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SubjectRe: [PATCH] mtd: nand: mxc_nand: fix a possible NULL dereference
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On Thu, Nov 12, 2015 at 9:53 AM, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> wrote:
> CC += devicetree@vger.kernel.org, gregkh

You added linux@pengutronix instead of devicetree.

>
> On Thu, Nov 12, 2015 at 09:36:55AM +0100, Frans Klaver wrote:
>> On Thu, Nov 12, 2015 at 9:26 AM, Uwe Kleine-König
>> <u.kleine-koenig@pengutronix.de> wrote:
>> > On Thu, Nov 12, 2015 at 09:03:11AM +0100, Frans Klaver wrote:
>> >> Hi,
>> >>
>> >> On Thu, Nov 12, 2015 at 8:46 AM, LABBE Corentin
>> >> <clabbe.montjoie@gmail.com> wrote:
>> >> > of_match_device could return NULL, and so cause a NULL pointer
>> >> > dereference later.
>> >>
>> >> Did you actually run into this? It seems to me that this driver is
>> >> only probed if and only if we have a match and that therefore
>> >> of_match_device will always return a valid pointer (it is using the
>> >> same match table). Am I missing something?
>> >
>> > Yes, you're missing something. The driver would probe for a dt snippet
>> > like:
>> >
>> > mxc_nand {
>> > compatible = "foobar";
>> > }
>> >
>> > In this case dev->of_node is non-NULL but of_match_device(mxcnd_dt_ids,
>> > dev) is.
>> >
>> > (I didn't actually test this, so there is a chance I'm wrong here. And
>> > if not I wonder if it is sensible at all to match the device name on
>> > driver name for of-created platform devices.)
>>
>> Yea, looks like you're right. platform devices check a number of
>> things to determine a match, among which is driver name if all else
>> fails (platform.c, platform_match()).
>
> Maybe something like this would help to reduce surprises:
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index f80aaaf9f610..a9fc22c86552 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -840,8 +840,8 @@ static int platform_match(struct device *dev, struct device_driver *drv)
> return !strcmp(pdev->driver_override, drv->name);
>
> /* Attempt an OF style match first */
> - if (of_driver_match_device(dev, drv))
> - return 1;
> + if (pdev->dev.of_node)
> + return of_driver_match_device(dev, drv);
>
> /* Then try ACPI style match */
> if (acpi_driver_match_device(dev, drv))

That looks sensible, yea. There is a chance that misbehaving DT nodes
will fail after this change, of course.

Thanks,
Frans


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