Re: [FFmpeg-devel] [PATCH 4/5] avcodec/hevcdec: Check ref frame

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Michael Niedermayer:
> Fixes: NULL pointer dereferences
> Fixes: 68197/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-6382538823106560
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/hevcdec.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> index fcfb275f63a..92b0e45eee0 100644
> --- a/libavcodec/hevcdec.c
> +++ b/libavcodec/hevcdec.c
> @@ -1969,13 +1969,13 @@ static void hls_prediction_unit(HEVCLocalContext *lc, int x0, int y0,
>  
>      if (current_mv.pred_flag & PF_L0) {
>          ref0 = refPicList[0].ref[current_mv.ref_idx[0]];
> -        if (!ref0 || !ref0->frame->data[0])
> +        if (!ref0 || !ref0->frame || !ref0->frame->data[0])
>              return;
>          hevc_await_progress(s, ref0, &current_mv.mv[0], y0, nPbH);
>      }
>      if (current_mv.pred_flag & PF_L1) {
>          ref1 = refPicList[1].ref[current_mv.ref_idx[1]];
> -        if (!ref1 || !ref1->frame->data[0])
> +        if (!ref1 || !ref1->frame || !ref1->frame->data[0])
>              return;
>          hevc_await_progress(s, ref1, &current_mv.mv[1], y0, nPbH);
>      }

Same as with 1/5: Checking for !ref0->frame is enough as HEVCFrame.f is
set if and only if the HEVCFrame.f->data[0] is set (with the possible
exception of hw-accelerated pixel formats that don't use AVFrame.data at
all (I don't know whether they exist); in any case, HEVCFrame.f is set
if and only if HEVCFrame.f->buf[0] is set).
Actually, I checked all the decoder that I ported to ProgressFrames for
this pattern, but apparently I overlooked way too much (maybe I only
checked for the ->buf[0] pattern?). Sorry for that.

- Andreas

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