Linux kernel OP-TEE driver: device opened before init lets local users crash or take over

In the Linux kernel, the following vulnerability has been resolved:

optee: register TEE devices only once fully initialized

optee_probe() called tee_device_register() on both the client and the supplicant device before the rest of struct optee had been initialized.

tee_device_register() calls cdev_device_add(), which does two things at once: it creates /dev/tee0 and /dev/teepriv0, and it links the device into the tee class so that class_find_device() can find it. From that moment on the device is reachable both from user space via tee_open() and from kernel space via tee_client_open_context(). The only gate in teedev_open() is tee_device_get(), which merely checks that teedev->desc is non-NULL, which was already set by tee_device_alloc(). Therefore, there is effectively no gate at all.

A context opened in that window can run against a struct optee where

• optee->call_queue.mutex is not initialized by optee_cq_init()
• optee->supp mutex and completions is not initialized by optee_supp_init()
• optee->rpmb_dev_mutex is not initialized yet,
• the message argument cache is not initialized by optee_shm_arg_cache_init()
• optee->ctx is still NULL

Any open session or invoke during this window takes uninitialized mutexes and dereferences a NULL pointer.

Fix it by moving both tee_device_register() calls down to the point where all of struct optee is set up.

[JW: adding fixes and cc]