Re: [FFmpeg-devel] [PATCH 5/6] avcodec/ffv1dec: consider run increase in minimal golomb frame size

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> On Thu, Jul 21, 2022 at 12:17:22AM +0200, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> On Tue, Jul 19, 2022 at 08:37:38AM -0300, James Almer wrote:
>>>>
>>>>
>>>> On 7/19/2022 8:34 AM, Michael Niedermayer wrote:
>>>>> Fixes: Timeout
>>>>> Fixes: 49160/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FFV1_fuzzer-5672826144686080
>>>>>
>>>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>>>> ---
>>>>>   libavcodec/ffv1dec.c | 6 +++++-
>>>>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
>>>>> index 01ddcaa512..9bdac0be4e 100644
>>>>> --- a/libavcodec/ffv1dec.c
>>>>> +++ b/libavcodec/ffv1dec.c
>>>>> @@ -883,7 +883,11 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *rframe,
>>>>>           if (buf_size < avctx->width * avctx->height / (128*8))
>>>>>               return AVERROR_INVALIDDATA;
>>>>>       } else {
>>>>> -        if (buf_size < avctx->height / 8)
>>>>> +        int i;
>>>>
>>>> for (int i...
>>>
>>> will apply with that change
>>>
>>> thx
>>>
>>
>> James' suggestion made you use an uninitialized i in the actual check;
> 
> yes
> 
> 
>> and even the original check is wrong, as one can overrun ff_log2_run
>> (unless there is a check that I am not missing). 
> 
> Theres a check but its too late
> 
> 
>> So it seems to me that
>> reverting 15785e044ee1265464bb4f3ed727e2a8074f97b4 is appropriate.
> 
> not against that but heres a quick fix attempt
> 

I thought that it would be easier to backport the fix if it were one
patch; of course it was never my intention to force you to revert this.

> 
> Author: Michael Niedermayer <michael@niedermayer.cc>
> Date:   Thu Jul 21 00:20:41 2022 +0200
> 
>     avcodec/ffv1dec: Fix AC_GOLOMB_RICE min size check
>     
>     Found-by: mkver

Please don't use my nickname in the future in commit messages.

>     
>     Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> 
> diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
> index d71584505d..c6eca3227c 100644
> --- a/libavcodec/ffv1dec.c
> +++ b/libavcodec/ffv1dec.c
> @@ -884,9 +884,14 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *rframe,
>              return AVERROR_INVALIDDATA;
>      } else {
>          int w = avctx->width;
> -        for (int i = 0; w > (1<<ff_log2_run[i]); i++)
> +        int s = 1 + w / (1<<23);
> +        int i;
> +
> +        w /= s;
> +
> +        for (i = 0; w > (1<<ff_log2_run[i]); i++)
>              w -= ff_log2_run[i];
> -        if (buf_size < (avctx->height + i + 6)/ 8)
> +        if (buf_size < (avctx->height + s*i + 6)/ 8)
>              return AVERROR_INVALIDDATA;
>      }
>  
>  
> 

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