On 7/12/19, Andreas Rheinhardt <andreas.rheinha...@gmail.com> wrote:
> Andreas Rheinhardt:
>> Andreas Rheinhardt:
>>> Andreas Rheinhardt:
>>>> Andreas Rheinhardt:
>>>>> The earlier version of the webm_chunk muxer had several bugs:
>>>>>
>>>>> 1. If the first packet of an audio stream didn't have a PTS of zero,
>>>>> then no chunk will be started before a packet is delivered to the
>>>>> underlying Matroska/WebM muxer, i.e. the AVFormatContext used to write
>>>>> these packets had a NULL as AVIOContext for output. This is behind the
>>>>> crash in ticket #5752.
>>>>>
>>>>> 2. If an error happens during writing a packet, the underlyimg
>>>>> Matroska/WebM muxer context is freed. This leads to a use-after-free
>>>>> coupled with a double-free in webm_chunk_write_trailer (which supposes
>>>>> that the underlying AVFormatContext is still valid).
>>>>>
>>>>> 3. Even when no error occurs at all, webm_chunk_write_trailer is still
>>>>> buggy: After the underlying Matroska/WebM muxer has written its
>>>>> trailer,
>>>>> ending the chunk implicitly flushes it again which is illegal at this
>>>>> point.
>>>>>
>>>>> These bugs have been fixed.
>>>>>
>>>>> Fixes #5752.
>>>>>
>>>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
>>>>> ---
>>>>> libavformat/webm_chunk.c | 44 +++++++++++++++++++++-------------------
>>>>> 1 file changed, 23 insertions(+), 21 deletions(-)
>>>>>
>>>>> diff --git a/libavformat/webm_chunk.c b/libavformat/webm_chunk.c
>>>>> index 2c99753b5b..391fee721a 100644
>>>>> --- a/libavformat/webm_chunk.c
>>>>> +++ b/libavformat/webm_chunk.c
>>>>> @@ -168,7 +168,7 @@ static int chunk_start(AVFormatContext *s)
>>>>> return 0;
>>>>> }
>>>>>
>>>>> -static int chunk_end(AVFormatContext *s)
>>>>> +static int chunk_end(AVFormatContext *s, int flush)
>>>>> {
>>>>> WebMChunkContext *wc = s->priv_data;
>>>>> AVFormatContext *oc = wc->avf;
>>>>> @@ -179,11 +179,14 @@ static int chunk_end(AVFormatContext *s)
>>>>> char filename[MAX_FILENAME_SIZE];
>>>>> AVDictionary *options = NULL;
>>>>>
>>>>> - if (wc->chunk_start_index == wc->chunk_index)
>>>>> + if (!oc->pb)
>>>>> return 0;
>>>>> - // Flush the cluster in WebM muxer.
>>>>> - oc->oformat->write_packet(oc, NULL);
>>>>> +
>>>>> + if (flush)
>>>>> + // Flush the cluster in WebM muxer.
>>>>> + oc->oformat->write_packet(oc, NULL);
>>>>> buffer_size = avio_close_dyn_buf(oc->pb, &buffer);
>>>>> + oc->pb = NULL;
>>>>> ret = get_chunk_filename(s, 0, filename);
>>>>> if (ret < 0)
>>>>> goto fail;
>>>>> @@ -194,7 +197,6 @@ static int chunk_end(AVFormatContext *s)
>>>>> goto fail;
>>>>> avio_write(pb, buffer, buffer_size);
>>>>> ff_format_io_close(s, &pb);
>>>>> - oc->pb = NULL;
>>>>> fail:
>>>>> av_dict_free(&options);
>>>>> av_free(buffer);
>>>>> @@ -216,27 +218,19 @@ static int
>>>>> webm_chunk_write_packet(AVFormatContext *s, AVPacket *pkt)
>>>>> }
>>>>>
>>>>> // For video, a new chunk is started only on key frames. For
>>>>> audio, a new
>>>>> - // chunk is started based on chunk_duration.
>>>>> - if ((st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
>>>>> + // chunk is started based on chunk_duration. Also, a new chunk is
>>>>> started
>>>>> + // unconditionally if there is no currently open chunk.
>>>>> + if (!oc->pb || (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
>>>>> (pkt->flags & AV_PKT_FLAG_KEY)) ||
>>>>> (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO &&
>>>>> - (pkt->pts == 0 || wc->duration_written >=
>>>>> wc->chunk_duration))) {
>>>>> + wc->duration_written >= wc->chunk_duration)) {
>>>>> wc->duration_written = 0;
>>>>> - if ((ret = chunk_end(s)) < 0 || (ret = chunk_start(s)) < 0) {
>>>>> - goto fail;
>>>>> + if ((ret = chunk_end(s, 1)) < 0 || (ret = chunk_start(s)) < 0)
>>>>> {
>>>>> + return ret;
>>>>> }
>>>>> }
>>>>>
>>>>> ret = oc->oformat->write_packet(oc, pkt);
>>>>> - if (ret < 0)
>>>>> - goto fail;
>>>>> -
>>>>> -fail:
>>>>> - if (ret < 0) {
>>>>> - oc->streams = NULL;
>>>>> - oc->nb_streams = 0;
>>>>> - avformat_free_context(oc);
>>>>> - }
>>>>>
>>>>> return ret;
>>>>> }
>>>>> @@ -245,12 +239,20 @@ static int
>>>>> webm_chunk_write_trailer(AVFormatContext *s)
>>>>> {
>>>>> WebMChunkContext *wc = s->priv_data;
>>>>> AVFormatContext *oc = wc->avf;
>>>>> + int ret;
>>>>> +
>>>>> + if (!oc->pb) {
>>>>> + ret = chunk_start(s);
>>>>> + if (ret < 0)
>>>>> + goto fail;
>>>>> + }
>>>>> oc->oformat->write_trailer(oc);
>>>>> - chunk_end(s);
>>>>> + ret = chunk_end(s, 0);
>>>>> +fail:
>>>>> oc->streams = NULL;
>>>>> oc->nb_streams = 0;
>>>>> avformat_free_context(oc);
>>>>> - return 0;
>>>>> + return ret;
>>>>> }
>>>>>
>>>>> #define OFFSET(x) offsetof(WebMChunkContext, x)
>>>>>
>>>>>
>>>> Ping for the last two patches of this patchset (i.e. this one and
>>>> https://ffmpeg.org/pipermail/ffmpeg-devel/2019-April/242902.html)
>>>>
>>>> - Andreas
>>>>
>>> And another ping for these two patches.
>>>
>>> - Andreas
>>>
>>
>> Ping #3.
>>
>> - Andreas
>>
> Ping.
Will apply first patch from this thread.
Is this OK?
>
> - Andreas
>
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