Add namespace sandbox class.

sandbox/linux/services/namespace_sandbox.h

+// Copyright 2015 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_NAMESPACE_SANDBOX_H_
+#define SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_
+
+#include "base/command_line.h"
+#include "base/macros.h"
+#include "base/process/launch.h"
+#include "base/process/process.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+
+// Helper class for starting a process inside a new user, PID, and network
+// namespace. Before using a namespace sandbox, check for namespaces support
+// using Credentials::CanCreateProcessInNewUserNS.
+//
+// A typical use for "A" launching a sandboxed process "B" would be:
+// 1. A sets up a command line and launch options for process B.
+// 2. A launches B with Launch.
+// 3. B should be prepared to assume the role of init(1). In particular, apart
+//    from SIGKILL and SIGSTOP, B cannot receive any signal for which it does
+//    not have an explicit signal handler registered.
+//    If B dies, all the processes in the namespace will die.
+//    B can fork() and the parent can assume the role of init(1), by using
+//    CreateInitProcessReaper().
+// 4. B chroots using Credentials::MoveToNewUserNS() and
+//    Credentials::DropFileSystemAccess().

[jln (very slow on Chromium), 2015/02/03 01:27:46]

Add the call to DropAllCapabilities() as well.

[rickyz (no longer on Chrome), 2015/02/03 01:35:39]

Done.

+class SANDBOX_EXPORT NamespaceSandbox {
+ public:
+  // Launch a new process inside its own user/PID/network namespaces (depending
+  // on kernel support). Requires at a minimum that user namespaces are
+  // supported (use Credentials::CanCreateProcessInNewUserNS to check this).
+  //
+  // pre_exec_delegate and clone_flags fields of LaunchOptions should be nullptr
+  // and 0, respectively, since this class overrides them.
+  static base::Process Launch(const base::CommandLine& cmdline,
+                       const base::LaunchOptions& options);

[jln (very slow on Chromium), 2015/02/03 01:27:46]

Nit: indent.

Could also be worth renaming to LaunchProcess for clarity.

[rickyz (no longer on Chrome), 2015/02/03 01:35:39]

Done.

+
+  // Returns whether the namespace sandbox created a new user, PID, and network
+  // namespace. In particular, InNewUserNamespace should return true iff the
+  // process was started via this class.
+  static bool InNewUserNamespace();
+  static bool InNewPidNamespace();
+  static bool InNewNetNamespace();
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(NamespaceSandbox);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_