Re: [PATCH stable 3.15 to 3.18] staging: comedi: dt282x: fix a null pointer deref on interrupt

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jul 12, 2019 at 03:02:37PM +0100, Ian Abbott wrote:
> commit b8336be66dec06bef518030a0df9847122053ec5 upstream.
> 
> The interrupt handler `dt282x_interrupt()` causes a null pointer
> dereference for those supported boards that have no analog output
> support.  For these boards, `dev->write_subdev` will be `NULL` and
> therefore the `s_ao` subdevice pointer variable will be `NULL`.  In that
> case, the following call near the end of the interrupt handler results
> in a null pointer dereference:
> 
> 	cfc_handle_events(dev, s_ao);
> 
> [ Upstream equivalent:
> 	comedi_handle_events(dev, s_ao);
>   -- IA ]
> 
> Fix it by only calling the above function if `s_ao` is valid.
> 
> (There are other uses of `s_ao` by the interrupt handler that may or may
> not be reached depending on values of hardware registers.  Trust that
> they are reliable for now.)
> 
> Fixes: f21c74fa4cfe ("staging: comedi: dt282x: use cfc_handle_events()")
> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/staging/comedi/drivers/dt282x.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Thanks for the patch, I've taken it for my 3.18-android tree.

greg k-h