linux-kernel - Re: [PATCH] [media] saa7146: fix a possible NULL pointer reference in saa7146_set

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Message-ID: <20140105061413.GF18213@core.coreip.homeip.net>
Date:	Sat, 4 Jan 2014 22:14:13 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ethan Zhao <ethan.kernel@...il.com>
Cc:	hans.verkuil@...co.com, m.chehab@...sung.com,
	gregkh@...uxfoundation.org, mchehab@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [media] saa7146: fix a possible NULL pointer reference
 in saa7146_set_position

On Sun, Jan 05, 2014 at 10:08:00AM +0800, Ethan Zhao wrote:
> Function saa7146_format_by_fourcc() may return NULL, reference of the returned
> result would cause NULL pointer issue without checking.
> 
> Signed-off-by: Ethan Zhao <ethan.kernel@...il.com>
> ---
>  drivers/media/common/saa7146/saa7146_hlp.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/common/saa7146/saa7146_hlp.c b/drivers/media/common/saa7146/saa7146_hlp.c
> index be746d1..3e23eab 100644
> --- a/drivers/media/common/saa7146/saa7146_hlp.c
> +++ b/drivers/media/common/saa7146/saa7146_hlp.c
> @@ -575,6 +575,7 @@ static void saa7146_set_position(struct saa7146_dev *dev, int w_x, int w_y, int
>  	 */
>  	u32 base = (u32)(unsigned long)vv->ov_fb.base;
>  
> +	int which = 1;
>  	struct	saa7146_video_dma vdma1;
>  
>  	/* calculate memory offsets for picture, look if we shall top-down-flip */
> @@ -608,10 +609,14 @@ static void saa7146_set_position(struct saa7146_dev *dev, int w_x, int w_y, int
>  		vdma1.pitch *= -1;
>  	}
>  
> -	vdma1.base_page = sfmt->swap;
> +	if (sfmt)
> +		vdma1.base_page = sfmt->swap;
> +	else
> +		which = 0;
> +
>  	vdma1.num_line_byte = (vv->standard->v_field<<16)+vv->standard->h_pixels;
>  
> -	saa7146_write_out_dma(dev, 1, &vdma1);
> +	saa7146_write_out_dma(dev, which, &vdma1);

If saa7146_format_by_fourcc() returns NULL you'll crash much earlier
when trying to do

	int depth = sfmt->depth;

I am not familiar with the code by it seems you are papering over the
problem. Will we ever get here with unknown pixel format?

Thanks.

-- 
Dmitry
--
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