Re: [FFmpeg-devel] [PATCH 4/4] avcodec/vp3: Check width to avoid assertion failure

From: Kieran Kunhya <kierank@obe.tv>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 4/4] avcodec/vp3: Check width to avoid assertion failure
Date: Mon, 27 Mar 2023 01:45:01 +0100
Message-ID: <CAK+ULv6TTAaEq8da=NUdt0R1s7DD76bxTY1PnCPf3FEy86hfzg@mail.gmail.com> (raw)
In-Reply-To: <20230326222642.2489-4-michael@niedermayer.cc>

On Sun, 26 Mar 2023, 23:27 Michael Niedermayer, <michael@niedermayer.cc>
wrote:

> Fixes: Assertion failure on x86-32
> Fixes:
> 39641/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_THEORA_fuzzer-5925660741206016
>
> 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/vp3.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
> index 9660def675f..22348559461 100644
> --- a/libavcodec/vp3.c
> +++ b/libavcodec/vp3.c
> @@ -2353,6 +2353,8 @@ static av_cold int vp3_decode_init(AVCodecContext
> *avctx)
>      s->avctx  = avctx;
>      s->width  = FFALIGN(avctx->coded_width, 16);
>      s->height = FFALIGN(avctx->coded_height, 16);
> +    if (s->width < 18)
> +        return AVERROR_PATCHWELCOME;
>      if (avctx->codec_id != AV_CODEC_ID_THEORA)
>          avctx->pix_fmt = AV_PIX_FMT_YUV420P;
>      avctx->chroma_sample_location = AVCHROMA_LOC_CENTER;
> @@ -2919,7 +2921,9 @@ static int theora_decode_header(AVCodecContext
> *avctx, GetBitContext *gb)
>      /* sanity check */
>      if (av_image_check_size(visible_width, visible_height, 0, avctx) < 0
> ||
>          visible_width  + offset_x > s->width ||
> -        visible_height + offset_y > s->height) {
> +        visible_height + offset_y > s->height ||
> +        visible_width < 18
> +    ) {
>          av_log(avctx, AV_LOG_ERROR,
>                 "Invalid frame dimensions - w:%d h:%d x:%d y:%d
> (%dx%d).\n",
>                 visible_width, visible_height, offset_x, offset_y,
> @@ -2965,6 +2969,8 @@ static int theora_decode_header(AVCodecContext
> *avctx, GetBitContext *gb)
>      } else
>          avctx->pix_fmt = AV_PIX_FMT_YUV420P;
>
> +    if (s->width < 18)
> +        return AVERROR_PATCHWELCOME;
>      ret = ff_set_dimensions(avctx, s->width, s->height);
>      if (ret < 0)
>          return ret;
> --
> 2.17.1
>

Please provide some explanation around the number "18"

Kieran

>
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