Re: [FFmpeg-devel] [PATCH v2] lavfi/drawtext: Add localtime_ms for millisecond precision

[Thilo Borgmann <thilo.borgmann@mail.de>]

Am 14.01.22 um 19:05 schrieb Andreas Rheinhardt:
> Thilo Borgmann:
>> Am 14.01.22 um 14:17 schrieb "zhilizhao(赵志立)":
>>>
>>>
>>>> On Jan 14, 2022, at 8:14 PM, Thilo Borgmann <thilo.borgmann@mail.de> wrote:
>>>>
>>>> Am 06.01.22 um 12:27 schrieb Thilo Borgmann:
>>>>> Am 03.01.22 um 16:22 schrieb Thilo Borgmann:
>>>>>> Am 29.12.21 um 12:46 schrieb Nicolas George:
>>>>>>> "zhilizhao(赵志立)" (12021-12-29):
>>>>>>>> How about add a restriction like this:
>>>>>>>>
>>>>>>>> if (format.endsWith(“%S"))
>>>>>>>>    enable the feature
>>>>>>>> else
>>>>>>>>    warning message
>>>>>>>>
>>>>>>>> It’s a useful feature, it shouldn't create unexpected results, but
>>>>>>>> doesn’t need to support every use case.
>>>>>>>
>>>>>>> I would not oppose it, but I find it inelegant, especially because it
>>>>>>> requires a different expansion function, localtime_ms instead of
>>>>>>> localtime.
>>>>>>>
>>>>>>> What about this: with the original function "localtime", if the format
>>>>>>> ends in "%3N", then append the millisecond. It can later be expanded to
>>>>>>> support %xN at any place in the format for any value of x.
>>>>>>
>>>>>> I think best will be to scan the format string for %S and extend it there with .ms part before expanding the rest of it, not? Shouldn't be too expensive for the filter.
>>>>>>
>>>>>> Just need to find time to actually implement it. 
>>>>>
>>>>> Like v5 as attached.
>>>
>>>
>>>> +    if (tag == 'M' || tag == 'm') {
>>>> +        char *seconds = av_stristr(fmt, "%S");
>>>> +        if (seconds) {
>>>> +            seconds += 2;
>>>> +            int len = seconds - fmt + 1;
>>>> +            char *tmp = av_malloc(len);
>>>> +            av_strlcpy(tmp, fmt, len);
>>>
>>> Firstly, mixed variable declaration and statements.
>>>
>>> Secondly, I think you don’t need ’tmp’, something like
>>>
>>> av_asprintf(“%.*s.%03d%s", len, fmt, (int)(unow % 1000000) / 1000, seconds);
>>
>> You know your printf format-string :)
>>
>> Thanks, v6 attached.
>> -Thilo
>>
>>
> 
>>
>> +            int len = seconds + 2 - fmt;
>> +            char *fmt_new = av_asprintf("%.*s.%03d%s", len, fmt, (int)(unow % 1000000) / 1000, seconds + 2);
>> +            av_bprint_strftime(bp, fmt_new, &tm);
>> +            return 0;
>> +        }
> 
> I see an unchecked allocation and a leak. 

Ok fmt_new might be null, where is the leak?


> And it seems you are using a
> format string that comes from the user. This is undefined behaviour if
> this string contains an invalid conversion specifier.

I think that was unfortunately true before the patch as well, was it not?
And if true or not, do we have something in place to check a user string?

Thanks,
Thilo


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