Re: [FFmpeg-devel] [PATCH 3/3] avcodec/mpeg4videodec: Replace always true check by assert

From: James Almer <jamrial@gmail.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 3/3] avcodec/mpeg4videodec: Replace always true check by assert
Date: Sun, 15 May 2022 22:24:53 -0300
Message-ID: <dbe17fa0-24a0-1efc-77e1-7f5fefa08b73@gmail.com> (raw)
In-Reply-To: <20220516011605.18792-3-michael@niedermayer.cc>

On 5/15/2022 10:16 PM, Michael Niedermayer wrote:
> Maybe helps coverity
> Helps: CID1433771
> 
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavcodec/mpeg4videodec.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
> index e2bde73639..715cb606c9 100644
> --- a/libavcodec/mpeg4videodec.c
> +++ b/libavcodec/mpeg4videodec.c
> @@ -1981,7 +1981,8 @@ static int mpeg4_decode_studio_block(MpegEncContext *s, int32_t block[64], int n
>                   return AVERROR_INVALIDDATA;
>               j = scantable[idx++];
>               block[j] = get_xbits(&s->gb, additional_code_len);
> -        } else if (group == 21) {
> +        } else {
> +            av_assert2(group == 21);

Group is used as index to access two arrays with 22 elements each at the 
beginning of the while loop here. Maybe just also check for group > 21 
and abort like we're doing for < 0, since it's clearly not a valid or 
expected value.

>               /* Escape */
>               if (idx > 63)
>                   return AVERROR_INVALIDDATA;
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