[FFmpeg-devel] [PATCH 4/4] avcodec/h264_slice: Fix overflow in recovery_frame computation

[James Almer]

On 6/8/2018 8:12 PM, James Almer wrote:
> On 6/8/2018 7:11 PM, Michael Niedermayer wrote:
>> Fixes: signed integer overflow: 15 + 2147483646 cannot be represented in type 'int'
>> Fixes: 8381/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_H264_fuzzer-6225533137321984
>>
>> 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/h264_sei.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/libavcodec/h264_sei.c b/libavcodec/h264_sei.c
>> index 9defcb80b9..2f16d95f56 100644
>> --- a/libavcodec/h264_sei.c
>> +++ b/libavcodec/h264_sei.c
>> @@ -261,10 +261,16 @@ static int decode_unregistered_user_data(H264SEIUnregistered *h, GetBitContext *
>>      return 0;
>>  }
>>  
>> -static int decode_recovery_point(H264SEIRecoveryPoint *h, GetBitContext *gb)
>> +static int decode_recovery_point(H264SEIRecoveryPoint *h, GetBitContext *gb, void *logctx)
>>  {
>> -    h->recovery_frame_cnt = get_ue_golomb_long(gb);
>> +    unsigned recovery_frame_cnt = get_ue_golomb_long(gb);
>>  
>> +    if (recovery_frame_cnt > (1<<16)) {
> 
> Maybe move MAX_LOG2_MAX_FRAME_NUM out of h264_ps.c and into h264_ps.h,
> then use it here?

And it should be "(1 << MAX_LOG2_MAX_FRAME_NUM) - 1", for that matter.
Or alternatively use sps->log2_max_frame_num from the active sps instead.

> 
>> +        av_log(logctx, AV_LOG_ERROR, "recovery_frame_cnt %d is out of range\n", recovery_frame_cnt);
> 
> It's unsigned, so %u. Some pedantic compilers (Like djgpp) may complain
> or downright fail otherwise.
> 
>> +        return AVERROR_INVALIDDATA;
>> +    }
>> +
>> +    h->recovery_frame_cnt = recovery_frame_cnt;
>>      /* 1b exact_match_flag,
>>       * 1b broken_link_flag,
>>       * 2b changing_slice_group_idc */
>> @@ -429,7 +435,7 @@ int ff_h264_sei_decode(H264SEIContext *h, GetBitContext *gb,
>>              ret = decode_unregistered_user_data(&h->unregistered, gb, logctx, size);
>>              break;
>>          case H264_SEI_TYPE_RECOVERY_POINT:
>> -            ret = decode_recovery_point(&h->recovery_point, gb);
>> +            ret = decode_recovery_point(&h->recovery_point, gb, logctx);
>>              break;
>>          case H264_SEI_TYPE_BUFFERING_PERIOD:
>>              ret = decode_buffering_period(&h->buffering_period, gb, ps, logctx);
>>
>