[v2,2/6] ACPI / bus: Do not traverse through non-existed device table

[Sinan Kaya <okaya@codeaurora.org>]

On 2/1/2018 3:20 PM, Andy Shevchenko wrote:
> When __acpi_match_device() is called it would be possible to have
> ACPI ID table a MULL pointer. To avoid potential dereference,

NULL

> check for this before traverse.
> 
> While here, remove redundant 'else'.
> 
> Fixes: 80212a162329 ("ACPI / bus: Introduce acpi_get_match_data() function")
> Cc: Sinan Kaya <okaya@codeaurora.org>
> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> Cc: Vinod Koul <vinod.koul@intel.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> v2: new patch
>  drivers/acpi/bus.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index a87a97bf75f8..f3a7c29e9190 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -745,11 +745,13 @@ static const struct acpi_device_id *__acpi_match_device(
>  
>  	list_for_each_entry(hwid, &device->pnp.ids, list) {
>  		/* First, check the ACPI/PNP IDs provided by the caller. */
> -		for (id = ids; id->id[0] || id->cls; id++) {
> -			if (id->id[0] && !strcmp((char *) id->id, hwid->id))
> -				return id;
> -			else if (id->cls && __acpi_match_device_cls(id, hwid))
> -				return id;
> +		if (ids) {
> +			for (id = ids; id->id[0] || id->cls; id++) {
> +				if (id->id[0] && !strcmp((char *)id->id, hwid->id))
> +					return id;
> +				if (id->cls && __acpi_match_device_cls(id, hwid))
> +					return id;
> +			}
>  		}
>  
>  		/*
> 

Why not bail out here immediately if ids is null?

__acpi_match_device()
{
	/*
	 * If the device is not present, it is unnecessary to load device
	 * driver for it.
	 */
	if (!device || !device->status.present)
		return NULL;
}