[FFmpeg-devel] [PATCH 1/3] avformat/av1dec: Fix padding in obu_get_packet()

[Andreas Rheinhardt]

James Almer:
> On 10/16/2020 7:46 AM, Michael Niedermayer wrote:
>> Fixes: stack buffer overflow (read)
>> Fixes: 26369/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-5721057325219840
>>
>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>> ---
>>  libavformat/av1dec.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libavformat/av1dec.c b/libavformat/av1dec.c
>> index 10c4560968..395eef6522 100644
>> --- a/libavformat/av1dec.c
>> +++ b/libavformat/av1dec.c
>> @@ -382,7 +382,7 @@ static int obu_read_header(AVFormatContext *s)
>>  static int obu_get_packet(AVFormatContext *s, AVPacket *pkt)
>>  {
>>      ObuContext *c = s->priv_data;
>> -    uint8_t header[MAX_OBU_HEADER_SIZE];
>> +    uint8_t header[MAX_OBU_HEADER_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
>>      int64_t obu_size;
>>      int size = av_fifo_space(c->fifo);
>>      int ret, len, type;
> 
> Where is header being overread? All reads and writes are always
> constrained to MAX_OBU_HEADER_SIZE bytes at most by the fifo.

read_obu_with_size() reads it via a GetBitContext which overreads (even
when not using the unchecked bitstream reader).

- Andreas