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

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Date:	Mon, 6 Jan 2014 13:47:03 +0800
From:	Ethan Zhao <ethan.kernel@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	hans.verkuil@...co.com, m.chehab@...sung.com,
	Greg KH <gregkh@...uxfoundation.org>, mchehab@...hat.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [media] saa7146: fix a possible NULL pointer reference in saa7146_set_position

Dmitry,
   Yup,thank you point out that, need NULL pointer checking in
calculate_video_dma_grab_packed() ,  I am not familiar with saa7146
too. wouldn't paper over it, just a fix to pass code review.

Thanks,
Ethan

On Sun, Jan 5, 2014 at 2:14 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> 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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