linux-kernel - Re: [PATCH v2] HID: wacom: Prevent potential null dereference after disconnect

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Message-ID: <20141008214045.GF15198@dtor-ws>
Date:	Wed, 8 Oct 2014 14:40:45 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Jason Gerecke <killertofu@...il.com>
Cc:	jkosina@...e.cz, benjamin.tissoires@...il.com, pinglinux@...il.com,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] HID: wacom: Prevent potential null dereference after
 disconnect

On Wed, Oct 08, 2014 at 11:25:42AM -0700, Jason Gerecke wrote:
> Repeated connect/disconnect cycles under GNOME can trigger an occasional
> OOPS from within e.g. wacom_led_select_store, presumably due to a timing
> issue where userspace begins setting a value immediately before the
> device disconnects and our shared data is whisked away.
> 
> Signed-off-by: Jason Gerecke <killertofu@...il.com>
> ---
> Changes in v2:
>  * Added in missing escape character
> 
>  drivers/hid/wacom_sys.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c
> index 8593047..265429b 100644
> --- a/drivers/hid/wacom_sys.c
> +++ b/drivers/hid/wacom_sys.c
> @@ -641,6 +641,9 @@ static ssize_t wacom_led_select_store(struct device *dev, int set_id,
>  	unsigned int id;
>  	int err;
>  
> +	if (!wacom)
> +		return -ENODEV;
> +

Strong NAK. If device could disappear before this check it could as well
disappear after your check.

This patch does not solve anything.

>  	err = kstrtouint(buf, 10, &id);
>  	if (err)
>  		return err;

Thanks.

-- 
Dmitry
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