Move a couple of utility functions to a new namespace_utils class.

sandbox/linux/services/credentials.h

 // Copyright (c) 2013 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 SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 #define SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 
 #include "build/build_config.h"
 // Link errors are tedious to track, raise a compile-time error instead.
 #if defined(OS_ANDROID)
@@ skipping 18 matching lines @@
   // the current process.
   static bool DropAllCapabilities() WARN_UNUSED_RESULT;
   // Return true iff there is any capability in any of the capabilities sets
   // of the current process.
   static bool HasAnyCapability();
   // Returns the capabilities of the current process in textual form, as
   // documented in libcap2's cap_to_text(3). This is mostly useful for
   // debugging and tests.
   static scoped_ptr<std::string> GetCurrentCapString();
 
-  // Returns whether the kernel supports CLONE_NEWUSER and whether it would be
-  // possible to immediately move to a new user namespace. There is no point
-  // in using this method right before calling MoveToNewUserNS(), simply call
-  // MoveToNewUserNS() immediately. This method is only useful to test kernel
-  // support ahead of time.
-  static bool SupportsNewUserNS();

[jln (very slow on Chromium), 2015/01/23 02:48:23]

I wonder if we should keep this as "CanCreateProcessInNewUserNS"?

[rickyz (no longer on Chrome), 2015/01/23 23:59:37]

Done - at this point, there pretty messy separation of responsibility between
namespace_utils.cc and credentials.cc - I'll try to clean this up after getting
the non-setuid sandbox in.

-
   // Move the current process to a new "user namespace" as supported by Linux
   // 3.8+ (CLONE_NEWUSER).
   // The uid map will be set-up so that the perceived uid and gid will not
   // change.
   // If this call succeeds, the current process will be granted a full set of
   // capabilities in the new namespace.
   static bool MoveToNewUserNS() WARN_UNUSED_RESULT;
 
   // Remove the ability of the process to access the file system. File
   // descriptors which are already open prior to calling this API remain
   // available.
   // The implementation currently uses chroot(2) and requires CAP_SYS_CHROOT.
   // CAP_SYS_CHROOT can be acquired by using the MoveToNewUserNS() API.
   // Make sure to call DropAllCapabilities() after this call to prevent
   // escapes.
   // To be secure, the caller must ensure that any directory file descriptors
   // are closed (for example, by checking the result of
   // ProcUtil::HasOpenDirectory with a file descriptor for /proc, then closing
   // that file descriptor). Otherwise it may be possible to escape the chroot.
   static bool DropFileSystemAccess() WARN_UNUSED_RESULT;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Credentials);
 };
 
 }  // namespace sandbox.
 
 #endif  // SANDBOX_LINUX_SERVICES_CREDENTIALS_H_