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)
--
2.21.0
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