linux-kernel - Re: [PATCH] input: touchscreen: wm97xx-core: Fix possible null-pointer dereferences in wm97xx_ts_input

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Message-ID: <20190726090626.GA54126@ediswmail.ad.cirrus.com>
Date:   Fri, 26 Jul 2019 10:06:26 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
CC:     <dmitry.torokhov@...il.com>, <gregkh@...uxfoundation.org>,
        <tglx@...utronix.de>, <allison@...utok.net>,
        <rdunlap@...radead.org>, <patches@...nsource.cirrus.com>,
        <linux-input@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] input: touchscreen: wm97xx-core: Fix possible
 null-pointer dereferences in wm97xx_ts_input_open()

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@...il.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,
Charles

> -- 
> 2.17.0
>