Re: [PATCH v2] iio: core: Prevent invalid memory access when there is no parent

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Jul 18, 2023 at 05:29:17PM +0200, Milan Zamazal wrote:
> Commit 813665564b3d ("iio: core: Convert to use firmware node handle
> instead of OF node") switched the kind of nodes to use for label
> retrieval in device registration.  Probably an unwanted change in that
> commit was that if the device has no parent then NULL pointer is
> accessed.  This is what happens in the stock IIO dummy driver when a
> new entry is created in configfs:

>   # mkdir /sys/kernel/config/iio/devices/dummy/foo
>   BUG: kernel NULL pointer dereference, address: ...
>   ...
>   Call Trace:
>   ...
>   asm_exc_page_fault
>   container_offline
>   __iio_device_register
>   krealloc
>   iio_device_attach_buffer
>   iio_simple_dummy_configure_buffer
>   iio_triggered_buffer_setup_ext
>   iio_dummy_probe
>   iio_sw_device_create
>   device_make_group
>   configfs_mkdir

Please, remove more unrelated lines in this backtrace. Ideally it should come
to ~4-5. For example, you posted a command line, it's obvious that you run
configfs, so the last (two) line(s) of the backtrace are redundant.
Then drop basic stuff, like:

   asm_exc_page_fault
   container_offline
   krealloc

Then remove unrelated IIO internals.

> Since there seems to be no reason to make a parent device of an IIO
> dummy device mandatory, let’s prevent the invalid memory access in
> __iio_device_register when the parent device is NULL.  With this
> change, the IIO dummy driver works fine with configfs.

The code wise it's okay now, so after addressing above
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko