linux-kernel - Re: [PATCH] driver core: platform: don't oops on unbound devices

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Date:   Sat, 12 Dec 2020 12:41:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: platform: don't oops on unbound devices

On Sat, Dec 12, 2020 at 04:14:26AM +0300, Dmitry Baryshkov wrote:
> Platform code stopped checking if the device is bound to the actual
> platform driver, thus calling non-existing drv->shutdown(). Verify that
> _dev->driver is not NULL before calling remove/shutdown callbacks.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Fixes: 9c30921fe799 ("driver core: platform: use bus_type functions")
> ---
>  drivers/base/platform.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 0358dc3ea3ad..93f44e69b472 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1342,7 +1342,7 @@ static int platform_remove(struct device *_dev)
>  	struct platform_device *dev = to_platform_device(_dev);
>  	int ret = 0;
>  
> -	if (drv->remove)
> +	if (_dev->driver && drv->remove)
>  		ret = drv->remove(dev);
>  	dev_pm_domain_detach(_dev, true);

I don't object to this, but it always feels odd to be doing pointer math
on a NULL value, wait until the static-checkers get ahold of this and
you get crazy emails saying you are crashing the kernel (hint, they are
broken).

But, I don't see why this check is needed?  If a driver is not bound to
a device, shouldn't this whole function just not be called?  Or error
out at the top?  

Uwe, I'd really like your review/ack of this before taking it.

thanks,

greg k-h