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

[Johan Hovold <johan@kernel.org>]

On Mon, Jan 23, 2017 at 02:22:44PM +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.
> 
> Cc: <stable@vger.kernel.org> # 4.9.x
> Signed-off-by: Rui Miguel Silva <rmfrfs@gmail.com>
> ---
> Greg,
> This patch does not contain the "commit <sha> upstream" snippet since you
> already removed the timesync code from the -next tree. So, It would never get
> there. However this will affect the greybus users of 4.9.x.

This code is still in Linus tree and 4.10-rc so this is just a normal
fix even if this is no longer an issue in -next.

>  drivers/staging/greybus/timesync_platform.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/greybus/timesync_platform.c b/drivers/staging/greybus/timesync_platform.c
> index 113f3d6c4b3a..7d3ccc2bc98c 100644
> --- a/drivers/staging/greybus/timesync_platform.c
> +++ b/drivers/staging/greybus/timesync_platform.c
> @@ -45,13 +45,18 @@ u32 gb_timesync_platform_get_clock_rate(void)
>  
>  int gb_timesync_platform_lock_bus(struct gb_timesync_svc *pdata)
>  {
> +	if (!arche_platform_change_state_cb)
> +		return 0;
> +
>  	return arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_TIME_SYNC,
>  					      pdata);
>  }
>  
>  void gb_timesync_platform_unlock_bus(void)
>  {
> -	arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE, NULL);
> +	if (arche_platform_change_state_cb)
> +		arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE,
> +					       NULL);

I'd use the same pattern here:

	if (!arche_platform_change_state_cb)
		return;

	arche_platform_change_state_cb(ARCHE_PLATFORM_STATE_ACTIVE, NULL);

Thanks,
Johan