolve symlinks, which we don't want here — symlink handling
+  // belongs at the filesystem-access layer, not the path layer).
+  final segments = <String>[];
+  for (final raw in path.split(Platform.pathSeparator)) {
+    if (raw.isEmpty || raw == '.') continue;
+    if (raw == '..') {
+      if (segments.isNotEmpty) segments.removeLast();
+      continue;
+    }
+    segments.add(raw);
+  }
+  final prefix = path.startsWith(Platform.pathSeparator) ? Platform.pathSeparator : '';
+  return '$prefix${segments.join(Platform.pathSeparator)}';
+}