[FFmpeg-cvslog] avcodec/vp3: Simplify shuffling frames, fix crash on alloc error

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Fri Sep 15 15:08:57 2023 +0200| [0e6fdebd0d5dafa07b4963f6b8ea7690ca124887] | committer: Andreas Rheinhardt

avcodec/vp3: Simplify shuffling frames, fix crash on alloc error

When decoding non-keyframes, the decoding process expects
there to be two reference frames, the last one and the golden
one. The existence of the golden one is checked and in case
it is there, it is presumed that the last one exists as well.

This assumption is wrong in case of memory allocation failure,
namely in case the call to ff_thread_ref_frame() that sets
the last frame fails.

Fix this by actually performing a shuffle without creating
new references. This can't fail and has the advantage of
fewer implicit allocations.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=0e6fdebd0d5dafa07b4963f6b8ea7690ca124887
---

 libavcodec/vp3.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
index 81dd6535c0..98dabfc907 100644
--- a/libavcodec/vp3.c
+++ b/libavcodec/vp3.c
@@ -2498,19 +2498,14 @@ static int update_frames(AVCodecContext *avctx)
     Vp3DecodeContext *s = avctx->priv_data;
     int ret = 0;
 
-    /* shuffle frames (last = current) */
-    ff_thread_release_ext_buffer(avctx, &s->last_frame);
-    ret = ff_thread_ref_frame(&s->last_frame, &s->current_frame);
-    if (ret < 0)
-        goto fail;
-
     if (s->keyframe) {
         ff_thread_release_ext_buffer(avctx, &s->golden_frame);
         ret = ff_thread_ref_frame(&s->golden_frame, &s->current_frame);
     }
+    /* shuffle frames */
+    ff_thread_release_ext_buffer(avctx, &s->last_frame);
+    FFSWAP(ThreadFrame, s->last_frame, s->current_frame);
 
-fail:
-    ff_thread_release_ext_buffer(avctx, &s->current_frame);
     return ret;
 }