[FFmpeg-devel] [PATCH v11 3/4] avfilter/vf_showinfo: display H.26[45] user data unregistered sei message

[Andreas Rheinhardt]

lance.lmwang at gmail.com:
> On Wed, Jun 10, 2020 at 08:13:59PM +0200, Andreas Rheinhardt wrote:
>> lance.lmwang at gmail.com:
>>> From: Limin Wang <lance.lmwang at gmail.com>
>>>
>>> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
>>> ---
>>>  libavfilter/vf_showinfo.c | 37 +++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 37 insertions(+)
>>>
>>> diff --git a/libavfilter/vf_showinfo.c b/libavfilter/vf_showinfo.c
>>> index 5d4aee4..2511da5 100644
>>> --- a/libavfilter/vf_showinfo.c
>>> +++ b/libavfilter/vf_showinfo.c
>>> @@ -37,6 +37,7 @@
>>>  #include "libavutil/timecode.h"
>>>  #include "libavutil/mastering_display_metadata.h"
>>>  #include "libavutil/video_enc_params.h"
>>> +#include "libavutil/avstring.h"
>>>  
>>>  #include "avfilter.h"
>>>  #include "internal.h"
>>> @@ -190,6 +191,39 @@ static void dump_video_enc_params(AVFilterContext *ctx, AVFrameSideData *sd)
>>>          av_log(ctx, AV_LOG_INFO, "%u blocks; ", par->nb_blocks);
>>>  }
>>>  
>>> +static int string_is_print(const uint8_t *str)
>>> +{
>>> +    while (av_isgraph(*str)) str++;
>>> +    return !*str;
>>
>> This is dangerous: The SEI message needn't be zero-terminated, so this
>> may segfault. Furthermore, it is also wrong: If the user data payload
>> happens to contain a binary zero preceded by printable ASCII characters,
>> it will be considered a string, even if there are unprintable characters
>> after the binary zero (which may really happen if the payload is
>> actually binary).
> 
> Give below test example, if a binary zero preceded by "hello", the %s will print
> out "hello" and ignore the other unprintable characters. I think it's expected.
> We only dump the printable result if it is string or parial string.
> 
>      unsigned char test[10];
> 
>      test[0] = 'h';
>      test[1] = 'e';
>      test[2] = 'l';
>      test[3] = 'l';
>      test[4] = 'o';
>      test[5] = 0;
>      test[6] = 133;
>      test[7] = 144;
> 
>      printf( "test: %s \n", test);
> 
> So I thbink it's safety after add one padding zero bytes for the user data
> buffer.
> 

And who says that what is before the first binary zero is actually a
string and not some actually binary data that just happens to be in the
printable ASCII range and will be gibberish when printed?

>>
>>> +}
>>> +
>>> +static void dump_sei_unregistered_metadata(AVFilterContext *ctx, AVFrameSideData *sd)
>>> +{
>>> +    const int uuid_size = 16;
>>> +    uint8_t *user_data = sd->data;
>>> +
>>> +    if (sd->size < uuid_size) {
>>> +        av_log(ctx, AV_LOG_ERROR, "invalid data(%d < UUID(%d-bytes))", sd->size, uuid_size);
>>> +        return;
>>> +    }
>>> +
>>> +    av_log(ctx, AV_LOG_INFO, "User Data Unregistered:\n");
>>> +    av_log(ctx, AV_LOG_INFO, "UUID=");
>>> +    for (int i = 0; i < uuid_size; i++) {
>>> +        av_log(ctx, AV_LOG_INFO, "%02x", user_data[i]);
>>> +        if (i == 3 || i == 5 || i == 7 || i == 9)
>>> +            av_log(ctx, AV_LOG_INFO, "-");
>>> +    }
>>> +    av_log(ctx, AV_LOG_INFO, "\n");
>>> +
>>> +    user_data += uuid_size;
>>> +    /* Only print the user data details if it's string */
>>> +    if (string_is_print(user_data)) {
>>> +        av_log(ctx, AV_LOG_INFO, "User Data=");
>>> +        av_log(ctx, AV_LOG_INFO, "%s", user_data);
>>
>> Given that the user_data needn't be zero-terminated, you must specify
>> the precision (i.e. the number of bytes to write) here.
>>
>>> +    }
>>> +}
>>> +
>>>  static void dump_color_property(AVFilterContext *ctx, AVFrame *frame)
>>>  {
>>>      const char *color_range_str     = av_color_range_name(frame->color_range);
>>> @@ -375,6 +409,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
>>>          case AV_FRAME_DATA_VIDEO_ENC_PARAMS:
>>>              dump_video_enc_params(ctx, sd);
>>>              break;
>>> +        case AV_FRAME_DATA_SEI_UNREGISTERED:
>>> +            dump_sei_unregistered_metadata(ctx, sd);
>>> +            break;
>>>          default:
>>>              av_log(ctx, AV_LOG_WARNING, "unknown side data type %d (%d bytes)",
>>>                     sd->type, sd->size);
>>>
>>
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>