[FFmpeg-devel] [PATCH 1/2] avformat/utils: Assert that stream_index is valid

[Gyan]

On 24-09-2019 11:39 PM, Gyan wrote:
>
>
> On 24-09-2019 11:38 PM, Marton Balint wrote:
>>
>>
>> On Tue, 24 Sep 2019, Gyan wrote:
>>
>>>
>>>
>>> On 24-09-2019 10:01 PM, Andreas Rheinhardt wrote:
>>>> There is currently an ordinary check for this (which would lead to a
>>>> memleak), but given that no demuxer should ever return a packet 
>>>> with an
>>>> invalid stream_index it is more appropriate for this to be an assert.
>>>>
>>>> FATE passes with this change.
>>>>
>>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>>>> ---
>>>>   libavformat/utils.c | 6 ++----
>>>>   1 file changed, 2 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/libavformat/utils.c b/libavformat/utils.c
>>>> index 3983a3f4ce..d8ef5fe54c 100644
>>>> --- a/libavformat/utils.c
>>>> +++ b/libavformat/utils.c
>>>> @@ -884,10 +884,8 @@ int ff_read_packet(AVFormatContext *s, 
>>>> AVPacket *pkt)
>>>>               continue;
>>>>           }
>>>>
>>>> -        if (pkt->stream_index >= (unsigned)s->nb_streams) {
>>>> -            av_log(s, AV_LOG_ERROR, "Invalid stream index %d\n", 
>>> pkt->stream_index);
>>>> -            continue;
>>>> -        }
>>>> +        av_assert0(pkt->stream_index < (unsigned)s->nb_streams &&
>>>> +                   "Invalid stream index.\n");
>>>
>>> The mpegts demuxer can send packets from new streams which appear 
>>> mid-way. See the check in ffmpeg.c process_input() which discards 
>>> these packets.
>>
>> That checks InputFile->nb_streams not AVFormatContext->nb_streams as 
>> far as I see.
>>
>>> Whereas the patch will lead to an abort in fftools and other user 
>>> apps transcoding a live feed.
>>
>> Are you sure? I think the demuxer always creates a new stream before 
>> returning a packet, so AVFormatContext->nb_streams should always be 
>> up-to-date when this code runs.
>
> No. I'll have to craft an input and check.

Tested. Yes, the format context is updated, but InputFiles isn't. 
Comment withdrawn. Sorry.

Gyan