Bootstrap Sandbox: Ensure swap_integer messages are read-only.

sandbox/mac/os_compatibility.h

 // Copyright 2014 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.
 
 // This file is used to handle differences in Mach message IDs and structures
 // that occur between different OS versions. The Mach messages that the sandbox
 // is interested in are decoded using information derived from the open-source
 // libraries, i.e. <http://www.opensource.apple.com/source/launchd/>. While
 // these messages definitions are open source, they are not considered part of
 // the stable OS API, and so differences do exist between OS versions.
 
 #ifndef SANDBOX_MAC_OS_COMPATIBILITY_H_
 #define SANDBOX_MAC_OS_COMPATIBILITY_H_
 
 #include <mach/mach.h>
 
 #include <string>
 
 namespace sandbox {
 
 typedef std::string (*LookUp2GetRequestName)(const mach_msg_header_t*);
 typedef void (*LookUp2FillReply)(mach_msg_header_t*, mach_port_t service_port);
 
+typedef bool (*SwapIntegerIsGetOnly)(const mach_msg_header_t*);
+
 struct LaunchdCompatibilityShim {
   // The msgh_id for look_up2.
   mach_msg_id_t msg_id_look_up2;
 
   // The msgh_id for swap_integer.
   mach_msg_id_t msg_id_swap_integer;
 
   // A function to take a look_up2 message and return the string service name
   // that was requested via the message.
   LookUp2GetRequestName look_up2_get_request_name;
 
   // A function to formulate a reply to a look_up2 message, given the reply
   // message and the port to return as the service.
   LookUp2FillReply look_up2_fill_reply;
+
+  // A function to take a swap_integer message and return true if the message
+  // is only getting the value of a key, neither setting it directly, nor
+  // swapping two kes.

[Mark Mentovai, 2014/05/15 22:36:56]

Spelling nit: keys.

I don’t actually see in the current launchd source what’s getting swapped.

[Robert Sesek, 2014/05/15 22:54:17]

Done.
Right, "swapping" seems to just mean get-and-set in a single operation.

+  SwapIntegerIsGetOnly swap_integer_is_get_only;
 };
 
 // Gets the compatibility shim for the launchd job subsystem.
 const LaunchdCompatibilityShim GetLaunchdCompatibilityShim();
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_MAC_OS_COMPATIBILITY_H_