Re: [PATCH v6 6/9] media: Add parsing for APP14 data segment in jpeg helpers

[Philipp Zabel]

Hi Mirela,

thank you for the update. Just two issues below:

On Tue, 2020-12-15 at 13:18 +0200, Mirela Rabulea (OSS) wrote:
> From: Mirela Rabulea <mirela.rabulea@xxxxxxx>
> 
> According to Rec. ITU-T T.872 (06/2012) 6.5.3
> APP14 segment is for color encoding, it contains a transform flag, which
> may have values of 0, 1 and 2 and are interpreted as follows:
> 0 - CMYK for images that are encoded with four components
>   - RGB for images that are encoded with three components
> 1 - An image encoded with three components using YCbCr colour encoding.
> 2 - An image encoded with four components using YCCK colour encoding.
> 
> This is used in imx-jpeg decoder, to distinguish between
> YUV444 and RGB24.
> 
> Signed-off-by: Mirela Rabulea <mirela.rabulea@xxxxxxx>
> ---
> Changes in v6:
>   Switch variable to lowercase Lp->lp
>   Check for "Adobe\0" in Ap1..6
>   Make the transform flag an enum
>   Removed a change in comment section, a leftover from a previous version
>   Thanks Philipp for feedback.
> 
>  drivers/media/v4l2-core/v4l2-jpeg.c | 43 +++++++++++++++++++++++++++--
>  include/media/v4l2-jpeg.h           | 18 ++++++++++++
>  2 files changed, 59 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-jpeg.c b/drivers/media/v4l2-core/v4l2-jpeg.c
> index 8947fd95c6f1..d1483e7a775c 100644
> --- a/drivers/media/v4l2-core/v4l2-jpeg.c
> +++ b/drivers/media/v4l2-core/v4l2-jpeg.c
> @@ -45,6 +45,7 @@ MODULE_LICENSE("GPL");
>  #define DHP	0xffde	/* hierarchical progression */
>  #define EXP	0xffdf	/* expand reference */
>  #define APP0	0xffe0	/* application data */
> +#define APP14	0xffee	/* application data for colour encoding */
>  #define APP15	0xffef
>  #define JPG0	0xfff0	/* extensions */
>  #define JPG13	0xfffd
> @@ -444,8 +445,41 @@ static int jpeg_skip_segment(struct jpeg_stream *stream)
>  	return jpeg_skip(stream, len - 2);
>  }
>  
> +/* Rec. ITU-T T.872 (06/2012) 6.5.3 */
> +static int jpeg_parse_app14_data(struct jpeg_stream *stream)
> +{
> +	int ret;
> +	int lp;
> +	int skip;
> +	int tf;
> +
> +	lp = jpeg_get_word_be(stream);
> +	if (lp < 0)
> +		return lp;

Here we should check that there are still 6 bytes available to compare:

	if (stream->curr + 6 > stream->end)
		return -EINVAL;

> +	/* Check for "Adobe\0" in Ap1..6 */
> +	if (strncmp(stream->curr, "Adobe\0", 6))
> +		return -EINVAL;
> +
> +	/* get to Ap12 */
> +	ret = jpeg_skip(stream, 11);
> +	if (ret < 0)
> +		return -EINVAL;
> +
> +	tf = jpeg_get_byte(stream);
> +	if (tf < 0)
> +		return tf;
> +
> +	skip = lp - 2 - 11;
> +	ret = jpeg_skip(stream, skip);
> +	if (ret < 0)
> +		return -EINVAL;
> +	else
> +		return tf;
> +}
> +
>  /**
> - * jpeg_parse_header - locate marker segments and optionally parse headers
> + * v4l2_jpeg_parse_header - locate marker segments and optionally parse headers
>   * @buf: address of the JPEG buffer, should start with a SOI marker
>   * @len: length of the JPEG buffer
>   * @out: returns marker segment positions and optionally parsed headers
> @@ -476,6 +510,9 @@ int v4l2_jpeg_parse_header(void *buf, size_t len, struct v4l2_jpeg_header *out)
>  	if (marker != SOI)
>  		return -EINVAL;
>  
> +	/* init value to signal if this marker is not present */
> +	out->app14_tf = -EINVAL;
> +

Here we set app14_tf to a value that is not part of the enum.
You could define a value V4L2_JPEG_APP14_TF_UNKNOWN for the
uninitialized / error state.

>  	/* loop through marker segments */
>  	while ((marker = jpeg_next_marker(&stream)) >= 0) {
>  		switch (marker) {
> @@ -519,7 +556,9 @@ int v4l2_jpeg_parse_header(void *buf, size_t len, struct v4l2_jpeg_header *out)
>  			ret = jpeg_parse_restart_interval(&stream,
>  							&out->restart_interval);
>  			break;
> -
> +		case APP14:
> +			out->app14_tf = jpeg_parse_app14_data(&stream);

Same as above in case of -EINVAL return. Apart from this,

Reviewed-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>

regards
Philipp