Re: [PATCH] input: touchscreen: wm97xx-core: Fix possible null-pointer dereferences in wm97xx_ts_input_open()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

On 2019/7/26 17:06, Charles Keepax wrote:
> On Fri, Jul 26, 2019 at 04:48:16PM +0800, Jia-Ju Bai wrote:
>> In wm97xx_ts_input_open(), there is an if statement on line 507 to check
>> whether wm->mach_ops is NULL:
>>      if (wm->mach_ops && wm->mach_ops->acc_enabled)
>>
>> When wm->mach_ops is NULL, it is used on line 521:
>>      wm97xx_init_pen_irq(wm);
>>          BUG_ON(!wm->mach_ops->irq_enable);
>>          BUG_ON(!wm->mach_ops->irq_gpio);
>>          wm97xx_reg_write(..., reg & ~(wm->mach_ops->irq_gpio))
>>
>> Thus, possible null-pointer dereferences may occur.
>>
>> To fix these bugs, wm->mach_ops is checked before calling
>> wm97xx_init_pen_irq().
>>
>> These bugs found by a static analysis tool STCheck written by us.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
>> ---
>>   drivers/input/touchscreen/wm97xx-core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/input/touchscreen/wm97xx-core.c b/drivers/input/touchscreen/wm97xx-core.c
>> index 0a174bd82915..f7bd0726a577 100644
>> --- a/drivers/input/touchscreen/wm97xx-core.c
>> +++ b/drivers/input/touchscreen/wm97xx-core.c
>> @@ -517,7 +517,7 @@ static int wm97xx_ts_input_open(struct input_dev *idev)
>>   	wm->ts_reader_interval = wm->ts_reader_min_interval;
>>   
>>   	wm->pen_is_down = 0;
>> -	if (wm->pen_irq)
>> +	if (wm->pen_irq && wm->mach_ops)
>>   		wm97xx_init_pen_irq(wm);
>>   	else
>>   		dev_err(wm->dev, "No IRQ specified\n");
> This doesn't quite feel like the right fix as it would print an
> error message saying "No IRQ specified", in the case the IRQ is
> specified but the mach_ops have not been set.
>
> I would suggest either extending the existing BUG_ON or adding a
> new check in wm97xx_init_pen_irq.

Thanks for the advice.
I will send a v2 patch of adding a new check in wm97xx_init_pen_irq().


Best wishes,
Jia-Ju Bai