fix path resolution for writeFile in nodefs

src/bun.js/node/node_fs.zig

@@ -5336,58 +5336,12 @@ pub const NodeFS = struct {
     }
 
     pub fn writeFileWithPathBuffer(pathbuf: *[bun.MAX_PATH_BYTES]u8, args: Arguments.WriteFile) Maybe(Return.WriteFile) {
-        var path: [:0]const u8 = undefined;
-        var pathbuf2: [bun.MAX_PATH_BYTES]u8 = undefined;
-
         const fd = switch (args.file) {
             .path => brk: {
-                // On Windows, we potentially mutate the path in posixToPlatformInPlace
-                // We cannot mutate JavaScript strings in-place. That will break many things.
-                // So we must always copy the path string on Windows.
-                path = path: {
-                    const temp_path = args.file.path.sliceZWithForceCopy(pathbuf, Environment.isWindows);
-                    if (Environment.isWindows) {
-                        bun.path.posixToPlatformInPlace(u8, temp_path);
-                    }
-                    break :path temp_path;
-                };
-
-                var is_dirfd_different = false;
-                var dirfd = args.dirfd;
-                if (Environment.isWindows) {
-                    while (std.mem.startsWith(u8, path, "..\\")) {
-                        is_dirfd_different = true;
-                        var buffer: bun.WPathBuffer = undefined;
-                        const dirfd_path_len = std.os.windows.kernel32.GetFinalPathNameByHandleW(args.dirfd.cast(), &buffer, buffer.len, 0);
-                        const dirfd_path = buffer[0..dirfd_path_len];
-                        const parent_path = bun.Dirname.dirname(u16, dirfd_path).?;
-                        if (std.mem.startsWith(u16, parent_path, &bun.windows.nt_maxpath_prefix)) @constCast(parent_path)[1] = '?';
-                        const newdirfd = switch (bun.sys.openDirAtWindows(bun.invalid_fd, parent_path, .{ .no_follow = true })) {
-                            .result => |fd| fd,
-                            .err => |err| {
-                                return .{ .err = err.withPath(path) };
-                            },
-                        };
-                        path = path[3..];
-                        dirfd = newdirfd;
-                    }
-                }
-                defer if (is_dirfd_different) {
-                    var d = dirfd.asDir();
-                    d.close();
-                };
-                if (Environment.isWindows) {
-                    // windows openat does not support path traversal, fix it here.
-                    // use pathbuf2 here since without it 'panic: @memcpy arguments alias' triggers
-                    if (std.mem.indexOf(u8, path, "\\.\\") != null or std.mem.indexOf(u8, path, "\\..\\") != null) {
-                        const fixed_path = bun.path.normalizeStringWindows(path, &pathbuf2, false, false);
-                        pathbuf2[fixed_path.len] = 0;
-                        path = pathbuf2[0..fixed_path.len :0];
-                    }
-                }
+                const path = args.file.path.sliceZWithForceCopy(pathbuf, true);
 
                 const open_result = Syscall.openat(
-                    dirfd,
+                    args.dirfd,
                     path,
                     @intFromEnum(args.flag) | os.O.NOCTTY,
                     args.mode,

test/js/node/fs/fs.test.ts

@@ -250,6 +250,17 @@ it("Dirent.name setter", () => {
   expect(dirent.name).toBe("hello");
 });
 
+it("writeFileSync should correctly resolve ../..", () => {
+  const base = join(tmpdir(), `fs-test-${Math.random().toString(36).slice(2)}`);
+  const path = join(base, "foo", "bar");
+  mkdirSync(path, { recursive: true });
+  const cwd = process.cwd();
+  process.chdir(path);
+  writeFileSync("../../test.txt", "hello");
+  expect(readFileSync(join(base, "test.txt"), "utf8")).toBe("hello");
+  process.chdir(cwd);
+});
+
 it("writeFileSync in append should not truncate the file", () => {
   const path = join(tmpdir(), "writeFileSync-should-not-append-" + (Date.now() * 10000).toString(16));
   var str = "";