Re: [PATCH v2 1/3] media: imx-jpeg: Enhance error handling in buffer allocation

[Sebastian Fricke]

Hey Ming,

In the title I'd suggest:
media: imx-jpeg: Cleanup after an allocation error

To be a bit more concrete, enhance error handling can mean pretty much
anything.

On 28.03.2025 14:30, ming.qian@xxxxxxxxxxx wrote:
> From: Ming Qian <ming.qian@xxxxxxxxxxx>
>
> In function mxc_jpeg_alloc_slot_data, driver will allocate some dma
> buffer, but only return error if certain allocation failed.
>
> Without cleanup the allocation failure, the next time it will return
> success directly, but let some buffer be uninitialized.
> It may result in accessing a null pointer.
>
> Clean up if error occurs in the allocation.

I'd suggest:

When allocation failures are not cleaned up by the driver, further allocation
errors will be false-positives, which will cause buffers to remain
uninitialized and cause NULL pointer dereferences.
Clean up the errors accordingly.

> Fixes: 2db16c6ed72c ("media: imx-jpeg: Add V4L2 driver for i.MX8 JPEG Encoder/Decoder")
> Signed-off-by: Ming Qian <ming.qian@xxxxxxxxxxx>
> ---
> v2
> - Add the Fixes tag
>
> .../media/platform/nxp/imx-jpeg/mxc-jpeg.c    | 47 +++++++++++--------
> 1 file changed, 27 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c
> index 0e6ee997284b..12661c177f5a 100644
> --- a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c
> +++ b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c
> @@ -752,6 +752,32 @@ static int mxc_get_free_slot(struct mxc_jpeg_slot_data *slot_data)
> 	return -1;
> }
>
> +static void mxc_jpeg_free_slot_data(struct mxc_jpeg_dev *jpeg)
> +{
> +	/* free descriptor for decoding/encoding phase */
> +	dma_free_coherent(jpeg->dev, sizeof(struct mxc_jpeg_desc),
> +			  jpeg->slot_data.desc,
> +			  jpeg->slot_data.desc_handle);
> +	jpeg->slot_data.desc = NULL;
> +	jpeg->slot_data.desc_handle = 0;
> +
> +	/* free descriptor for encoder configuration phase / decoder DHT */
> +	dma_free_coherent(jpeg->dev, sizeof(struct mxc_jpeg_desc),
> +			  jpeg->slot_data.cfg_desc,
> +			  jpeg->slot_data.cfg_desc_handle);
> +	jpeg->slot_data.cfg_desc_handle = 0;
> +	jpeg->slot_data.cfg_desc = NULL;
> +
> +	/* free configuration stream */
> +	dma_free_coherent(jpeg->dev, MXC_JPEG_MAX_CFG_STREAM,
> +			  jpeg->slot_data.cfg_stream_vaddr,
> +			  jpeg->slot_data.cfg_stream_handle);
> +	jpeg->slot_data.cfg_stream_vaddr = NULL;
> +	jpeg->slot_data.cfg_stream_handle = 0;
> +
> +	jpeg->slot_data.used = false;
> +}
> +
> static bool mxc_jpeg_alloc_slot_data(struct mxc_jpeg_dev *jpeg)
> {
> 	struct mxc_jpeg_desc *desc;
> @@ -794,30 +820,11 @@ static bool mxc_jpeg_alloc_slot_data(struct mxc_jpeg_dev *jpeg)
> 	return true;
> err:
> 	dev_err(jpeg->dev, "Could not allocate descriptors for slot %d", jpeg->slot_data.slot);
> +	mxc_jpeg_free_slot_data(jpeg);
>
> 	return false;
> }
>
> -static void mxc_jpeg_free_slot_data(struct mxc_jpeg_dev *jpeg)
> -{
> -	/* free descriptor for decoding/encoding phase */
> -	dma_free_coherent(jpeg->dev, sizeof(struct mxc_jpeg_desc),
> -			  jpeg->slot_data.desc,
> -			  jpeg->slot_data.desc_handle);
> -
> -	/* free descriptor for encoder configuration phase / decoder DHT */
> -	dma_free_coherent(jpeg->dev, sizeof(struct mxc_jpeg_desc),
> -			  jpeg->slot_data.cfg_desc,
> -			  jpeg->slot_data.cfg_desc_handle);
> -
> -	/* free configuration stream */
> -	dma_free_coherent(jpeg->dev, MXC_JPEG_MAX_CFG_STREAM,
> -			  jpeg->slot_data.cfg_stream_vaddr,
> -			  jpeg->slot_data.cfg_stream_handle);
> -
> -	jpeg->slot_data.used = false;
> -}

Can you split the moving of the code from the changes you do?
Otherwise the reviewer is forced to get the diff manually.

Regards,
Sebastian Fricke