linux-kernel - Re: [PATCH] ALSA: i2c: ak4xxx-adda: Fix a possible null pointer dereference in build_adc

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Message-ID: <s5hy30myuvw.wl-tiwai@suse.de>
Date:   Thu, 25 Jul 2019 17:52:03 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Jia-Ju Bai" <baijiaju1990@...il.com>
Cc:     <tglx@...utronix.de>, <gregkh@...uxfoundation.org>,
        <perex@...ex.cz>, <rfontana@...hat.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: i2c: ak4xxx-adda: Fix a possible null pointer dereference in build_adc_controls()

On Thu, 25 Jul 2019 10:27:33 +0200,
Jia-Ju Bai wrote:
> 
> In build_adc_controls(), there is an if statement on line 773 to check
> whether ak->adc_info is NULL:
> 	if (! ak->adc_info || 
> 		! ak->adc_info[mixer_ch].switch_name)
> 
> When ak->adc_info is NULL, it is used on line 792:
>     knew.name = ak->adc_info[mixer_ch].selector_name;
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, referring to lines 773 and 774, ak->adc_info 
> and ak->adc_info[mixer_ch].selector_name are checked before being used.
> 
> This bug is found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  sound/i2c/other/ak4xxx-adda.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/i2c/other/ak4xxx-adda.c b/sound/i2c/other/ak4xxx-adda.c
> index 5f59316f982a..9a891470e84a 100644
> --- a/sound/i2c/other/ak4xxx-adda.c
> +++ b/sound/i2c/other/ak4xxx-adda.c
> @@ -775,11 +775,13 @@ static int build_adc_controls(struct snd_akm4xxx *ak)
>  				return err;
>  
>  			memset(&knew, 0, sizeof(knew));
> -			knew.name = ak->adc_info[mixer_ch].selector_name;
> -			if (!knew.name) {
> +			if (! ak->adc_info ||
> +				! ak->adc_info[mixer_ch].selector_name) {
>  				knew.name = "Capture Channel";
>  				knew.index = mixer_ch + ak->idx_offset * 2;
>  			}
> +			else
> +				knew.name = ak->adc_info[mixer_ch].selector_name;
>  
>  			knew.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
>  			knew.info = ak4xxx_capture_source_info;

The code change itself looks good, but please follow the standard
coding style.  In short: please run checkpatch.pl, fix errors (some
warnings may be ignored) and resubmit.


thanks,

Takashi