[FFmpeg-devel] [PATCH 1/4] avcodec/jpeg2000dec: clear pointer which become stale in get_ppt()

[Gautam Ramakrishnan]

On Sun, May 31, 2020 at 7:21 PM Michael Niedermayer
<michael at niedermayer.cc> wrote:
>
> Fixes: use after free
> Fixes: 22484/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5671488765296640
>
> 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/jpeg2000dec.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/libavcodec/jpeg2000dec.c b/libavcodec/jpeg2000dec.c
> index 65555424ed..b7766459c4 100644
> --- a/libavcodec/jpeg2000dec.c
> +++ b/libavcodec/jpeg2000dec.c
> @@ -928,6 +928,7 @@ static int get_ppt(Jpeg2000DecoderContext *s, int n)
>          tile->packed_headers = new;
>      } else
>          return AVERROR(ENOMEM);
> +    memset(&tile->packed_headers_stream, 0, sizeof(tile->packed_headers_stream));
>      memcpy(tile->packed_headers + tile->packed_headers_size,
>             s->g.buffer, n - 3);
>      tile->packed_headers_size += n - 3;
> --
> 2.17.1
>
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I do not understand this. Wouldn't the memcpy overwrite the address anyway?

-- 
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Gautam |