linux-kernel - Re: [PATCH] rtc: snvs: fix uninitialized usage of "lpcr" in snvs_rtc

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Message-ID: <20191004191202.GB4106@piout.net>
Date:   Fri, 4 Oct 2019 21:12:02 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Yizhuo <yzhai003@....edu>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: snvs: fix uninitialized usage of "lpcr" in
 snvs_rtc_enable()

On 04/10/2019 11:52:06-0700, Yizhuo wrote:
> Inside function snvs_rtc_enable(), variable "lpcr" could be
> uninitialized if regmap_read() returns -EINVAL. However,"lpcr"
> is used later in the if statement, which is potentially unsafe.
> 

This is not true, regmap_read either lock up the cpu or not fail in this
driver.

> Similar cases happened in function snvs_rtc_irq_handler() with
> variable "lpsr" and function snvs_rtc_read_alarm() with variables
> "lptar", "lpsr". The patch for those two are not easy since
> -EINVAL is not an acceptable return value for these functions.
> 
> Signed-off-by: Yizhuo <yzhai003@....edu>
> ---
>  drivers/rtc/rtc-snvs.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-snvs.c b/drivers/rtc/rtc-snvs.c
> index 757f4daa7181..dadcc3e193b2 100644
> --- a/drivers/rtc/rtc-snvs.c
> +++ b/drivers/rtc/rtc-snvs.c
> @@ -124,12 +124,16 @@ static int snvs_rtc_enable(struct snvs_rtc_data *data, bool enable)
>  {
>  	int timeout = 1000;
>  	u32 lpcr;
> +	int ret;
>  
>  	regmap_update_bits(data->regmap, data->offset + SNVS_LPCR, SNVS_LPCR_SRTC_ENV,
>  			   enable ? SNVS_LPCR_SRTC_ENV : 0);
>  
>  	while (--timeout) {
> -		regmap_read(data->regmap, data->offset + SNVS_LPCR, &lpcr);
> +		ret = regmap_read(data->regmap,
> +					data->offset + SNVS_LPCR, &lpcr);
> +		if (ret)
> +			return ret;
>  
>  		if (enable) {
>  			if (lpcr & SNVS_LPCR_SRTC_ENV)
> -- 
> 2.17.1
> 

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com