macOS Kernel 10.12.3 (16D32) - Use-After-Free Due to Double-Release in posix_spawn

EDB-ID: 41791
Author: Google Security Research
Published: 2017-04-04
CVE: CVE-2017-2472
Type: Dos
Platform: macOS
Aliases: N/A
Advisory/Source: Link
Tags: Denial of Service (DoS)
Vulnerable App: N/A

 Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1104 

exec_handle_port_actions is responsible for handling the xnu port actions extension to posix_spawn.

It supports 4 different types of port (PSPA_SPECIAL, PSPA_EXCEPTION, PSPA_AU_SESSION and PSPA_IMP_WATCHPORTS)

For the special, exception and audit ports it tries to update the new task to reflect the port action
by calling either task_set_special_port, task_set_exception_ports or audit_session_spawnjoin and if
any of those calls fail it calls ipc_port_release_send(port).

task_set_special_port and task_set_exception_ports don't drop a reference on the port if they fail
but audit_session_spawnjoin (which calls to audit_session_join_internal) *does* drop a reference on
the port on failure. It's easy to make audit_session_spawnjoin fail by specifying a port which isn't
an audit session port.

This means we can cause two references to be dropped on the port when only one is held leading to a
use after free in the kernel.

Tested on MacOS 10.12.3 (16D32) on MacBookAir5,2
*/

// ianbeer
#if 0
MacOS/iOS kernel uaf due to double-release in posix_spawn

exec_handle_port_actions is responsible for handling the xnu port actions extension to posix_spawn.

It supports 4 different types of port (PSPA_SPECIAL, PSPA_EXCEPTION, PSPA_AU_SESSION and PSPA_IMP_WATCHPORTS)

For the special, exception and audit ports it tries to update the new task to reflect the port action
by calling either task_set_special_port, task_set_exception_ports or audit_session_spawnjoin and if
any of those calls fail it calls ipc_port_release_send(port).

task_set_special_port and task_set_exception_ports don't drop a reference on the port if they fail
but audit_session_spawnjoin (which calls to audit_session_join_internal) *does* drop a reference on
the port on failure. It's easy to make audit_session_spawnjoin fail by specifying a port which isn't
an audit session port.

This means we can cause two references to be dropped on the port when only one is held leading to a
use after free in the kernel.

Tested on MacOS 10.12.3 (16D32) on MacBookAir5,2
Related Posts

Comments