Re: [FFmpeg-devel] [PATCH 2/5] avcodec/smacker: Check input before allocation

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

Michael Niedermayer:
> On Thu, Jul 03, 2025 at 09:14:42PM +0200, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> Fixes: Timeout
>>> Fixes: 421650030/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SMACKAUD_fuzzer-6144441767493632
>>>
>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>> ---
>>>  libavcodec/smacker.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
>>> index bd08bc7be28..99009bfd361 100644
>>> --- a/libavcodec/smacker.c
>>> +++ b/libavcodec/smacker.c
>>> @@ -662,6 +662,10 @@ static int smka_decode_frame(AVCodecContext *avctx, AVFrame *frame,
>>>          } else
>>>              values[i] = h.entries[0].value;
>>>      }
>>> +    if (get_bits_left(&gb) < (stereo+1) * (bits+1) * 8) {
>>> +        ret = AVERROR_INVALIDDATA;
>>> +        goto error;
>>> +    }
>>>  
>>>      if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
>>>          return ret;
>>
>> What about constant output (which you even optimized in
>> 08e82e5b572b440f4faf160d2eac923ca47a59f8)?
> 
> from this:
> 
>     if(bits) { //decode 16-bit data
>         for(i = stereo; i >= 0; i--)
>             pred[i] = av_bswap16(get_bits(&gb, 16));
> ...
>     } else { //8-bit data
>         for(i = stereo; i >= 0; i--)
>             pred[i] = get_bits(&gb, 8);
> ...
>     }
> 
> I assumed that there are at least (stereo+1) * (bits+1) * 8 bits
> bits can only be 0 or 1
> 
> did i miss something ?
> 
No. Seems fine.

- Andreas

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