linux-kernel - Re: [PATCH][V2][next] rtc: ds1307: check for failed memory allocation on wdt

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Date:   Thu, 2 Apr 2020 19:51:20 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     "linux@...ck-us.net" <linux@...ck-us.net>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH][V2][next] rtc: ds1307: check for failed memory allocation
 on wdt

On Thu, 2020-04-02 at 14:52 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently a failed memory allocation will lead to a null pointer
> dereference on point wdt.  Fix this by checking for a failed
> allocation
> and adding error return handling to function ds1307_wdt_register.
> Also move the error exit label "exit" to allow a return statement to
> be removed.
> 
> Addresses-Coverity: ("Dereference null return")
> Fixes: fd90d48db037 ("rtc: ds1307: add support for watchdog timer on
> ds1388")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
> V2: move error exit label and remove a return statement, thanks to 
>     Walter Harms for spotting this clean up.
> ---
>  drivers/rtc/rtc-ds1307.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
> index fad042118862..c058b02efb4d 100644
> --- a/drivers/rtc/rtc-ds1307.c
> +++ b/drivers/rtc/rtc-ds1307.c
> @@ -1665,14 +1665,16 @@ static const struct watchdog_ops
> ds1388_wdt_ops = {
>  
>  };
>  
> -static void ds1307_wdt_register(struct ds1307 *ds1307)
> +static int ds1307_wdt_register(struct ds1307 *ds1307)
>  {
>  	struct watchdog_device	*wdt;
>  
>  	if (ds1307->type != ds_1388)
> -		return;
> +		return 0;
>  
>  	wdt = devm_kzalloc(ds1307->dev, sizeof(*wdt), GFP_KERNEL);
> +	if (!wdt)
> +		return -ENOMEM;

My original intention was that the wdt support was optional. I'd
suggest just

+	if (!wdt)
+		return;

Which should keep Coverity happy.

>  	wdt->info = &ds1388_wdt_info;
>  	wdt->ops = &ds1388_wdt_ops;
> @@ -1683,10 +1685,13 @@ static void ds1307_wdt_register(struct ds1307
> *ds1307)
>  	watchdog_init_timeout(wdt, 0, ds1307->dev);
>  	watchdog_set_drvdata(wdt, ds1307);
>  	devm_watchdog_register_device(ds1307->dev, wdt);
> +
> +	return 0;
>  }
>  #else
> -static void ds1307_wdt_register(struct ds1307 *ds1307)
> +static int ds1307_wdt_register(struct ds1307 *ds1307)
>  {
> +	return 0;
>  }
>  #endif /* CONFIG_WATCHDOG_CORE */
>  
> @@ -1979,10 +1984,7 @@ static int ds1307_probe(struct i2c_client
> *client,
>  
>  	ds1307_hwmon_register(ds1307);
>  	ds1307_clks_register(ds1307);
> -	ds1307_wdt_register(ds1307);
> -
> -	return 0;
> -
> +	err = ds1307_wdt_register(ds1307);
>  exit:
>  	return err;
>  }