linux-kernel - Re: [PATCH] powercap: fix possible name leak while device

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Date:   Wed, 23 Nov 2022 20:00:14 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Yang Yingliang <yangyingliang@...wei.com>
Cc:     linux-pm@...r.kernel.org, rafael@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powercap: fix possible name leak while device_register() fails

On Sat, Nov 12, 2022 at 10:42 AM Yang Yingliang
<yangyingliang@...wei.com> wrote:
>
> If device_register() returns error, the name allocated by
> dev_set_name() need be freed. In technical, we should call
> put_device() to give up the reference and free the name in
> driver core, but in some cases the device is not intizalized,
> put_device() can not be called, so don't complicate the code,
> just call kfree_const() to free name in the error path.
>
> Fixes: 75d2364ea0ca ("PowerCap: Add class driver")
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
>  drivers/powercap/powercap_sys.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/powercap/powercap_sys.c b/drivers/powercap/powercap_sys.c
> index f0654a932b37..11e742dc83b9 100644
> --- a/drivers/powercap/powercap_sys.c
> +++ b/drivers/powercap/powercap_sys.c
> @@ -572,6 +572,7 @@ struct powercap_zone *powercap_register_zone(
>  err_name_alloc:
>         idr_remove(power_zone->parent_idr, power_zone->id);
>  err_idr_alloc:
> +       kfree_const(dev_name(&power_zone->dev));
>         if (power_zone->allocated)
>                 kfree(power_zone);
>         mutex_unlock(&control_type->lock);
> @@ -622,6 +623,7 @@ struct powercap_control_type *powercap_register_control_type(
>         dev_set_name(&control_type->dev, "%s", name);
>         result = device_register(&control_type->dev);
>         if (result) {
> +               kfree_const(dev_name(&control_type->dev));

Why is it necessary to free a device name explicitly after a failing
device_register()?

If it is really necessary, then there is a problem in
device_register() itself AFAICS, because it uses dev_set_name() at
least in the dev->init_name present case.

>                 if (control_type->allocated)
>                         kfree(control_type);
>                 return ERR_PTR(result);
> --