Re: [PATCH v2] gpiolib: Fix line event handling in syscall compatible mode

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Mon, Sep 14, 2020 at 04:55:31PM +0200, Arnd Bergmann wrote:
> On Mon, Sep 14, 2020 at 4:37 PM Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> >
> > The introduced line even handling ABI in the commit
> >
> >   61f922db7221 ("gpio: userspace ABI for reading GPIO line events")
> >
> > missed the fact that 64-bit kernel may serve for 32-bit applications.
> > In such case the very first check in the lineevent_read() will fail
> > due to alignment differences.
> >
> > To workaround this introduce lineeven_to_user() helper which returns actual
> > size of the structure and copies its content to user if asked.
> >
> > Fixes: 61f922db7221 ("gpio: userspace ABI for reading GPIO line events")
> > Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> 
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

Thanks!

> > diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> > index e6c9b78adfc2..95af4a470f1e 100644
> > --- a/drivers/gpio/gpiolib-cdev.c
> > +++ b/drivers/gpio/gpiolib-cdev.c
> > @@ -423,6 +423,21 @@ static __poll_t lineevent_poll(struct file *file,
> >         return events;
> >  }
> >
> > +static ssize_t lineevent_get_size(void)
> > +{
> > +#ifdef __x86_64__
> > +       /* i386 has no padding after 'id' */
> > +       if (in_ia32_syscall()) {
> 
> Christoph Hellwig has recently suggested adding a new macro for this
> that would be always available and just evaluate to false on other
> architectures.
> 
> I'd just merge your version for now and backport to to stable kernels,
> but change this instance and a couple of others to use the new
> macro in mainline afterwards.
> 
> Incidentally that would also address CONFIG_OABI_COMPAT
> mode, if anyone cares.

Good to know (for both items).

-- 
With Best Regards,
Andy Shevchenko