Re: [FFmpeg-devel] [PATCH] avcodec/pcm_rechunk_bsf: unref packet before putting a new one in

From: Marton Balint <cus@passwd.hu>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avcodec/pcm_rechunk_bsf: unref packet before putting a new one in
Date: Sun, 10 Apr 2022 18:50:15 +0200 (CEST)
Message-ID: <1ce2e239-5496-45cb-4b8d-2c20bea338b@passwd.hu> (raw)
In-Reply-To: <20220410141413.GC2829255@pb2>

On Sun, 10 Apr 2022, Michael Niedermayer wrote:

> On Sat, Apr 09, 2022 at 08:56:05PM +0200, Marton Balint wrote:
>>
>>
>> On Wed, 30 Mar 2022, Michael Niedermayer wrote:
>>
>>> On Tue, Mar 29, 2022 at 06:33:06PM -0300, James Almer wrote:
>>>> On 3/29/2022 6:24 PM, Michael Niedermayer wrote:
>>>>> Fixes: memleak
>>>>> Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_BSF_PCM_RECHUNK_fuzzer-5562089618407424
>>>>>
>>>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>>>> ---
>>>>>   libavcodec/pcm_rechunk_bsf.c | 1 +
>>>>>   1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/libavcodec/pcm_rechunk_bsf.c b/libavcodec/pcm_rechunk_bsf.c
>>>>> index 108d9e90b9..3f43934fe9 100644
>>>>> --- a/libavcodec/pcm_rechunk_bsf.c
>>>>> +++ b/libavcodec/pcm_rechunk_bsf.c
>>>>> @@ -153,6 +153,7 @@ static int rechunk_filter(AVBSFContext *ctx, AVPacket *pkt)
>>>>>               }
>>>>>           }
>>>>> +        av_packet_unref(s->in_pkt);
>>>>
>>>> This looks to me like it revealed a bug in the code above, which is meant to
>>>> ensure s->in_pkt will be blank at this point. It should be fixed there
>>>> instead.
>>>
>>> IIRC the problem was a input packet with size 0
>>> the code seems to assume 0 meaning no packet
>>
>> Is that valid here? The docs says that the encoders can generate 0 sized
>> packets if there is side data in them. However - the PCM rechunk BSF using
>> PCM packets - I am not sure this is intentional here.
>
> where exactly is this written ?

In the docs of av_bsf_send_packet() there is a reference to packet with no 
data but side data only. Also in the docs of AVPacket there is this:
Encoders are allowed to output empty packets, with no compressed data, 
containing only side data (e.g. to update some stream parameters at the 
end of encoding).

Regards,
Marton
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