Re: [FFmpeg-devel] [PATCH] avcodec/h263dec: Check against previous dimensions instead of coded

[Kacper Michajlow <kasper93@gmail.com>]

On Thu, 30 Jan 2025 at 02:57, Michael Niedermayer
<michael@niedermayer.cc> wrote:
>
> Fixes: out of array access
> Fixes: crash-a41ef3db699013f669b076f02f36942925f5a98c
>
> Found-by: Kacper Michajlow <kasper93@gmail.com>
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/h263dec.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
> index 0c23012584e..5eefdc4602b 100644
> --- a/libavcodec/h263dec.c
> +++ b/libavcodec/h263dec.c
> @@ -431,6 +431,7 @@ int ff_h263_decode_frame(AVCodecContext *avctx, AVFrame *pict,
>      MpegEncContext *s  = avctx->priv_data;
>      int ret;
>      int slice_ret = 0;
> +    int bak_width, bak_height;
>
>      /* no supplementary picture */
>      if (buf_size == 0) {
> @@ -482,6 +483,9 @@ retry:
>      if (ret < 0)
>          return ret;
>
> +    bak_width  = s->width;
> +    bak_height = s->height;
> +
>      /* let's go :-) */
>      if (CONFIG_WMV2_DECODER && s->msmpeg4_version == MSMP4_WMV2) {
>          ret = ff_wmv2_decode_picture_header(s);
> @@ -501,11 +505,12 @@ retry:
>      }
>
>      if (ret < 0 || ret == FRAME_SKIPPED) {
> -        if (   s->width  != avctx->coded_width
> -            || s->height != avctx->coded_height) {
> +        if (   s->width  != bak_width
> +            || s->height != bak_height) {
>                  av_log(s->avctx, AV_LOG_WARNING, "Reverting picture dimensions change due to header decoding failure\n");
> -                s->width = avctx->coded_width;
> -                s->height= avctx->coded_height;
> +                s->width = bak_width;
> +                s->height= bak_height;
> +
>          }
>      }
>      if (ret == FRAME_SKIPPED)
> --
> 2.48.1
>

Works for me. Thanks.

- Kacper
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