[FFmpeg-devel] [PATCH] lavc/cbs_h2645: Fix incorrect max size of nalu unit

[Andreas Rheinhardt]

Andriy Gelman:
> From: Andriy Gelman <andriy.gelman at gmail.com>
> 
> In the worst case the startcode prefix has 4 bytes.
> 
> This fixes a trigerred assertion:
> Assertion dp <= max_size failed at libavcodec/cbs_h2645.c:1451
> 
> Found-by:libFuzzer
> Signed-off-by: Andriy Gelman <andriy.gelman at gmail.com>
> ---
>  libavcodec/cbs_h2645.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
> index 88fa0029cd6..5f71d805848 100644
> --- a/libavcodec/cbs_h2645.c
> +++ b/libavcodec/cbs_h2645.c
> @@ -1395,7 +1395,7 @@ static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
>      max_size = 0;
>      for (i = 0; i < frag->nb_units; i++) {
>          // Start code + content with worst-case emulation prevention.
> -        max_size += 3 + frag->units[i].data_size * 3 / 2;
> +        max_size += 4 + frag->units[i].data_size * 3 / 2;
>      }
>  
>      data = av_realloc(NULL, max_size + AV_INPUT_BUFFER_PADDING_SIZE);
> 
LGTM. I presume you used a NAL unit of size 1?

(I found this out, too, when I tried (and postponed) to add mp4
writing support for H.264.)

- Andreas