Re: [FFmpeg-devel] [PATCH] avcodec/vorbisdec: don't abort on EOD when decoding residuals

[Michael Niedermayer <michael@niedermayer.cc>]

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Hi James

On Fri, Feb 07, 2025 at 01:47:51PM -0300, James Almer wrote:
> Fixes ticket #11427
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
> It may be a good idea to ensure the timeout fuzzer case doesn't regress
> after this.
> 
>  libavcodec/vorbisdec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c
> index 218e855f7a..321408723d 100644
> --- a/libavcodec/vorbisdec.c
> +++ b/libavcodec/vorbisdec.c
> @@ -1470,7 +1470,7 @@ static av_always_inline int vorbis_residue_decode_internal(vorbis_context *vc,
>                              vorbis_codebook codebook = vc->codebooks[vqbook];
>  
>                              if (get_bits_left(gb) <= 0)
> -                                return AVERROR_INVALIDDATA;
> +                                return 0;

This looks suspect

For the test sample from #11427 get_bits_left() at this point is -8
that means 8 bits have already been read beyond the buffer.
wherever the error is, reading 8 bits beyond is unlikely to be
the correct and intended behavior

I think the question would be, what created this file and how
exactly does libvorbis handle it, does it also read beyond the buffer

That is, do we have a encoder or a decoder bug, and what is that
bug exactly

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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