Re: [FFmpeg-devel] [PATCH 1/2] avcodec/pngdec: avoid erroring with sBIT on indexed-color images

[Marton Balint <cus@passwd.hu>]

On Fri, 12 Jul 2024, Leo Izen wrote:

> Indexed color images use three colors for sBIT, but the function
> ff_png_get_nb_channels returns 1 in this case. We should avoid erroring
> out on valid files in this scenario.

Please mention that this is a regression since 
84b454935fae2633a8a5dd075e22393f3e8f932f.

>
> Signed-off-by: Leo Izen <leo.izen@gmail.com>
> Reported-by: Ramiro Polla <ramiro.polla@gmail.com>
> ---
> libavcodec/pngdec.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> index 180806e5e1..b0d02c97dd 100644
> --- a/libavcodec/pngdec.c
> +++ b/libavcodec/pngdec.c
> @@ -1084,7 +1084,7 @@ static int decode_sbit_chunk(AVCodecContext *avctx, PNGDecContext *s,
>         return AVERROR_INVALIDDATA;
>     }
>
> -    channels = ff_png_get_nb_channels(s->color_type);
> +    channels = s->color_type & PNG_COLOR_MASK_PALETTE ? 3 : ff_png_get_nb_channels(s->color_type);
>

LGTM, also please backport this to the affected branches!

Thanks,
Marton


>     if (bytestream2_get_bytes_left(gb) != channels)
>         return AVERROR_INVALIDDATA;
> -- 
> 2.45.2
>
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