Re: [FFmpeg-devel] [PATCH] avcodec/jpegxl_parser: add sanity check for frame size

[Kacper Michajlow <kasper93@gmail.com>]

On Tue, 15 Jul 2025 at 20:02, Leo Izen <leo.izen@gmail.com> wrote:
>
> If a frame size is absolutely massive, this can spin the parser as it
> attempts to decode a permuted TOC. We add a sanity check here for eight
> times the size of the image for an internal frame to prevent malicious
> bitstreams from slowing the parser down to a crawl.
>
> Signed-off-by: Leo Izen <leo.izen@gmail.com>
> Reported-by: Kacper Michajłow <kasper93-at-gmail.com@ffmpeg.org>

Please use my real email, instead this wrapped one, thanks.

> ---
>  libavcodec/jpegxl_parser.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/jpegxl_parser.c b/libavcodec/jpegxl_parser.c
> index 68404229a5..e40b4fbf96 100644
> --- a/libavcodec/jpegxl_parser.c
> +++ b/libavcodec/jpegxl_parser.c
> @@ -1315,6 +1315,11 @@ static int parse_frame_header(void *avctx, JXLParseContext *ctx, GetBitContext *
>      if (get_bits1(gb)) {
>          JXLEntropyDecoder dec;
>          int64_t end, lehmer = 0;
> +        /* parser sanity check to prevent TOC perm from spinning cpu */
> +        if (width > meta->coded_width * 8 || height > meta->coded_height * 8) {
> +            av_log(avctx, AV_LOG_WARNING, "massive frame detectived, aborting parser\n");

detected? Also maybe make it more formal like "frame of size %dx%d
exceeds limit of %dx%d, aborting" or something along those lines.
"massive frame" doesn't really tell much.

- Kacper
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