linux-kernel - Re: [PATCH 2/2] hwmon: core: fix potential memory leak in *hwmon_device

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Date:   Tue, 28 May 2019 08:06:40 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eduardo Valentin <eduval@...zon.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] hwmon: core: fix potential memory leak in
 *hwmon_device_register*

Hi Eduardo,

On Fri, May 17, 2019 at 04:13:37PM -0700, Eduardo Valentin wrote:
> When registering a hwmon device with HWMON_C_REGISTER_TZ flag
> in place, the hwmon subsystem will attempt to register the device
> also with the thermal subsystem. When the of-thermal registration
> fails, __hwmon_device_register jumps to ida_remove, leaving
> the locally allocated hwdev pointer and also the hdev registered.
> 
> This patch fixes both issues by jumping to a new label that
> will first unregister hdev and the fall into the kfree of hwdev
> to finally remove the idas and propagate the error code.
> 
> Cc: Jean Delvare <jdelvare@...e.com>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: linux-hwmon@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Eduardo Valentin <eduval@...zon.com>
> ---
>  drivers/hwmon/hwmon.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
> index 6b3559f58b67..6f1194952189 100644
> --- a/drivers/hwmon/hwmon.c
> +++ b/drivers/hwmon/hwmon.c
> @@ -637,7 +637,7 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
>  								hwdev, j);
>  					if (err) {
>  						device_unregister(hdev);
> -						goto ida_remove;
> +						goto device_unregister;

Good find, but device_unregister() is already called above.
You need to either remove that, or replace the goto to point to free_hwmon.
The new label would probably the cleaner solution since it follows the
coding style.

Thanks
Guenter

>  					}
>  				}
>  			}
> @@ -646,6 +646,8 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
>  
>  	return hdev;
>  
> +device_unregister:
> +	device_unregister(hdev);
>  free_hwmon:
>  	kfree(hwdev);
>  ida_remove:
> -- 
> 2.21.0
>