linux-kernel - Re: [PATCH] media: nxp: imx8-isi: Check whether pad is non-NULL before access

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Message-ID: <a9283349-c58d-47e6-ac33-77b5a6b893fe@gocontroll.com>
Date: Wed, 20 Aug 2025 16:07:55 +0200
From: Maud Spierings <maudspierings@...ontroll.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>,
 Stefan Riedmueller <s.riedmueller@...tec.de>,
 Jacopo Mondi <jacopo@...ndi.org>, Christian Hemp <c.hemp@...tec.de>,
 Guoniu Zhou <guoniu.zhou@....com>, Dong Aisheng <aisheng.dong@....com>,
 linux-media@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: nxp: imx8-isi: Check whether pad is non-NULL
 before access

On 8/20/25 16:01, Laurent Pinchart wrote:
> Hi Maud,
> 
> On Mon, Aug 18, 2025 at 02:31:43PM +0200, Maud Spierings via B4 Relay wrote:
>> From: Maud Spierings <maudspierings@...ontroll.com>
>>
>> media_pad_remote_pad_first() can return NULL if no valid link is found.
>> Check for this possibility before dereferencing it in the next line.
>>
>> Reported/investigated in [1]:
>>
>> Link: https://lore.kernel.org/all/1536a61b-b405-4762-9fb4-7e257f95e49e@gocontroll.com/ [1]
>> Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
>> Signed-off-by: Maud Spierings <maudspierings@...ontroll.com>
>> ---
>> I'm not sure if this should be a dev_dbg(), just following the pattern
>> around it for now, also not sure if EPIPE is the correct error.
> 
> I've submitted
> https://lore.kernel.org/linux-media/20250820140021.8026-1-laurent.pinchart@ideasonboard.com,
> which should fix this issue in a more generic way.

Saw it, but I think my patch technically is still correct as the 
function documentation states it can potentially return NULL right? [1]

Link: 
https://www.kernel.org/doc/html/latest/driver-api/media/mc-core.html [1]

I will test you patches tomorrow.

>> ---
>>   drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
>> index ede6cc74c0234049fa225ad82aaddaad64aa53d7..1ed8b031178b7d934b04a8752747f556bd1fc5a9 100644
>> --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
>> +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-crossbar.c
>> @@ -160,6 +160,13 @@ mxc_isi_crossbar_xlate_streams(struct mxc_isi_crossbar *xbar,
>>   	}
>>   
>>   	pad = media_pad_remote_pad_first(&xbar->pads[sink_pad]);
>> +
>> +	if (pad == NULL) {
>> +		dev_dbg(xbar->isi->dev, "no valid link found to pad %u\n",
>> +			sink_pad);
>> +		return ERR_PTR(-EPIPE);
>> +	}
>> +
>>   	sd = media_entity_to_v4l2_subdev(pad->entity);
>>   	if (!sd) {
>>   		dev_dbg(xbar->isi->dev,
>>
>> ---
>> base-commit: 3ac864c2d9bb8608ee236e89bf561811613abfce
>> change-id: 20250818-imx8_isi-954898628bb6
>