Re: [FFmpeg-devel] [PATCH] lavc/vvc: Error pps_single_slice_per_subpic_flag

[Frank Plowman <post@frankplowman.com>]

On 02/02/2024 14:39, Nuo Mi wrote:
> On Thu, Feb 1, 2024 at 10:01 PM <post@frankplowman.com> wrote:
> 
>> From: Frank Plowman <post@frankplowman.com>
>>
>> pps_single_slice_per_subpic_flag is not yet supported.  Support is WIP,
>> but in the meantime throw an error when trying to decode a bitstream
>> with it set, avoiding an out-of-bounds array access.
>>
>> Fixes: out-of-bounds array access for conformance bitstreams
>> SUBPIC_C_ERICSSON_1, SUBPIC_D_ERICSSON_1, MNUT_A_Nokia_4 and
>> MNUT_B_Nokia_3.
>>
>> Signed-off-by: Frank Plowman <post@frankplowman.com>
>> ---
>>   libavcodec/vvc/vvc_ps.c | 21 ++++++++++++++++-----
>>   1 file changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/libavcodec/vvc/vvc_ps.c b/libavcodec/vvc/vvc_ps.c
>> index 2cf156b323..bd81d70e71 100644
>> --- a/libavcodec/vvc/vvc_ps.c
>> +++ b/libavcodec/vvc/vvc_ps.c
>> @@ -381,11 +381,16 @@ static void pps_multi_tiles_slice(VVCPPS *pps, const
>> int tile_idx, const int i,
>>       }
>>   }
>>
>> -static void pps_rect_slice(VVCPPS* pps)
>> +static int pps_rect_slice(VVCPPS* pps)
>>   {
>>       const H266RawPPS* r = pps->r;
>>       int tile_idx = 0, off = 0;
>>
>> +    if (r->pps_single_slice_per_subpic_flag) {
>> +        avpriv_report_missing_feature(NULL,
>> "pps_single_slice_per_subpic_flag");
>> +        return AVERROR_PATCHWELCOME;
>> +    }
>> +
>>       for (int i = 0; i < r->pps_num_slices_in_pic_minus1 + 1; i++) {
>>           if (!r->pps_slice_width_in_tiles_minus1[i] &&
>>               !r->pps_slice_height_in_tiles_minus1[i]) {
>> @@ -396,9 +401,11 @@ static void pps_rect_slice(VVCPPS* pps)
>>           }
>>           tile_idx = next_tile_idx(tile_idx, i, r);
>>       }
>> +
>> +    return 0;
>>   }
>>
>> -static void pps_no_rect_slice(VVCPPS* pps)
>> +static int pps_no_rect_slice(VVCPPS* pps)
>>   {
>>       const H266RawPPS* r = pps->r;
>>       int ctu_x, ctu_y, off = 0;
>> @@ -409,20 +416,24 @@ static void pps_no_rect_slice(VVCPPS* pps)
>>               pps_add_ctus(pps, &off, ctu_x, ctu_y,
>> r->col_width_val[tile_x], r->row_height_val[tile_y]);
>>           }
>>       }
>> +
>> +    return 0;
>>   }
>>
>>   static int pps_slice_map(VVCPPS *pps)
>>   {
>> +    int ret;
>> +
>>       pps->ctb_addr_in_slice = av_calloc(pps->ctb_count,
>> sizeof(*pps->ctb_addr_in_slice));
>>       if (!pps->ctb_addr_in_slice)
>>           return AVERROR(ENOMEM);
>>
>>       if (pps->r->pps_rect_slice_flag)
>> -        pps_rect_slice(pps);
>> +        ret = pps_rect_slice(pps);
>>       else
>> -        pps_no_rect_slice(pps);
>> +        ret = pps_no_rect_slice(pps);
>>
>> -    return 0;
>> +    return ret;
>>   }
>>
> Thank you Frank. This changed  too much code.
> How about we only check the sps_num_subpics_minus1 in decode_sps.

I wrote it like this so that the avpriv_report_missing_feature is where 
the feature would need to be, helping readability and searchability.  I 
could remove the return from pps_rect_slice and pps_no_rect_slice which 
would get rid of a handful of changed lines but the changes are trivial 
so it is not a big deal imo.
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