Right now it is possible for the pointer for the current frame to be set in the context even when it could not be properly set up; this does not influence various the ordinary ref frames, but only VP8Context.prev_frame. And since this code has been ported to the ProgressFrame API in d48d7bc434f30dfbdf346f16715e4f2044b3e000, this leads to segfaults, because the ProgressFrame API is less forgiving than the ThreadFrame API (waiting on an uninitialized ProgressFrame segfaults, waiting on an uninitialized ThreadFrame is a no-op (the code behaves as if frame-threading is not in use)). Fix this by maintaining the consistency of the frame pointers in the context (by setting them later). Fixes: NULL pointer dereference Fixes: 68192/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP8_fuzzer-6180311026171904 Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com> --- libavcodec/vp8.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/libavcodec/vp8.c b/libavcodec/vp8.c index d6df018655..8945447eb6 100644 --- a/libavcodec/vp8.c +++ b/libavcodec/vp8.c @@ -541,9 +541,12 @@ static int vp7_fade_frame(VP8Context *s, int alpha, int beta) /* preserve the golden frame, write a new previous frame */ if (s->framep[VP8_FRAME_GOLDEN] == s->framep[VP8_FRAME_PREVIOUS]) { - s->framep[VP8_FRAME_PREVIOUS] = vp8_find_free_buffer(s); - if ((ret = vp8_alloc_frame(s, s->framep[VP8_FRAME_PREVIOUS], 1)) < 0) + VP8Frame *prev_frame = vp8_find_free_buffer(s); + + ret = vp8_alloc_frame(s, prev_frame, 1); + if (ret < 0) return ret; + s->framep[VP8_FRAME_PREVIOUS] = prev_frame; dst = s->framep[VP8_FRAME_PREVIOUS]->tf.f; @@ -2699,7 +2702,7 @@ int vp78_decode_frame(AVCodecContext *avctx, AVFrame *rframe, int *got_frame, &s->frames[i] != s->framep[VP8_FRAME_ALTREF]) vp8_release_frame(&s->frames[i]); - curframe = s->framep[VP8_FRAME_CURRENT] = vp8_find_free_buffer(s); + curframe = vp8_find_free_buffer(s); if (!s->colorspace) avctx->colorspace = AVCOL_SPC_BT470BG; @@ -2723,6 +2726,7 @@ int vp78_decode_frame(AVCodecContext *avctx, AVFrame *rframe, int *got_frame, if ((ret = vp8_alloc_frame(s, curframe, referenced)) < 0) goto err; + s->framep[VP8_FRAME_CURRENT] = curframe; if (s->keyframe) curframe->tf.f->flags |= AV_FRAME_FLAG_KEY; else -- 2.40.1