Linux Sandbox: move init processes to new session id.

sandbox/linux/suid/client/setuid_sandbox_client.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 SANDBOX_LINUX_SUID_SETUID_SANDBOX_CLIENT_H_
 #define SANDBOX_LINUX_SUID_SETUID_SANDBOX_CLIENT_H_
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
@@ skipping 20 matching lines @@
 // 6. B performs various initializations that require access to the file
 //    system.
 // 6.b (optional) B uses sandbox::Credentials::HasOpenDirectory() to verify
 //    that no directory is kept open (which would allow bypassing the setuid
 //    sandbox).
 // 7. B should be prepared to assume the role of init(1). In particular, B
 //    cannot receive any signal from any other process, excluding SIGKILL.
 //    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().
-// 8. B requests being chroot-ed through ChrootMe() and
+// 8. B uses CreateNewSession() to move to a new session ID and process group.
+//    This prevents a sandboxed process from signaling its process group and
+//    get signals delivered across the PID namespace boundary.
+// 9. B requests being chroot-ed through ChrootMe() and
 //    requests other sandboxing status via the status functions.
 class SANDBOX_EXPORT SetuidSandboxClient {
  public:
   // All instantation should go through this factory method.
   static class SetuidSandboxClient* Create();
   ~SetuidSandboxClient();
 
   // Close the dummy file descriptor leftover from the sandbox ABI.
   void CloseDummyFile();
   // Ask the setuid helper over the setuid sandbox IPC channel to chroot() us
   // to an empty directory.
   // Will only work if we have been launched through the setuid helper.
   bool ChrootMe();
+  // Create a new session and a new process group. This helps isolate processes
+  // outside of the sandbox from processes inside.
+  bool CreateNewSession();
   // When a new PID namespace is created, the process with pid == 1 should
   // assume the role of init.
   // See sandbox/linux/services/init_process_reaper.h for more information
   // on this API.
   bool CreateInitProcessReaper(base::Closure* post_fork_parent_callback);
 
   // Did we get launched through an up to date setuid binary ?
   bool IsSuidSandboxUpToDate() const;
   // Did we get launched through the setuid helper ?
   bool IsSuidSandboxChild() const;
@@ skipping 32 matching lines @@
   // Holds the environment. Will never be NULL.
   base::Environment* env_;
   bool sandboxed_;
 
   DISALLOW_COPY_AND_ASSIGN(SetuidSandboxClient);
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SUID_SETUID_SANDBOX_CLIENT_H_