[FFmpeg-devel] [PATCH 2/5] avcodec/smacker: Check input before allocation
Andreas Rheinhardt
andreas.rheinhardt at outlook.com
Thu Jul 3 23:27:04 EEST 2025
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 at 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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