Linux sandbox: Make ChrootToSafeEmptyDir() faster.

sandbox/linux/services/credentials_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/services/credentials.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <sys/stat.h>
@@ skipping 119 matching lines @@
   ASSERT_TRUE(WorkingDirectoryIsRoot());
 }
 
 SANDBOX_TEST(Credentials, DISABLE_ON_LSAN(DropFileSystemAccessIsSafe)) {
   CHECK(Credentials::DropAllCapabilities());
   // Probably missing kernel support.
   if (!Credentials::MoveToNewUserNS()) return;
   CHECK(Credentials::DropFileSystemAccess());
   CHECK(!base::DirectoryExists(base::FilePath("/proc")));
   CHECK(WorkingDirectoryIsRoot());
+  CHECK(base::IsDirectoryEmpty(base::FilePath("/")));
   // We want the chroot to never have a subdirectory. A subdirectory
   // could allow a chroot escape.
   CHECK_NE(0, mkdir("/test", 0700));
 }
 
 // Check that after dropping filesystem access and dropping privileges
 // it is not possible to regain capabilities.
 SANDBOX_TEST(Credentials, DISABLE_ON_LSAN(CannotRegainPrivileges)) {
   CHECK(Credentials::DropAllCapabilities());
   // Probably missing kernel support.
   if (!Credentials::MoveToNewUserNS()) return;
   CHECK(Credentials::DropFileSystemAccess());
   CHECK(Credentials::DropAllCapabilities());
 
   // The kernel should now prevent us from regaining capabilities because we
   // are in a chroot.
   CHECK(!Credentials::SupportsNewUserNS());
   CHECK(!Credentials::MoveToNewUserNS());
 }
 
 }  // namespace.
 
 }  // namespace sandbox.