Re: [FFmpeg-devel] [PATCH 1/6] avcodec/utils: allocate a line more for VC1 and WMV3

From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/6] avcodec/utils: allocate a line more for VC1 and WMV3
Date: Thu, 12 Jan 2023 08:38:08 +0100
Message-ID: <AS8P250MB07440FD9F6FFF27AE06C4B698FFD9@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20230111204221.22550-1-michael@niedermayer.cc>

Michael Niedermayer:
> Fixes: out of array read on 32bit
> Fixes: 54857/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1_fuzzer-5840588224462848
> 
> The chroma MC code reads over the currently allocated frame.
> Alternative fixes would be allocating a few bytes more at the end instead of a whole
> line extra or to adjust the threshold where the edge emu code is activated
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/utils.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index 2b63a498b9..1aa0a05a31 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -321,6 +321,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
>      *width  = FFALIGN(*width, w_align);
>      *height = FFALIGN(*height, h_align);
>      if (s->codec_id == AV_CODEC_ID_H264 || s->lowres ||
> +        s->codec_id == AV_CODEC_ID_VC1  || s->codec_id == AV_CODEC_ID_WMV3 ||
>          s->codec_id == AV_CODEC_ID_VP5  || s->codec_id == AV_CODEC_ID_VP6 ||
>          s->codec_id == AV_CODEC_ID_VP6F || s->codec_id == AV_CODEC_ID_VP6A
>      ) {

Does this only happen on 32bit systems? If so, why?

- Andreas

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