Re: [FFmpeg-devel] [PATCH 2/3] avcodec/vlc: Attempt to free buf after use in ff_vlc_init_multi_from_lengths()

[Paul B Mahol <onemda@gmail.com>]

On Thu, Sep 14, 2023 at 1:48 AM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> Fixes: use after free
> Fixes:
> 62153/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MAGICYUV_fuzzer-4702814909366272
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by
> <https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by>:
> Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/vlc.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/vlc.c b/libavcodec/vlc.c
> index b353d2e86c2..f4bab0ae529 100644
> --- a/libavcodec/vlc.c
> +++ b/libavcodec/vlc.c
> @@ -471,10 +471,13 @@ int ff_vlc_init_multi_from_lengths(VLC *vlc,
> VLC_MULTI *multi, int nb_bits, int
>              goto fail;
>          }
>      }
> -    ret = vlc_common_end(vlc, nb_bits, j, buf, flags, localbuf);
> +    ret = vlc_common_end(vlc, nb_bits, j, buf, flags, buf);
>      if (ret < 0)
>          goto fail;
> -    return vlc_multi_gen(multi->table, vlc, nb_elems, j, nb_bits, buf,
> logctx);
> +    ret = vlc_multi_gen(multi->table, vlc, nb_elems, j, nb_bits, buf,
> logctx);
> +    if (buf != localbuf)
> +        av_free(buf);
> +    return ret;
>  fail:
>      if (buf != localbuf)
>          av_free(buf);
> --
> 2.17.1
>
>
LGTM


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