[FFmpeg-devel] [PATCH 1/2] MxPEG decoder

[Anatoly Nenashev]

On 06.11.2010 06:01, Michael Niedermayer wrote:
> On Thu, Nov 04, 2010 at 05:39:40PM +0300, Anatoly Nenashev wrote:
>    
>> On 04.11.2010 03:16, Michael Niedermayer wrote:
>>      
>>> On Tue, Nov 02, 2010 at 01:58:21PM +0300, Anatoly Nenashev wrote:
>>>
>>>        
>>>>    int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
>>>>    {
>>>>        int len, nb_components, i, width, height, pix_fmt_id;
>>>> @@ -342,14 +376,12 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
>>>>                s->avctx->pix_fmt = PIX_FMT_GRAY16;
>>>>        }
>>>>
>>>> -    if(s->picture.data[0])
>>>> -        s->avctx->release_buffer(s->avctx,&s->picture);
>>>> -
>>>> -    s->picture.reference= 0;
>>>> -    if(s->avctx->get_buffer(s->avctx,&s->picture)<   0){
>>>> -        av_log(s->avctx, AV_LOG_ERROR, "get_buffer() failed\n");
>>>> -        return -1;
>>>> +    if (s->avctx->codec_id == CODEC_ID_MXPEG&&   !s->got_picture) {
>>>> +        if (mxpeg_allocate_picture(s)<   0) return -1;
>>>> +    } else {
>>>> +        if (mjpeg_allocate_picture(s)<   0) return -1;
>>>>        }
>>>>
>>>>          
>>> looks like s->picture.reference will b wrong for the first pic
>>>
>>>
>>>
>>>        
>> No, s->picture.reference will be always 1 for MxPEG frames. But I've
>> reimplemented this code to be more clean. See attachment.
>>      
>>> [...]
>>>
>>>        
>>>> +static int mxpeg_decode_mxm(MJpegDecodeContext *s, char *buf, int len)
>>>> +{
>>>> +    int32_t  mb_width, mb_height, bitmask_size, i;
>>>> +    uint32_t mb_count;
>>>> +
>>>> +    mb_width  = AV_RL16(&buf[4]);
>>>> +    mb_height = AV_RL16(&buf[6]);
>>>> +    mb_count = (uint32_t)mb_width*mb_height;
>>>> +
>>>> +    if (!mb_count || mb_count>   0x7FFFFFF8) {
>>>> +        av_log(s->avctx, AV_LOG_ERROR, "MXM wrong macroblocks count");
>>>> +        return AVERROR(EINVAL);
>>>> +    }
>>>> +
>>>> +    bitmask_size = (int32_t)(mb_count + 7)>>   3;
>>>> +
>>>> +    if (bitmask_size>   (len - 12)) {
>>>> +        av_log(s->avctx, AV_LOG_ERROR, "MXM bitmask is not complete");
>>>> +        return AVERROR(EINVAL);
>>>> +    }
>>>> +
>>>> +    av_freep(&s->mxctx.comment_buffer);
>>>> +    s->mxctx.comment_buffer = buf;
>>>> +    s->mxctx.mxm_bitmask = buf + 12;
>>>> +
>>>> +    if (!s->got_picture&&   s->picture.data[0]) {
>>>> +        if (mxpeg_allocate_picture(s)<   0) return -1;
>>>> +        s->got_picture = 1;
>>>> +    }
>>>>
>>>>          
>>> allocating pictures in the comment parsing code is not a good idea IMHO
>>>
>>>        
>> I don't agree.
>> There are 3 types of frames in MxPEG stream:
>> 1) clear JPEG which contains SOF, DHT, DQT, SOS  - may be the first
>> frame in stream or (in new cameras firmware) may be periodically
>> available.
>> 2) Pseudo-I frame which contains SOF, DHT, DQT, MXM bitmask (in COM),
>> SOS - must be periodically available but doesn't need to contain full
>> parts of image.
>> 3) P-frame which contains MXM bitmask, SOS and optional DHT, DQT - just
>> usual frame.
>>
>> So where I must allocate picture for the last frame type? I've decided
>> to do it in MXM parser.
>>
>>
>>      
>>> also maybe it would be easier to use reget_buffer() ?
>>>
>>>
>>>
>>>        
>> No, I think reget_buffer is a bad idea. We don't need to copy all
>> reference frame but only non-changed part of it.
>> And we had talking about it in August. It was your idea to remove
>> reget_buffer from this code to reject full image copying.
>>      
> both methods have their advantages and disadvantages.
> i dont care which is implemented but it should be done cleanly
> allocating the frame in the comment parsing code is not ok.
> Allocating a picture currently implicates that a SOF has been successfully
> parsed as the later code checks for this.
> Simply allocating a picture without successfully running the SOF parsing but
> maybe having it run just to the middle where it failed could lead to
> exploitable security issues
>
>
>
>    

As I have specified before there are frames which don't contain SOF 
marker. I've named them P-frames.
If we have got Pseudo-I frame before then new picture for P-frame will 
be allocated according to previously parsed params.
Otherwise no picture will be allocated. Allocating picture for P-frame 
in SOS parser is too late because we can't get here due to s->got_picture=0.
So if you see the right place for P-frames' picture allocation please 
tell me.