[FFmpeg-devel] [PATCH] avcodec/bsf: make sure the AVBSFInternal stored packet is reference counted

[James Almer]

Some bitstream filters may buffer said packet in their own contexts
for latter use.
The documentation for av_bsf_send_packet() doesn't forbid feeding
it non-reference counted packets, which depending on the way said
packets were internally buffered by the bsf it may result in the
data described in them to become invalid or unavailable at any time.

This was the case with vp9_superframe after commit e1bc3f4396, which
was then promptly fixed in 37f4a093f7 and 7a02b364b6. It is still the
case even today with vp9_reorder_raw.

With this change the bitstream filters will not have to worry how to
store or consume the packets fed to them.

Signed-off-by: James Almer <jamrial at gmail.com>
---
Regarding vp9_raw_reorder, see "[PATCH] avcodec/vp9_raw_reorder: cache
input packets using new references" for a local fix similar to what
vp9_superframe got with 37f4a093f7 and 7a02b364b6.

A simple reproducer if you're curious is:

ffmpeg -i INPUT -c:v copy -bsf:v vp9_raw_reorder -f null -

Which segfauls with current git master.

"[PATCH 2/2] ffmpeg: pass reference counted packets on codec copy
when possible" also works around this in most cases by doing what its
subject describes, but only affects the ffmpeg CLI only and not the
API itself, of course.

 libavcodec/bsf.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/libavcodec/bsf.c b/libavcodec/bsf.c
index 38b423101c..25f7a20ad6 100644
--- a/libavcodec/bsf.c
+++ b/libavcodec/bsf.c
@@ -188,7 +188,15 @@ int av_bsf_send_packet(AVBSFContext *ctx, AVPacket *pkt)
         ctx->internal->buffer_pkt->side_data_elems)
         return AVERROR(EAGAIN);
 
-    av_packet_move_ref(ctx->internal->buffer_pkt, pkt);
+    if (pkt->buf)
+        av_packet_move_ref(ctx->internal->buffer_pkt, pkt);
+    else {
+        int ret = av_packet_ref(ctx->internal->buffer_pkt, pkt);
+
+        if (ret < 0)
+            return ret;
+        av_packet_unref(pkt);
+    }
 
     return 0;
 }
-- 
2.16.2