add a LinuxSandbox::HasOpenDirectories() sanity check

content/common/sandbox_linux.h

 // 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.
 
 #ifndef CONTENT_COMMON_SANDBOX_LINUX_H_
 #define CONTENT_COMMON_SANDBOX_LINUX_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 39 matching lines @@
   // Returns the Status of the renderers' sandbox. Can only be queried after
   // going through PreinitializeSandbox(). This is a bitmask and uses the
   // constants defined in "enum LinuxSandboxStatus". Since the status needs to
   // be provided before the sandboxes are actually started, this returns what
   // will actually happen once the various Start* functions are called from
   // inside a renderer.
   int GetStatus() const;
   // Returns true if the current process is single-threaded or if the number
   // of threads cannot be determined.
   bool IsSingleThreaded() const;
+  // Returns true if it can be determined that the current process has open
+  // directories (besides /proc).

[jln (very slow on Chromium), 2013/10/22 01:10:50]

Let's just say "that are not managed by the LinuxSandbox class". We could even
add: "This would be a vulnerability as it would allow to bypass the setuid
sandbox".

Let's also make it private for now.

[Mostyn Bramley-Moore, 2013/10/23 23:15:19]

Done in patchset 2.

+  bool HasOpenDirectories() const;
   // Did we start Seccomp BPF?
   bool seccomp_bpf_started() const;
 
   // Simple accessor for our instance of the setuid sandbox. Will never return
   // NULL.
   // There is no StartSetuidSandbox(), the SetuidSandboxClient instance should
   // be used directly.
   sandbox::SetuidSandboxClient* setuid_sandbox_client() const;
 
   // Check the policy and eventually start the seccomp-bpf sandbox. This should
@@ skipping 25 matching lines @@
   scoped_ptr<sandbox::SetuidSandboxClient> setuid_sandbox_client_;
 
   ~LinuxSandbox();
   DISALLOW_IMPLICIT_CONSTRUCTORS(LinuxSandbox);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_SANDBOX_LINUX_H_