[FFmpeg-devel] [PATCH] Revert "avformat/mov: disallow a zero sample size in trun atoms"

[Chris Ribble]

> More strict enforcement of sample size was introduced to avoid DOS/Timeout
> with crafted (fuzzed) files and disallow emitting zero sized packets.
>
> Invalid file support is not something that is always worth doing, there
> are other, more important factors, like limiting code complexity or
> improving resiliance against denial of service. The problem here is that I
> honestly don't know if a zero sample size is against spec, just stupid, or
> there is a legitimate use for it.
>
> So I sent a 2 patch series which fixes the original issue differently.
> Please test and review them if you can.

Marton,

Thank you for looking into this further.

I tried your patch series and FFmpeg still generates an error
(AVERROR_INVALIDDATA) while processing the moof fragment with
zero-sized samples.

It seems like !(flags & MOV_TRUN_SAMPLE_SIZE) evaluates to true when
the flag is set (512 is "inverted" to 1). Is that what you had in
mind?

If I change it to this, things work as expected for my input mp4:
if (entries && !frag->size && (flags & MOV_TRUN_SAMPLE_SIZE !=
MOV_TRUN_SAMPLE_SIZE))
  return AVERROR_INVALIDDATA;

Sorry if I was supposed to provide this feedback on the patch series
itself; I'm happy to do so there as needed.

Thanks,
Chris