linux-kernel - Re: [PATCH] media: v4l2-jpeg: ignore the unknown APP14 marker

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Message-ID: <44dda824-c18a-afb6-d802-bfb87f069f04@oss.nxp.com>
Date:   Sat, 18 Feb 2023 23:50:52 +0200
From:   "mirela.rabulea@....nxp.com" <mirela.rabulea@....nxp.com>
To:     Ming Qian <ming.qian@....com>, mchehab@...nel.org,
        hverkuil-cisco@...all.nl
Cc:     shawnguo@...nel.org, s.hauer@...gutronix.de, kernel@...gutronix.de,
        festevam@...il.com, xiahong.bao@....com, linux-imx@....com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] media: v4l2-jpeg: ignore the unknown APP14 marker

Hi,

On 16.12.2022 11:08, Ming Qian wrote:
> The legal identifier of APP14 is "Adobe\0",
> but sometimes it may be
> "This is an unknown APP marker . Compliant decoders must ignore it."
> In this case, just ignore it.
> It won't affect the decode result.

I'm not sure, based on the specs only, what the decoders should do if 
the segment does not follow the definition.

I only found this in T.81:
"The APPn (Application) segments are reserved for application use. Since 
these segments may be defined differently for
different applications, they should be removed when the data are 
exchanged between application environments."

And in T.872, the mention about "Adobe\0".

But, I agree ignoring it is more robust, and I confirm imx-jpeg can 
decode such jpegs.

Reviewed-by: Mirela Rabulea <mirela.rabulea@....com>

> 
> Fixes: b8035f7988a8 ("media: Add parsing for APP14 data segment in jpeg helpers")
> Signed-off-by: Ming Qian <ming.qian@....com>
> ---
>   drivers/media/v4l2-core/v4l2-jpeg.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-jpeg.c b/drivers/media/v4l2-core/v4l2-jpeg.c
> index 75c2af763d55..94435a7b6816 100644
> --- a/drivers/media/v4l2-core/v4l2-jpeg.c
> +++ b/drivers/media/v4l2-core/v4l2-jpeg.c
> @@ -460,7 +460,7 @@ static int jpeg_parse_app14_data(struct jpeg_stream *stream,
>   	/* Check for "Adobe\0" in Ap1..6 */
>   	if (stream->curr + 6 > stream->end ||
>   	    strncmp(stream->curr, "Adobe\0", 6))
> -		return -EINVAL;
> +		return jpeg_skip(stream, lp - 2);
>   
>   	/* get to Ap12 */
>   	ret = jpeg_skip(stream, 11);