[PATCH v2] staging: greybus: timesync: validate platform state callback

[Johan Hovold]

On Mon, Jan 23, 2017 at 04:32:57PM +0000, Rui Miguel Silva wrote:
> When tearingdown timesync, and not in arche platform, the state platform
> callback is not initialized. That will trigger the following NULL
> dereferencing.
> CallTrace:
> 
>  ? gb_timesync_platform_unlock_bus+0x11/0x20 [greybus]
>  gb_timesync_teardown+0x85/0xc0 [greybus]
>  gb_timesync_svc_remove+0xab/0x190 [greybus]
>  gb_svc_del+0x29/0x110 [greybus]
>  gb_hd_del+0x14/0x20 [greybus]
>  ap_disconnect+0x24/0x60 [gb_es2]
>  usb_unbind_interface+0x7a/0x2c0
>  __device_release_driver+0x96/0x150
>  device_release_driver+0x1e/0x30
>  bus_remove_device+0xe7/0x130
>  device_del+0x116/0x230
>  usb_disable_device+0x97/0x1f0
>  usb_disconnect+0x80/0x260
>  hub_event+0x5ca/0x10e0
>  process_one_work+0x126/0x3b0
>  worker_thread+0x55/0x4c0
>  ? process_one_work+0x3b0/0x3b0
>  kthread+0xc4/0xe0
>  ? kthread_park+0xb0/0xb0
>  ret_from_fork+0x22/0x30
> 
> So, fix that by adding checks before use the callback.
> 
> Fixes: 970dc85bd95d ("greybus: timesync: Add timesync core driver")
> Cc: <stable at vger.kernel.org> # 4.9.x
> Signed-off-by: Rui Miguel Silva <rmfrfs at gmail.com>

Reviewed-by: Johan Hovold <johan at kernel.org>