Add namespace sandbox class.

sandbox/linux/services/namespace_sandbox.h

Index: sandbox/linux/services/namespace_sandbox.h
diff --git a/sandbox/linux/services/namespace_sandbox.h b/sandbox/linux/services/namespace_sandbox.h
new file mode 100644
index 0000000000000000000000000000000000000000..d08ac1149e4d795127e3a4da8a86dfb8f858cb34
--- /dev/null
+++ b/sandbox/linux/services/namespace_sandbox.h
@@ -0,0 +1,77 @@
+// 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/files/scoped_file.h"
+#include "base/process/launch.h"
+#include "base/process/process_handle.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+
+// Helper class for starting a process inside a new user, PID, and network
+// namespace. The expected usage looks like:
+//
+// A typical use for "A" launching a sandboxed process "B" would be:
+// 1. A sets up a command line for process B.
+// 2. A calls SetupLaunchOptions which sets up the a pipe for communicating with
+//    the child.
+// 3. A launches B with base::LaunchProcess.
+// 4. A calls PrepareSandboxedProcess, at which point B begins running.
+// 5. 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().
+// 6. B chroots using Credentials::MoveToNewUserNS() and
+//    Credentials::DropFileSystemAccess().
+//
+// An instance of this class may only be used once.
+class SANDBOX_EXPORT NamespaceSandbox {
+ public:
+  NamespaceSandbox();
+  ~NamespaceSandbox();
+
+  // Setup the launch options for the sandboxed process. The caller is
+  // responsible for setting options->fds_to_remap = fds_to_remap.
+  void SetupLaunchOptions(base::LaunchOptions* options,
+                          base::FileHandleMappingVector* fds_to_remap);
+
+  // Prepares the child process before it execs the new program. This adds an
+  // identity mapping for the uid and gid inside the user namespace, then
+  // signals the child to exec the new program.
+  void PrepareSandboxedProcess(base::ProcessId pid);
+
+  // 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:
+  class ReadFromPipeDelegate : public base::LaunchOptions::PreExecDelegate {
+   public:
+    ReadFromPipeDelegate();
+    ~ReadFromPipeDelegate() override;
+    void RunAsyncSafe() override;
+    void set_fd(int fd);
+
+   private:
+    int fd_;
+    DISALLOW_COPY_AND_ASSIGN(ReadFromPipeDelegate);
+  };
+  // Pipe fds used to communicate with the child process.
+  base::ScopedFD read_fd_;
+  base::ScopedFD write_fd_;
+
+  ReadFromPipeDelegate read_from_pipe_delegate_;
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_