[FFmpeg-devel] [PATCH 1/3] avcodec/agm: Do not crash on invalid codes

[Paul B Mahol]

On 4/21/19, Michael Niedermayer <michael at niedermayer.cc> wrote:
> I do not know if such vlc trees are allowed in agm, I have no specification
> So i do not know if these should be treated as error, or not.
> But the code does contain a check for idx < 0 already ...
>
> untested due to lack of valid samples using this codepath
>
> Fixes: Stack-buffer-overflow in get_tree_codes
> Fixes:
> 14189/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AGM_fuzzer-5745747003179008
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/agm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/agm.c b/libavcodec/agm.c
> index f5fd5d065e..f3d81bf163 100644
> --- a/libavcodec/agm.c
> +++ b/libavcodec/agm.c
> @@ -913,7 +913,7 @@ static void get_tree_codes(uint32_t *codes, Node *nodes,
> int idx, uint32_t pfx,
>  {
>      if (idx < 256 && idx >= 0) {
>          codes[idx] = pfx;
> -    } else {
> +    } else if (idx >= 0) {
>          get_tree_codes(codes, nodes, nodes[idx].child[0], pfx + (0 <<
> bitpos), bitpos + 1);
>          get_tree_codes(codes, nodes, nodes[idx].child[1], pfx + (1 <<
> bitpos), bitpos + 1);
>      }
> --
> 2.21.0
>
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lgtm