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

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Message-ID: <20250405113936.oepkmoz2czytbuxy@basti-XPS-13-9310>
Date: Sat, 5 Apr 2025 13:39:36 +0200
From: Sebastian Fricke <sebastian.fricke@...labora.com>
To: ming.qian@....nxp.com
Cc: mchehab@...nel.org, hverkuil-cisco@...all.nl,
	mirela.rabulea@....nxp.com, shawnguo@...nel.org,
	s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
	xiahong.bao@....com, eagle.zhou@....com, linux-imx@....com,
	imx@...ts.linux.dev, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] media: imx-jpeg: Enhance error handling in buffer
 allocation

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@....nxp.com wrote:
>From: Ming Qian <ming.qian@....nxp.com>
>
>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@....nxp.com>
>---
>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