linux-kernel - Re: [PATCH 1/1] media: video/cx18, fix potential null dereference

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Date:	Mon, 11 Jan 2010 18:48:29 -0500
From:	Andy Walls <awalls@...ix.net>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	mchehab@...hat.com, hverkuil@...all.nl, ivtv-devel@...vdriver.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	jirislaby@...il.com
Subject: Re: [PATCH 1/1] media: video/cx18, fix potential null dereference

On Sun, 2010-01-10 at 09:56 +0100, Jiri Slaby wrote:
> Stanse found a potential null dereference in cx18_dvb_start_feed
> and cx18_dvb_stop_feed. There is a check for stream being NULL,
> but it is dereferenced earlier. Move the dereference after the
> check.
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>

Reviewed-by: Andy Walls <awalls@...ix.net>
Acked-by: Andy Walls <awalls@...ix.net>

Regards,
Andy

> ---
>  drivers/media/video/cx18/cx18-dvb.c |   18 ++++++++++--------
>  1 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/video/cx18/cx18-dvb.c b/drivers/media/video/cx18/cx18-dvb.c
> index 71ad2d1..0ad5b63 100644
> --- a/drivers/media/video/cx18/cx18-dvb.c
> +++ b/drivers/media/video/cx18/cx18-dvb.c
> @@ -213,10 +213,14 @@ static int cx18_dvb_start_feed(struct dvb_demux_feed *feed)
>  {
>  	struct dvb_demux *demux = feed->demux;
>  	struct cx18_stream *stream = (struct cx18_stream *) demux->priv;
> -	struct cx18 *cx = stream->cx;
> +	struct cx18 *cx;
>  	int ret;
>  	u32 v;
>  
> +	if (!stream)
> +		return -EINVAL;
> +
> +	cx = stream->cx;
>  	CX18_DEBUG_INFO("Start feed: pid = 0x%x index = %d\n",
>  			feed->pid, feed->index);
>  
> @@ -253,9 +257,6 @@ static int cx18_dvb_start_feed(struct dvb_demux_feed *feed)
>  	if (!demux->dmx.frontend)
>  		return -EINVAL;
>  
> -	if (!stream)
> -		return -EINVAL;
> -
>  	mutex_lock(&stream->dvb.feedlock);
>  	if (stream->dvb.feeding++ == 0) {
>  		CX18_DEBUG_INFO("Starting Transport DMA\n");
> @@ -279,13 +280,14 @@ static int cx18_dvb_stop_feed(struct dvb_demux_feed *feed)
>  {
>  	struct dvb_demux *demux = feed->demux;
>  	struct cx18_stream *stream = (struct cx18_stream *)demux->priv;
> -	struct cx18 *cx = stream->cx;
> +	struct cx18 *cx;
>  	int ret = -EINVAL;
>  
> -	CX18_DEBUG_INFO("Stop feed: pid = 0x%x index = %d\n",
> -			feed->pid, feed->index);
> -
>  	if (stream) {
> +		cx = stream->cx;
> +		CX18_DEBUG_INFO("Stop feed: pid = 0x%x index = %d\n",
> +				feed->pid, feed->index);
> +
>  		mutex_lock(&stream->dvb.feedlock);
>  		if (--stream->dvb.feeding == 0) {
>  			CX18_DEBUG_INFO("Stopping Transport DMA\n");

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