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Subject: Re: [PATCH] input: touchscreen: wm97xx-core: Fix possible
 null-pointer dereferences in wm97xx_ts_input_open()
To:     Charles Keepax <ckeepax@opensource.cirrus.com>
Cc:     dmitry.torokhov@gmail.com, gregkh@linuxfoundation.org,
        tglx@linutronix.de, allison@lohutok.net, rdunlap@infradead.org,
        patches@opensource.cirrus.com, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190726084816.8487-1-baijiaju1990@gmail.com>
 <20190726090626.GA54126@ediswmail.ad.cirrus.com>
From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Message-ID: <8abe9ecd-d6b4-1892-e496-edeeb62199c4@gmail.com>
Date:   Fri, 26 Jul 2019 17:08:44 +0800
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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